```

[Federal Register Volume 79, Number 213 (Tuesday, November 4, 2014)]
[Rules and Regulations]
[Pages 65507-65540]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: 2014-25789]

[[Page 65507]]

Vol. 79

Tuesday,

No. 213

November 4, 2014

Part III

 Department of Transportation

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Federal Aviation Administration

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14 CFR Parts 25 and 33

 Airplane and Engine Certification Requirements in Supercooled Large 
Drop, Mixed Phase, and Ice Crystal Icing Conditions; Final Rule

Federal Register / Vol. 79 , No. 213 / Tuesday, November 4, 2014 / 
Rules and Regulations

[[Page 65508]]

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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Parts 25 and 33

[Docket No. FAA-2010-0636; Amendment Nos. 25-140 and 33-34]
RIN 2120-AJ34

Airplane and Engine Certification Requirements in Supercooled 
Large Drop, Mixed Phase, and Ice Crystal Icing Conditions

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Final rule.

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SUMMARY: The Federal Aviation Administration is amending the 
airworthiness standards applicable to certain transport category 
airplanes certified for flight in icing conditions and the icing 
airworthiness standards applicable to certain aircraft engines. The 
regulations will improve safety by addressing supercooled large drop 
icing conditions for transport category airplanes most affected by 
these icing conditions; mixed phase and ice crystal conditions for all 
transport category airplanes; and supercooled large drop, mixed phase, 
and ice crystal icing conditions for all turbojet, turbofan, and 
turboprop engines.

DATES: Effective January 5, 2015.

ADDRESSES: For information on where to obtain copies of rulemaking 
documents and other information related to this final rule, see ``How 
To Obtain Additional Information'' in the SUPPLEMENTARY INFORMATION 
section of this document.

FOR FURTHER INFORMATION CONTACT: For part 25 technical questions 
contact Robert Hettman, FAA, Propulsion/Mechanical Systems Branch, ANM-
112, Transport Airplane Directorate, Aircraft Certification Service, 
1601 Lind Avenue SW., Renton, WA 98057-3356; telephone (425) 227-2683; 
facsimile (425) 227-1320; email robert.hettman@faa.gov.
    For part 33 technical questions contact John Fisher, FAA, 
Rulemaking and Policy Branch, ANE-111, Engine and Propeller Directorate 
Standards Staff, Aircraft Certification Service, 12 New England 
Executive Park, Burlington, MA 01803; telephone (781) 238-7149; 
facsimile (781) 238-7199; email john.fisher@faa.gov.
    For part 25 legal questions contact Douglas Anderson, FAA, Office 
of the Regional Counsel, ANM-7, Northwest Mountain Region, 1601 Lind 
Avenue SW., Renton, WA 98057-3356; telephone (425) 227-2166; facsimile 
(425) 227-1007; email douglas.anderson@faa.gov.
    For part 33 legal questions contact Vince Bennett, FAA, Office of 
the Regional Counsel, ANE-007, New England Region, 12 New England 
Executive Park, Burlington, MA 01803; telephone (781) 238-7044; 
facsimile (781) 238-7055; email vincent.bennett@faa.gov.

SUPPLEMENTARY INFORMATION:

Authority for This Rulemaking

    The FAA's authority to issue rules on aviation safety is found in 
Title 49 of the United States Code. Subtitle I, Section 106 describes 
the authority of the FAA Administrator. Subtitle VII, Aviation 
Programs, describes in more detail the scope of the agency's authority.
    This rulemaking is under the authority described in Subtitle VII, 
Part A, Subpart III, Section 44701, ``General requirements.'' Under 
that section, the FAA is charged with promoting safe flight of civil 
aircraft in air commerce by prescribing minimum standards required in 
the interest of safety for the design and performance of aircraft; 
regulations and minimum standards in the interest of safety for 
inspecting, servicing, and overhauling aircraft; and regulations for 
other practices, methods, and procedures the Administrator finds 
necessary for safety in air commerce. This regulation is within the 
scope of that authority because it prescribes--
     New safety standards for the design and performance of 
certain transport category airplanes and aircraft engines; and
     New safety requirements necessary for the design, 
production, and operation of those airplanes, and for other practices, 
methods, and procedures relating to those airplanes and engines.

Overview of Final Rule

    The FAA is adopting this final rule to revise certain regulations 
in Title 14, Code of Federal Regulations (14 CFR) part 25 
(Airworthiness Standards: Transport Category Airplanes) and part 33 
(Airworthiness Standards: Aircraft Engines) related to the 
certification of transport category airplanes and turbine airplane 
engines in icing conditions. We are also creating the following new 
regulations: Sec.  25.1324--Angle of attack systems; Sec.  25.1420--
Supercooled Large Drop Icing Conditions; Appendix O to Part 25--
Supercooled Large Drop Icing Conditions; Appendix C to Part 33 (this is 
intentionally left blank as a placeholder for potential future 
rulemaking unrelated to icing); and Appendix D to Part 33 Mixed Phase 
and Ice Crystal Icing Envelope (Deep Convective Clouds). To improve the 
safety of transport category airplanes operating in supercooled large 
drop (SLD), mixed phase, and ice crystal icing conditions, these 
regulations will:
     Require airplanes most affected by SLD icing conditions to 
meet certain safety standards in an expanded certification icing 
environment that includes freezing drizzle and freezing rain. These 
safety standards include airplane performance and handling qualities 
requirements.
     Expand the engine and engine installation certification, 
and some airplane component certification regulations (for example, 
angle of attack and airspeed indicating systems) to include freezing 
drizzle, freezing rain, mixed phase, and ice crystal icing conditions.

Summary of the Costs and Benefits of the Final Rule

    The benefits and costs are summarized in the table below. As shown 
in the table, the total estimated benefits exceed the total estimated 
costs for this final rule.

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                                                 2012$                               7% Present value
                              ----------------------------------------------------------------------------------
                                      Benefit                Cost               Benefit               Cost
----------------------------------------------------------------------------------------------------------------
Part 33 Engines..............  Qualitative..........        $13,936,000  Qualitative.........        $11,375,927
Large Part 25 Airplanes......  $362,319,857.........         14,126,333  $76,861,295.........        $11,531,295
Other Part 25 Airplanes......  $220,570,582.........         33,198,788  $50,028,690.........        $19,385,401
                              ----------------------------------------------------------------------------------
    Total....................  $582,890,439.........         61,261,121  $126,889,985........        $42,292,624
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[[Page 65509]]

Background

    Safety concerns about the adequacy of the icing certification 
standards were brought to the forefront of public and governmental 
attention by a 1994 accident in Roselawn, Indiana, involving an Avions 
de Transport R[eacute]gional (ATR) ATR 72 series airplane. The National 
Transportation Safety Board (NTSB), with assistance from ATR, the FAA, 
the French Direction G[eacute]n[eacute]ral de l'Aviation Civile, Bureau 
D'Enquetes et D'Analyses, the National Aeronautics and Space 
Administration (NASA), and others, conducted an extensive investigation 
of this accident. This investigation determined that freezing drizzle-
sized drops created a ridge of ice on the wing's upper surface aft of 
the deicing boots and forward of the ailerons. The investigation 
further concluded that this ridge of ice contributed to an uncommanded 
roll of the airplane. Based on these findings, the NTSB recommended 
changes to the icing certification requirements.
    The atmospheric icing conditions for certification are specified in 
part 25, appendix C. The atmospheric condition (freezing drizzle) that 
contributed to the Roselawn accident is outside the icing envelope 
currently used for certifying transport category airplanes. The term 
``icing envelope'' is used in part 25, appendix C, and in this rule to 
refer to the environmental icing conditions within which the airplane 
must be shown to be able to safely operate. The term ``transport 
category airplanes'' is used throughout this rulemaking document to 
include all airplanes type-certificated to part 25 regulations.
    Another atmospheric icing environment outside the current icing 
envelope is freezing rain. The FAA has not required airplane 
manufacturers to show that airplanes can operate safely in a freezing 
drizzle or freezing rain icing environment.
    As a result of this accident and consistent with related NTSB 
recommendations,\1\ the FAA tasked the Aviation Rulemaking Advisory 
Committee (ARAC),\2\ through its Ice Protection Harmonization Working 
Group (IPHWG), to do the following:
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    \1\ NTSB Safety Recommendations A-96-54 and A-96-56 are 
available in the rule Docket No. FAA-2010-0636 and on the Internet 
at http://www.ntsb.gov/doclib/recletters/1996/A96_48_69.pdf.
    \2\ Published in the Federal Register on December 8, 1997 (62 FR 
64621). http://www.gpo.gov/fdsys/pkg/FR-1997-12-08/pdf/97-32034.pdf.
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     Define an icing environment that includes SLD conditions.
     Consider the need to define a mixed phase icing 
environment (supercooled liquid and ice crystals).
     Devise requirements to assess the ability of an airplane 
to either safely operate without restrictions in SLD and mixed phase 
conditions or safely operate until it can exit these conditions.
     Study the effects icing requirement changes could have on 
Sec. Sec.  25.773, Pilot compartment view; 25.1323, Airspeed indicating 
system; and 25.1325, Static pressure systems.
     Consider the need for a regulation on ice protection for 
angle of attack probes.
    The FAA ultimately determined that the revised icing certification 
standards should include SLD, mixed phase, and ice crystal icing 
conditions. This rule is based on ARAC's recommendations to the FAA.

A. Related Actions

    ARAC's IPHWG submitted additional icing rulemaking recommendations 
to the FAA that led to the Part 25 and Part 121 Activation of Ice 
Protection final rules.\3\ For certain airplanes certificated for 
flight in icing, those rulemaking actions revise the certification and 
operating rules for flight in icing conditions by requiring either 
installation of ice detection equipment or changes to the airplane 
flight manual (AFM) to ensure timely activation of the airframe ice 
protection system. Although those rulemaking actions address flight in 
icing conditions, they do not directly impact this final rule.
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    \3\ Part 25 Activation of Ice Protection, Docket No. FAA-2007-
27654, published in the Federal Register on August 3, 2009 (74 FR 
38328). Part 121 Activation of Ice Protection, Docket No. FAA-2009-
0675, published in the Federal Register on August 22, 2011 (76 FR 
52241).
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B. NTSB Recommendations

    The NTSB issued NTSB Safety Recommendation Numbers A-96-54 and A-
96-56 as a result of the Roselawn accident previously discussed. This 
rulemaking partially addresses those NTSB recommendations. The FAA is 
considering separate rulemaking activities associated with revisions to 
14 CFR part 23 regulations for small airplanes and 14 CFR part 121 
operational regulations to complete the FAA response to these NTSB 
recommendations. The NTSB recommendations are as follows:
1. A-96-54
    Revise the icing criteria published in 14 CFR parts 23 and 25, in 
light of both recent research into aircraft ice accretion under varying 
conditions of liquid water content (LWC), drop size distribution, and 
temperature, and recent developments in both the design and use of 
aircraft. Also, expand the appendix C icing certification envelope to 
include freezing drizzle/freezing rain and mixed water/ice crystal 
conditions, as necessary (A-96-54 supersedes A-81-116 and -118).
2. A-96-56
    Revise the icing certification testing regulation to ensure that 
airplanes are properly tested for all conditions in which they are 
authorized to operate, or are otherwise shown to be capable of safe 
flight into such conditions. If safe operations cannot be demonstrated 
by the manufacturer, operational limitations should be imposed to 
prohibit flight in such conditions, and flightcrews should be provided 
with the means to positively determine when they are in icing 
conditions that exceed the limits for aircraft certification.

C. Summary of the Notice of Proposed Rulemaking

    The notice of proposed rulemaking (NPRM), Notice No. 10-10, 
published in the Federal Register on June 29, 2010 (75 FR 37311), is 
the basis for this final rule. After receiving several requests to 
extend the public comment period, the FAA extended the comment period 
by 30 days to September 29, 2010, with a document published in the 
Federal Register on August 16, 2010 (75 FR 49865).
    To improve the safety of transport category airplanes operating in 
SLD, mixed phase, and ice crystal icing conditions, the FAA proposed 
new regulations in the NPRM to:
     Expand the certification icing environment to include 
freezing drizzle and freezing rain environments.
     Require airplanes most affected by SLD icing conditions to 
meet certain safety standards in the expanded certification icing 
environment, including airplane performance and handling qualities 
requirements.
     Expand the engine and engine installation certification 
regulations, and some airplane component certification regulations (for 
example, angle of attack and airspeed indicating systems), to include 
freezing rain environments, freezing drizzle environments, mixed phase, 
and ice crystal icing conditions. For certain regulations, we proposed 
using a subset of these icing conditions.

D. General Overview of Comments

    The FAA received comments from 31 commenters during the public 
comment period: Five private citizens, the Aerospace Industries 
Association (AIA), Airbus Industrie (Airbus), AirDat LLC, the Airline 
Pilots Association (ALPA),

[[Page 65510]]

American Kestrel Company, LLC, (AKC), The Boeing Company, Bombardier, 
Cessna, Dassault Aviation, Embraer, Eurocopter, the European Aviation 
Safety Agency (EASA), Foster Technology, LLC, the General Aviation 
Manufacturers Association (GAMA), GE Aviation, Gulfstream, Goodrich 
Sensors and Integrated Systems (GSIS), Honeywell Engines, the National 
Research Council (NRC), the NTSB, Pratt & Whitney Canada, the Regional 
Airline Association (RAA), the Swiss Federal Office of Civil Aviation 
(FOCA), Snecma, Transport Canada Civil Aviation (TCCA), and Turbomeca. 
Each commenter submitted multiple comments.
    Twelve commenters stated specific support for the rulemaking, 
recognized the efforts made by the ARAC working group, and suggested 
specific changes intended to clarify the regulations or to clarify the 
intent. The NTSB and two private citizens were disappointed that the 
rulemaking took so long.
    Fourteen commenters stated neither support nor opposition, but 
suggested specific changes or identified areas for clarification.
    Two commenters, a rotorcraft manufacturer and a rotorcraft engine 
manufacturer, opposed the proposed changes to Sec. Sec.  33.68 and 
33.77. These commenters suggested the FAA make provisions to exclude 
rotorcraft from the revised regulations.
    Two private citizens expressed concern for the data and methods 
used to define the SLD conditions proposed in part 25, appendix O.
    One commenter suggested that the FAA should begin a certification 
process toward use of a new methodology for detecting ice over a pitot 
inlet, for which the commenter has filed a provisional patent.
    The FAA received additional comments in a letter dated June 21, 
2011, signed by four private citizens. The letter provided additional 
explanation for previously submitted comments. The FAA also considered 
this additional information while drafting this final rule.
    The FAA made changes to the final rule in response to the public 
comments. Summaries of the issues raised by the public comments and FAA 
responses, including explanations of changes, are provided below. The 
full text of each commenter's submission is available in the docket for 
this rulemaking.

Discussion of Public Comments and Final Rule

Proposed Appendix O to Part 25

    In the NPRM, the FAA proposed to expand the existing icing 
conditions identified in appendix C of part 25 to include new SLD icing 
conditions defined in a new appendix O. The FAA made changes to 
appendix O as a result of comments received, but the general format 
remains unchanged. Appendix O is structured like part 25, appendix C, 
with part I defining icing conditions and part II defining airframe ice 
accretions for showing compliance with the airplane performance and 
handling qualities requirements of part 25, subpart B.
    Three private citizens provided comments related to the flight data 
collection approach used to acquire information about SLDs, the flight 
data used, and the analysis approach to generate the SLD engineering 
standards in part 25, appendix O. We will address these three 
commenters as a group.
    One concern was with the methods related to collecting and 
evaluating SLD icing conditions. One commenter stated that the research 
aircraft were well equipped to document the environment; however, both 
research aircraft had serious deficiencies regarding their on-board 
ability to document aircraft performance degradation from icing.
    Two commenters were concerned that only the database jointly 
created by Environment Canada and NASA was used to define the SLD icing 
conditions. Another commenter was concerned about the statistical 
significance of the data collected and did not think there was enough 
flight test evidence collected to provide the same level of probability 
established for part 25, appendix C, icing conditions. Two commenters 
stated that the flight test campaign failed to relate their data 
collection results to previously published results, such as those 
published by the University of Wyoming. Specifically, the commenters 
noted that appendix O does not contain data for a LWC greater than 0.45 
grams per cubic meter.
    One commenter also stated that other published analysis methods for 
an SLD encounter, such as the University of Wyoming LWC/drop size 
technique, result in the most adverse icing conditions and are not 
contained within appendix O. The commenter also noted that a clear 
distinction does not exist between the icing conditions defined in part 
25, appendix C, and the conditions defined in part 25, appendix O. This 
uncertainty would leave the pilot with the responsibility of making a 
scientific finding of which icing conditions the airplane was in, 
unless on-board droplet size and LWC measurement means and droplet data 
processing are provided.
    Regarding the flight research project's lack of on-board ability to 
document aircraft performance degradation from icing, we agree. 
However, obtaining measurements of aircraft performance within icing 
conditions was the lowest priority objective of the flight research 
project. The primary objectives of the test were to identify icing 
conditions beyond those covered in appendix C of part 25, and to 
identify a method for presenting the data in a way that could be used 
as an engineering standard. Specific aircraft performance and handling 
degradations in icing conditions are unique for each aircraft design. 
Performance degradation and handling qualities criteria for appendix C 
and appendix O icing encounters will need to be determined by the 
design approval holder for each aircraft design based on the applicable 
regulations, guidance materials, and testing as necessary to 
demonstrate compliance. This final rule specifies the expanded 
environmental icing conditions for consideration during the 
certification process as well as the performance and handling qualities 
that must be demonstrated.
    Regarding the sufficiency of the flight test data to form a 
statistically reliable database, we disagree. In developing appendix O, 
we used all historically available flight research data on SLD, not 
just the Environment Canada-NASA flight test data. This broad 
collection of data is statistically similar to the data that was used 
to develop appendix C.
    Regarding the comments about our proposed definition of SLD in 
appendix O, we also disagree. The University of Wyoming data were 
included in the FAA master database on SLD icing conditions. However, 
these data were not used to support the final determinations for the 
LWC values for the appendix O engineering standards. The University of 
Wyoming aircraft was not equipped with two-dimensional optical array 
probes, which were deemed essential by the IPHWG. Without the probes, 
it was not possible to distinguish between cloud drops and ice 
particles. Therefore, the University of Wyoming cloud data were not 
considered usable for supporting the analysis of SLD LWC/drop size 
properties for appendix O. As a result, the Environment Canada-NASA 
database was used to determine the engineering standards because of the 
quality of the data contained therein and the analysis methods used in 
that database. Both the quality of the data

[[Page 65511]]

and the analysis method used by the database ensured the accuracy of 
the definition for appendix O icing conditions.
    Regarding the comment that the University of Wyoming LWC/drop size 
technique results in the most adverse icing conditions and are not 
contained within appendix O, we disagree. That analysis technique 
suggests that one type of icing condition would be severe for all 
airplanes, regardless of the type of ice protection system used, or the 
extent of the protection. Appendix O contains a variety of icing 
conditions, not just those deemed most severe using the University of 
Wyoming analysis technique.
    In response to other comments, figures 1 and 4 of appendix O have 
been revised in this final rule to reflect the LWC proposed by the 
IPHWG. As a result, freezing drizzle conditions with a median volume 
diameter (MVD) greater than 40 microns fall within the adverse region 
that would be identified using the University of Wyoming LWC/drop size 
technique. No changes to appendix O were made as a result of these 
comments.
    With regard to the comment suggesting that the pilot will have to 
make a scientific finding to determine which icing conditions the 
airplane is in, we disagree. For those types of airplanes most 
vulnerable to SLD icing conditions, the level of operations in SLD 
icing conditions for which the airplane is approved will be determined 
during the airplane certification process in accordance with Sec.  
25.1420. If approval is requested for operations in a portion of the 
icing conditions defined in appendix O, then the airplane manufacturer 
will have to show that the pilot can determine if the operational 
envelope for which the airplane is certified has been exceeded as 
required by Sec.  25.1420(a)(2). Since part of the certification will 
be evaluating the means used to distinguish when the airplane is in 
icing conditions outside the certified envelope, the pilot will not be 
faced with the ambiguity of trying to determine the distribution of 
water drops in the environment in which he or she is flying.
    Several commenters said that proposed figures 1, 4, and 7 in 
appendix O of the NPRM were different than what was proposed by the 
IPHWG, and that the FAA did not provide an explanation for those 
differences. The commenters also noted that the higher LWC contained in 
the figures proposed in the NPRM could have a significant impact on an 
applicant's design. GSIS specifically noted that the higher water 
content defined in appendix O will have the effect of greatly 
increasing power requirements for electro-thermal deicing systems. 
Several commenters also suggested that figures 1, 3, 4, and 6 of 
appendix O would be easier to use if the corner data points were 
defined in the figures.
    We agree. We reviewed the figures proposed in the NPRM and the data 
used by the IPHWG to generate the figures. We revised figures 1 and 4 
to reflect the lower water content values proposed by the IPHWG, but 
the water content in appendix O is still higher than within appendix C 
at the same temperature. The higher water content may increase the 
power requirements for some electro-thermal deicing system designs, but 
not to the extent that may have been necessary with the water contents 
proposed in the NPRM. The environmental conditions defined in appendix 
O are valid conditions that will need to be considered for applicable 
future designs. Our review of the data used to generate the scaling 
factor curve in figure 7 indicates that the figure 7 proposed by the 
IPHWG in the task 2 working group report was incorrect; \4\ figure 7 in 
the NPRM was correct. Therefore, figure 7 in this final rule remains as 
proposed in the NPRM. Figures 1, 3, 4, and 6 of appendix O in this 
final rule have been revised to identify the corner data points for 
clarity.
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    \4\ The data used to complete the IPHWG report is detailed in 
report DOT/FAA/AR-09/10, Data and Analysis for the Development of an 
Engineering Standard for Supercooled Large Drop Conditions, dated 
March 2009. A copy of the report is available in the rule Docket No. 
FAA-2010-0636. The data used for figure 7 are described on pages 34-
39 of that report.
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    GSIS asked if there is a scientific basis for applying the 
horizontal extent of 17.4 nautical miles. GSIS also noted that the same 
MVD, temperature, and LWC at altitude exist in both appendix O and 
appendix C and asked the FAA to clearly define the mass distribution 
boundary between appendix O and appendix C.
    Our application of the 17.4 nautical mile horizontal extent in 
appendix O was made on a practical basis and not on a purely scientific 
basis; it was selected for consistency with the appendix C continuous 
maximum icing conditions with which designers are already familiar. We 
are unaware of any scientific reasons for not applying the 17.4 
nautical mile horizontal extent in this manner.
    The LWC values in appendix O are based on an analysis of the data 
from the jointly created Environment Canada-NASA flight research SLD 
database, report DOT/FAA/AR-09/10.\5\ Figure 11 of that report shows a 
plot of temperature versus LWC for appendix O freezing drizzle 
environments that is valid for the reference distance of 17.4 nautical 
miles (32.2 km). Appendix C and appendix O define environmental 
conditions that overlap one another as the conditions transition from 
appendix C to appendix O. Therefore, there is not a clear mass 
distribution boundary that can be defined.
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    \5\ A copy of the report is in the rule Docket No. FAA-2010-
0636.
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    One commenter, a private citizen, noted that the NPRM did not 
identify the vertical extent for part 25, appendix O, figure 6. We 
disagree. The pressure altitude range and vertical extent for freezing 
rain were provided in appendix O, part I, paragraph (b) in the NPRM 
located under figure 3. We clarified appendix O, part I, by moving all 
of the general text describing the meteorological parameters, including 
vertical extent, ahead of the figures.
    One commenter suggested that the icing conditions in appendix O 
should be revised to reflect water drop distribution as a function of 
mean effective diameter (MED) as opposed to MVD. We do not agree. MED 
is the term used in part 25, appendix C. Examination of National 
Advisory Committee for Aeronautics (NACA) references \6\ shows that MED 
is the same as MVD if certain assumptions are made about the drop 
distribution, namely that it is one of the Langmuir distributions. MVD, 
as the more general term, is applicable to any drop distribution. Since 
the drop distribution described in appendix O does not follow a 
Langmuir distribution, MVD is more appropriate. We did not change the 
final rule or appendix O as a result of this comment.
---------------------------------------------------------------------------

    \6\ National Advisory Committee for Aeronautics Technical Note 
2738, A Probability Analysis of the Factors Conducive to Aircraft 
Icing in the United States, by William Lewis and Norman R. Bergrun, 
July 1952.
---------------------------------------------------------------------------

    A private citizen commented that appendix O should define a time to 
use for delayed recognition of entry into icing conditions and the time 
to exit icing conditions. We do not agree. The responsibility for 
proposing delayed recognition times, delayed ice protection system 
activation times, or times required to exit icing conditions, based on 
unique operational procedures or performance characteristics of the ice 
protection system, rests with the applicant. We did not change the rule 
based on this comment.
    Boeing suggested a change to appendix O, part I, paragraph (c), to 
add an equation to determine the LWC for

[[Page 65512]]

horizontal distances other than 17.4 nautical miles.
    We agree that adding such an equation could be beneficial. The 
equation proposed by Boeing, however, expressed horizontal distance in 
kilometers, which would be inconsistent with other figures in appendix 
O. Instead of the equation proposed by Boeing, we added to appendix O, 
part I, paragraph (c), a similar equation that uses units of nautical 
miles.
    Several commenters noted that appendix O, part II, paragraph 
(b)(5)(ii), in the NPRM made reference to Sec. Sec.  25.143(k) and 
25.207(k). However, Sec. Sec.  25.143(k) and 25.207(k) do not exist in 
the current part 25 and were not added by the NPRM.
    We agree. The references to those sections were inadvertently 
included in the NPRM. We revised appendix O to delete the statement 
referencing Sec. Sec.  25.143(k) and 25.207(k).
    Airbus noted that part II, paragraph (c)(7)(v) of appendix O states 
that crew activation of the ice protection system is in accordance with 
a normal operating procedure provided in the AFM, except that after 
beginning the takeoff roll, it must be assumed that the crew does not 
take any action to activate the ice protection system until the 
airplane is at least 400 feet above the takeoff surface. Airbus 
commented that this appears to be a direct cut and paste from the 
appendix C regulations and recommended removing the sentence. Airbus 
claimed that while this is perhaps understandable for appendix C icing 
conditions, it would seem reasonable to expect the crew to activate the 
wing anti-ice system (WAIS) prior to takeoff if there are SLD icing 
conditions within 400 feet of the runway, whether the AFM specifically 
states that it is required or not.
    We do not agree. The rule addresses flightcrew actions occurring 
after beginning the takeoff roll, while Airbus' comment refers to 
actions that the flightcrew would take before beginning the takeoff. 
Nevertheless, the FAA does not expect flightcrews to be aware of all 
SLD icing conditions that may exist up to a height of 400 feet above 
the takeoff surface, nor do we agree that it would be reasonable to 
expect the flightcrew to activate the WAIS prior to takeoff if there 
was no procedure telling them to do so. We did not change the rule 
based on this comment.
    Embraer commented that the last sentence in appendix O, part II, 
paragraph (b)(2)(ii), which proposed to define the holding ice 
conditions in part 25, appendix O, part II, paragraph (b)(2), should be 
applicable to the whole of paragraph (b)(2), and not just to the 
transit time through one appendix O cloud and one appendix C cloud 
specified in paragraph (b)(2)(ii). Embraer commented that it would be 
clearer to describe the total holding time in a separate paragraph 
(b)(2)(iii) that says: ``The total exposure to the icing conditions 
need not exceed 45 minutes.'' We agree, and changed appendix O, part 
II, paragraph (b)(2), to indicate that the total exposure time for 
holding ice does not need to exceed 45 minutes.

Availability of Engineering Tools To Show Compliance With the Rule

    Several commenters stated that available engineering tools (icing 
wind tunnels and tankers, ice accretion prediction codes, and other 
analysis methods) are inadequate for showing compliance with the new 
rule. Bombardier commented that without validated tools, it is not 
practical to implement the requirements proposed in the NPRM. 
Bombardier believed that efforts should be focused on implementing 
incremental regulatory changes in parallel with the appropriate 
technological developments to meet that regulatory change.
    Boeing commented similarly, stating that the FAA and NASA had 
developed a plan several years ago to align the timing of the new 
regulations with the availability of validated engineering tools and 
test capabilities for SLD conditions. Boeing added that the tools and 
test facilities necessary to effectively demonstrate compliance with 
the regulations are not available, and that this lack of availability 
will be particularly problematic for applicants desiring to operate 
within appendix O conditions. Boeing noted that the current situation 
will require applicants to either use highly conservative approaches, 
build new icing wind tunnel facilities, or expend great efforts to 
conduct extensive flight testing in search of a meteorological 
condition, which occurs very infrequently. Boeing said that this was 
not the approach anticipated by industry, and that it will impose a 
severe burden on many applicants beyond that established in the 
economic evaluation of the proposed regulation, without adding any 
commensurate safety benefit.
    AKC also commented that current test facilities are limited in 
their ability to produce freezing drizzle, in particular drop 
distributions greater than 40 microns MVD. The water drop distribution 
curves provided in appendix O are not produced by any facility known to 
AKC, and there are no facilities that produce freezing rain in a 
fashion that duplicates either the flight or ground test environment.
    The NRC of Canada's comments reflected concerns about how the water 
drop distribution curves in appendix O are to be used. Further, a 
private citizen commented that the droplet diameters for appendix O 
conditions can only be reproduced in a few icing wind tunnels.
    We do not agree that available engineering tools (icing wind 
tunnels and tankers, ice accretion prediction codes, and other analysis 
methods) are inadequate for showing compliance with the new rule. We 
recognize that the current engineering tools available to show 
compliance with the new SLD rule have not been validated in every 
aspect, and also have some limitations. We also recognize that for 
freezing rain, few validated engineering tools are available. However, 
methods are available to simulate freezing drizzle. Further, we 
recognize that relying upon available simulation methods, combined with 
engineering judgment, will be required for finding compliance with the 
appendix O requirements of part 25, especially for freezing rain 
conditions.
    After reviewing the current state of available compliance methods 
and engineering tools, the FAA has determined that there is sufficient 
capability for applicants to effectively demonstrate compliance with 
this final rule. The IPHWG evaluated the current capabilities of these 
tools in 2008-2009 during a review requested by industry members 
through ARAC. The IPHWG evaluation of SLD engineering tools, which 
proposed methods of compliance based on the current state of the 
available engineering tools, supports the FAA conclusion. The FAA 
considered estimates provided by industry and has made adjustments to 
the proposed economic evaluation, which is incorporated in the economic 
evaluation for this final rule. This adjustment increases the cost for 
complying with the requirements of this final rule; however, this final 
rule remains cost beneficial. A summary of the final regulatory 
evaluation is provided in the ``Regulatory Notices and Analyses'' 
section of this final rule and the complete document is included in the 
public docket.
    As to freezing drizzle, the current icing wind tunnel test 
capabilities for SLD icing conditions have been demonstrated. However, 
we recognize that some limitations exist: Icing wind tunnel spray 
systems evaluated during the IPHWG's review do not support bi-modal 
mass distributions (mass ``peaks'' for two different drop sizes) 
provided in appendix O and do not produce realistic freezing rain 
simulations for the

[[Page 65513]]

majority of those conditions. NASA examined alternate spray methods to 
simulate portions of a bi-modal spray using spray sequencing techniques 
to approximate drop distributions found in natural conditions 
(reference: American Institute of Aeronautics and Astronautics report 
AIAA 2005-76, Simulation of a Bimodal Large Droplet Icing Cloud in the 
NASA Icing Research Tunnel \7\). NASA demonstrated the water spray 
sequencing technique for an airfoil with unprotected surfaces and the 
results showed rougher ice accretion textures than appendix C ice 
shapes.
---------------------------------------------------------------------------

    \7\ A copy of this report is available in the rule Docket No. 
FAA-2010-0636.
---------------------------------------------------------------------------

    Experience indicates that SLD icing conditions generally result in 
rougher ice accretion textures. NASA has also developed preliminary 
scaling methods for SLD test applications and has developed large 
droplet algorithm improvements to its ice accretion prediction code by 
adding SLD subroutines. Other ice accretion code developers have 
incorporated SLD capabilities in their respective computational tools. 
A number of icing wind tunnel owners have tested SLD icing conditions 
in their facilities and are capable of performing tests for at least a 
portion of the appendix O environments.
    Regarding flight testing, Sec.  25.1420 requires that applicants 
provide analysis to establish that ice protection for the various 
airplane components is adequate, taking into account the various 
operational configurations. Section 25.1420 also describes flight 
testing in natural or simulated icing conditions, as necessary, to 
support the analysis. The IPHWG acknowledged the difficulties in flight 
testing in natural SLD, and agreed it would not be specifically 
required under Sec.  25.1420. We concur, and have left flight testing 
as an option in the regulation. Until the engineering tools become more 
mature, flight tests in natural appendix O icing conditions may be 
necessary to achieve certification for unrestricted flight in appendix 
O conditions in accordance with Sec.  25.1420(a)(3).

Proposed Revisions to Sec.  33.68 Should Not Apply to Engines Installed 
on Rotorcraft

    Eurocopter and Turbomeca noted the proposed part 33 changes would 
apply to all turbine engines, including turboshaft engines intended for 
installation in rotorcraft. The proposed revision to Sec.  33.68 would 
require all turbine engines to be capable of operating in the extended 
icing conditions defined in part 25, appendix O. However, the IPHWG 
task 2 report and the NPRM only addressed airplane accidents and 
incidents; it did not include rotorcraft. Eurocopter and Turbomeca 
proposed provisions to exclude rotorcraft from the new engine 
requirements. The FAA did not receive any comments providing specific 
support for the proposed applicability to rotorcraft.
    We agree. The IPHWG did not review rotorcraft accidents or 
incidents in icing conditions and did not propose rulemaking associated 
with rotorcraft. As a result, we revised the proposed Sec.  33.68 to 
separate the icing requirements for turboshaft engines used for 
rotorcraft from turbojet, turbofan, and turboprop engines used for 
airplanes. The icing requirements pertaining to turboshaft engines are 
unchanged and require that turboshaft engines operate safely throughout 
the icing conditions defined in part 29, appendix C. Section 33.68 now 
requires that turbojet, turbofan, and turboprop engines not installed 
on rotorcraft operate safely throughout the icing conditions defined in 
part 25, appendix C, the SLD conditions defined in part 25, appendix O, 
and the mixed phase and ice crystal conditions defined in part 33, 
appendix D.

Applicability of Proposed Sec.  25.1420

    In the NPRM, the FAA proposed to add a new Sec.  25.1420. Proposed 
Sec.  25.1420 would have required specific airplanes certified for 
flight in icing conditions to be capable of either: (1) Operating 
safely within the new SLD icing conditions defined in part 25, appendix 
O; (2) operating safely in a portion of the new appendix O conditions, 
with the capability to detect when conditions beyond those used for 
certification have been encountered, and then safely exit all icing 
conditions; or (3) have a means to detect when appendix O icing 
conditions are encountered, and be capable of safely exiting all icing 
conditions. The FAA proposed to limit the applicability of Sec.  
25.1420 to airplanes that have a maximum takeoff weight (MTOW) of less 
than 60,000 pounds, or airplanes equipped with reversible flight 
controls regardless of MTOW.
    The applicability of Sec.  25.1420 was discussed within the IPHWG 
and consensus could not be reached. A discussion of this issue was 
provided in the NPRM under the heading ``Differences from the ARAC 
Recommendations.'' Bombardier, ALPA, EASA, Goodrich, Gulfstream, the 
NTSB, and the TCCA provided comments to the NPRM that supported the 
majority position of the IPHWG, questioning the technical justification 
used to exclude airplanes with a MTOW of 60,000 pounds or greater. 
Airbus, AIA, Boeing, and GAMA provided comments in response to the NPRM 
to support the proposed applicability based on MTOW because airplanes 
with a MTOW of 60,000 pounds or greater have not previously experienced 
accidents or incidents associated with flight in SLD. Embraer and Pratt 
& Whitney Canada comments to the NPRM specifically noted support for 
AIA's position.
    A review of the IPHWG analysis indicates that airplanes with a MTOW 
of 60,000 pounds or greater have not experienced accidents or incidents 
associated with flight in SLD. The FAA originally considered including 
all new airplanes in the applicability for Sec.  25.1420, regardless of 
MTOW; however, the projected costs of extending the rule to include 
airplanes with a MTOW of 60,000 pounds or greater exceeded the 
projected benefits due to the positive in-service history (i.e., lack 
of accidents) of these airplanes in SLD.
    The commenters did not present any new data or information that was 
not discussed within the IPHWG, or discussed within the NPRM. The 
commenters that opposed limiting the applicability of the rule 
suggested that lift and control surface size, or wing chord length, are 
important parameters affecting sensitivity to a given ice accretion. 
They based their opposition on airplane weight, in part, because the 
ratio of wing and control surface sizes to airplane weight varies 
between airplane designs.
    We agree that design features such as control surface size and wing 
chord length are important parameters, which can affect the sensitivity 
of a wing to the icing conditions described in part 25, appendix O. As 
proposed in the NPRM, in order to issue a rule with estimated costs 
commensurate with the estimated benefits, the applicability of Sec.  
25.1420 is limited based on airplane weight due to the positive service 
histories of certified airplanes.
    If future designs for larger airplanes contain novel or unusual 
design features that affect this successful in-service history, and 
those design features make the airplane more susceptible to the effects 
of flight in SLD icing conditions, the FAA can issue special conditions 
to provide adequate safety standards. The FAA issues special conditions 
in accordance with Sec.  21.16. No changes have been made to the 
applicability of Sec.  25.1420 as a result of these comments.

[[Page 65514]]

Clarification of Definitions

    Embraer noted that Sec.  25.1420(b) uses the terms ``simulated 
icing tests'' and ``simulated ice shapes'' in various subparagraphs. 
Embraer suggested that subparagraphs Sec.  25.1420(b)(1) and (b)(2) use 
the phrase ``artificial ice'' as defined in Advisory Circular (AC) 25-
28, Compliance of Transport Category Airplanes with Certification 
Requirements for Flight in Icing Conditions, instead of ``simulated 
icing tests.''
    We do not agree. Section 25.1420(b)(1) and (b)(2) describe test 
methods, not the resulting ice shapes. The terminology ``simulated 
icing tests'' is used in Sec.  25.1420 consistently with Sec.  25.1419. 
We added definitions for ``Simulated Ice Shape'' and ``Simulated Icing 
Test'' to Sec.  25.1420 that are consistent with previously issued 
guidance.
    AIA, Boeing, and GAMA suggested a clarification to the definition 
of ``reversible flight controls.'' AIA and GAMA suggested that the 
addition of servo tab inputs in the examples provides a more complete 
and accurate description.
    We agree and have clarified the definition of ``reversible flight 
controls'' to include the example of servo tab inputs. In addition, 
since the definition of ``reversible flight controls'' is necessary to 
determine the applicability of Sec.  25.1420, we added the definition 
to Sec.  25.1420.

Applicability of Proposed Appendix O Icing Conditions to Part 23 
Airplanes and Previously Certified Part 25 Airplanes

    The NTSB and a private citizen commented that the icing conditions 
proposed in appendix O should be applicable to part 23 airplanes 
because they are the type of airplanes most affected by flight into 
icing conditions. The NTSB also stated that the proposed rule should be 
expanded beyond newly certified airplanes to include all deice boot-
equipped airplanes currently in service that are certified for flight 
in icing conditions (reference NTSB Safety Recommendation A-07-16).\8\ 
The NTSB pointed out SLD is an atmospheric condition that can create 
dangerous flight conditions for both the current fleet of aircraft and 
newly certified aircraft.
---------------------------------------------------------------------------

    \8\ NTSB Safety Recommendation A-07-16 is available in the rule 
Docket No. FAA-2010-0636 and on the Internet at http://www.ntsb.gov/doclib/recletters/2007/A07_12_17.pdf.
---------------------------------------------------------------------------

    Regarding the applicability of proposed appendix O to part 23 
airplanes, we disagree with adding part 23 airplanes to the 
applicability, as that is beyond the scope of this rulemaking. However, 
we chartered an Aviation Rulemaking Committee (ARC) to review the 
IPHWG's rulemaking recommendations for part 25 and to make similar 
recommendations for part 23. The ARC transmitted a report detailing 
part 23 rulemaking recommendations to the FAA in a letter dated 
February 19, 2011, and provided supplemental recommendations in a 
letter dated April 27, 2011. The ARC transmitted its recommendations 
for a final task in early 2012. We are studying these recommendations 
and may pursue additional rulemaking for part 23 airplanes.
    We agree that severe icing conditions, including SLD, can create 
dangerous flight conditions for both current and future airplanes. 
However, we do not agree that the part 25 and part 33 rule changes 
discussed in this amendment should apply to existing airplanes. Such a 
retroactive application would, in effect, be changing the certification 
basis of operational airplanes to correct an unsafe condition, 
something generally done by airworthiness directive (AD). To address 
the unsafe condition, we have already issued ADs to mandate procedures 
to activate the ice protection equipment at the first sign of ice 
accretion, and to incorporate procedures into the AFM so the flightcrew 
can identify when they are in severe icing conditions that exceed 
certificated limitations, and safely exit.
    New airworthiness standards are not intended to correct an unsafe 
condition; rather, they are intended to improve the level of safety for 
new airplane designs. In the context of SLD, we are considering 
operational rules to mandate certain elements of the airworthiness 
standards adopted in this rulemaking for previously certified 
airplanes. However, those requirements are beyond the scope of this 
rulemaking and require separate rulemaking action.

Applicability of Part 33, Appendix D, to Sec.  25.1093, Induction 
System Icing Protection, and Sec.  33.68, Induction System Icing

    The NTSB supported changes to Sec. Sec.  33.68 and 33.77, noting 
that since we issued an icing-related AD for the Beechjet 400A no 
additional reports of unsafe icing conditions on that airplane have 
been noted. The FAA infers that the NTSB was referring to AD 2006-21-
02.\9\ That AD was issued following reports of dual engine flameouts in 
high altitude icing conditions believed to include ice crystals. AIA, 
Airbus, Boeing, and GAMA supported the addition of mixed phase and ice 
crystal conditions, such as those defined in part 33, appendix D.
---------------------------------------------------------------------------

    \9\ AD 2006-21-02, Docket No. FAA-2006-26004, published in the 
Federal Register on October 10, 2006 (71 FR 29363), is applicable to 
Raytheon (Beech) Model 400, 400A, and 400T series airplanes; and 
Raytheon (Mitsubishi) Model MU-300 airplanes.
---------------------------------------------------------------------------

    Honeywell commented that the current lack of and/or immature state 
of engine test facilities to demonstrate compliance to part 33, 
appendix D, could result in a significant increase in an applicant's 
activities to show compliance because of the additional flight testing 
required to locate the ice crystal conditions. Honeywell also noted 
that flying in actual ice crystal conditions would put the flightcrew 
at considerable risk. Honeywell recommended that appendix D be removed 
until test facilities have developed the capabilities to run tests for 
ice crystal conditions. Honeywell also suggested that the FAA make 
research funds available to facilities to develop this capability.
    We agree, in part. We agree that only limited capability exists for 
testing engines in ice crystal conditions. We also agree that 
flightcrews unnecessarily operating in icing conditions puts them at 
risk. We do not agree, however, that appendix D should be removed until 
test facilities develop the capabilities to run tests for ice crystal 
conditions, or that FAA make funds available for research to develop 
these capabilities. Section 33.68(e) allows for certification 
demonstration by test, analysis, or combination of the two. Consistent 
with ARAC Engine Harmonization Working Group (EHWG) recommendations, 
until ice crystal tools and test techniques have been developed and 
validated, the engine manufacturer may use a comparative analysis to 
specific field events. This analysis should show that the new engine 
cycle or design feature, or both, would result in acceptable engine 
operation when operating in the ice crystal environment defined in 
appendix D to part 33. This comparative analysis should also take into 
account both suspected susceptible design features, as well as 
mitigating design features. We did not change the rule based on this 
comment.
    GSIS suggested that provisions be made for a detect-and-exit 
strategy for part 33, appendix D, conditions; similar to what was 
proposed in the NPRM for part 25, appendix O, conditions.
    We disagree. We do not believe part 33, appendix D, conditions can 
be detected with enough time to exit before damage occurs. Therefore, a 
detect-and-

[[Page 65515]]

exit strategy for part 33, appendix D, conditions is inappropriate. As 
proposed in the NPRM, the mixed phase and ice crystal icing conditions 
defined in part 33, appendix D, have been added to Sec. Sec.  
25.1093(b)(1) and 33.68(a).

Applicability of Proposed Appendix O to Sec.  25.1093, Induction System 
Icing Protection, and Sec.  33.68, Induction System Icing

    AIA, Airbus, Boeing, and GAMA provided comments that there are no 
known events that support a safety concern due to engine induction 
system icing in SLD aloft. In particular, the EHWG evaluated known 
icing-related engine events since 1988 and found no events in SLD 
aloft. The EHWG credited this result to the current rigorous compliance 
to part 25, appendix C, conditions for engines. The commenters believe 
that the safety of these systems for flight in appendix O conditions 
has already been proven by service history. The commenters state that 
continuing to certify future systems to the requirements for appendix C 
icing conditions, in conjunction with consideration of excellent 
service history of similar designs in appendix O conditions, should be 
acceptable assurance of the safety of future designs. The commenters 
suggested that consideration of the icing conditions defined in 
appendix O be removed from Sec.  25.1093.
    We agree that there are no known events that support a safety 
concern due to engine induction system icing in SLD aloft. However, 
there have been reports of engine fan damage or high vibration while 
operating in SLD icing conditions. The ARAC database on engine events 
contains 231 icing events reported by engine manufacturers from 
approximately 1988 through 2003, and includes part 25, appendix C; part 
25, appendix O; and part 33, appendix D events. Although the intent of 
the event database was to focus on icing events outside of appendix C, 
there are several appendix C events included in this database. The 
event database does not include any accidents.
    The EHWG identified 46 part 25, appendix O (SLD) events. All events 
occurred on the ground and resulted in fan damage and/or high 
vibrations so a precise effect on the safety of these events was not 
discernible.
    Additionally, the EHWG identified nine additional events that it 
thought might have been related to operations in SLD icing conditions: 
Four were in-flight and all nine were on tail mounted engine 
configurations. Again, the events resulted in fan damage and/or high 
vibrations, with indeterminable power loss. Although these nine events 
are of concern, the EHWG did not judge them to be safety significant.
    An additional 14 in-flight events were not clearly identifiable as 
SLD events but were described as heavy icing below 22,000 feet and 
resulted in fan damage and/or high vibrations. These events did not 
clearly fall within conditions defined in either appendix C or appendix 
O. However, the general description of the icing conditions and engine 
damage is consistent with reports of engine damage that occurred within 
the icing conditions defined in appendix O, so those might have been 
SLD events.
    After reviewing the data, the EHWG clearly identified SLD as a 
threat for engine damage during ground operations. Furthermore, the 
EHWG could not rule out SLD as a potential in-flight safety threat, and 
decided to include it as part of its recommendations to the FAA. As 
proposed in the NPRM, the part 25, appendix O, SLD icing conditions 
have been added to Sec.  33.68. Also, as proposed in the NPRM, Sec.  
33.77 contains requirements to demonstrate engine capability to ingest 
the applicable minimum ice slab defined in Table 1 of Sec.  33.77. The 
ice slab sizes defined in Table 1 of Sec.  33.77 are a function of the 
engine inlet diameter. Turbojet, turbofan, and turboprop engine 
manufacturers must demonstrate, in part, that the engine will continue 
to operate throughout its power range in the icing conditions defined 
in part 25, appendix O, and following ingestion of an ice slab that is 
a function of the engine inlet diameter. The changes to the 
requirements in Sec. Sec.  33.68 and 33.77 are intended to improve the 
level of safety for turbojet, turbofan, and turboprop engines used on 
transport category airplanes in icing conditions, in part because of 
reports of engine damage or high engine vibrations while operating in 
SLD conditions.
    We agree large airplanes that have likely encountered appendix O 
conditions have had a successful in-service history with no clearly 
identifiable safety significant events. After considering the comments 
received, we revised Sec.  25.1093(b), compared to what was proposed in 
the NPRM, so consideration of the icing conditions described in 
appendix O does not apply to airplanes with a MTOW equal to or greater 
than 60,000 pounds. As proposed in the NPRM, the applicability of the 
icing conditions described in part 25, appendix C; part 33, appendix D; 
and falling and blowing snow remain applicable to all turbine engine 
installations on transport category airplanes. In addition, the engine 
requirements in Sec. Sec.  33.68 and 33.77 for operation in all icing 
conditions still apply to engines installed on part 25 airplanes 
regardless of the airplanes' MTOW. The applicability of appendix O 
conditions in Sec.  25.1093(b) as a function of airplane weight is 
consistent with the revised applicability of Sec.  25.1420, which 
establishes minimum airworthiness standards for detection and safe 
operation in appendix O conditions. Airplanes that have been 
susceptible to performance issues while operating in SLD icing 
conditions have been smaller airplanes with a MTOW less than 60,000 
pounds.
    Section 25.1093(b) was revised to provide relief for larger 
airplanes because of the successful in-service history of existing 
larger airplane designs and larger airplane engine inlet designs. As 
previously discussed, the changes to the requirements in Sec. Sec.  
33.68 and 33.77 are intended to improve the level of safety for turbine 
engines used on all airplanes, including large airplanes, while 
operating in SLD conditions. If future designs for larger airplanes 
contain novel or unusual design features that affect this successful 
in-service history, and those design features make the airplane more 
susceptible to the effects of flight in SLD icing conditions, the FAA 
can issue special conditions to provide adequate safety standards.
    Boeing, AIA, and GAMA also provided comments on the results of an 
SLD analysis, including the use of the NASA Lewis Ice Accretion 
Program, commonly referred to as LEWICE. The analysis yielded overly 
conservative accreted ice mass calculations resulting in large amounts 
of ice on the radome. The results from this analysis indicated to 
Boeing that radome ice shedding would be a concern, and it would 
require ice protection on the currently unprotected radome surfaces to 
reduce ice build-up to acceptable limits. The weight increase for 
radome ice protection equipment would result in increased fuel burn and 
increased operational costs that were not included in the IPHWG 
economic analysis. Boeing also stated that most large airplanes are 
operating without restrictions today and are safely encountering SLD 
conditions.
    Analytical methods used by Boeing to determine SLD ice accretions 
on radomes show considerably higher ice mass accretions than either 
past calculations or past experience has indicated for other icing 
conditions. These analyses were never presented to the IPHWG and 
details were not

[[Page 65516]]

included with Boeing's comments to support the FAA's evaluation of 
Boeing's methods. As previously discussed, we revised Sec.  25.1093(b) 
compared to what was proposed in the NPRM. For the purposes of 
compliance with Sec.  25.1093(b), the icing conditions defined in 
appendix O are not applicable to airplanes with a MTOW equal to or 
greater than 60,000 pounds. To show compliance with Sec.  25.1093(b), 
analysis may be used for the radome as a potential airframe ice source. 
For compliance with Sec.  25.1093(b), applicants may use qualitative 
analysis supported by similarity to a previous design with a successful 
service history to show that ice accretions ingested into the engine 
from the new airplane design will be less than the ice slab size 
presented in Sec.  33.77 Table 1, ``Minimum Ice Slab Dimensions Based 
on Engine Inlet Size.''

Applicability of Proposed Appendix O to Sec.  25.773, Pilot Compartment 
View

    AIA, Airbus, Boeing, and GAMA commented that there are no known 
events that support a safety concern due to windshield icing in SLD 
aloft. The commenters state the safety of these systems for flight in 
appendix O conditions has been proven by service history. They believe 
that continuing to certify future systems to the requirements for 
appendix C icing conditions, in conjunction with consideration of 
excellent service history of similar designs in appendix O conditions, 
should be an acceptable assurance of the safety of future designs. One 
commenter, an individual, commented that Sec.  25.773 should not be 
changed, as ice accretion on the windshield is one of the few 
indications used to recognize the condition.
    We do not agree. Section 25.773 is intended to ensure that a clear 
portion of the windshield is maintained in icing conditions, which 
enhances safety in icing conditions. For airplanes certified to detect 
appendix O conditions, or a portion of appendix O conditions, and 
required to exit all icing conditions when the icing conditions used 
for certification have been exceeded, the pilot must have a clear view 
out the windshield; not only when the airplane is in appendix O icing 
conditions, but also during the time it takes to detect and exit all 
icing conditions within which the airplane is not approved to operate. 
For airplanes not certified with the detect-and-exit strategy, appendix 
C and appendix O conditions need to be considered for the entire time 
the airplane is in the applicable icing conditions.
    Section 25.773 does not require the windshield to be completely 
free of ice in all icing conditions. Therefore, this requirement does 
not preclude using ice accreting in certain locations on the windshield 
as an indication that the airplane is in icing conditions beyond those 
in which it is approved to operate. We did not change the rule based on 
these comments.

Applicability of Proposed Appendix O to Sec.  25.1323, Airspeed 
Indicating System, Sec.  25.1324, Angle of Attack System, and Sec.  
25.1325, Static Pressure Systems

    AIA, Airbus, Boeing, and GAMA commented that there are no known 
events that support an in-flight safety concern for angle of attack 
systems in SLD aloft. They believe the safety of these component 
systems for flight in appendix O conditions has already been proven by 
service history. The commenters recommended the reference to appendix O 
be removed from the requirements in Sec. Sec.  25.1323, 25.1324, and 
25.1325.
    We do not agree. If certification for flight in icing is desired, 
part 25 requires the airplane to be capable of safely operating in 
icing conditions. The airplane and its components are taken into 
account during flight in icing certification programs. For these 
reasons, all icing conditions should be considered. Sections 25.1323, 
25.1324, and 25.1325 include considerations for the SLD icing 
environment defined in part 25, appendix O.

Applicability of Proposed Appendix O to Sec.  25.929, Propeller Deicing

    AIA and GAMA commented that there are no known events that support 
a safety concern with propeller icing in SLD. In particular, AIA and 
GAMA noted the EHWG evaluated all known icing-related events since 1988 
and found no events in SLD aloft. The commenters credit the current 
rigorous compliance using appendix C conditions for this result. The 
commenters believe the safety of these systems for flight in appendix O 
conditions has already been proven by service history. They further 
believe that continuing to certify future systems to the requirements 
for appendix C icing conditions, in conjunction with consideration of 
excellent service history of similar designs in appendix O conditions, 
should be acceptable assurance for the safety of future designs.
    We do not agree. Propeller icing is typically not implicated in 
events because ice accretion on the propeller is usually not visible in 
flight. However, in one suspected SLD event \10\ included in the IPHWG 
list of applicable events, the NTSB Performance Group reported that the 
flight data recorder derived drag increment was much higher than an 
increment measured in flight test with intercycle ice (by a factor of 2 
near the time where the pilot lost control of the airplane). The NTSB 
report does not speculate what caused the large drag increment, but it 
could have been airframe SLD ice accretion, propeller SLD ice 
accretion, or a combination of both. In addition, appendix J in AC 20-
73A, Aircraft Ice Protection, dated August 16, 2006, documents a flight 
test encounter in which suspected SLD caused a severe performance 
penalty due to propeller ice accretion. FAA research tests, documented 
in report DOT/FAA/AR-06/60, Propeller Icing Tunnel Test on a Full-Scale 
Turboprop Engine,\11\ have duplicated the event discussed in the AC, 
and showed that propeller ice accretion and resulting propeller 
efficiency loss is greater in SLD compared to appendix C conditions.
---------------------------------------------------------------------------

    \10\ NTSB Investigation No. DFCA01MA031, Embraer EMB-120 Zero 
Injury Incident Near West Palm Beach, Florida on March 19, 2001, 
http://www.ntsb.gov.
    \11\ FAA Data Report DOT/FAA/AR-06/60, Propeller Icing Tunnel 
Test on a Full-Scale Turboprop Engine, dated March 2010. A copy of 
this report is available in the rule Docket No. FAA-2010-0636.
---------------------------------------------------------------------------

    After further consideration, we have revised Sec.  25.929 to 
require a means to prevent or remove hazardous ice accumulations that 
could form in the icing conditions defined in appendix C and the 
portions of appendix O for which the airplane is approved for flight. 
As compared to the NPRM, the phrase ``defined in appendices C and O'' 
has been replaced with ``defined in appendix C and in the portions of 
appendix O of this part for which the airplane is approved for 
flight.''
    A private citizen commented that the words ``would jeopardize 
engine performance'' in the last portion of Sec.  25.929(a) makes this 
requirement specific to engine performance. The commenter requested 
that the words be stricken from the regulation. The commenter did not 
provide justification to substantiate his proposed change.
    We do not agree. First, we did not propose a change to this portion 
of the rule. Second, we reviewed the wording presented by the IPHWG and 
agree with its intent and its phrasing. Its applicability is broader 
than just an engine rule. We did not change the rule based on this 
comment.

[[Page 65517]]

Engine and Engine Installation Requirements

    The RAA commented that current facilities lack the capability to 
test large turbofans at very cold temperatures, and, while new sites 
may come on-line in the future, such facilities could not be 
constructed to comply with the proposed test conditions. The RAA also 
pointed out that future airplanes would not be certified for operations 
below zero degrees Fahrenheit when ``freezing fog'' is present, so it 
would create a restriction to what is currently considered a safe 
operating condition.
    Airbus, AIA, Boeing, GAMA, GE, and a private citizen suggested that 
the choice of ambient temperature for the ground freezing fog rime 
icing demonstration should be driven by critical point analysis, as 
required by Sec.  33.68(b)(1). This analysis could also be used to show 
that a more critical point does not exist at temperatures below the 
Table 1, condition 2, test temperatures in Sec.  33.68. Airbus, AIA, 
Boeing, GAMA, GE, a private citizen, and RAA further suggested that the 
applicant should be permitted to use analysis to demonstrate safe 
operation of the engine at temperatures below the required test 
demonstration temperature. If safe operation is shown by this analysis, 
a temperature limitation would not be required for the AFM.
    Airbus also suggested a further change to Sec.  25.1093(b)(2) to 
ensure that the test is performed in accordance with aircraft 
procedures to provide adequate conservatism. These procedures are 
defined in collaboration with the engine manufacturer and may be 
defined on the basis of engine certification or development test 
results.
    EASA and the FAA have recently addressed cold ground fog 
conditions. Specifically, the choice of ambient temperature for the 
ground freezing fog rime icing demonstration should be driven by 
critical point analysis (as required by Sec.  33.68(b)(1)). We 
determined this analysis may also be used to show that at colder 
temperatures below the Table 1, condition 2, test temperatures in Sec.  
33.68, a more critical point does not exist. The analysis may also be 
used to demonstrate safe operation of the engine at temperatures below 
the required test demonstration. If an applicant does not show 
unlimited cold temperature operation, then the minimum ambient 
temperature that was demonstrated through test and analysis should also 
be a limitation. Finally, the acceleration to takeoff power or thrust 
should be accomplished in accordance with the procedures defined in the 
AFM. As a result, we changed Sec. Sec.  25.1093(b)(2) and 25.1521(c)(3) 
based on these comments, to reflect these changes and recent 
developments with EASA.
    AIA, GAMA, and a private citizen commented that the MVD for high 
LWC in Table 2 of Sec.  33.68 may be difficult to achieve in practice 
due to icing facility constraints, and may result in repetitive 
equivalent level of safety (ELOS) findings. Expanding the upper limits 
of droplet size ranges will allow flexibility in test demonstrations. 
An upper limit of 30 microns for glaze ice conditions (points 1 and 3 
in Table 1) and 23 microns for rime ice conditions (point 2 in Table 1) 
can be accepted if the critical point analysis shows that the engine is 
tested to equivalent or greater severity.
    AIA, GAMA, and a private citizen also suggested changes to the drop 
diameters in Table 1 of Sec.  33.68, noting that practical application 
of the required conditions dictates a wider acceptable droplet diameter 
range, without measurably impacting the severity of the intended engine 
test demonstration.
    We agree. Although the commenters did not provide any data to 
validate the suggested change in drop diameters, we are aware of test 
facility limitations, and concur that the upper tolerance of drop size 
is limiting for some test facilities. As a result, the proposed 3 micron droplet tolerance has been removed and a range for the 
MVDs is specified instead. This will still provide an adequate safety 
margin. Likewise, the upper drop size limit has also been increased to 
represent current test facility capabilities while preserving an 
adequate safety margin. Section 33.68, Table 1, has been revised to 
reflect these changes.
    AIA and GAMA also suggested that the ground test conditions in 
Table 1, condition (iii), of Sec.  25.1093 and Table 2, condition 4, of 
Sec.  33.68(d) should have a consistent range of droplet sizes based on 
the values from part 25, appendix O.
    We agree. We changed Table 2, condition 4, in Sec.  33.68 by 
removing the maximum drop diameter so it is consistent with Table 1, 
condition (iii), in Sec.  25.1093. Table 2 in Sec.  33.68 was also 
revised to correct the conversion of degrees Centigrade to degrees 
Fahrenheit.
    A private citizen remarked that including parenthetical examples in 
the rule text of Sec.  33.68(a)(3) was not helpful and may be construed 
to be exclusionary of other pertinent, topical considerations. 
Furthermore, their absence does not diminish the clarity or 
understanding of the requirement.
    We agree. We removed the parenthetical examples from the regulatory 
text in Sec.  33.68.
    A private citizen suggested a word change to our proposed wording 
of Sec.  33.68(d). In the NPRM, we proposed to change Sec.  33.68(d) to 
state that the engine should be run at ground idle speed for a minimum 
of 30 minutes in each of the icing conditions shown in Table 2. The 
commenter suggested replacing the phrase ``should be run'' with ``must 
demonstrate the ability to acceptably operate.'' The commenter noted 
that use of the word ``should'' is ambiguous and contrary to existing 
Sec.  33.68, which uses the word ``must.'' Furthermore, the commenter 
suggested that eliminating the word ``run'' would be more consistent 
with the demonstration methods for snow, ice, and large drop glaze ice 
conditions (i.e., test, analysis, or combination of both) shown in 
Table 2 of Sec.  33.68.
    We agree and have clarified Sec. Sec.  25.1093(b)(2) and 33.68(d) 
to state that the engine must operate at ground idle speed in the 
specified icing conditions.

Alternatives to Rulemaking

    Several commenters said that operational solutions have proven to 
be extremely effective in managing weather related risks (e.g., 
thunderstorms and windshear). They suggested that the FAA should have 
been, or should start, placing at least as much emphasis on advancing 
alternatives to rulemaking as it does on creating new certification 
requirements. ALPA encouraged continuous research and development of 
technical systems that would automatically detect the presence of 
hazardous ice, measure the rate of accumulation, and then alert the 
crew as appropriate to take action in order to avoid a potentially 
unsafe flight condition. AirDat, LLC, commented that the FAA may have 
overlooked state-of-the-art meteorological tools, including airborne 
sensors, that are commercially available today, fully deployed, and in 
operation. AIA, Airbus, Boeing, and GAMA commented that the IPHWG did 
not thoroughly consider any alternatives to new rulemaking because the 
tasking statement did not include this option.
    We agree in part. We agree that careful operations and new 
technologies may often enhance safety. However, we note that rulemaking 
is at the discretion of the agency, and we have exercised our 
discretionary rulemaking authority in this instance. This rule provides 
additional safety for the flying public when icing conditions are 
encountered, and it will improve the level of safety of future airplane 
designs.

[[Page 65518]]

Applicability of Mixed Phase and Ice Crystal Conditions to Airspeed 
Indicating Systems

    We received several comments suggesting that the mixed phase and 
ice crystal environment in part 33, appendix D, should be used instead 
of the mixed phase and ice crystal environment that was proposed in 
Table 1 of Sec.  25.1323. AIA, Airbus, Boeing, and GAMA stated the NPRM 
acknowledged new information is available to guide development of an 
ice crystal envelope appropriate for evaluation of airspeed indication 
systems. They also noted that proposed Table 1 of Sec.  25.1323 does 
not reflect the current understanding of the ice crystal environment, 
nor does it include known pitot icing events, which are published in 
``Interim Report no. 2,'' Bureau D'Enquetes et D'Analyses pour la 
securite d'aviation civile (BEA) F-GZCP.\12\ GSIS recommended that 
Table 1 of Sec.  25.1323, which defines a subset of part 33, appendix 
D, conditions, should be removed. Instead, the rule should require that 
airspeed indication systems must not malfunction in any of the 
conditions specified in appendix D.
---------------------------------------------------------------------------

    \12\ This report can be found on the BEA Web site at http://www.bea.aero/docspa/2009/f-cp090601e2.en/pdf/f-cp090601e2.en.pdf.
---------------------------------------------------------------------------

    EASA stated that the proposed environment in Table 1 of Sec.  
25.1323 would not address known events of airspeed indicating system 
malfunctions. EASA also fully supported including in part 25, the 
proposed mixed phase and ice crystal parameters in proposed part 33, 
appendix D. TCCA suggested that the FAA reconsider the icing conditions 
for the airspeed indicating system proposed in the NPRM within Table 1 
of Sec.  25.1323 and include the -60 [deg]C conditions described in 
part 33, appendix D, instead.
    Airbus supported the application of appendix D icing conditions to 
pitot and pitot-static probes, but pointed out it is necessary to 
develop an acceptable means of compliance that takes into account the 
capabilities of the existing engineering tools (for example, models and 
icing tunnels) and provide guidance on these new requirements. GSIS 
also commented that recent testing suggests testing at sea level 
atmospheric conditions may not be a conservative assumption for ice 
crystal testing.
    NRC noted the requirements of Sec.  25.1323 do not appear to take 
into account the effects of displacing the free stream ice water 
content around the fuselage of the airplane. If the probe is in a 
region affected by this, then the concentration detected by the probe 
would be higher than that of the free stream. Airbus mentioned that one 
test facility has made significant improvements in its capability to 
reproduce icing conditions but it is limited by the size of the test 
article it can accommodate. However, no test facilities are currently 
capable of reproducing the full range of icing conditions and flight 
conditions required by part 33, appendix D. Considering the state of 
the art of the engineering tools, there is a need for an agreed means 
of compliance.
    We agree that the mixed phase and ice crystal environment in part 
33, appendix D, should be used instead of the mixed phase and ice 
crystal environment proposed in Table 1 of Sec.  25.1323. Therefore, 
Sec. Sec.  25.1323 and 25.1324 have been revised to add a requirement 
to prevent malfunctions in the mixed phase and ice crystal environment 
defined in part 33, appendix D.
    With regard to comments suggesting that testing at sea level 
atmospheric conditions may not be a conservative assumption, or that 
ice crystal concentrations at an exterior mounted probe could be higher 
than the free stream conditions, we agree. The conditions defined in 
part 33, appendix D, are atmospheric conditions. These atmospheric 
conditions include parameters for total water content as a function of 
temperature, altitude, and horizontal extent. We also agree that 
altitude may be an important parameter. Altitude is a parameter 
identified in part 33, appendix D, and must be considered when 
developing the test conditions and supporting analysis necessary to 
show compliance.
    We also agree that depending on airplane size and the location of 
the probe, the ice water content at the probe may be higher than the 
ice water content values defined in part 33, appendix D. Since part 33, 
appendix D, describes atmospheric conditions, the potential for higher 
ice crystal concentrations at the probe location compared to the 
atmospheric concentrations defined in part 33, appendix D, must be 
considered when developing the test conditions and supporting analysis 
necessary to show compliance. Installation effects could be evaluated 
with a combination of computational fluid dynamics codes and icing 
tunnels. Devices mounted on smaller surfaces could be assessed in an 
icing tunnel. However, if the device is mounted on the fuselage and 
tunnel blockage effects would preclude a meaningful icing tunnel test, 
then codes that adequately predict the shadowing and concentration 
effects may be acceptable compliance methods.
    Foster Technology, LLC (Foster), is an engineering consulting firm 
that has filed a provisional patent that includes a methodology for 
detecting ice over a pitot inlet, providing a corrected airspeed, and 
removing ice deposits. Foster suggested that the FAA should certify its 
new methodology.
    We agree that existing regulations would allow certification of a 
new pitot probe with ice detection capability. However, we would 
certify a new pitot probe as part of a product's type design to be 
approved for installation, not the methodology described by Foster. If 
Foster seeks independent certification of a new pitot probe, we suggest 
Foster complete and submit an application for a supplemental type 
certificate, at which time we will evaluate the new probe.

Heavy Rain Requirements for Airspeed Indication and Angle of Attack 
Systems

    Airbus and EASA fully supported a new requirement to cover the 
heavy rain conditions being considered in the NPRM. Airbus commented 
that some testing at high LWCs, such as those proposed in the NPRM, 
would help to ensure that water drainage in rain conditions, especially 
at takeoff, is adequate. A private citizen commented that the maximum 
freezing rain static temperature under consideration would be unlikely 
to result in ice accretion and is not in line with figure 4 of appendix 
O. AIA, Boeing, and GAMA commented that the proposed expanded 
parameters, the source of which was not provided, do not appear 
congruous with hard data from extensive icing research. GSIS commented 
that it wanted to understand how the specific values for LWC, 
horizontal extent, and mean droplet diameter were determined and what 
the technical justifications are for these levels.
    We consider analysis of heavy rain conditions as proposed in the 
NPRM to be necessary to substantiate that water drainage from the 
airspeed indication and angle of attack systems is adequate. If the 
water drainage is inadequate, then the residual water may freeze as the 
pitot probes or angle of attack sensors are subjected to below freezing 
temperatures as the airplane climbs following takeoff. The heavy rain 
conditions are not intended as an icing condition as described in the 
NPRM. The heavy rain LWC is based on heavy rainfall data documented in 
MIL-STD-210C, Military Standard: Climatic Information to Determine 
Design and Test Requirements for Military Systems

[[Page 65519]]

and Equipment.\13\ The same rain data was used for the AIA Propulsion 
Committee Study, Project PC 338-1 documented in part 33, appendix B. 
Heavy rain conditions have been added to Sec. Sec.  25.1323 and 
25.1324. However, the conditions have been revised compared to the 
conditions proposed in the NPRM by removing temperature as a parameter.
---------------------------------------------------------------------------

    \13\ A copy of MIL-STD-210C, dated January 9, 1987, is available 
in the rule Docket No. FAA-2010-0636. MIL-STD-210 has since been 
superseded by MIL-HDBK-310, dated June 23, 1997, which is also 
available in the rule docket.
---------------------------------------------------------------------------

Applicability of the Icing Requirements in Part 25, Appendix O, and 
Part 33, Appendix D, to All Airspeed Indicating Systems

    EASA and TCCA suggested that Sec. Sec.  25.1323 and 25.1324 be 
revised to include the icing certification of all external probes for 
flight instruments. EASA proposed a specific regulation including, but 
not limited to, pitot, pitot-static, static, angle-of-attack, sideslip 
angle, and temperature sensors. The regulation proposed by EASA would 
require addressing the icing conditions in part 25, appendix C; part 
25, appendix O; and part 33, appendix D. Similarly, since total air 
temperature (TAT) is an input to calculating true airspeed, Goodrich 
requested clarification of whether or not TAT sensors should be 
considered part of the airspeed indicating system when addressing 
``preventing malfunction'' in part 25, appendix O, and part 33, 
appendix D, environments as described in Sec.  25.1323(i).
    We do not agree with the commenters' suggestions to include icing 
requirements for all external probes and sensors in Sec. Sec.  25.1323 
and 25.1324. Section 25.1323(i) has traditionally applied to pitot 
probes (indicated airspeed), and the FAA did not propose a change to 
this applicability in the NPRM. As such, we did not intend to include 
TAT sensors, or other externally mounted instrument probes in Sec.  
25.1323(i). In addition, Sec.  25.1324 was proposed specifically for 
angle-of-attack sensors. Revising Sec. Sec.  25.1323 and 25.1324 so 
that all externally mounted flight instrument probes and sensors must 
operate in the various icing conditions is beyond the scope of this 
rulemaking. We did not change the rule in response to these comments.

Proposal To Add Indication System for External Probes

    EASA advised that some failures of the pitot probe heating 
resistance may not be seen by the flightcrew due to the low current 
detection system installed on the airplane. As a result, failure to 
provide proper pitot probe deicing may not be detected. EASA suggested 
that a new regulation be created to explicitly cover abnormal 
functioning of the heating system for externally mounted probes.
    We do not agree. If insufficient functioning of an externally 
mounted probe creates an unsafe operating condition, then warning 
information must be provided to the flightcrew in accordance with Sec.  
25.1309(c). Since we did not propose warning information specific to 
failure modes for certain externally mounted probes in the NPRM and the 
public did not have the opportunity to comment, we consider the EASA 
proposal to be beyond the scope of this rulemaking. No changes to the 
final rule have been made as a result of EASA's proposal.

Expand the Parameters for Part 33, Appendix D

    AIA, Boeing, and GAMA commented that part 33, appendix D, should be 
expanded to reflect new engine power loss and airspeed data loss events 
in ice crystal conditions. Appendix D is based on a theoretical model, 
and Airbus agreed that the conditions in appendix D should be applied.
    We do not agree that appendix D should be expanded in this final 
rule. The majority of recent airspeed data anomalies occurred within 
the altitude and temperature range described in part 33, appendix D. We 
know of only one temporary loss of airspeed data event just outside or 
at the perimeter of the altitude and temperature range in part 33, 
appendix D. Other conditions described in appendix D, such as what the 
ice water content actually was during the loss of airspeed data event, 
are unknown because it was not measured. We agree that appendix D is 
based on a theoretical atmospheric model. We are continuing to support 
the research necessary to validate the part 33, appendix D, conditions 
with flight test data, and it would be premature to expand the appendix 
D environment at this time. Expansion of part 33, appendix D, is out of 
scope of the originally proposed rulemaking. We did not change appendix 
D based on these comments.
    Airbus commented that using the EHWG event database and referring 
to the flight distance between a TAT sensor anomaly and the engine 
event, one can see that almost half of the engine events occurred at a 
flight distance equal to or less than 10 nautical miles from the 
occurrence of the TAT anomaly, with the majority of events happening 
within less than 4 nautical miles. Based on these facts, Airbus 
concluded that short cloud exposures are the most critical. However, 
the new appendix D definition implies that the longest clouds are the 
most critical for engines and auxiliary power units (APUs), and adds a 
factor of 2 to the conservatism of the definitions already defined in 
EASA documents CS-E 780, Tests in Ice-Forming Conditions, and AMC 
25.1419, Ice Protection.\14\ Airbus commented that it is inappropriate 
to add an additional factor of 2 to the icing conditions for long 
exposures in appendix D icing conditions considering the uncertainty in 
the new rule.
---------------------------------------------------------------------------

    \14\ Both of these documents are available on the EASA Web site 
at http://www.easa.europa.eu.
---------------------------------------------------------------------------

    We do not agree. We acknowledge that a TAT sensor anomaly may be 
one indicator of ice crystals; however, it is not a very reliable 
indicator. The amount and concentration of ice crystals required to 
create a TAT sensor anomaly is not understood. Also, the TAT sensor 
anomaly was only present in a portion of the engine events in the EHWG 
database. Therefore, the TAT anomaly data cannot accurately show cloud 
extent. Additionally, detailed review of the event data indicated that 
once the TAT probe iced over enough to cause an indication anomaly, the 
engine often would demonstrate a power upset very soon after the TAT 
probe anomaly. This period of time was insufficient for the pilot to 
take action since the ice accretion within the engine had already 
progressed to an advanced stage. Therefore, we concluded that TAT probe 
anomalies are poor precursor indications of the ice crystal threat to 
engines, in terms of reliability of the indication and the time period 
in advance of power loss. When establishing the cloud extent factor in 
part 33, appendix D, the EHWG and FAA did take into account EASA CS-E-
780 cloud definition requirements. However, the EHWG was not able to 
validate the analysis used to develop the cloud extent factor in EASA 
CS-E-780. The cloud extent factor proposed by the EHWG for part 33, 
appendix D, represents the most accurate cloud extent factor that can 
be established using the available data. No changes were made as a 
result of these comments.
    Snecma commented that the y-axis value in proposed part 33, 
appendix D, figure D3, was incorrect. The value should be 0.6 but the 
NPRM showed the value as zero.
    We concur. We also found that both the x- and y-axis values 
proposed in the NPRM were incorrect. We changed part

[[Page 65520]]

33, appendix D, figure D3, to depict the correct axis values. The 
lowest x-axis value is now 1 and the lowest y-axis value is now 0.6.
    Several commenters noted that the horizontal cloud length proposed 
in the NPRM was stated in statute miles, and commented it should be 
provided in nautical miles. The commenters suggested that changing to 
nautical miles would make the distance measurement consistent with 
other tables and figures in appendix D.
    We agree, and changed Table 1 to identify that the horizontal cloud 
length is depicted in nautical miles.
    Several commenters asked why we included the reference to 
``Reference 1'' in the text immediately following Table 1 in proposed 
part 33, appendix D, especially considering the material constituting 
``Reference 1'' was not identified anywhere within the NPRM.
    We agree. We removed the reference to ``Reference 1'' from the 
final rule.

Establishing New Operating Limitations

    TCCA stated that it was not clear if the proposed requirements to 
exit all icing conditions were applicable only to in-flight icing 
encounters, or if they were also applicable to the takeoff phase of 
flight.
    We agree that clarification is needed. We changed Sec.  25.1533(c) 
to clarify that the additional limitations apply to all phases of 
flight.

Additional Requirements for Safe Operation

    AIA, Boeing, and GAMA commented that proposed appendix O, paragraph 
(b) does not define takeoff ice accretions for airplanes not certified 
for takeoff in appendix O conditions. Therefore, they suggested that 
Sec.  25.207(e)(1), which defines stall warning requirements for 
takeoff with ice accretions, should be added to the list of exceptions 
specified in Sec.  25.21(g)(3).
    We agree. We added the stall warning requirements in Sec.  
25.207(e)(1) to the exceptions listed in Sec.  25.21(g)(3). As a 
result, applicants will not need to determine the stall warning margin 
for takeoff with appendix O ice accretions for airplanes not certified 
to take off in appendix O icing conditions.
    TCCA commented that exposure to appendix O icing conditions may 
result in icing accretions further aft on fuselage, wing and stabilizer 
surfaces, and control surfaces, beyond what would normally be obtained 
in appendix C conditions. Therefore, TCCA suggested that compliance to 
Sec.  25.251(b) through (e) should be shown for appendix O conditions.
    We proposed to retain the provision from Amendment 25-121 for not 
requiring compliance with Sec.  25.251(b) through (e) in appendix C 
icing conditions and extend it to include appendix O icing conditions. 
Although Amendment 25-121 only addressed appendix C icing conditions, 
the conclusion that compliance to Sec.  25.251(b) through (e) need not 
be shown in icing conditions was based on a review of in-service 
experience in all icing conditions, not just appendix C icing 
conditions. Therefore, including Sec.  25.251(b) through (e) within the 
exceptions listed in Sec.  25.21(g) for certifications is equally 
applicable to either appendix C or appendix O conditions. No changes 
were made to the final rule as a result of this comment.
    Dassault commented that the proposed ice accretion definitions in 
part II of appendix O did not include an ice accretion specific to the 
flight phase covered by Sec.  25.121(a). Dassault added that the ice 
accretion used for showing compliance with Sec.  25.121(a)(1) should be 
the accretion occurring between liftoff and the point at which the 
landing gear is fully retracted. Dassault requested that the FAA add 
the following definition: ``Takeoff--landing gear extended ice is the 
most critical ice accretion on unprotected surfaces, and any ice 
accretion on protected surfaces appropriate to normal ice protection 
system operation, occurring between liftoff and the point at which the 
landing gear is fully retracted, assuming accretion starts at liftoff 
in the icing conditions defined in Part I of this appendix.''
    Instead of adding a definition for the ice accretion during the 
initial takeoff segment covered by Sec.  25.121(a), we have 
reconsidered this issue and determined that this flight segment does 
not last long enough for significant ice accretions to occur, even in 
appendix O icing conditions. Therefore, we added Sec.  25.121(a) to the 
list of requirements in Sec.  25.21(g)(4) that do not have to be met 
with appendix O ice accretions. We also agree that our proposed 
definition for takeoff ice was inadequate. We did not intend to require 
that applicants include the small effect (if any) of ice accretion from 
the point of liftoff to the end of the takeoff distance in determining 
the takeoff distance under Sec.  25.113, which the appendix C 
definition and the proposed appendix O definition may have implied. 
Therefore, we revised the definitions of takeoff ice and final takeoff 
ice in part 25, appendix C and appendix O, such that the ice accretion 
begins at the end of the takeoff distance, not at the point of liftoff. 
This change better aligns the definition of the takeoff and final 
takeoff ice with that of the takeoff path used for determining takeoff 
performance under Sec. Sec.  25.111, 25.113, and 25.115.

Request To Revise Sec.  25.629

    TCCA commented that for airplanes exempt from Sec.  25.1420, no 
evaluation of aeroelastic stability is required in appendix O icing 
conditions. For that reason, TCCA recommended that all icing 
considerations be included directly in Sec.  25.629.
    We do not agree. Section 25.629(b)(1) requires aeroelastic 
stability evaluations of the airplane in normal conditions. For 
airplanes approved for operation in icing conditions, ice accumulations 
are considered a normal condition under the rule. Since Sec.  25.629 
does not specifically distinguish between various types of icing 
conditions, all icing conditions for which the airplane is approved are 
considered normal conditions. For airplanes exempt from Sec.  25.1420, 
or for which approval is not sought for flight in appendix O icing 
conditions, Sec.  25.629(d)(3) requires that ice accumulations due to 
inadvertent icing encounters must be considered for airplanes not 
approved for operation in icing conditions. The intent is to consider 
ice accumulations due to inadvertent icing encounters from any icing 
conditions for which the airplane is not approved, including appendix O 
conditions. We did not change the rule as a result of this comment.

Miscellaneous Issues

    After the FAA issued the NPRM to this rulemaking, we issued a final 
rule for Harmonization of Various Airworthiness Standards for Transport 
Category Airplanes--Flight Rules (docket number FAA-2010-0310). That 
final rule revised Sec.  25.21(g)(1) to add the requirement that the 
stall warning margin requirements of Sec.  25.207(c) and (d) must be 
met in the landing configuration in the icing conditions of appendix C. 
That final rule also revised Sec.  25.253(c) to define the maximum 
speeds at which the static lateral-directional stability requirements 
of Sec.  25.177(a) through (c) and the directional and lateral control 
requirements of Sec.  25.147(f) must be met in the icing conditions of 
appendix C. We have retained those changes in Sec. Sec.  25.21(g)(2) 
and 25.253(c) of this final rule. For consistency, we also revised 
Sec.  25.21(g)(4) to require that Sec.  25.207(c) and (d) must be met 
in the landing configuration in the appendix O icing conditions for 
which certification is sought. This revision is a logical outgrowth of 
the notice in this

[[Page 65521]]

rulemaking because the purpose of Sec.  25.21(g)(4) is to ensure safe 
operation in appendix O conditions during all phases of flight, 
including the landing phase.
    The FAA finds that clarifying the applicability of the proposed 
icing conditions to APU installations is necessary. Section 25.901(d) 
currently requires that each auxiliary power unit installation must 
meet the applicable provisions of the subpart. This requirement is 
unchanged by this rulemaking. The FAA considers Sec.  25.1093(b) to be 
applicable to APU installations because they are turbine engines. An 
essential APU is used to provide air and/or power necessary to maintain 
safe airplane operation. A non-essential APU is used to provide air 
and/or power as a matter of convenience and may be shutdown without 
jeopardizing safe airplane operation. The FAA has traditionally 
required that essential APU installations continue to operate in part 
25, appendix C, icing conditions. Non-essential APU installations 
either have restricted operation or are required to demonstrate that 
operation in icing conditions does not affect the safe operation of the 
airplane. References to part 25, appendix O, and part 33, appendix D, 
have been added to Sec.  25.1093(b).
    As previously discussed, the applicability of appendix O conditions 
in Sec.  25.1093(b) excludes all turbine engine installations that are 
used on airplanes with a MTOW equal to or greater than 60,000 pounds. 
The FAA still considers APUs to be turbine engines that must comply 
with the installation requirements in Sec. Sec.  25.901 and 25.1093; 
therefore, this rulemaking is not creating separate requirements for 
APU installations. Essential APU installations must continue to operate 
in the icing conditions applicable under Sec.  25.1093(b). Non-
essential APU installations must not affect the safe operation of the 
airplane when the icing conditions applicable under Sec.  25.1093(b) 
are inadvertently encountered.
    Also as previously discussed, the applicability of appendix O 
conditions in Sec.  25.1093(b) was revised to provide relief for larger 
airplanes because of the successful in-service history of existing 
larger airplane and larger airplane turbine engine inlet designs. If 
future APU installations contain novel or unusual design features that 
affect this successful in-service history, and those design features 
make the airplane more susceptible to the effects of flight in SLD 
icing conditions, the FAA can issue special conditions to provide 
adequate safety standards.
    A private citizen identified potential flightcrew training issues 
associated with this rulemaking. The commenter noted that while 
practical test standards for post-stall recovery procedures are clearly 
related to icing safety, they are not regulatory and may be changed 
without formal notice. The commenter also remarked that a common pilot 
input characteristic to add power and maintain the pitch angle of the 
airplane has been observed on the flight data recorder time histories 
related to several icing related accidents. In some cases, nose up 
pitch input was applied even against the nose down force being applied 
by the airplane's ``stick pusher'' that is designed to rapidly reduce 
the angle of attack. The commenter noted that these habit patterns are 
developed and reinforced as the required response in simulator training 
in accordance with FAA practical test standards for stall 
identification and recovery for minimum altitude loss. For example, 
``Minimum altitude loss'' is trained as ``zero altitude loss.''
    The flightcrew training issues addressed by the commenter are 
important safety considerations. However, flightcrew training is beyond 
the scope of this rulemaking because this rulemaking addresses design 
requirements. On July 6, 2010, the FAA published Safety Alert for 
Operators (SAFO) 10012. The SAFO discusses the possible 
misinterpretation of the practical test standards language ``minimal 
loss of altitude.'' \15\
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    \15\ This document can be found at http://www.faa.gov/other_visit/aviation_industry/airline_operators/airline_safety/safo/all_safos/media/2010/SAFO10012.pdf.
---------------------------------------------------------------------------

    In addition, on September 30, 2010, the FAA established the Stick 
Pusher and Adverse Weather Event Training Aviation Rulemaking 
Committee. One of the rulemaking committee objectives is to identify 
the best goals, procedures, and training practices that will enable air 
carrier pilots to accurately and consistently respond to unexpected 
stick pusher activations, icing conditions, and microburst and 
windshear events.\16\ The ARC has submitted recommendations to the FAA, 
which are being considered for additional rulemaking activities. Such 
activities are beyond the scope of this rulemaking.
---------------------------------------------------------------------------

    \16\ A copy of the charter is available at http://www.faa.gov/about/office_org/headquarters_offices/avs/offices/afs/afs200/media/208_ARC_Charter.pdf.
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Regulatory Notices and Analyses

Regulatory Evaluation

    Changes to Federal regulations must undergo several economic 
analyses. First, Executive Order 12866 and Executive Order 13563 direct 
that each Federal agency shall propose or adopt a regulation only upon 
a reasoned determination that the benefits of the intended regulation 
justify its costs. Second, the Regulatory Flexibility Act of 1980 (Pub. 
L. 96-354) requires agencies to analyze the economic impact of 
regulatory changes on small entities. Third, the Trade Agreements Act 
(Pub. L. 96-39) prohibits agencies from setting standards that create 
unnecessary obstacles to the foreign commerce of the United States. In 
developing U.S. standards, this Trade Act requires agencies to consider 
international standards and, where appropriate, that they be the basis 
of U.S. standards. Fourth, the Unfunded Mandates Reform Act of 1995 
(Pub. L. 104-4) requires agencies to prepare a written assessment of 
the costs, benefits, and other effects of proposed or final rules that 
include a Federal mandate likely to result in the expenditure by State, 
local, or tribal governments, in the aggregate, or by the private 
sector, of $100 million or more annually (adjusted for inflation with 
base year of 1995). This portion of the preamble summarizes the FAA's 
analysis of the economic impacts of this final rule. We suggest readers 
seeking greater detail read the full regulatory evaluation, a copy of 
which we have placed in the docket for this rulemaking.
    In conducting these analyses, the FAA has determined that this 
final rule: (1) Has benefits that justify its costs, (2) is not an 
economically ``significant regulatory action'' as defined in section 
3(f) of Executive Order 12866, (3) is ``not significant'' as defined in 
DOT's Regulatory Policies and Procedures; (4) will not have a 
significant economic impact on a substantial number of small entities; 
(5) will not create unnecessary obstacles to the foreign commerce of 
the United States; and (6) will not impose an unfunded mandate on 
state, local, or tribal governments, or on the private sector by 
exceeding the threshold identified above. These analyses are summarized 
below.

Total Benefits and Costs of This Final Rule

[[Page 65522]]

                                 Table 1--Total Benefits and Costs of This Rule
----------------------------------------------------------------------------------------------------------------
                                                 2012$                               7% Present value
                              ----------------------------------------------------------------------------------
                                      Benefit                Cost               Benefit               Cost
----------------------------------------------------------------------------------------------------------------
Part 33 Engines..............  Qualitative..........        $13,936,000  Qualitative.........        $11,375,927
Large Part 25 Airplanes......  $362,319,857.........         14,126,333  $76,861,295.........         11,531,295
Other Part 25 Airplanes......  $220,570,582.........         33,198,788  $50,028,650.........         19,385,401
                              ----------------------------------------------------------------------------------
    Total....................  $582,890,439.........         61,261,121  $126,889,985........         42,292,624
----------------------------------------------------------------------------------------------------------------
* Details may not add to row or column totals due to rounding.

Persons Potentially Affected by This Final Rule
Part 25 airplane manufacturers,
Engine manufacturers, and
Operators of affected equipment.
Assumptions
    The deliveries and affected fleets are analyzed over appropriate 
time periods and are customized based upon actual historical data. The 
fleet development is customized to the various (and different) airplane 
types. We conservatively assume that all certifications will occur in 
2015 and deliveries will occur in the following year. As production 
time spans differ by size of airplane, it is important for the reader 
to focus on present value benefits and costs.

Present Value Discount rate--7%
Value of an Averted Fatality--$9.1 million in 2012

    Both Costs and Benefits are expressed in 2012 dollars.
Benefits of This Final Rule
    The FAA has analyzed events that would have been prevented if this 
final rule were in place at the time of certification. The events were 
evaluated for applicability and preventability in context with the 
requirements contained in this final rule.
    For the categories of airplanes, first, we develop casualty rates 
for fatalities, injuries, investigations, and destroyed airplanes based 
on historical ice-related accidents. Next, we multiply the total annual 
affected airplanes by the annual risk per airplane. Lastly, we multiply 
the casualty rates by the projected number of part 25 newly 
certificated deliveries. When summed over time, the total estimated 
benefits are shown in Table 1.
    Viewed from a breakeven analysis using only preventable fatalities, 
with each fatality valued at $9.1 million, this rule has benefits 
exceeding costs with only 7 fatalities prevented.
Costs of This Final Rule
    The total estimated costs are shown in Table 1. We obtained the 
basis of our cost estimates from the industry. Since the NPRM, we have 
modified the estimates based upon industry comments and clarifications 
to those comments. The compliance costs are analyzed in context of the 
part 25 and part 33 certification requirements.
    As summarized in Table 2, the cost categories in the regulatory 
evaluation incorporate both certification and operational costs. We 
analyze each cost category separately. The cost categories in this 
evaluation are the same as those provided by industry to comply with 
the requirements contained in this rule.

                          Table 2--Cost Summary
------------------------------------------------------------------------
                                       Nominal cost        7% PV cost
------------------------------------------------------------------------
Engine Certification Cost.........         $7,936,000         $6,478,140
Engine Capital Cost...............          6,000,000          4,897,787
                                   -------------------------------------
    Total Engine Cost.............         13,936,000         11,375,927
                                   -------------------------------------
New Large Airplane Certification           14,126,333         11,531,295
 Cost.............................
Large Airplane Hardware Cost......                  0                  0
Large Airplane Fuel Cost..........                  0                  0
                                   -------------------------------------
    Total Large Airplane Cost.....         14,126,333         11,531,295
                                   -------------------------------------
Other Airplane Certification Cost.         19,066,026         15,563,557
Other Airplane Hardware Cost......          2,475,000          1,312,609
Other Airplane Fuel Burn Cost.....         11,657,762          2,509,236
                                   -------------------------------------
    Total Other Airplane Costs....         33,198,788         19,385,401
------------------------------------------------------------------------
        Total Costs...............         61,261,121         42,292,624
------------------------------------------------------------------------
* Details may not add to row or column totals due to rounding.

Alternatives Considered
    Alternative 1--Make the entire rule applicable to all airplanes.
    Not all the requirements in this rule extend to large transport 
category airplanes (those with a MTOW greater than 60,000 pounds). 
Under this alternative, the proposed design requirements would extend 
to all transport category airplanes. This alternative was rejected 
because this alternative would add significant costs without a 
commensurate increase in benefits.
    Alternative 2--Limit the scope of applicability to small transport 
category airplanes.
    Although this alternative would decrease the estimated cost, the 
FAA believes that medium and large airplanes are at risk of an SLD 
icing

[[Page 65523]]

event. The FAA does not want a significant proportion of the future 
fleet to be disproportionately at risk.

Regulatory Flexibility Determination

    The Regulatory Flexibility Act of 1980 (Pub. L. 96-354) (RFA) 
establishes as a principle of regulatory issuance that agencies shall 
endeavor, consistent with the objectives of the rule and of applicable 
statutes, to fit regulatory and informational requirements to the scale 
of the businesses, organizations, and governmental jurisdictions 
subject to regulation. To achieve this principle, agencies are required 
to solicit and consider flexible regulatory proposals and to explain 
the rationale for their actions to assure that such proposals are given 
serious consideration. The RFA covers a wide-range of small entities, 
including small businesses, not-for-profit organizations, and small 
governmental jurisdictions.
    Agencies must perform a review to determine whether a rule will 
have a significant economic impact on a substantial number of small 
entities. If the agency determines that it will, the agency must 
prepare a regulatory flexibility analysis as described in the RFA.
    However, if an agency determines that a rule is not expected to 
have a significant economic impact on a substantial number of small 
entities, section 605(b) of the RFA provides that the head of the 
agency may so certify and a regulatory flexibility analysis is not 
required. The certification must include a statement providing the 
factual basis for this determination, and the reasoning should be 
clear. Our initial determination was that the proposed rule would not 
have a significant economic impact on a substantial number of small 
entities. We received no public comments regarding our initial 
determination. As such, this final rule will not have a significant 
economic impact on a substantial number of small entities for the 
following reasons.
Airplane and Engine Manufacturers
    Airplane and engine manufacturers will be affected by the 
requirements contained in this rule.
    For airplane manufacturers, we use the size standards from the 
Small Business Administration for Air Transportation and Aircraft 
Manufacturing specifying companies having less than 1,500 employees as 
small entities. The current United States part 25 airplane 
manufacturers include Boeing, Cessna Aircraft, Gulfstream Aerospace, 
Learjet (owned by Bombardier), Lockheed Martin, Raytheon Aircraft, and 
Sabreliner Corporation. Because all U.S. transport-category airplane 
manufacturers have more than 1,500 employees, none are considered small 
entities.
    United States aircraft engine manufacturers include General 
Electric, CFM International, Pratt & Whitney, International Aero 
Engines, Rolls-Royce Corporation, Honeywell, and Williams 
International. All but one exceeds the Small Business Administration 
small-entity criteria for aircraft engine manufacturers. Williams 
International is the only one of these manufacturers that is a U.S. 
small business.
    The FAA estimated that Williams International engines power 
approximately four percent of the engines on active U.S. airplanes. 
Assuming that future deliveries of newly certificated airplanes with 
Williams International engines will have the same percentage as the 
active fleet, we calculated that this final rule will add about 0.2 
percent of their annual revenue. We do not consider a cost of 0.2 
percent of annual revenue significant.
Operators
    In addition to the certification cost incurred by manufacturers, 
operators will incur fuel costs due to the estimated additional impact 
of weight changes from equipment on affected airplanes. On average, 
operators affected by the final rule will incur no additional annual 
fuel costs for newly certificated large part 25 airplanes, and $189, in 
present value, in additional fuel costs for other newly certificated 
part 25 airplanes. This final rule will apply to airplanes that have 
yet to be designed; there will be no immediate cost to small entities. 
The other airplane annual fuel cost of $189, in present value, is not 
significant in terms of total operating expenses. We do not consider 
these annual fuel costs a significant economic impact.
    This final rule will not have a significant economic impact on a 
substantial number of airplane manufacturers, engine manufacturers, or 
operators. Therefore, as the FAA Administrator, I certify that this 
rule will not have a significant economic impact on a substantial 
number of small entities.

International Trade Analysis

    The Trade Agreements Act of 1979 (Pub. L. 96-39), as amended by the 
Uruguay Round Agreements Act (Pub. L. 103-465), prohibits Federal 
agencies from establishing standards or engaging in related activities 
that create unnecessary obstacles to the foreign commerce of the United 
States. Pursuant to these Acts, the establishment of standards is not 
considered an unnecessary obstacle to the foreign commerce of the 
United States, so long as the standard has a legitimate domestic 
objective, such as the protection of safety, and does not operate in a 
manner that excludes imports that meet this objective. The statute also 
requires consideration of international standards and, where 
appropriate, that they be the basis for U.S. standards.
    The FAA has assessed the effect of this final rule and determined 
that it will not be an unnecessary obstacle to the foreign commerce of 
the United States as the purpose of this rule is to ensure aviation 
safety.

Unfunded Mandates Assessment

    Title II of the Unfunded Mandates Reform Act of 1995 (Pub. L. 104-
4) requires each Federal agency to prepare a written statement 
assessing the effects of any Federal mandate in a proposed or final 
agency rule that may result in an expenditure of $100 million or more 
(in 1995 dollars) in any one year by State, local, and tribal 
governments, in the aggregate, or by the private sector; such a mandate 
is deemed to be a ``significant regulatory action.'' The FAA currently 
uses an inflation-adjusted value of $143.1 million in lieu of $100 
million. This final rule does not contain such a mandate; therefore, 
the requirements of Title II do not apply.

Paperwork Reduction Act

    The Paperwork Reduction Act of 1995 (44 U.S.C. 3507(d)) requires 
that the FAA consider the impact of paperwork and other information 
collection burdens imposed on the public. The information collection 
requirements associated with this final rule have been previously 
approved by the Office of Management and Budget (OMB) under the 
provisions of the Paperwork Reduction Act of 1995 (44 U.S.C. 3507(d)) 
and have been assigned OMB Control Number 2120-0018.

International Compatibility and Cooperation

    (1) In keeping with U.S. obligations under the Convention on 
International Civil Aviation, it is FAA policy to conform to 
International Civil Aviation Organization (ICAO) Standards and 
Recommended Practices to the maximum extent practicable. The FAA has 
reviewed the corresponding ICAO Standards and Recommended Practices and 
has identified no differences with these regulations.

[[Page 65524]]

    (2) Executive Order 13609, Promoting International Regulatory 
Cooperation, promotes international regulatory cooperation to meet 
shared challenges involving health, safety, labor, security, 
environmental, and other issues and to reduce, eliminate, or prevent 
unnecessary differences in regulatory requirements. The FAA has 
analyzed this action under the policies and agency responsibilities of 
Executive Order 13609, and has determined that this action will have no 
effect on international regulatory cooperation.

Environmental Analysis

    FAA Order 1050.1E identifies FAA actions that are categorically 
excluded from preparation of an environmental assessment or 
environmental impact statement under the National Environmental Policy 
Act in the absence of extraordinary circumstances. The FAA has 
determined this rulemaking action qualifies for the categorical 
exclusion identified in paragraph 4(j) and involves no extraordinary 
circumstances.

Regulations Affecting Intrastate Aviation in Alaska

    Section 1205 of the FAA Reauthorization Act of 1996 (110 Stat. 
3213) requires the FAA, when modifying its regulations in a manner 
affecting intrastate aviation in Alaska, to consider the extent to 
which Alaska is not served by transportation modes other than aviation, 
and to establish appropriate regulatory distinctions. In the NPRM, the 
FAA requested comments on whether the proposed rule should apply 
differently to intrastate operations in Alaska. The agency did not 
receive any comments, and has determined, based on the administrative 
record of this rulemaking, that there is no need to make any regulatory 
distinctions applicable to intrastate aviation in Alaska.

Executive Order Determinations

Executive Order 13132, Federalism

    The FAA has analyzed this final rule under the principles and 
criteria of Executive Order 13132, Federalism. The agency determined 
that this action will not have a substantial direct effect on the 
States, or the relationship between the Federal Government and the 
States, or on the distribution of power and responsibilities among the 
various levels of government, and, therefore, does not have Federalism 
implications.

Executive Order 13211, Regulations That Significantly Affect Energy 
Supply, Distribution, or Use

    The FAA analyzed this final rule under Executive Order 13211, 
Actions Concerning Regulations that Significantly Affect Energy Supply, 
Distribution, or Use (May 18, 2001). The agency has determined that it 
is not a ``significant energy action'' under the executive order and it 
is not likely to have a significant adverse effect on the supply, 
distribution, or use of energy.

How To Obtain Additional Information

Rulemaking Documents

    An electronic copy of a rulemaking document may be obtained by 
using the Internet--
    1. Search the Federal eRulemaking Portal (http://www.regulations.gov);
    2. Visit the FAA's Regulations and Policies Web page at http://www.faa.gov/regulations_policies/ or
    3. Access the Government Printing Office's Web page at http://www.gpo.gov/fdsys/browse/collection.action?collectionCode=FR.
    Copies may also be obtained by sending a request (identified by 
notice, amendment, or docket number of this rulemaking) to the Federal 
Aviation Administration, Office of Rulemaking, ARM-1, 800 Independence 
Avenue SW., Washington, DC 20591, or by calling (202) 267-9680.

Comments Submitted to the Docket

    Comments received may be viewed by going to http://www.regulations.gov and following the online instructions to search the 
docket number for this action. Anyone is able to search the electronic 
form of all comments received into any of the FAA's dockets by the name 
of the individual submitting the comment (or signing the comment, if 
submitted on behalf of an association, business, labor union, etc.).

Small Business Regulatory Enforcement Fairness Act

    The Small Business Regulatory Enforcement Fairness Act (SBREFA) of 
1996 requires FAA to comply with small entity requests for information 
or advice about compliance with statutes and regulations within its 
jurisdiction. A small entity with questions regarding this document, 
may contact its local FAA official, or the person listed under the FOR 
FURTHER INFORMATION CONTACT heading at the beginning of the preamble. 
To find out more about SBREFA on the Internet, visit http://www.faa.gov/regulations_policies/rulemaking/sbre_act/.

List of Subjects

14 CFR Part 25

    Aircraft, Aviation safety, Reporting and recordkeeping 
requirements, Safety, Transportation.

14 CFR Part 33

    Aircraft, Aviation safety.

The Amendment

    In consideration of the foregoing, the Federal Aviation 
Administration amends chapter I of title 14, Code of Federal 
Regulations as follows:

PART 25--AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY AIRPLANES

0
1. The authority citation for part 25 continues to read as follows:

    Authority:  49 U.S.C. 106(g), 40113, 44701, 44702 and 44704.

0
2. Amend Sec.  25.21 by revising paragraphs (g)(1) and (2) and adding 
paragraphs (g)(3) and (4) to read as follows:

Sec.  25.21  Proof of compliance.

* * * * *
    (g) * * *
    (1) Paragraphs (g)(3) and (4) of this section apply only to 
airplanes with one or both of the following attributes:
    (i) Maximum takeoff gross weight is less than 60,000 lbs; or
    (ii) The airplane is equipped with reversible flight controls.
    (2) Each requirement of this subpart, except Sec. Sec.  25.121(a), 
25.123(c), 25.143(b)(1) and (2), 25.149, 25.201(c)(2), 25.239, and 
25.251(b) through (e), must be met in the icing conditions specified in 
Appendix C of this part. Section 25.207(c) and (d) must be met in the 
landing configuration in the icing conditions specified in Appendix C, 
but need not be met for other configurations. Compliance must be shown 
using the ice accretions defined in part II of Appendix C of this part, 
assuming normal operation of the airplane and its ice protection system 
in accordance with the operating limitations and operating procedures 
established by the applicant and provided in the airplane flight 
manual.
    (3) If the applicant does not seek certification for flight in all 
icing conditions defined in Appendix O of this part, each requirement 
of this subpart, except Sec. Sec.  25.105, 25.107, 25.109, 25.111, 
25.113, 25.115, 25.121, 25.123, 25.143(b)(1), (b)(2), and (c)(1), 
25.149, 25.201(c)(2), 25.207(c), (d), and (e)(1), 25.239, and 25.251(b) 
through (e), must be met in the Appendix O icing conditions for which 
certification is not

[[Page 65525]]

sought in order to allow a safe exit from those conditions. Compliance 
must be shown using the ice accretions defined in part II, paragraphs 
(b) and (d) of Appendix O, assuming normal operation of the airplane 
and its ice protection system in accordance with the operating 
limitations and operating procedures established by the applicant and 
provided in the airplane flight manual.
    (4) If the applicant seeks certification for flight in any portion 
of the icing conditions of Appendix O of this part, each requirement of 
this subpart, except Sec. Sec.  25.121(a), 25.123(c), 25.143(b)(1) and 
(2), 25.149, 25.201(c)(2), 25.239, and 25.251(b) through (e), must be 
met in the Appendix O icing conditions for which certification is 
sought. Section 25.207(c) and (d) must be met in the landing 
configuration in the Appendix O icing conditions for which 
certification is sought, but need not be met for other configurations. 
Compliance must be shown using the ice accretions defined in part II, 
paragraphs (c) and (d) of Appendix O, assuming normal operation of the 
airplane and its ice protection system in accordance with the operating 
limitations and operating procedures established by the applicant and 
provided in the airplane flight manual.

0
3. Amend Sec.  25.105 by revising paragraph (a)(2) introductory text to 
read as follows:

Sec.  25.105  Takeoff.

    (a) * * *
    (2) In icing conditions, if in the configuration used to show 
compliance with Sec.  25.121(b), and with the most critical of the 
takeoff ice accretion(s) defined in Appendices C and O of this part, as 
applicable, in accordance with Sec.  25.21(g):
* * * * *

0
4. Amend Sec.  25.111 by revising paragraphs (c)(5)(i) and (ii) to read 
as follows:

Sec.  25.111  Takeoff path.

* * * * *
    (c) * * *
    (5) * * *
    (i) With the most critical of the takeoff ice accretion(s) defined 
in Appendices C and O of this part, as applicable, in accordance with 
Sec.  25.21(g), from a height of 35 feet above the takeoff surface up 
to the point where the airplane is 400 feet above the takeoff surface; 
and
    (ii) With the most critical of the final takeoff ice accretion(s) 
defined in Appendices C and O of this part, as applicable, in 
accordance with Sec.  25.21(g), from the point where the airplane is 
400 feet above the takeoff surface to the end of the takeoff path.
* * * * *

0
5. Amend Sec.  25.119 by revising paragraph (b) to read as follows:

Sec.  25.119  Landing climb: All-engines-operating.

* * * * *
    (b) In icing conditions with the most critical of the landing ice 
accretion(s) defined in Appendices C and O of this part, as applicable, 
in accordance with Sec.  25.21(g), and with a climb speed of 
VREF determined in accordance with Sec.  25.125(b)(2)(ii).

0
6. Amend Sec.  25.121 by revising paragraphs (b)(2)(ii) introductory 
text, (c)(2)(ii) introductory text, and (d)(2)(ii) to read as follows:

Sec.  25.121  Climb: One-engine-inoperative.

* * * * *
    (b) * * *
    (2) * * *
    (ii) In icing conditions with the most critical of the takeoff ice 
accretion(s) defined in Appendices C and O of this part, as applicable, 
in accordance with Sec.  25.21(g), if in the configuration used to show 
compliance with Sec.  25.121(b) with this takeoff ice accretion:
* * * * *
    (c) * * *
    (2) * * *
    (ii) In icing conditions with the most critical of the final 
takeoff ice accretion(s) defined in Appendices C and O of this part, as 
applicable, in accordance with Sec.  25.21(g), if in the configuration 
used to show compliance with Sec.  25.121(b) with the takeoff ice 
accretion used to show compliance with Sec.  25.111(c)(5)(i):
* * * * *
    (d) * * *
    (2) * * *
    (ii) In icing conditions with the most critical of the approach ice 
accretion(s) defined in Appendices C and O of this part, as applicable, 
in accordance with Sec.  25.21(g). The climb speed selected for non-
icing conditions may be used if the climb speed for icing conditions, 
computed in accordance with paragraph (d)(1)(iii) of this section, does 
not exceed that for non-icing conditions by more than the greater of 3 
knots CAS or 3 percent.

0
7. Amend Sec.  25.123 by revising paragraph (b)(2) introductory text to 
read as follows:

Sec.  25.123  En route flight paths.

* * * * *
    (b) * * *
    (2) In icing conditions with the most critical of the en route ice 
accretion(s) defined in Appendices C and O of this part, as applicable, 
in accordance with Sec.  25.21(g), if:
* * * * *

0
8. Amend Sec.  25.125 by revising paragraphs (a)(2), (b)(2)(ii)(B), and 
(b)(2)(ii)(C) to read as follows:

Sec.  25.125  Landing.

    (a) * * *
    (2) In icing conditions with the most critical of the landing ice 
accretion(s) defined in Appendices C and O of this part, as applicable, 
in accordance with Sec.  25.21(g), if VREF for icing 
conditions exceeds VREF for non-icing conditions by more 
than 5 knots CAS at the maximum landing weight.
    (b) * * *
    (2) * * *
    (ii) * * *
    (B) 1.23 VSR0 with the most critical of the landing ice 
accretion(s) defined in Appendices C and O of this part, as applicable, 
in accordance with Sec.  25.21(g), if that speed exceeds 
VREF selected for non-icing conditions by more than 5 knots 
CAS; and
    (C) A speed that provides the maneuvering capability specified in 
Sec.  25.143(h) with the most critical of the landing ice accretion(s) 
defined in Appendices C and O of this part, as applicable, in 
accordance with Sec.  25.21(g).
* * * * *

0
9. Amend Sec.  25.143 by revising paragraphs (c) introductory text, 
(i)(1), and (j) introductory text to read as follows:

Sec.  25.143  General.

* * * * *
    (c) The airplane must be shown to be safely controllable and 
maneuverable with the most critical of the ice accretion(s) appropriate 
to the phase of flight as defined in Appendices C and O of this part, 
as applicable, in accordance with Sec.  25.21(g), and with the critical 
engine inoperative and its propeller (if applicable) in the minimum 
drag position:
* * * * *
    (i) * * *
    (1) Controllability must be demonstrated with the most critical of 
the ice accretion(s) for the particular flight phase as defined in 
Appendices C and O of this part, as applicable, in accordance with 
Sec.  25.21(g);
* * * * *
    (j) For flight in icing conditions before the ice protection system 
has been activated and is performing its intended function, it must be 
demonstrated in flight with the most critical of the ice accretion(s) 
defined in Appendix C, part

[[Page 65526]]

II, paragraph (e) of this part and Appendix O, part II, paragraph (d) 
of this part, as applicable, in accordance with Sec.  25.21(g), that:
* * * * *

0
10. Amend Sec.  25.207 by revising paragraphs (b), (e)(1), (e)(2), 
(e)(3), (e)(4), (e)(5), and (h) introductory text as follows:

Sec.  25.207  Stall warning.

* * * * *
    (b) The warning must be furnished either through the inherent 
aerodynamic qualities of the airplane or by a device that will give 
clearly distinguishable indications under expected conditions of 
flight. However, a visual stall warning device that requires the 
attention of the crew within the cockpit is not acceptable by itself. 
If a warning device is used, it must provide a warning in each of the 
airplane configurations prescribed in paragraph (a) of this section at 
the speed prescribed in paragraphs (c) and (d) of this section. Except 
for the stall warning prescribed in paragraph (h)(3)(ii) of this 
section, the stall warning for flight in icing conditions must be 
provided by the same means as the stall warning for flight in non-icing 
conditions.
* * * * *
    (e) * * *
    (1) The most critical of the takeoff ice and final takeoff ice 
accretions defined in Appendices C and O of this part, as applicable, 
in accordance with Sec.  25.21(g), for each configuration used in the 
takeoff phase of flight;
    (2) The most critical of the en route ice accretion(s) defined in 
Appendices C and O of this part, as applicable, in accordance with 
Sec.  25.21(g), for the en route configuration;
    (3) The most critical of the holding ice accretion(s) defined in 
Appendices C and O of this part, as applicable, in accordance with 
Sec.  25.21(g), for the holding configuration(s);
    (4) The most critical of the approach ice accretion(s) defined in 
Appendices C and O of this part, as applicable, in accordance with 
Sec.  25.21(g), for the approach configuration(s); and
    (5) The most critical of the landing ice accretion(s) defined in 
Appendices C and O of this part, as applicable, in accordance with 
Sec.  25.21(g), for the landing and go-around configuration(s).
* * * * *
    (h) The following stall warning margin is required for flight in 
icing conditions before the ice protection system has been activated 
and is performing its intended function. Compliance must be shown using 
the most critical of the ice accretion(s) defined in Appendix C, part 
II, paragraph (e) of this part and Appendix O, part II, paragraph (d) 
of this part, as applicable, in accordance with Sec.  25.21(g). The 
stall warning margin in straight and turning flight must be sufficient 
to allow the pilot to prevent stalling without encountering any adverse 
flight characteristics when:
* * * * *

0
11. Amend Sec.  25.237 by revising paragraph (a)(3)(ii) to read as 
follows:

Sec.  25.237  Wind velocities.

    (a) * * *
    (3) * * *
    (ii) Icing conditions with the most critical of the landing ice 
accretion(s) defined in Appendices C and O of this part, as applicable, 
in accordance with Sec.  25.21(g).
* * * * *

0
12. Amend Sec.  25.253 by revising paragraph (c) introductory text to 
read as follows:

Sec.  25.253  High-speed characteristics.

* * * * *
    (c) Maximum speed for stability characteristics in icing 
conditions. The maximum speed for stability characteristics with the 
most critical of the ice accretions defined in Appendices C and O of 
this part, as applicable, in accordance with Sec.  25.21(g), at which 
the requirements of Sec. Sec.  25.143(g), 25.147(f), 25.175(b)(1), 
25.177(a) through (c), and 25.181 must be met, is the lower of:
* * * * *

0
13. Amend Sec.  25.773 by revising paragraph (b)(1)(ii) to read as 
follows:

Sec.  25.773  Pilot compartment view.

* * * * *
    (b) * * *
    (1) * * *
    (ii) The icing conditions specified in Appendix C of this part and 
the following icing conditions specified in Appendix O of this part, if 
certification for flight in icing conditions is sought:
    (A) For airplanes certificated in accordance with Sec.  
25.1420(a)(1), the icing conditions that the airplane is certified to 
safely exit following detection.
    (B) For airplanes certificated in accordance with Sec.  
25.1420(a)(2), the icing conditions that the airplane is certified to 
safely operate in and the icing conditions that the airplane is 
certified to safely exit following detection.
    (C) For airplanes certificated in accordance with Sec.  
25.1420(a)(3) and for airplanes not subject to Sec.  25.1420, all icing 
conditions.
* * * * *

0
14. Amend Sec.  25.903 by adding a new paragraph (a)(3) to read as 
follows:

Sec.  25.903  Engines.

    (a) * * *
    (3) Each turbine engine must comply with one of the following 
paragraphs:
    (i) Section 33.68 of this chapter in effect on January 5, 2015, or 
as subsequently amended; or
    (ii) Section 33.68 of this chapter in effect on February 23, 1984, 
or as subsequently amended before January 5, 2015, unless that engine's 
ice accumulation service history has resulted in an unsafe condition; 
or
    (iii) Section 33.68 of this chapter in effect on October 1, 1974, 
or as subsequently amended prior to February 23, 1984, unless that 
engine's ice accumulation service history has resulted in an unsafe 
condition; or
    (iv) Be shown to have an ice accumulation service history in 
similar installation locations which has not resulted in any unsafe 
conditions.
* * * * *

0
15. Amend Sec.  25.929 by revising paragraph (a) to read as follows:

Sec.  25.929  Propeller deicing.

    (a) If certification for flight in icing is sought there must be a 
means to prevent or remove hazardous ice accumulations that could form 
in the icing conditions defined in Appendix C of this part and in the 
portions of Appendix O of this part for which the airplane is approved 
for flight on propellers or on accessories where ice accumulation would 
jeopardize engine performance.
* * * * *

0
16. Amend Sec.  25.1093 by revising paragraph (b) to read as follows:

Sec.  25.1093  Induction system icing protection.

* * * * *
    (b) Turbine engines. Except as provided in paragraph (b)(3) of this 
section, each engine, with all icing protection systems operating, 
must:
    (1) Operate throughout its flight power range, including the 
minimum descent idling speeds, in the icing conditions defined in 
Appendices C and O of this part, and Appendix D of part 33 of this 
chapter, and in falling and blowing snow within the limitations 
established for the airplane for such operation, without the 
accumulation of ice on the engine, inlet system components, or airframe 
components that would do any of the following:
    (i) Adversely affect installed engine operation or cause a 
sustained loss of power or thrust; or an unacceptable increase in gas 
path operating

[[Page 65527]]

temperature; or an airframe/engine incompatibility; or
    (ii) Result in unacceptable temporary power loss or engine damage; 
or
    (iii) Cause a stall, surge, or flameout or loss of engine 
controllability (for example, rollback).
    (2) Operate at ground idle speed for a minimum of 30 minutes on the 
ground in the following icing conditions shown in Table 1 of this 
section, unless replaced by similar test conditions that are more 
critical. These conditions must be demonstrated with the available air 
bleed for icing protection at its critical condition, without adverse 
effect, followed by an acceleration to takeoff power or thrust in 
accordance with the procedures defined in the airplane flight manual. 
During the idle operation, the engine may be run up periodically to a 
moderate power or thrust setting in a manner acceptable to the 
Administrator. Analysis may be used to show ambient temperatures below 
the tested temperature are less critical. The applicant must document 
the engine run-up procedure (including the maximum time interval 
between run-ups from idle, run-up power setting, and duration at 
power), the associated minimum ambient temperature, and the maximum 
time interval. These conditions must be used in the analysis that 
establishes the airplane operating limitations in accordance with Sec.  
25.1521.
    (3) For the purposes of this section, the icing conditions defined 
in appendix O of this part, including the conditions specified in 
Condition 3 of Table 1 of this section, are not applicable to airplanes 
with a maximum takeoff weight equal to or greater than 60,000 pounds.

                                                       Table 1--Icing Conditions for Ground Tests
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                            Water concentration      Mean effective
             Condition              Total air temperature        (minimum)          particle diameter                     Demonstration
--------------------------------------------------------------------------------------------------------------------------------------------------------
1. Rime ice condition.............  0 to 15 [deg]F (18 to  Liquid--0.3 g/m\3\...  15-25 microns.......  By test, analysis or combination of the two.
                                     -9 [deg]C).
2. Glaze ice condition............  20 to 30 [deg]F (-7    Liquid--0.3 g/m\3\...  15-25 microns.......  By test, analysis or combination of the two.
                                     to -1 [deg]C).
3. Large drop condition...........  15 to 30 [deg]F (-9    Liquid--0.3 g/m\3\...  100 microns           By test, analysis or combination of the two.
                                     to -1 [deg]C).                                (minimum).
--------------------------------------------------------------------------------------------------------------------------------------------------------

* * * * *

0
17. Amend Sec.  25.1323 by revising paragraph (i) to read as follows:

Sec.  25.1323  Airspeed indicating system.

* * * * *
    (i) Each system must have a heated pitot tube or an equivalent 
means of preventing malfunction in the heavy rain conditions defined in 
Table 1 of this section; mixed phase and ice crystal conditions as 
defined in part 33, Appendix D, of this chapter; the icing conditions 
defined in Appendix C of this part; and the following icing conditions 
specified in Appendix O of this part:
    (1) For airplanes certificated in accordance with Sec.  
25.1420(a)(1), the icing conditions that the airplane is certified to 
safely exit following detection.
    (2) For airplanes certificated in accordance with Sec.  
25.1420(a)(2), the icing conditions that the airplane is certified to 
safely operate in and the icing conditions that the airplane is 
certified to safely exit following detection.
    (3) For airplanes certificated in accordance with Sec.  
25.1420(a)(3) and for airplanes not subject to Sec.  25.1420, all icing 
conditions.

                       Table 1--Heavy Rain Conditions for Airspeed Indicating System Tests
----------------------------------------------------------------------------------------------------------------
                 Altitude range                   Liquid water          Horizontal extent           Droplet MVD
------------------------------------------------     content    ------------------------------------------------
                                                ----------------
             (ft)                     (m)            (g/m3)           (km)           (nmiles)       ([micro]m)
----------------------------------------------------------------------------------------------------------------
0 to 10 000..................  0 to 3000.......               1             100             50              1000
                                                              6               5              3              2000
                                                             15               1              0.5            2000
----------------------------------------------------------------------------------------------------------------

* * * * *

0
18. Amend part 25 by adding a new section Sec.  25.1324 to read as 
follows:

Sec.  25.1324  Angle of attack system.

    Each angle of attack system sensor must be heated or have an 
equivalent means of preventing malfunction in the heavy rain conditions 
defined in Table 1 of Sec.  25.1323, the mixed phase and ice crystal 
conditions as defined in part 33, Appendix D, of this chapter, the 
icing conditions defined in Appendix C of this part, and the following 
icing conditions specified in Appendix O of this part:
    (a) For airplanes certificated in accordance with Sec.  
25.1420(a)(1), the icing conditions that the airplane is certified to 
safely exit following detection.
    (b) For airplanes certificated in accordance with Sec.  
25.1420(a)(2), the icing conditions that the airplane is certified to 
safely operate in and the icing conditions that the airplane is 
certified to safely exit following detection.
    (c) For airplanes certificated in accordance with Sec.  
25.1420(a)(3) and for airplanes not subject to Sec.  25.1420, all icing 
conditions.

0
19. Amend Sec.  25.1325 by revising paragraph (b) to read as follows:

Sec.  25.1325  Static pressure systems.

* * * * *
    (b) Each static port must be designed and located so that:
    (1) The static pressure system performance is least affected by 
airflow variation, or by moisture or other foreign matter; and
    (2) The correlation between air pressure in the static pressure 
system and true ambient atmospheric static pressure is not changed when 
the airplane is exposed to the icing conditions defined in Appendix C 
of

[[Page 65528]]

this part, and the following icing conditions specified in Appendix O 
of this part:
    (i) For airplanes certificated in accordance with Sec.  
25.1420(a)(1), the icing conditions that the airplane is certified to 
safely exit following detection.
    (ii) For airplanes certificated in accordance with Sec.  
25.1420(a)(2), the icing conditions that the airplane is certified to 
safely operate in and the icing conditions that the airplane is 
certified to safely exit following detection.
    (iii) For airplanes certificated in accordance with Sec.  
25.1420(a)(3) and for airplanes not subject to Sec.  25.1420, all icing 
conditions.
* * * * *

0
20. Amend part 25 by adding a new Sec.  25.1420 to read as follows:

Sec.  25.1420  Supercooled large drop icing conditions.

    (a) If certification for flight in icing conditions is sought, in 
addition to the requirements of Sec.  25.1419, an airplane with a 
maximum takeoff weight less than 60,000 pounds or with reversible 
flight controls must be capable of operating in accordance with 
paragraphs (a)(1), (2), or (3), of this section.
    (1) Operating safely after encountering the icing conditions 
defined in Appendix O of this part:
    (i) The airplane must have a means to detect that it is operating 
in Appendix O icing conditions; and
    (ii) Following detection of Appendix O icing conditions, the 
airplane must be capable of operating safely while exiting all icing 
conditions.
    (2) Operating safely in a portion of the icing conditions defined 
in Appendix O of this part as selected by the applicant:
    (i) The airplane must have a means to detect that it is operating 
in conditions that exceed the selected portion of Appendix O icing 
conditions; and
    (ii) Following detection, the airplane must be capable of operating 
safely while exiting all icing conditions.
    (3) Operating safely in the icing conditions defined in Appendix O 
of this part.
    (b) To establish that the airplane can operate safely as required 
in paragraph (a) of this section, an applicant must show through 
analysis that the ice protection for the various components of the 
airplane is adequate, taking into account the various airplane 
operational configurations. To verify the analysis, one, or more as 
found necessary, of the following methods must be used:
    (1) Laboratory dry air or simulated icing tests, or a combination 
of both, of the components or models of the components.
    (2) Laboratory dry air or simulated icing tests, or a combination 
of both, of models of the airplane.
    (3) Flight tests of the airplane or its components in simulated 
icing conditions, measured as necessary to support the analysis.
    (4) Flight tests of the airplane with simulated ice shapes.
    (5) Flight tests of the airplane in natural icing conditions, 
measured as necessary to support the analysis.
    (c) For an airplane certified in accordance with paragraph (a)(2) 
or (3) of this section, the requirements of Sec.  25.1419(e), (f), (g), 
and (h) must be met for the icing conditions defined in Appendix O of 
this part in which the airplane is certified to operate.
    (d) For the purposes of this section, the following definitions 
apply:
    (1) Reversible Flight Controls. Flight controls in the normal 
operating configuration that have force or motion originating at the 
airplane's control surface (for example, through aerodynamic loads, 
static imbalance, or trim or servo tab inputs) that is transmitted back 
to flight deck controls. This term refers to flight deck controls 
connected to the pitch, roll, or yaw control surfaces by direct 
mechanical linkages, cables, or push-pull rods in such a way that pilot 
effort produces motion or force about the hinge line.
    (2) Simulated Icing Test. Testing conducted in simulated icing 
conditions, such as in an icing tunnel or behind an icing tanker.
    (3) Simulated Ice Shape. Ice shape fabricated from wood, epoxy, or 
other materials by any construction technique.

0
21. Amend Sec.  25.1521 by redesignating paragraph (c)(3) as paragraph 
(c)(4), revising newly redesignated paragraph (c)(4), and adding new 
paragraph (c)(3) to read as follows:

Sec.  25.1521  Powerplant limitations.

* * * * *
    (c) * * *
    (3) Maximum time interval between engine run-ups from idle, run-up 
power setting and duration at power for ground operation in icing 
conditions, as defined in Sec.  25.1093(b)(2).
    (4) Any other parameter for which a limitation has been established 
as part of the engine type certificate except that a limitation need 
not be established for a parameter that cannot be exceeded during 
normal operation due to the design of the installation or to another 
established limitation.
* * * * *

0
22. Amend Sec.  25.1533 by adding a new paragraph (c) to read as 
follows:

Sec.  25.1533  Additional operating limitations.

* * * * *
    (c) For airplanes certified in accordance with Sec.  25.1420(a)(1) 
or (2), an operating limitation must be established to:
    (1) Prohibit intentional flight, including takeoff and landing, 
into icing conditions defined in Appendix O of this part for which the 
airplane has not been certified to safely operate; and
    (2) Require exiting all icing conditions if icing conditions 
defined in Appendix O of this part are encountered for which the 
airplane has not been certified to safely operate.

0
23. Amend Appendix C to part 25, in part II, by revising paragraph 
(a)(1), the second sentence of paragraph (a)(2), and paragraph (d)(2) 
to read as follows:

Appendix C to Part 25

* * * * *

PART II--AIRFRAME ICE ACCRETIONS FOR SHOWING COMPLIANCE WITH SUBPART B

    (a) * * *
    (1) Takeoff ice is the most critical ice accretion on 
unprotected surfaces and any ice accretion on the protected surfaces 
appropriate to normal ice protection system operation, occurring 
between the end of the takeoff distance and 400 feet above the 
takeoff surface, assuming accretion starts at the end of the takeoff 
distance in the takeoff maximum icing conditions defined in part I 
of this Appendix.
    (2) * * * Ice accretion is assumed to start at the end of the 
takeoff distance in the takeoff maximum icing conditions of part I, 
paragraph (c) of this Appendix.
* * * * *
    (d) * * *
    (2) The ice accretion starts at the end of the takeoff distance.
* * * * *

0
24. Amend part 25 by adding new Appendix O to read as follows:

Appendix O to Part 25--Supercooled Large Drop Icing Conditions

    This Appendix consists of two parts. Part I defines this 
Appendix as a description of supercooled large drop icing conditions 
in which the drop median volume diameter (MVD) is less than or 
greater than 40 [micro]m, the maximum mean effective drop diameter 
(MED) of Appendix C of this part continuous maximum (stratiform 
clouds) icing conditions. For this Appendix, supercooled large drop 
icing conditions consist of freezing drizzle and freezing rain 
occurring in and/or below stratiform clouds. Part II defines ice 
accretions used to show compliance with the airplane performance and 
handling qualities requirements of subpart B of this part.

[[Page 65529]]

PART I--METEOROLOGY

    In this Appendix icing conditions are defined by the parameters 
of altitude, vertical and horizontal extent, temperature, liquid 
water content, and water mass distribution as a function of drop 
diameter distribution.
    (a) Freezing Drizzle (Conditions with spectra maximum drop 
diameters from 100[micro]m to 500 [micro]m):
    (1) Pressure altitude range: 0 to 22,000 feet MSL.
    (2) Maximum vertical extent: 12,000 feet.
    (3) Horizontal extent: Standard distance of 17.4 nautical miles.
    (4) Total liquid water content.

    Note: Liquid water content (LWC) in grams per cubic meter (g/
m\3\) based on horizontal extent standard distance of 17.4 nautical 
miles.
    (5) Drop diameter distribution: Figure 2.
    (6) Altitude and temperature envelope: Figure 3.
    (b) Freezing Rain (Conditions with spectra maximum drop 
diameters greater than 500 [micro]m):
    (1) Pressure altitude range: 0 to 12,000 ft MSL.
    (2) Maximum vertical extent: 7,000 ft.
    (3) Horizontal extent: Standard distance of 17.4 nautical miles.
    (4) Total liquid water content.

    Note: LWC in grams per cubic meter (g/m\3\) based on horizontal 
extent standard distance of 17.4 nautical miles.
    (5) Drop Diameter Distribution: Figure 5.
    (6) Altitude and temperature envelope: Figure 6.
    (c) Horizontal extent.
    The liquid water content for freezing drizzle and freezing rain 
conditions for horizontal extents other than the standard 17.4 
nautical miles can be determined by the value of the liquid water 
content determined from Figure 1 or Figure 4, multiplied by the 
factor provided in Figure 7, which is defined by the following 
equation:

S = 1.266 - 0.213 log10(H)
Where:
S = Liquid Water Content Scale Factor (dimensionless) and
H = horizontal extent in nautical miles
BILLING CODE 4910-13-P
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[[Page 65530]]

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[[Page 65531]]

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[[Page 65533]]

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[[Page 65534]]

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BILLING CODE 4910-13-C

PART II--AIRFRAME ICE ACCRETIONS FOR SHOWING COMPLIANCE WITH SUBPART B 
OF THIS PART

    (a) General.
    The most critical ice accretion in terms of airplane performance 
and handling qualities for each flight phase must be used to show 
compliance with the applicable airplane performance and handling 
qualities requirements for icing conditions contained in subpart B 
of this part. Applicants must demonstrate that the full range of 
atmospheric icing conditions specified in part I of this Appendix 
have been considered, including drop diameter distributions, liquid 
water content, and temperature appropriate to the flight conditions 
(for example, configuration, speed, angle of attack, and altitude).
    (1) For an airplane certified in accordance with Sec.  
25.1420(a)(1), the ice accretions for each flight phase are defined 
in part II, paragraph (b) of this Appendix.
    (2) For an airplane certified in accordance with Sec.  
25.1420(a)(2), the most critical ice accretion for each flight phase 
defined in part II, paragraphs (b) and (c) of this Appendix, must be 
used. For the ice accretions defined in part II, paragraph (c) of 
this Appendix, only the portion of part I of this Appendix in which 
the airplane is capable of operating safely must be considered.
    (3) For an airplane certified in accordance with Sec.  
25.1420(a)(3), the ice accretions for each flight phase are defined 
in part II, paragraph (c) of this Appendix.
    (b) Ice accretions for airplanes certified in accordance with 
Sec.  25.1420(a)(1) or (2).
    (1) En route ice is the en route ice as defined by part II, 
paragraph (c)(3), of this Appendix, for an airplane certified in 
accordance with Sec.  25.1420(a)(2), or defined by part II, 
paragraph (a)(3), of Appendix C of this part, for an airplane 
certified in accordance with Sec.  25.1420(a)(1), plus:
    (i) Pre-detection ice as defined by part II, paragraph (b)(5), 
of this Appendix; and
    (ii) The ice accumulated during the transit of one cloud with a 
horizontal extent of 17.4 nautical miles in the most critical of the 
icing conditions defined in part I of this Appendix and one cloud 
with a horizontal extent of 17.4 nautical miles in the continuous 
maximum icing conditions defined in Appendix C of this part.
    (2) Holding ice is the holding ice defined by part II, paragraph 
(c)(4), of this Appendix, for an airplane certified in accordance 
with Sec.  25.1420(a)(2), or defined by part II, paragraph (a)(4), 
of Appendix C of this part, for an airplane certified in accordance 
with Sec.  25.1420(a)(1), plus:
    (i) Pre-detection ice as defined by part II, paragraph (b)(5), 
of this Appendix; and
    (ii) The ice accumulated during the transit of one cloud with a 
17.4 nautical miles horizontal extent in the most critical of the 
icing conditions defined in part I of this Appendix and one cloud 
with a horizontal extent of 17.4 nautical miles in the continuous 
maximum icing conditions defined in Appendix C of this part.
    (iii) Except the total exposure to holding ice conditions does 
not need to exceed 45 minutes.
    (3) Approach ice is the more critical of the holding ice defined 
by part II, paragraph (b)(2), of this Appendix, or the ice 
calculated in the applicable paragraphs (b)(3)(i) or (ii) of part 
II, of this Appendix:
    (i) For an airplane certified in accordance with Sec.  
25.1420(a)(2), the ice accumulated during descent from the maximum 
vertical extent of the icing conditions defined in part I of this 
Appendix to 2,000 feet above the landing surface in the cruise 
configuration, plus transition to the approach configuration, plus:
    (A) Pre-detection ice, as defined by part II, paragraph (b)(5), 
of this Appendix; and
    (B) The ice accumulated during the transit at 2,000 feet above 
the landing surface of one cloud with a horizontal extent of 17.4 
nautical miles in the most critical of the icing conditions defined 
in part I of this Appendix and one cloud with a horizontal extent of 
17.4 nautical miles in the continuous maximum icing conditions 
defined in Appendix C of this part.

[[Page 65535]]

    (ii) For an airplane certified in accordance with Sec.  
25.1420(a)(1), the ice accumulated during descent from the maximum 
vertical extent of the maximum continuous icing conditions defined 
in part I of Appendix C to 2,000 feet above the landing surface in 
the cruise configuration, plus transition to the approach 
configuration, plus:
    (A) Pre-detection ice, as defined by part II, paragraph (b)(5), 
of this Appendix; and
    (B) The ice accumulated during the transit at 2,000 feet above 
the landing surface of one cloud with a horizontal extent of 17.4 
nautical miles in the most critical of the icing conditions defined 
in part I of this Appendix and one cloud with a horizontal extent of 
17.4 nautical miles in the continuous maximum icing conditions 
defined in Appendix C of this part.
    (4) Landing ice is the more critical of the holding ice as 
defined by part II, paragraph (b)(2), of this Appendix, or the ice 
calculated in the applicable paragraphs (b)(4)(i) or (ii) of part II 
of this Appendix:
    (i) For an airplane certified in accordance with Sec.  
25.1420(a)(2), the ice accretion defined by part II, paragraph 
(c)(5)(i), of this Appendix, plus a descent from 2,000 feet above 
the landing surface to a height of 200 feet above the landing 
surface with a transition to the landing configuration in the icing 
conditions defined in part I of this Appendix, plus:
    (A) Pre-detection ice, as defined in part II, paragraph (b)(5), 
of this Appendix; and
    (B) The ice accumulated during an exit maneuver, beginning with 
the minimum climb gradient required by Sec.  25.119, from a height 
of 200 feet above the landing surface through one cloud with a 
horizontal extent of 17.4 nautical miles in the most critical of the 
icing conditions defined in part I of this Appendix and one cloud 
with a horizontal extent of 17.4 nautical miles in the continuous 
maximum icing conditions defined in Appendix C of this part.
    (ii) For an airplane certified in accordance with Sec.  
25.1420(a)(1), the ice accumulated in the maximum continuous icing 
conditions defined in Appendix C of this part, during a descent from 
the maximum vertical extent of the icing conditions defined in 
Appendix C of this part, to 2,000 feet above the landing surface in 
the cruise configuration, plus transition to the approach 
configuration and flying for 15 minutes at 2,000 feet above the 
landing surface, plus a descent from 2,000 feet above the landing 
surface to a height of 200 feet above the landing surface with a 
transition to the landing configuration, plus:
    (A) Pre-detection ice, as described by part II, paragraph 
(b)(5), of this Appendix; and
    (B) The ice accumulated during an exit maneuver, beginning with 
the minimum climb gradient required by Sec.  25.119, from a height 
of 200 feet above the landing surface through one cloud with a 
horizontal extent of 17.4 nautical miles in the most critical of the 
icing conditions defined in part I of this Appendix and one cloud 
with a horizontal extent of 17.4 nautical miles in the continuous 
maximum icing conditions defined in Appendix C of this part.
    (5) Pre-detection ice is the ice accretion before detection of 
flight conditions in this Appendix that require exiting per Sec.  
25.1420(a)(1) and (2). It is the pre-existing ice accretion that may 
exist from operating in icing conditions in which the airplane is 
approved to operate prior to encountering the icing conditions 
requiring an exit, plus the ice accumulated during the time needed 
to detect the icing conditions, followed by two minutes of further 
ice accumulation to take into account the time for the flightcrew to 
take action to exit the icing conditions, including coordination 
with air traffic control.
    (i) For an airplane certified in accordance with Sec.  
25.1420(a)(1), the pre-existing ice accretion must be based on the 
icing conditions defined in Appendix C of this part.
    (ii) For an airplane certified in accordance with Sec.  
25.1420(a)(2), the pre-existing ice accretion must be based on the 
more critical of the icing conditions defined in Appendix C of this 
part, or the icing conditions defined in part I of this Appendix in 
which the airplane is capable of safely operating.
    (c) Ice accretions for airplanes certified in accordance with 
Sec. Sec.  25.1420(a)(2) or (3). For an airplane certified in 
accordance with Sec.  25.1420(a)(2), only the portion of the icing 
conditions of part I of this Appendix in which the airplane is 
capable of operating safely must be considered.
    (1) Takeoff ice is the most critical ice accretion on 
unprotected surfaces, and any ice accretion on the protected 
surfaces, occurring between the end of the takeoff distance and 400 
feet above the takeoff surface, assuming accretion starts at the end 
of the takeoff distance in the icing conditions defined in part I of 
this Appendix.
    (2) Final takeoff ice is the most critical ice accretion on 
unprotected surfaces, and any ice accretion on the protected 
surfaces appropriate to normal ice protection system operation, 
between 400 feet and either 1,500 feet above the takeoff surface, or 
the height at which the transition from the takeoff to the en route 
configuration is completed and VFTO is reached, whichever 
is higher. Ice accretion is assumed to start at the end of the 
takeoff distance in the icing conditions defined in part I of this 
Appendix.
    (3) En route ice is the most critical ice accretion on the 
unprotected surfaces, and any ice accretion on the protected 
surfaces appropriate to normal ice protection system operation, 
during the en route flight phase in the icing conditions defined in 
part I of this Appendix.
    (4) Holding ice is the most critical ice accretion on the 
unprotected surfaces, and any ice accretion on the protected 
surfaces appropriate to normal ice protection system operation, 
resulting from 45 minutes of flight within a cloud with a 17.4 
nautical miles horizontal extent in the icing conditions defined in 
part I of this Appendix, during the holding phase of flight.
    (5) Approach ice is the ice accretion on the unprotected 
surfaces, and any ice accretion on the protected surfaces 
appropriate to normal ice protection system operation, resulting 
from the more critical of the:
    (i) Ice accumulated in the icing conditions defined in part I of 
this Appendix during a descent from the maximum vertical extent of 
the icing conditions defined in part I of this Appendix, to 2,000 
feet above the landing surface in the cruise configuration, plus 
transition to the approach configuration and flying for 15 minutes 
at 2,000 feet above the landing surface; or
    (ii) Holding ice as defined by part II, paragraph (c)(4), of 
this Appendix.
    (6) Landing ice is the ice accretion on the unprotected 
surfaces, and any ice accretion on the protected surfaces 
appropriate to normal ice protection system operation, resulting 
from the more critical of the:
    (i) Ice accretion defined by part II, paragraph (c)(5)(i), of 
this Appendix, plus ice accumulated in the icing conditions defined 
in part I of this Appendix during a descent from 2,000 feet above 
the landing surface to a height of 200 feet above the landing 
surface with a transition to the landing configuration, followed by 
a go-around at the minimum climb gradient required by Sec.  25.119, 
from a height of 200 feet above the landing surface to 2,000 feet 
above the landing surface, flying for 15 minutes at 2,000 feet above 
the landing surface in the approach configuration, and a descent to 
the landing surface (touchdown) in the landing configuration; or
    (ii) Holding ice as defined by part II, paragraph (c)(4), of 
this Appendix.
    (7) For both unprotected and protected parts, the ice accretion 
for the takeoff phase must be determined for the icing conditions 
defined in part I of this Appendix, using the following assumptions:
    (i) The airfoils, control surfaces, and, if applicable, 
propellers are free from frost, snow, or ice at the start of 
takeoff;
    (ii) The ice accretion starts at the end of the takeoff 
distance;
    (iii) The critical ratio of thrust/power-to-weight;
    (iv) Failure of the critical engine occurs at VEF; 
and
    (v) Crew activation of the ice protection system is in 
accordance with a normal operating procedure provided in the 
airplane flight manual, except that after beginning the takeoff 
roll, it must be assumed that the crew takes no action to activate 
the ice protection system until the airplane is at least 400 feet 
above the takeoff surface.
    (d) The ice accretion before the ice protection system has been 
activated and is performing its intended function is the critical 
ice accretion formed on the unprotected and normally protected 
surfaces before activation and effective operation of the ice 
protection system in the icing conditions defined in part I of this 
Appendix. This ice accretion only applies in showing compliance to 
Sec. Sec.  25.143(j) and 25.207(h).
    (e) In order to reduce the number of ice accretions to be 
considered when demonstrating compliance with the requirements of 
Sec.  25.21(g), any of the ice accretions defined in this Appendix 
may be used for any other flight phase if it is shown to be at least 
as critical as the specific ice accretion defined for that flight 
phase. Configuration differences and their effects on ice accretions 
must be taken into account.
    (f) The ice accretion that has the most adverse effect on 
handling qualities may be used for airplane performance tests 
provided any difference in performance is conservatively taken into 
account.

[[Page 65536]]

PART 33--AIRWORTHINESS STANDARDS: AIRCRAFT ENGINES

0
25. The authority citation for part 33 is revised to read as follows:

    Authority:  49 U.S.C. 106(g), 40113, 44701, 44702, 44704.

0
26. Revise Sec.  33.68 to read as follows:

Sec.  33.68  Induction system icing.

    Each engine, with all icing protection systems operating, must:
    (a) Operate throughout its flight power range, including the 
minimum descent idle rotor speeds achievable in flight, in the icing 
conditions defined for turbojet, turbofan, and turboprop engines in 
Appendices C and O of part 25 of this chapter, and Appendix D of this 
part, and for turboshaft engines in Appendix C of part 29 of this 
chapter, without the accumulation of ice on the engine components that:
    (1) Adversely affects engine operation or that causes an 
unacceptable permanent loss of power or thrust or unacceptable increase 
in engine operating temperature; or
    (2) Results in unacceptable temporary power loss or engine damage; 
or
    (3) Causes a stall, surge, or flameout or loss of engine 
controllability. The applicant must account for in-flight ram effects 
in any critical point analysis or test demonstration of these flight 
conditions.
    (b) Operate throughout its flight power range, including minimum 
descent idle rotor speeds achievable in flight, in the icing conditions 
defined for turbojet, turbofan, and turboprop engines in Appendices C 
and O of part 25 of this chapter, and for turboshaft engines in 
Appendix C of part 29 of this chapter. In addition:
    (1) It must be shown through Critical Point Analysis (CPA) that the 
complete ice envelope has been analyzed, and that the most critical 
points must be demonstrated by engine test, analysis, or a combination 
of the two to operate acceptably. Extended flight in critical flight 
conditions such as hold, descent, approach, climb, and cruise, must be 
addressed, for the ice conditions defined in these appendices.
    (2) It must be shown by engine test, analysis, or a combination of 
the two that the engine can operate acceptably for the following 
durations:
    (i) At engine powers that can sustain level flight: A duration that 
achieves repetitive, stabilized operation for turbojet, turbofan, and 
turboprop engines in the icing conditions defined in Appendices C and O 
of part 25 of this chapter, and for turboshaft engines in the icing 
conditions defined in Appendix C of part 29 of this chapter.
    (ii) At engine power below that which can sustain level flight:
    (A) Demonstration in altitude flight simulation test facility: A 
duration of 10 minutes consistent with a simulated flight descent of 
10,000 ft (3 km) in altitude while operating in Continuous Maximum 
icing conditions defined in Appendix C of part 25 of this chapter for 
turbojet, turbofan, and turboprop engines, and for turboshaft engines 
in the icing conditions defined in Appendix C of part 29 of this 
chapter, plus 40 percent liquid water content margin, at the critical 
level of airspeed and air temperature; or
    (B) Demonstration in ground test facility: A duration of 3 cycles 
of alternating icing exposure corresponding to the liquid water content 
levels and standard cloud lengths starting in Intermittent Maximum and 
then in Continuous Maximum icing conditions defined in Appendix C of 
part 25 of this chapter for turbojet, turbofan, and turboprop engines, 
and for turboshaft engines in the icing conditions defined in Appendix 
C of part 29 of this chapter, at the critical level of air temperature.
    (c) In addition to complying with paragraph (b) of this section, 
the following conditions shown in Table 1 of this section unless 
replaced by similar CPA test conditions that are more critical or 
produce an equivalent level of severity, must be demonstrated by an 
engine test:

                         Table 1--Conditions That Must Be Demonstrated by an Engine Test
----------------------------------------------------------------------------------------------------------------
                                                    Supercooled
                                   Total air           water
          Condition               temperature     concentrations   Median volume drop diameter      Duration
                                                     (minimum)
----------------------------------------------------------------------------------------------------------------
1. Glaze ice conditions......  21 to 25 [deg]F   2 g/m\3\........  25 to 35 microns...........  (a) 10-minutes
                                (-6 to -4                                                        for power below
                                [deg]C).                                                         sustainable
                                                                                                 level flight
                                                                                                 (idle descent).
                                                                                                (b) Must show
                                                                                                 repetitive,
                                                                                                 stabilized
                                                                                                 operation for
                                                                                                 higher powers
                                                                                                 (50%, 75%,
                                                                                                 100%MC).
2. Rime ice conditions.......  -10 to 0 [deg]F   1 g/m\3\........  15 to 25 microns...........  (a) 10-minutes
                                (-23 to -18                                                      for power below
                                [deg]C).                                                         sustainable
                                                                                                 level flight
                                                                                                 (idle descent).
                                                                                                (b) Must show
                                                                                                 repetitive,
                                                                                                 stabilized
                                                                                                 operation for
                                                                                                 higher powers
                                                                                                 (50%, 75%,
                                                                                                 100%MC).
3. Glaze ice holding           Turbojet and      Alternating       20 to 30 microns...........  Must show
 conditions.                    Turbofan, only:   cycle: First                                   repetitive,
(Turbojet, turbofan, and        10 to 18 [deg]F   1.7 g/m\3\ (1                                  stabilized
 turboprop only).               (-12 to -8        minute), Then                                  operation (or
                                [deg]C).          0.3 g/m\3\ (6                                  45 minutes
                                                  minute).                                       max).
                               Turboprop, only:  ................  ...........................  ................
                                2 to 10 [deg]F
                                (-17 to -12
                                [deg]C).
4. Rime ice holding            Turbojet and      0.25 g/m\3\.....  20 to 30 microns...........  Must show
 conditions.                    Turbofan, only:                                                  repetitive,
(Turbojet, turbofan, and        -10 to 0 [deg]F                                                  stabilized
 turboprop only).               (-23 to -18                                                      operation (or
                                [deg]C).                                                         45 minutes
                                                                                                 max).
                               Turboprop, only:  ................  ...........................  ................
                                2 to 10 [deg]F
                                (-17 to -12
                                [deg]C).
----------------------------------------------------------------------------------------------------------------

[[Page 65537]]

    (d) Operate at ground idle speed for a minimum of 30 minutes at 
each of the following icing conditions shown in Table 2 of this section 
with the available air bleed for icing protection at its critical 
condition, without adverse effect, followed by acceleration to takeoff 
power or thrust. During the idle operation, the engine may be run up 
periodically to a moderate power or thrust setting in a manner 
acceptable to the Administrator. Analysis may be used to show ambient 
temperatures below the tested temperature are less critical. The 
applicant must document any demonstrated run ups and minimum ambient 
temperature capability in the engine operating manual as mandatory in 
icing conditions. The applicant must demonstrate, with consideration of 
expected airport elevations, the following:

                          Table 2--Demonstration Methods for Specific Icing Conditions
----------------------------------------------------------------------------------------------------------------
                                                    Supercooled
                                   Total air           water         Mean effective particle
          Condition               temperature     concentrations             diameter             Demonstration
                                                     (minimum)
----------------------------------------------------------------------------------------------------------------
1. Rime ice condition........  0 to 15 [deg]F (- Liquid--0.3 g/    15-25 microns..............  By engine test.
                                18 to -9          m\3\.
                                [deg]C).
2. Glaze ice condition.......  20 to 30 [deg]F   Liquid--0.3 g/    15-25 microns..............  By engine test.
                                (-7 to -1         m\3\.
                                [deg]C).
3. Snow ice condition........  26 to 32 [deg]F   Ice--0.9 g/m\3\.  100 microns................  By test,
                                (-3 to 0                           (minimum)..................   analysis or
                                [deg]C).                                                         combination of
                                                                                                 the two.
4. Large drop glaze ice        15 to 30 [deg]F   Liquid--0.3 g/    100 microns (minimum)......  By test,
 condition (Turbojet,           (-9 to -1         m\3\.                                          analysis or
 turbofan, and turboprop        [deg]C).                                                         combination of
 only).                                                                                          the two.
----------------------------------------------------------------------------------------------------------------

    (e) Demonstrate by test, analysis, or combination of the two, 
acceptable operation for turbojet, turbofan, and turboprop engines in 
mixed phase and ice crystal icing conditions throughout Appendix D of 
this part, icing envelope throughout its flight power range, including 
minimum descent idling speeds.

0
27. Amend Sec.  33.77 by adding paragraph (a) and revising paragraphs 
(c) introductory text, (c)(1), (d), and (e) to read as follows:

Sec.  33.77  Foreign object ingestion ice.

    (a) Compliance with the requirements of this section must be 
demonstrated by engine ice ingestion test or by validated analysis 
showing equivalence of other means for demonstrating soft body damage 
tolerance.
* * * * *
    (c) Ingestion of ice under the conditions of this section may not--
    (1) Cause an immediate or ultimate unacceptable sustained power or 
thrust loss; or
* * * * *
    (d) For an engine that incorporates a protection device, compliance 
with this section need not be demonstrated with respect to ice formed 
forward of the protection device if it is shown that--
    (1) Such ice is of a size that will not pass through the protective 
device;
    (2) The protective device will withstand the impact of the ice; and
    (3) The ice stopped by the protective device will not obstruct the 
flow of induction air into the engine with a resultant sustained 
reduction in power or thrust greater than those values defined by 
paragraph (c) of this section.
    (e) Compliance with the requirements of this section must be 
demonstrated by engine ice ingestion test under the following ingestion 
conditions or by validated analysis showing equivalence of other means 
for demonstrating soft body damage tolerance.
    (1) The minimum ice quantity and dimensions will be established by 
the engine size as defined in Table 1 of this section.
    (2) The ingested ice dimensions are determined by linear 
interpolation between table values, and are based on the actual 
engine's inlet hilite area.
    (3) The ingestion velocity will simulate ice from the inlet being 
sucked into the engine.
    (4) Engine operation will be at the maximum cruise power or thrust 
unless lower power is more critical.

                         Table 1--Minimum Ice Slab Dimensions Based on Engine Inlet Size
----------------------------------------------------------------------------------------------------------------
                                                                     Thickness
               Engine Inlet Hilite area (sq. inch)                    (inch)       Width (inch)    Length (inch)
----------------------------------------------------------------------------------------------------------------
0...............................................................            0.25               0             3.6
80..............................................................            0.25               6             3.6
300.............................................................            0.25              12             3.6
700.............................................................            0.25              12             4.8
2800............................................................            0.35              12             8.5
5000............................................................            0.43              12            11.0
7000............................................................            0.50              12            12.7
7900............................................................            0.50              12            13.4
9500............................................................            0.50              12            14.6
11300...........................................................            0.50              12            15.9
13300...........................................................            0.50              12            17.1
16500...........................................................            0.5               12            18.9
20000...........................................................            0.5               12            20.0
----------------------------------------------------------------------------------------------------------------

[[Page 65538]]

Appendix C [Added and Reserved]

0
28. Amend part 33 by adding and reserving a new Appendix C.

0
29. Amend part 33 by adding a new Appendix D to read as follows:

Appendix D to Part 33--Mixed Phase and Ice Crystal Icing Envelope (Deep 
Convective Clouds)

    The ice crystal icing envelope is depicted in Figure D1 of this 
Appendix.
BILLING CODE 4910-13-P
[GRAPHIC] [TIFF OMITTED] TR04NO14.008

    Within the envelope, total water content (TWC) in g/m\3\ has 
been determined based upon the adiabatic lapse defined by the 
convective rise of 90% relative humidity air from sea level to 
higher altitudes and scaled by a factor of 0.65 to a standard cloud 
length of 17.4 nautical miles. Figure D2 of this Appendix displays 
TWC for this distance over a range of ambient temperature within the 
boundaries of the ice crystal envelope specified in Figure D1 of 
this Appendix.

[[Page 65539]]

[GRAPHIC] [TIFF OMITTED] TR04NO14.009

    Ice crystal size median mass dimension (MMD) range is 50-200 
microns (equivalent spherical size) based upon measurements near 
convective storm cores.
    The TWC can be treated as completely glaciated (ice crystal) 
except as noted in the Table 1 of this Appendix.

               Table 1--Supercooled Liquid Portion of TWC
------------------------------------------------------------------------
                                          Horizontal cloud      LWC-- g/
      Temperature range--deg C         length--nautical miles     m\3\
------------------------------------------------------------------------
0 to -20............................  pre>
```