67278 Federal Register / Vol. 70, No. 213 / Friday, November 4, 2005 / Proposed Rules 

DEPARTMENT OF TRANSPORTATION 

Federal Aviation Administration 

14 CFR Part 25 

[Docket No. 2005–22840; Notice No. 05–10] 

RIN 2120–AI14 

Airplane Performance and Handling 

Qualities in Icing Conditions 

AGENCY: Federal Aviation 

Administration (FAA), DOT. 

ACTION: Notice of proposed rulemaking 

(NPRM). 

SUMMARY: This action proposes to 

introduce new airworthiness standards 

to evaluate the performance and 

handling characteristics of transport 

category airplanes in icing conditions. 

This proposed action would improve 

the level of safety for new airplane 

designs when operating in icing 

conditions, and would harmonize the 

U.S. and European airworthiness 

standards for flight in icing conditions. 

DATES: Send your comments on or 

before February 2, 2006. 

ADDRESSES: You may send comments 

identified by Docket Number FAA– 

2005–22840 using any of the following 

methods: 

• DOT Docket Web site: Go to http:// 

dms.dot.gov and follow the instructions 

for sending your comments 

electronically. 

• Government-wide Regulations and 

Policies Web site: Go to http:// 

www.faa.gov/regulations_policies/ and 

follow the instructions for sending your 

comments electronically. 

• Mail: Docket Management Facility; 

U.S. Department of Transportation, 400 

Seventh Street, SW., Nassif Building, 

Room PL–401, Washington, DC 20590– 

001. 

• Fax: 1–202–493–2251. 

• Hand Delivery: Room PL–401 on 

the plaza level of the Nassif Building, 

400 Seventh Street, SW., Washington, 

DC, between 9 a.m. and 5 p.m., Monday 

through Friday, except Federal holidays. 

For more information on the 

rulemaking process, see the 

SUPPLEMENTARY INFORMATION section of 

this document. 

Privacy: We will post all comments 

we receive, without change, to http:// 

dms.dot.gov, including any personal 

information you provide. For more 

information, see the Privacy Act 

discussion in the SUPPLEMENTARY

INFORMATION section of this document. 

Docket: To read background 

documents or comments received, go to 

http://dms.dot.gov at any time or to 

Room PL–401 on the plaza level of the 

Nassif Building, 400 Seventh Street, 

SW., Washington, DC, between 9 a.m. 

and 5 p.m., Monday through Friday, 

except Federal holidays. 

FOR FURTHER INFORMATION CONTACT: Don 

Stimson, FAA, Airplane & Flight Crew 

Interface Branch, ANM–111, Transport 

Airplane Directorate, Aircraft 

Certification Service, 1601 Lind Avenue 

SW., Renton, WA 98055–4056; 

telephone: (425) 227–1129; fax: (425) 

227–1149, e-mail: don.stimson@faa.gov. 

SUPPLEMENTARY INFORMATION: 

Comments Invited 

The FAA invites interested persons to 

participate in this rulemaking by 

submitting written comments, data, or 

views. We also invite comments relating 

to the economic, environmental, energy, 

or federalism impacts that might result 

from adopting the proposals in this 

document. The most helpful comments 

reference a specific portion of the 

proposal, explain the reason for any 

recommended change, and include 

supporting data. We ask that you send 

us two copies of written comments. 

We will file in the docket all 

comments we receive, as well as a 

report summarizing each substantive 

public contact with FAA personnel 

concerning this proposed rulemaking. 

The docket is available for public 

inspection before and after the comment 

closing date. If you wish to review the 

docket in person, go to the address in 

the ADDRESSES section of this preamble 

between 9 a.m. and 5 p.m., Monday 

through Friday, except Federal holidays. 

You may also review the docket using 

the Internet at the Web address in the 

ADDRESSES section. 

Privacy Act: Using the search function 

of our docket Web site, anyone can find 

and read the comments received into 

any of our dockets, including the name 

of the individual sending the comment 

(or signing the comment of behalf of an 

association, business, labor union, etc.). 

You may review DOT’s complete 

Privacy Act statement in the Federal 

Register published on April 11, 2000 

(65 FR 19477–78) or you may visit 

http://dms.dot.gov. 

Before acting on this proposal, we 

will consider all comments we receive 

on or before the closing date for 

comments. We will consider comments 

filed late if it is possible to do so 

without incurring expense or delay. We 

may change this proposal in light of the 

comments we receive. 

If you want the FAA to acknowledge 

receipt of your comments on this 

proposal, include with your comments 

a pre-addressed, stamped postcard on 

which the docket number appears. We 

will stamp the date on the postcard and 

mail it to you. 

Availability of Rulemaking Documents 

You can get an electronic copy using 

the Internet by: 

(1) Searching the Department of 

Transportation’s electronic Docket 

Management System (DMS) Web page 

(http://dms.dot.gov/search); 

(2) Visiting the Office of Rulemaking’s 

Web page at http://www.faa.gov/avr/ 

arm/index.cfm; or 

(3) Accessing the Government 

Printing Office’s Web page at http:// 

www.gpoaccess.gov/fr/index.html. 

You can also get a copy by sending a 

request to the Federal Aviation 

Administration, Office of Rulemaking, 

ARM–1, 800 Independence Avenue 

SW., Washington, DC 20591, or by 

calling (202) 267–9680. Make sure to 

identify the docket number, notice 

number, or amendment number of this 

rulemaking. 

Authority for This Rulemaking 

The FAA’s authority to issue rules 

regarding 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 promulgated 

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. This regulation is within the 

scope of that authority because it 

prescribes new safety standards for the 

design of transport category airplanes. 

Organization of This NPRM 

Discussion of this proposal is 

organized under the headings listed 

below. Whenever there is a reference to 

a document being included in the 

docket for this NPRM, the docket 

referred to is Docket Number FAA– 

2005–22840. A list of acronyms used is 

included in an appendix located at the 

end of the preamble material, between 

the regulatory evaluation and the text of 

the proposed amendments. Unless 

stated otherwise, rule sections 

referenced in this NPRM are part of 

Title 14, Code of Federal Regulations 

(14 CFR). 

I. Executive Summary 

If adopted, this rulemaking would 

revise certain sections of part 25 of Title 

Federal Register / Vol. 70, No. 213 / Friday, November 4, 2005 / Proposed Rules 67279 

1These accidents were selected from the National 

Transportation Safety Board’s (NTSB) accident 

database, and are discussed in Appendix 3 of this 

premable. 

2A JAA AMJ is similar to an FAA advisory 

circular. 

14 Code of Federal Regulations (14 

CFR). Part 25 contains the airworthiness 

standards for type certification of 

transport category airplanes, but it does 

not currently include specific 

requirements for airplane performance 

or handling qualities for flight in icing 

conditions. Although part 25 requires 

airplanes with approved ice protection 

features to be able to operate safely in 

icing conditions, there is no standard set 

of criteria defining what ‘‘to safely 

operate’’ in icing conditions means in 

terms of airplane performance and 

handling qualities. Further, because the 

existing icing regulations only address 

airplanes with ice protection provisions, 

it is unclear what requirements apply in 

cases where the applicant is seeking to 

have an airplane without an ice 

protection system certificated for flight 

in icing conditions. 

This notice proposes to amend part 25 

by adding a comprehensive set of 

airworthiness requirements that must be 

met to receive certification approval for 

flight in icing conditions, including 

specific performance and handling 

qualities requirements, and the ice 

accretion (that is, the size, shape, 

location, and texture of the ice) that 

must be considered for each phase of 

flight. These proposed revisions would 

ensure that minimum operating speeds 

determined during the certification of 

all future transport category airplanes 

would provide adequate maneuver 

capability in icing conditions for all 

phases of flight and all airplane 

configurations. 

This notice proposes to require the 

same airplane handling characteristics 

that apply in non-icing conditions to 

continue to apply in icing conditions. 

Additionally, a specific evaluation for 

susceptibility to tailplane stall in icing 

conditions would be added. This 

proposal, if adopted, would harmonize 

the U.S. and European airworthiness 

standards for flight in icing conditions. 

It would benefit the public interest 

while retaining or enhancing the current 

level of safety for operation in icing 

conditions. 

If adopted, this rulemaking would 

affect manufacturers, modifiers, and 

operators of transport category airplanes 

(but only for new designs or significant 

changes to current designs that would 

affect the safety of flight in icing 

conditions). Manufacturers and 

modifiers may need to develop new 

tests and analyses to determine ice 

accretions and to estimate performance 

effects for design and certification to 

address icing conditions. Operators may 

need to develop new or revised 

procedures regarding identification of 

icing conditions and the operation of 

the ice protection system. 

Service history shows that flight in 

icing conditions may be a safety risk for 

transport category airplanes. There have 

been nine accidents since 1983 that may 

have been prevented if this proposed 

rule had been in effect.1 The service 

history that we examined includes 

airplanes certificated to part 25, to its 

predecessor, the Civil Air Regulations 

(CAR) 4b, or to part 25 icing standards 

when the airplane was certified under 

part 23. In evaluating the potential for 

this rulemaking to avoid future 

accidents, we only considered past 

accidents involving tailplane stall or 

potential airframe ice accretion effects 

on drag or controllability. Accidents 

related to ground deicing were not 

considered. 

The NTSB has issued several safety 

recommendations related to airframe 

icing, some of which are addressed, at 

least in part, by this notice. If adopted, 

this rulemaking would require, during 

type certification, that manufacturers of 

transport category airplanes: 

• Investigate the susceptibility of 

their airplanes to ice-contaminated 

tailplane stall (ICTS); 

• Provide for adequate warning on 

the flight deck of an impending stall in 

icing conditions; 

• Show that their airplanes meet the 

same maneuvering capability and 

handling characteristics requirements in 

icing conditions as in non-icing 

conditions; and 

• Show that their airplanes have 

adequate performance capability in 

icing conditions. 

As discussed in more detail later, the 

FAA has tentatively determined that 

this rulemaking would have the 

following costs and benefits over a 45- 

year analysis period. The cost of the 

proposed rule would be $22.0 million 

(present value). The FAA assumes the 

initial certification costs of $6.7 million 

for four new airplane models are 

incurred in year one of a 45-year 

analysis period. The future additional 

fuel burn expense is estimated to be 

$59.7 million and would be incurred 

over the 45-year analysis period. The 

benefits of this proposed rule consist of 

the value of lives saved due to avoiding 

accidents involving part 25 airplanes 

operating in icing conditions. Over the 

45-year period of analysis, the potential 

benefit of the proposed rule would be 

$89.9 million ($23.7 million in present 

value at seven percent). 

A. Past Regulatory Approach 

Currently, § 25.1419, ‘‘Ice protection,’’

requires transport category airplanes 

with approved ice protection features be 

capable of operating safely within the 

icing conditions identified in appendix 

C of part 25. This section also requires 

flight testing and analyses to be 

performed to make this determination. 

Although an airplane’s performance 

capability and handling qualities are 

important in determining whether an 

airplane can operate safely, part 25 does 

not have specific airplane performance 

or handling qualities requirements for 

flight in icing conditions, nor does the 

FAA have a standard set of criteria 

defining what ‘‘to safely operate’’ in 

icing conditions means in terms of 

airplane performance and handling 

qualities. The proposed revisions to part 

25 would provide a comprehensive set 

of harmonized requirements for airplane 

performance and handling qualities to 

address safe operation of transport 

category airplanes in icing conditions. 

Further, § 25.1419 requires an 

applicant to demonstrate that the 

airplane can operate safely in icing 

conditions only when the applicant is 

seeking to certificate ice protection 

features. It fails to address certification 

approval for flight in icing conditions 

for airplanes without ice protection 

features. 

In contrast, the European 

airworthiness standards specifically 

address certification for flight in icing 

conditions, independent of whether the 

airplane includes ice protection 

features. In addition, the European Joint 

Aviation Authorities (JAA) proposed 

additional guidance material in the 

early 1990s to provide criteria for 

determining whether an airplane’s 

performance and handling qualities 

would allow the airplane to operate 

safely in icing conditions. The JAA’s 

guidance material was proposed in draft 

Advisory Material—Joint (AMJ) 

25.1419.2 The JAA’s draft AMJ was 

published on April 23, 1993, as a Notice 

of Proposed Amendment (NPA) 25F–

219, ‘‘Flight in Icing Conditions—

Acceptable Handling Characteristics 

and Performance Effects.’’

B. Harmonization of U.S. and European 

Regulatory Standards 

1. Federal Aviation Administration 

Title 14 CFR part 25 contains the U.S. 

airworthiness standards for type 

certification of transport category 

airplanes. The part 25 standards apply 

to airplanes manufactured within the 

67280 Federal Register / Vol. 70, No. 213 / Friday, November 4, 2005 / Proposed Rules 

3Published in the Federal Register (56 FR 2190), 

on January 22, 1991. 

4Published in the Federal Register (56 FR 2190), 

on June 10, 1994. 

5The complete text of the FTHWG’s report is 

available at http://www.faa.gov/avr/arm/arac/ 

aractasks/fr0404report.pdf. The FTHWG preferred 

the term ‘‘ice accretion’’ rather than ‘‘ice shape’’

because it includes physical characteristics of the 

ice build-up such as texture and surface roughness 

in addition to its general size and shape. 

U.S. and to airplanes manufactured in 

other countries and imported to the U.S. 

under a bilateral airworthiness 

agreement. 

2. Joint Aviation Authorities 

The JAR–25 contains the European 

airworthiness standards for type 

certification of transport category 

airplanes. Thirty-seven European 

countries accept airplanes type 

certificated to the JAR–25 standards, 

including airplanes manufactured in the 

U.S. that are type certificated to JAR–25 

standards for export to Europe. 

3. European Aviation Safety Agency 

(EASA) 

The European Community established 

a new aviation regulatory body, EASA, 

to develop standards to ensure the 

highest level of safety and 

environmental protection, oversee their 

uniform application across Europe, and 

promote them internationally. The 

EASA formally became operational for 

certification of aircraft, engines, parts, 

and appliances on September 28, 2003. 

The EASA will eventually absorb all of 

the functions and activities of the JAA, 

including its efforts to harmonize the 

European airworthiness certification 

regulations with those of the U.S. 

The JAR–25 standards have been 

incorporated into the EASA’s 

‘‘Certification Specifications for Large 

Aeroplanes,’’ (CS)–25, in similar if not 

identical language. The EASA’s CS–25 

became effective October 17, 2003. 

The proposals contained in this notice 

were developed in coordination with 

the JAA. However, since the JAA’s JAR–

25 and the EASA’s CS–25 are essentially 

the same, all of the discussions of these 

proposals relative to JAR–25 also apply 

to CS–25. 

The FAA’s rulemaking proposal, if 

adopted, would parallel the JAA’s 

rulemaking proposal, ‘‘Notice of 

Proposed Amendment (NPA) 25B, E, F–

332,’’ published on June 1, 2002. 

The EASA recently published for 

comment NPA 16/2004, ‘‘Draft Decision 

of the Executive Director of the Agency 

on Certification Conditions.’’ This NPA, 

published for comment in late 2004, is 

based on the standards that the JAA 

were expected to adopt. 

Although the FAA, the JAA, and 

EASA intend to harmonize the 

standards for airplane performance and 

handling qualities for flight in icing 

conditions, there are some differences 

between this rulemaking proposal and 

the standards proposed by the JAA and 

EASA. The differences are primarily 

editorial and are not intended to result 

in significant regulatory differences. 

C. Proposal Development—Aviation 

Rulemaking Advisory Committee 

The FAA, in cooperation with the 

JAA and representatives of the 

American and European aerospace 

industries, recognized that a common 

set of standards would not only 

economically benefit the aviation 

industry, but also maintain a high level 

of safety. In 1988, the FAA and the JAA 

began a process to harmonize their 

respective airworthiness standards. To 

assist in the harmonization efforts, the 

FAA established the Aviation 

Rulemaking Advisory Committee 

(ARAC) in 1991,3 to: 

1. Provide advice and 

recommendations concerning the full 

range of our safety-related rulemaking 

activity; 

2. Develop better rules in less overall 

time using fewer FAA resources than 

are currently needed; and 

3. Obtain firsthand information and 

insight from interested parties regarding 

proposed new rules or revisions of 

existing rules. 

There are 73 member organizations on 

the committee, representing a wide 

range of interests within the aviation 

community. 

We tasked the ARAC Flight Test 

Harmonization Working Group 

(FTHWG) to recommend to the ARAC 

new or revised requirements and 

compliance methods related to airplane 

performance and handling qualities in 

icing conditions.4

The FTHWG reviewed in-service 

incidents and accidents involving 

transport category airplanes. This 

review revealed numerous incidents 

resulting from the effects of ice on 

airplane performance. The same review 

showed that the icing-related accidents 

resulted from a loss of control of the 

airplane due to the effect of the ice on 

airplane handling qualities. Considering 

this service history, the FTHWG 

determined that airplanes should 

generally meet the same handling 

qualities standards in icing conditions 

that they currently must meet for nonicing conditions. In certain areas, 

however, the FTHWG decided that the 

current handling qualities standards 

were inappropriate for flight in icing 

conditions. In these areas, the FTHWG 

developed alternative criteria that 

would apply to icing conditions. 

Since airplane performance 

degradation was not a causal factor in 

any of the icing-related accidents, the 

FTHWG concluded that the current 

performance standards already provide 

some safety margin to offset the negative 

effects of ice accretion. On the basis of 

this service history, the FTHWG 

decided that the general approach to 

airplane performance in icing 

conditions used by the JAA in their 

draft AMJ 25.1419 was appropriate and 

used this approach in its 

recommendations to the FAA. This 

approach allows a limited reduction in 

airplane performance capability due to 

ice before the effects of icing must be 

fully taken into account in the 

performance data provided in the 

Airplane Flight Manual (AFM). Such an 

approach minimizes the costs to 

manufacturers and operators while 

increasing the current level of safety for 

flight in icing conditions. 

This proposed rulemaking is based on 

the FTHWG’s report, which ARAC 

approved and forwarded to the FAA, 

and refers to the ice accretions to be 

used in showing compliance. These ice 

accretions are defined in a new 

subsection of appendix C to part 25.5

D. Related Rulemaking Activity 

1. Amendment 25–108 

This Amendment, ‘‘1-g Stall Speed as 

the Basis for Compliance With Part 25 

of the Federal Aviation Regulations’’

(referred to as the 1-g stall rule) (67 FR 

708112, November 26, 2002) redefines 

the criteria for determining the stall 

speed for transport category airplanes. 

The stall speed is important because it 

is used as a reference speed for defining 

minimum operating speeds that provide 

a safety margin above the speed at 

which the airplane will stall. The 

previous part 25 definition of stall speed 

defined it as the minimum speed 

reached in a stalling maneuver. This 

definition could result in a stall speed 

being defined that is too low to support 

the weight of the airplane in level flight. 

The recently adopted 1-g stall rule 

defines the stall speed as the speed at 

which the aerodynamic lift can support 

the weight of the airplane in 1-g flight. 

The 1-g stall rule also introduces a 

requirement to demonstrate adequate 

maneuver capability at the minimum 

operating speeds for airplane 

configurations associated with low 

speed operations around airports. The 

JAA adopted the same 1-g stall speed 

requirements in Change 15 to JAR–25. 

Federal Register / Vol. 70, No. 213 / Friday, November 4, 2005 / Proposed Rules 67281 

2. Ice Protection Harmonization 

Working Group (IPHWG) 

Recommendations 

The FAA tasked the ARAC to 

consider whether airplane 

manufacturers or operators should be 

required to install ice detectors or 

provide some other acceptable way to 

warn flightcrews of potentially unsafe 

ice accumulations. The ARAC assigned 

this task to the IPHWG. The IPHWG 

recommended to the ARAC that the 

FAA adopt an operating rule for certain 

types of airplanes that would require a 

reliable method of informing pilots 

when to activate the ice protection 

system as well as a way of knowing 

when ice is accumulating aft of areas 

protected by the ice protection system. 

The IPHWG is also working on a 

recommendation for a type certification 

requirement that would identify 

acceptable ways to inform the flightcrew 

when to activate the ice protection 

system. 

We also tasked the ARAC to: 

• Define an icing environment that 

includes supercooled large drop (SLD) 

icing conditions; 

• Recommend requirements to assess 

the ability of aircraft to safely operate in 

SLD icing conditions, either for the 

period of time necessary to exit or to 

operate without restriction; and 

• Consider mixed phase conditions (a 

mixture of supercooled water droplets 

and ice crystals) if such conditions are 

more hazardous than the liquid phase 

icing environment containing 

supercooled water droplets. 

When ARAC finishes its tasks, we 

expect it to forward to us a report 

containing their recommendations. 

These recommendations may lead to 

future rulemaking to address SLD icing 

conditions, but would not directly 

impact this rulemaking. 

E. Advisory Material 

In addition to being tasked to 

recommend new or revised 

requirements related to airplane 

performance and handling qualities in 

icing conditions, the ARAC FTHWG 

was tasked to recommend advisory 

material identifying acceptable ways to 

comply with the proposed new or 

revised requirements. The FTHWG 

developed a proposed Advisory 

Circular, (AC) 25.21–1X, ‘‘Performance 

and Handling Characteristics in the 

Icing Conditions Specified in Part 25, 

Appendix C.’’ We are requesting public 

comments on this proposed advisory 

circular through a separate notice of 

availability in this edition of the Federal 

Register. 

II. Discussion of the Proposals 

A. Proof of Compliance (§ 25.21) 

We propose to add paragraph (g), to 

specify the requirements that must be 

met in icing conditions if an applicant 

seeks certification approval for flight in 

icing conditions. As discussed above, a 

review of icing-related incidents and 

accidents revealed loss of control to be 

the greatest threat to safety of flight in 

icing conditions. Consequently, the 

FTHWG identified the existing part 25 

requirements that could prevent loss of 

control if they were applied to icing 

conditions. The FTHWG found, and we 

tentatively agree, that airplanes should 

continue to comply with most of 

subpart B of part 25 with ice on the 

airplane to ensure safe flight in icing 

conditions. The subpart B regulations 

that would be excluded by paragraph 

(g)(1) were determined to be beyond 

what was necessary to determine an 

airplane’s ability to operate safely in 

icing conditions. 

Because the airplane performance and 

handling qualities requirements are 

flight-related requirements, it is 

appropriate to place the proposed 

requirements for flight in icing 

conditions in part 25, subpart B (Flight) 

rather than in the current ice protection 

rule in § 25.1419. Section 25.1419 is in 

subpart F (Equipment), and, though it is 

closely linked with the subpart B 

requirements proposed in this notice, it 

primarily applies to the ice protection 

equipment on the airplane. 

The proposed subpart B requirements 

would provide the minimum 

performance and handling qualities 

requirements corresponding to the 

§ 25.1419 requirement that the airplane 

‘‘be able to safely operate in the 

continuous maximum and intermittent 

maximum icing conditions of appendix 

C.’’ Additionally, the proposed 

requirements would supply the means 

for determining, from a performance 

and handling qualities standpoint, 

whether the ice protection system and 

its components are effective, as required 

by § 25.1419(b). 

Compliance with the proposed 

performance and handling qualities 

requirements may be shown by a variety 

of means that would be evaluated 

during the particular airplane type 

certification program. These means may 

include flight testing in natural icing 

conditions or in non-icing conditions 

using artificial ice shapes, wind tunnel 

testing and analysis, engineering 

simulator testing and analysis, 

engineering analysis, and comparison to 

previous similar airplanes. 

The proposed requirements would not 

specifically require performance and 

handling qualities flight testing to be 

conducted in natural icing conditions. 

However, we expect that for most new 

airplane designs, and for significant 

changes to existing designs, at least a 

limited set of tests would be flown in 

natural icing conditions. The purpose of 

these tests would be to confirm the 

airplane handling qualities and 

performance results found through other 

means. The proposed advisory material 

will provide guidance on an acceptable 

flight test program, including the 

specific tests that should be conducted 

in natural icing conditions. 

Historically, flight tests in measured 

natural icing conditions have also been 

conducted to verify analyses used to 

generate ice accretions for compliance 

with § 25.1419(b), and to confirm the 

general physical characteristics and 

location of ice accretions used to 

evaluate airplane performance and 

handling qualities. This proposed rule is 

not intended to alter this practice or 

interpretation of § 25.1419(b). Existing 

AC 25.1419–1, ‘‘Certification of 

Transport Category Airplanes for Flight 

in Icing Conditions,’’ provides guidance 

on comparing the ice accretions used to 

evaluate airplane performance and 

handling qualities with those obtained 

in natural icing conditions. 

Proposed paragraph (g)(1) would 

apply the same airplane handling 

qualities requirements to flight in icing 

conditions as are currently required for 

non-icing conditions. Paragraph (g)(1) 

would also apply most of the airplane 

performance requirements currently 

required for non-icing conditions to 

flight in icing conditions. The icing 

conditions for showing compliance 

would be defined in appendix C to part 

25. These requirements would apply to 

normal operations of the airplane and 

its ice protection system as specified in 

the AFM. By referencing the AFM, this 

paragraph would require that this 

manual include the limitations and 

operating procedures that are specific to 

operating in icing conditions. 

As noted in the introductory 

discussion, some degradation in 

airplane performance capability would 

be permitted when showing compliance 

with the requirements for non-icing 

conditions. The amount of performance 

degradation permitted in each case is 

identified in the discussion of the 

individual performance regulations. 

Proposed paragraph (g)(2) would 

prevent the use of different load, weight, 

and center-of-gravity limits for flight in 

icing, except where compliance with the 

applicable performance requirements 

impose more restrictive weight limits. 

The reason for these proposed 

requirements is that operation in icing 

67282 Federal Register / Vol. 70, No. 213 / Friday, November 4, 2005 / Proposed Rules 

conditions should be essentially 

transparent to the flightcrew. There 

should not be any special procedures or 

methods used for operating in icing 

conditions other than activating ice 

protection systems. This philosophy 

comes from applying human factors 

principles to reduce operational 

complexity and flightcrew workload. 

B. Stall Speed (§ 25.103) 

We propose to revise § 25.103 to 

require applicants to determine stall 

speeds with ice on the airplane. The 

proposed § 25.103(b)(3) adds ice 

accretion as a variable that must be 

considered when determining stall 

speeds to use for the different part 25 

airplane performance standards. 

Determining stall speeds with ice 

accretions is necessary to identify any 

increase in stall speeds from those 

determined for non-icing conditions. 

The applicant would then compare any 

change in stall speed due to ice 

accretion with the allowable stall and 

operating speed effects contained in the 

proposed airplane performance 

standards to determine whether or not 

airplane performance data must be 

determined specifically for icing 

conditions. 

C. Takeoff (§ 25.105) 

We propose to revise § 25.105(a) to 

add the net takeoff flight path described 

in § 25.115 to the list of airplane takeoff 

performance parameters that must be 

determined under the conditions 

specified in this paragraph. 

Additionally, § 25.105(a) would specify 

when compliance must be shown 

specifically for icing conditions. 

We consider the proposed changes 

necessary to ensure the safety of takeoff 

operations in icing conditions. Ice on 

the wings and control surfaces can 

reduce the safety margins that currently 

are provided to prevent stalling the 

airplane. It can also degrade airplane 

climb performance, and cause 

controllability problems. We 

acknowledge that many transport 

category airplanes have safely operated 

in icing conditions using takeoff speeds 

determined for non-icing conditions. 

We agree with the FTHWG, however, 

that it is in the interest of safety to 

consider the effects of ice accretions on 

airplane takeoff performance. 

In developing this proposal, the 

FTHWG and the FAA considered four 

factors: 

• Operating rules and practices 

intended to ensure that critical surfaces 

of the airplane are free of snow or ice 

before beginning a takeoff; 

• The use of anti-icing fluids that 

provide some protection from icing 

during the takeoff; 

• Increasing use of ice detectors and 

deicing/anti-icing systems on airplanes 

that can be operated while the airplane 

is still on the ground; and 

• The icing conditions that we 

propose to use for the takeoff flight 

phase. 

Existing operating rules, §§ 91.527(a), 

121.629(b), and 135.227(a), prohibit 

pilots from taking off with snow or ice 

adhering to the wings or other critical 

airplane surfaces. Additionally, 

§§ 121.629(c) and 135.227(b) require 

airplane operators to have either an 

approved ground deicing/anti-icing 

program or conduct a pre-takeoff 

contamination check within five 

minutes before beginning a takeoff to 

ensure that the wings, control surfaces, 

and other critical surfaces are free of 

frost, ice, or snow. Operators must train 

the pilots on the effects of these 

contaminants on airplane performance 

and controllability, on how to recognize 

airplane contamination, and on 

procedures intended to ensure that 

contamination is removed before 

takeoff. 

Ground deicing/anti-icing programs 

include the use of deicing/anti-icing 

fluids to remove ice and snow and 

prevent them from reappearing on 

airplane surfaces during freezing 

precipitation conditions. Although these 

fluids are designed to flow off the 

airplane during the takeoff roll, we 

expect the fluids to continue to provide 

some protection throughout the takeoff 

ground run. 

On some older airplane models, the 

wing ice protection system was 

designed for use in flight and cannot be 

operated while the airplane is on the 

ground. Yet many of the current 

generation of airplanes have ice 

protection systems that can be operated 

while the airplane is on the ground. 

Some of these systems are also coupled 

with ice detector systems that will 

automatically activate the ice protection 

system in icing conditions. These 

features tend to reduce the chances that 

ice will adhere to critical airfoil surfaces 

during airplane ground operations in 

atmospheric icing conditions. 

As discussed later, we propose to 

revise appendix C of part 25 to define 

atmospheric icing conditions 

specifically for the takeoff phase of 

flight. These proposed atmospheric 

icing conditions would apply 

throughout the takeoff path, but are 

based on the more critical conditions 

that would be expected to occur at the 

end of the takeoff path. These 

conditions do not include freezing 

precipitation on the ground. At earlier 

points in the takeoff path, while the 

airplane is closer to the ground, the 

proposed takeoff icing conditions would 

be conservative, that is, they would 

predict larger ice accretions than would 

be likely to occur. If these conditions 

were to actually occur at ground level, 

they would form a freezing fog 

condition that would probably reduce 

visibility to the point that takeoffs could 

not be made. 

An important part of determining the 

effects of ice accretion on takeoff 

performance is to decide at what point 

in the takeoff ice accretion is considered 

to begin. For the purposes of this 

rulemaking, we consider ice accretion to 

begin when the airplane lifts off the 

runway surface during takeoff. 

Proposed § 25.105(a) would require 

applicants to determine airplane takeoff 

performance for icing conditions if the 

ice that can accrete during takeoff 

results in increasing the reference stall 

speed (VSR) or degrading climb 

performance beyond specified limits. 

Section 25.105(a) references all 

regulations related to the takeoff path. 

As a result, the performance for the 

entire takeoff path, including takeoff 

speeds and distances, must be 

determined for icing conditions if the 

stall speed or climb performance 

degradation limits are exceeded. 

Section 25.105(a)(2)(i) of the proposal 

would require applicants to determine 

takeoff path performance for icing 

conditions if the stall speed increases by 

more than 3 knots in calibrated airspeed 

or 3 percent due to ice accretions. This 

proposed requirement would be more 

stringent than the guidance used by the 

JAA in their draft AMJ 25.1419. The 

draft AMJ allowed up to a 5 knot or 5 

percent increase in stall speed before 

the takeoff performance would need to 

be recomputed for icing conditions. 

Several commenters on the AMJ, 

including us, expressed concern over 

allowing such a large increase in stall 

speed believing it would result in a 

significant reduction in safety margin 

between the minimum operating speeds 

and the stall speed. We agree with the 

FTHWG recommendation that a 3 knot 

or 3 percent increase in stall speeds is 

the maximum that should be permitted 

before the takeoff performance data 

should be recalculated to consider the 

effects of icing. 

Also, the JAA’s draft AMJ 25.1419 

used the effect of ice accretions on 

airplane drag rather than on climb 

performance to determine when the 

takeoff performance data must be 

provided for icing conditions. However, 

we agree with the FTHWG 

recommendation to consider the effect 

Federal Register / Vol. 70, No. 213 / Friday, November 4, 2005 / Proposed Rules 67283 

of ice accretions in terms of climb 

performance in § 25.105(a)(2)(ii) because 

it would cover more operating variables 

than just the effect of ice on airplane 

drag. 

The part 25 takeoff climb 

requirements include a safety margin by 

requiring applicants to determine a net 

flight path based on the airplane’s actual 

climb performance capability reduced 

by a set value that depends on the 

number of engines on the airplane. 

Proposed § 25.105(a)(2)(ii) would 

require applicants to determine takeoff 

path performance specifically for icing 

conditions if more than half of this 

safety margin would be lost due to the 

effects of ice accretion. 

Part 25 divides the takeoff climb 

performance requirements into several 

segments. To establish the allowable 

limit for takeoff climb performance 

degradation in icing conditions, 

§ 25.105(a)(2)(ii) would consider the 

effect of ice accretions on just the 

takeoff climb segment defined by 

§ 25.121(b). For most transport category 

airplanes, this segment most often limits 

the allowable takeoff weight, and 

therefore is the most critical to safety. If 

the effects of ice accretions during the 

takeoff climb segment defined in 

§ 25.121(b) are beyond specified limits, 

the airplane performance for the entire 

takeoff path must be determined with 

ice accretions on the airplane. This 

would include from the beginning of the 

takeoff roll until the airplane is at least 

1,500 feet above the takeoff surface. 

Thus, for airplanes that would be most 

affected by ice accretions during the 

takeoff climb, additional safety margins 

would also be provided for the takeoff 

ground run even though ice accretion is 

assumed not to begin until liftoff. 

D. Takeoff Speeds (§ 25.107) 

We propose to revise § 25.107(c)(3) 

and (g) to change the reference for 

maneuver capability considerations 

from § 25.143(g) to § 25.143(h). This is 

an editorial change due to the 

redesignation of § 25.143(g) to 

§ 25.143(h) proposed below. 

We also propose to revise § 25.107 by 

adding a new paragraph (h). This new 

paragraph would state that the 

minimum control speeds (VMCG and 

VMC) and minimum unstick speeds 

(VMU) determined for the airplane in 

non-icing conditions may also be used 

for the airplane in icing conditions. The 

VMU, VMCG, and VMC speeds are used to 

determine the takeoff speeds V1, VR, and 

V2. 

The minimum unstick speed (VMU) is 

defined in § 25.107(d) as the airspeed at 

and above which the airplane can safely 

lift off the ground and continue the 

takeoff. Takeoff speeds must be 

established sufficiently above this speed 

to assure the airplane can safely take off 

considering the variations in procedures 

and conditions that can reasonably be 

expected in day-to-day operations. 

Because these proposals assume that ice 

accretion does not begin until liftoff, 

this proposal would allow the VMU

speeds for non-icing conditions to be 

used for determining takeoff speeds in 

icing conditions. 

The ground minimum control speed 

(VMCG) is used in determining the 

takeoff V1 speed. The takeoff V1 speed 

is the highest speed at which the pilot 

must take the first action to be able to 

safely stop the airplane during a rejected 

takeoff and the lowest speed at which 

the takeoff can be safely continued after 

an engine failure. Since VMCG, like VMU, 

occurs before the airplane lifts off the 

runway, the assumption is that ice has 

not yet begun accreting on the airplane. 

Therefore, this proposal would allow 

the VMCG speeds determined for nonicing conditions to be used for 

determining V1 for icing conditions. 

The air minimum control speed, VMC

(commonly referred to as VMCA), is 

defined in § 25.149(b) as the airspeed at 

which it is possible to maintain control 

of the airplane, with no more than 5 

degrees of bank, when the critical 

engine is suddenly made inoperative. 

Section 25.107 requires the rotation 

speed (VR) and the takeoff safety speed 

(V2) to be sufficiently higher than VMCA

to assure that the airplane will be safely 

controllable if the critical engine fails 

during the takeoff. Since VR occurs 

before liftoff, like VMU and VMCG, this 

proposal would allow the VMCA speeds 

determined for non-icing conditions to 

be used for determining VR for icing 

conditions. 

Several concerns must be addressed if 

we are to allow VMCA speeds 

determined in non-icing conditions to 

be used to determine V2 in icing 

conditions. Unlike VR, V2 occurs after 

liftoff and ice could have begun 

accreting on the airplane. Ice may 

accrete at V2 because ice protection 

systems are typically not turned on until 

the airplane climbs more than 400 feet 

after takeoff. Also, many airplanes do 

not have any ice protection on the 

vertical stabilizer. These concerns could 

lead to a reduction in the airplane’s 

directional control capability if ice 

accretion occurs. To alleviate these 

concerns, the proposed § 25.143(c) 

would require applicants to show that 

airplanes are safely controllable and 

maneuverable at the minimum V2 speed 

with the critical engine inoperative and 

with the ice accretion applicable to the 

takeoff flight phase. 

E. Takeoff Path (§ 25.111) 

Currently, § 25.111 defines the takeoff 

path, describes the airplane 

configuration that applies to each 

portion of the takeoff path, and provides 

airplane performance requirements that 

must be met. We propose to revise 

§ 25.111 by adding a new paragraph 

(c)(5) stating that the airplane’s drag 

used to determine the takeoff path after 

liftoff would be based on the ice 

accretions defined in the proposed 

revision to appendix C. To 

accommodate the addition of the new 

paragraph, the ‘‘and’’ at the end of 

§ 25.111(c)(3) would be moved to the 

end of § 25.111(c)(4). 

The takeoff path begins at the start of 

the takeoff roll and ends when the 

airplane is either 1,500 feet above the 

takeoff surface, or at the altitude at 

which the transition from the takeoff to 

the en route configuration is completed 

and the final takeoff speed attained, 

whichever is higher. The takeoff path 

typically has two distinct climb 

segments: One from the point at which 

the airplane is 35 feet above the runway 

up to 400 feet, and the other from a 

height of 400 feet to the end of the 

takeoff path. The proposed changes to 

§ 25.111 would identify when the 

takeoff path must be determined for 

flight in icing conditions and specify the 

ice accretion that must be used for these 

two climb segments. 

New paragraph (c)(5) would refer back 

to the proposed § 25.105(a)(2) to identify 

when the takeoff path must be 

determined for flight in icing 

conditions. The ice accretions 

referenced in new paragraph (c)(5) 

would apply to the airborne portions of 

the takeoff path, since we are assuming 

that ice accretion does not begin until 

liftoff. If takeoff path performance must 

be determined for icing conditions, then 

the takeoff path must use the takeoff 

speeds of the proposed § 25.107 for 

icing conditions, using the ice 

accretions specified in paragraph (c)(5). 

F. Landing Climb: All-EnginesOperating (§ 25.119) 

We propose to revise § 25.119 by 

requiring the airplane landing climb 

performance to be determined for both 

non-icing and icing conditions; adding 

references to the appropriate paragraphs 

of the proposed § 25.125 revision for the 

landing climb speed to use for non-icing 

and icing conditions; referring to the 

proposed appendix C revision to 

identify the ice accretion that would be 

used in determining landing climb 

performance in icing conditions; and 

changing the speed used to show 

67284 Federal Register / Vol. 70, No. 213 / Friday, November 4, 2005 / Proposed Rules 

compliance with § 25.119 from a speed 

less than or equal to VREF to VREF. 

We consider the approach and 

landing phases of flight to be the flight 

phases most affected by icing conditions 

because of the potential for descending 

into and holding in icing conditions 

prior to landing. In addition, service 

history has shown that the majority of 

icing accidents and incidents occur in 

the holding, approach, and landing 

flight phases. For these reasons, our 

policy for the last 40 years has been for 

applicants to account for the effects of 

airframe ice accretion in their airplane’s 

approach and landing climb 

performance data provided in the 

Airplane Flight Manual. (Approach and 

landing climb performance refer to the 

airplane’s climb capability in the 

approach and landing configurations 

during the approach and landing flight 

phases. Sections 25.121(d) and 25.119 

require minimum level of approach and 

landing climb performance to ensure 

that airplanes can abort an approach or 

landing attempt and safely climb away.) 

The proposed changes to §§ 25.119 and 

25.121(d) (see below) serve to codify 

this policy. 

G. Climb: One-Engine-Inoperative 

(§ 25.121) 

We propose to revise § 25.121 by 

rearranging paragraphs (b), (c), and (d) 

to specify when the required climb 

performance must be determined for 

icing conditions; refer to the proposed 

appendix C revision to identify the ice 

accretion that would be used in 

calculating approach climb performance 

in icing conditions; and provide the 

conditions under which the approach 

climb speed must be increased to 

account for the effect of ice accretion. 

Sections 25.121(b) and (c) provide the 

climb performance requirements for the 

takeoff path segments beginning at the 

point the landing gear is fully retracted 

and ending at the end of the takeoff 

path. As in the proposed revision to 

§ 25.105, we propose to revise 

§ 25.121(b) and (c) to require takeoff 

climb performance to be determined for 

icing conditions if the effect of ice: (1) 

Increases the stall speed at maximum 

takeoff weight by more than 3 knots or 

3 percent, or (2) reduces the climb 

performance determined in § 25.121(b) 

by more than half the safety margin 

provided by the net gradient adjustment 

required by § 25.115. 

Section 25.121(a) provides the climb 

performance requirements for the 

takeoff path segment beginning at liftoff 

and ending when the landing gear is 

fully retracted. Since we are assuming 

that ice accretion does not begin until 

liftoff, only a minimal amount of ice 

could be accreted during this climb 

segment. Therefore, the proposal for 

§ 25.21(g)(1) excludes compliance with 

§ 25.121(a) with ice accretions on the 

airplane. 

We propose revising § 25.121(d) to 

state when the approach climb speed 

must be adjusted for use in icing 

conditions. Unlike the speeds used in 

the takeoff path, the need to adjust the 

approach climb speed would not be 

based on the effect of ice accretions on 

the airplane’s stall speed. Instead, the 

measure for determining whether the 

approach climb speed needs to be 

adjusted for icing conditions is based on 

the effect of ice accretions on the 

approach climb speed. If the approach 

climb speed for icing conditions does 

not exceed the climb speed for nonicing conditions by more than the 

greater of 3 knots calibrated airspeed 

(CAS) or 3 percent VSR, then non-icing 

speeds may be used for calculating 

approach climb performance for icing 

conditions. 

The existing requirement for 

determining the approach climb speed 

in non-icing conditions provides 

applicants some flexibility by only 

specifying the maximum allowable 

approach climb speed. No lower limit is 

specified and we have accepted 

approach climb speeds as low as 1.13 

VSR (that is, 13 percent above the 

reference stall speeds). We would accept 

this same level of flexibility for 

establishing the approach climb speeds 

in icing conditions. The approach climb 

speeds for icing conditions should also 

be evaluated to ensure that they provide 

adequate maneuver capability. 

This proposal for the approach climb 

segment is less stringent than the 3 

knots or 3 percent VSR standard used for 

takeoff path speeds. For example, if the 

approach climb speed is 1.25 VSR and 

VSR is 100 knots, 3 percent of the 

approach climb speed is 3.75 knots, 

while 3 percent of VSR would be only 

3 knots. The approach climb speed 

could increase by 3.75 knots without 

requiring this increased approach climb 

speed to be used for calculating the 

approach climb performance in icing 

conditions. We consider this small 

alleviation to be acceptable since it is 

only relative to the need for increasing 

the approach climb speed for icing 

conditions. The approach climb 

performance must be recalculated with 

the holding ice accretion and presented 

in the AFM regardless of whether the 

approach climb speed is adjusted for 

operations in icing conditions. 

H. En Route Flight Paths (§ 25.123) 

We propose to revise § 25.123(a) by 

specifying a minimum allowable speed 

for determining en route flight paths, 

which would apply to both icing and 

non-icing conditions. The proposed 

speed, VFTO, is currently used as the 

minimum allowable speed for the final 

takeoff. 

Additionally, the proposed revision to 

§ 25.123(b) would state when an 

applicant must determine the en route 

flight paths specifically for icing 

conditions. Similar to the takeoff path 

requirements of the proposed revision to 

§ 25.111, en route flight path 

performance needs to be specifically 

determined for icing conditions if the 

effect of ice: (1) Increases the en route 

speed by more than 3 knots or 3 percent, 

or (2) reduces climb performance by 

more than half the safety margin 

provided by the net gradient adjustment 

required by § 25.123(b). The ice 

accretion to be used would be specified 

in the proposed revision to appendix C. 

The reason for proposing to limit the 

minimum allowable en route climb 

speed to VFTO to is to prevent applicants 

from showing compliance with § 25.123 

by trading altitude for airspeed when 

transitioning from the final takeoff to 

the en route climb segment. This 

clarifying change is consistent with our 

original intent for § 25.123(a). 

Another reason for not allowing an en 

route climb speed less than VFTO is that 

VFTO is the speed at which the 

maneuver capability requirements 

contained in the existing § 25.143(g) 

must be met in the en route 

configuration. Allowing an en route 

climb speed lower than VFTO would not 

ensure that the airplane has adequate 

maneuvering capability during the en 

route climb phase of flight. 

We are not proposing any changes to 

the two-engine-inoperative en route 

flight path requirements contained in 

§ 25.123(c) for flight in icing conditions. 

We do not expect the pilot to stay in 

icing conditions with one engine 

inoperative for a long enough duration 

for the failure of a second engine in 

icing conditions to be an issue. 

En route and takeoff flight paths have 

similar safety issues. Therefore, we are 

proposing requirements for identifying 

when en route climb flight paths must 

be determined for icing conditions that 

are similar to those proposed for takeoff 

flight paths. The only significant 

difference is that for the en route climb 

paths, a speed of 1.18 VSR determined 

with the en route ice accretion of 

proposed appendix C is compared to the 

en route climb speed selected for nonicing conditions instead of comparing 

stall speeds with and without ice 

accretions. 

The reason for this difference is to 

provide a more stringent requirement 

Federal Register / Vol. 70, No. 213 / Friday, November 4, 2005 / Proposed Rules 67285 

for airplanes that use the minimum 

allowable en route climb speed of 1.18 

VSR. (1.18 VSR is the minimum 

allowable value of VFTO prescribed by 

§ 25.107(g)). Airplanes that use a higher 

en route climb speed have a larger speed 

margin to the stall speed and more 

maneuvering capability in the en route 

climb phase to help offset the negative 

effects of ice accumulation. 

Due to differences in their methods of 

generating thrust, propeller-driven 

airplanes generally have better climb 

performance at lower airspeeds than 

turbojet-powered airplanes. To optimize 

performance, the en route climb speed 

used for propeller-driven airplanes is 

usually the minimum allowable speed 

of 1.18 VSR, while the en route climb 

speed used for turbojet-powered 

airplanes is usually higher. Therefore, 

the proposed requirement would be 

more stringent for propeller-driven 

airplanes. We consider the increased 

stringency for propeller-driven airplanes 

to be desirable for the following reasons: 

• Propeller-driven airplanes generally 

have deicing systems that cycle on and 

off, allowing ice to accrete on the 

protected surfaces before removing it. 

Also, these deicing systems typically do 

not remove all of the ice with each 

cycle, leaving some residual ice. Both of 

these effects result in drag increases that 

are generally not present on turbojet 

airplanes that have ice protection 

systems using hot bleed air from the 

engines. 

• Propeller-driven airplanes will 

likely be subjected to increased 

exposure to icing conditions, due to 

their slower operating speeds, shorter 

flight lengths, and lower cruising 

altitudes. 

I. Landing (§ 25.125) 

We propose to revise § 25.125(a) to 

identify when the landing distance must 

be determined specifically for icing 

conditions. The proposed requirement 

would specify that the landing distance 

must be determined for icing conditions 

if the VREF in icing conditions exceeds 

the VREF in non-icing conditions by 

more than 5 knots CAS. For icing 

conditions, the landing distance would 

be determined with the landing ice 

accretion defined in the proposed 

revision to appendix C. 

Additionally, a new paragraph (b) 

would be added to include the landing 

distance requirements that would be 

moved from the existing paragraph (a). 

The new paragraph (b) would also set 

the requirements for determining the 

landing speeds to use in determining 

the landing distances for both icing and 

non-icing conditions. For icing 

conditions, the landing speed must not 

be lower than 1.23 VSR0 with the 

landing ice accretion on the airplane if 

that speed exceeds the VREF for nonicing conditions by more than 5 knots 

CAS. 

The existing paragraphs (b) through (f) 

would be redesignated as (c) through (g). 

Whether landing distances or landing 

speeds must be determined specifically 

for icing conditions depends on whether 

VREF needs to be increased by more than 

5 knots CAS to counteract the effect of 

ice on airplane stall speeds. The reasons 

behind allowing VREF to increase by up 

to 5 knots CAS in icing conditions 

before requiring landing distance 

performance to be recomputed for icing 

conditions are: 

• As part of the flight testing to 

demonstrate compliance with the 

landing distance requirements, we 

typically evaluate airplane 

controllability when landing at speeds 

lower than the normal landing speeds. 

We usually perform this evaluation at a 

speed 5 knots below VREF to cover 

inadvertent speed variations that may 

occur in operational service. Plus or 

minus five knots variation from VREF is 

frequently used as a guideline for 

evaluating expected operational 

variations in landing speeds. 

• Normal approaches in transport 

category airplanes are typically flown at 

speeds above VREF to provide speed 

margins to account for wind gusts. 

Although the additional speed should 

be bled off by the time that the airplane 

is over the landing threshold, it may not 

be. Service history does not indicate any 

safety problems with the resulting 

longer landing distance. 

• Many transport category airplanes 

are flown at a speed 5 knots higher than 

VREF during final approach to counter 

any inadvertent speed loss. Often this 

additional speed has not been bled off 

before reaching the landing threshold. 

Again, service history does not indicate 

any safety problems with the resulting 

longer landing distance. 

• A 5-knot increase above the VREF

speed for non-icing conditions equates 

to approximately 3 percent of the 1-g 

stall speed (slightly less than 3 percent 

for larger airplanes). This is consistent 

with the allowable stall speed increase 

proposed for the takeoff path 

requirements for icing conditions. 

As a further safety consideration for 

the VREF speed, § 25.125(b)(ii)(c) would 

require that VREF for icing conditions 

must provide the same maneuvering 

capability (with ice accretions on the 

airplane) as is currently required at VREF

for non-icing conditions. This may 

result in an increase to VREF for icing 

conditions even if this increase is less 

than 5 knots. 

The current § 25.125(a)(2), which 

would be redesignated as 

§ 25.125(b)(2)(i), requires VREF for nonicing conditions to be not less than the 

landing minimum control speed, VMCL. 

This existing requirement ensures that 

adequate directional control is available 

in case an engine fails during a goaround. Under the proposed new rule, 

the VMCL determined for non-icing 

conditions would continue to be used 

for icing conditions. This would be 

similar to the takeoff flight phase, where 

the takeoff minimum control speeds, 

VMCG and VMCA, determined for nonicing conditions would continue to be 

used for icing conditions. Unlike the 

takeoff case; however, the continued use 

of the non-icing VMCL is not explicitly 

stated. We consider the proposed 

requirements to adequately address this 

issue without proposing an additional 

explicit requirement. Section 

25.125(b)(2)(ii) requires VREF for icing 

conditions to be not less than VREF for 

non-icing conditions. Under 

§ 25.125(b)(2)(i), VREF for non-icing 

conditions must be not less than VMCL

for non-icing conditions. Taken 

together, these two proposed 

requirements would allow the VMCL

determined for non-icing conditions to 

continue to be used for icing conditions. 

To assure that using the VMCL

determined for non-icing conditions 

will provide safe controllability and 

maneuverability for icing conditions, 

the proposed §§ 25.143(c)(2) and (c)(3) 

would require the applicant to show 

that the airplane will be safely 

controllable and maneuverable during 

an approach and go-around and an 

approach and landing, both with the 

critical engine inoperative. For added 

safety during certification flight testing, 

these maneuvers may be accomplished 

with a simulated engine failure (as 

noted in the proposed advisory material 

associated with this proposal). 

J. Controllability and Maneuverability—

General (§ 25.143) 

We propose to revise § 25.143 to add 

a new paragraph (c) that requires the 

applicant to show that the airplane with 

ice accretions and with the critical 

engine inoperative is safely controllable 

and maneuverable during takeoff, an 

approach and go-around, and an 

approach and landing; a new paragraph 

(i) to identify the ice accretions that 

must be used in showing compliance 

with § 25.143 in icing conditions, and to 

introduce two specific controllability 

requirements that apply to flight in icing 

conditions; and a new paragraph (j) to 

specify tests for ensuring that the 

airplane has adequate controllability for 

flight in icing conditions before the ice 

67286 Federal Register / Vol. 70, No. 213 / Friday, November 4, 2005 / Proposed Rules 

protection system is activated and 

performing its intended function of 

removing any ice accretions from 

protected surfaces. 

In addition, existing paragraphs (c) 

through (g) would be redesignated as 

paragraphs (d) through (h), and 

paragraph references in the newly 

designated paragraphs (d), (e), and (f) 

would be revised accordingly. 

The requirements proposed in new 

paragraph (c) are intended to ensure that 

using the minimum control speeds for 

non-icing conditions would not result in 

controllability and maneuverability 

safety concerns when the same speeds 

are used for icing conditions. 

The proposed new paragraph (i)(1) 

would require compliance with all of 

§ 25.143 in icing conditions except 

paragraphs (b)(1) and (2). Sections 

25.143(b)(1) and (2) are excepted from 

icing analysis under proposed section 

25.21(g). 

These proposed requirements assume 

a conventional empennage (that is, 

wing/fuselage/tailplane) configuration. 

Special conditions, issued in 

accordance with § 21.16, may be 

necessary for certification of airplanes 

with an unconventional empennage 

configuration. 

Applicants can minimize the number 

of ice accretions to be tested by using 

one accretion that is shown to be the 

most critical accretion for several flight 

phases. 

In many cases, a thin, rough, layer of 

ice (defined as sandpaper ice in the 

proposed revision to appendix C) has 

been shown to have a more detrimental 

effect on handling qualities for airplanes 

with unpowered control systems than 

larger ice accretions. The effect of 

sandpaper ice accretions may be more 

significant than larger ice accretions on 

these airplanes. In some cases, such an 

accretion has resulted in control surface 

hinge moment reversals that required 

the flightcrew to apply extremely high 

forces to the controls to regain control 

of the airplane. Applicants would have 

to consider sandpaper ice in showing 

compliance with the proposed 

§ 25.143(i). 

The proposed paragraph (i)(2) would 

require applicants to conduct a 

pushover maneuver down to a zero g 

load factor with the critical ice accretion 

on the airplane. (If the airplane lacks 

enough elevator power to get to a zero 

g load factor, the maneuver may be 

ended at the lowest load factor 

obtainable.) The purpose of this 

proposed requirement is to evaluate an 

airplane’s susceptibility to a 

phenomenon known as icecontaminated tailplane stall (ICTS). Icecontaminated tailplane stall can be 

characterized either by completely 

stalled airflow over the horizontal 

stabilizer, or by an elevator hinge 

moment reversal due to separated flow 

on the lower surface of the horizontal 

stabilizer caused by ice accretions on 

the tailplane. 

Several incidents and accidents have 

been caused by ICTS. These incidents 

and accidents have typically occurred 

during landing approach when the 

flightcrew either lowered the flaps or 

abruptly decreased the airplane’s pitch 

attitude. Either of these actions will 

increase the angle-of-attack (AOA) of the 

local airflow over the tailplane. If there 

is ice on the tailplane, the increased 

AOA may lead to an ICTS. 

The proposed pushover maneuver 

increases the AOA on an icecontaminated tailplane by inducing a 

nose down pitch rate. An airplane is not 

susceptible to an ICTS if, during the 

pushover maneuver: 

• The pilot must continue to apply a 

push force to the pitch control 

throughout the maneuver (that is, the 

airplane will not continue the maneuver 

to or toward a zero g load factor unless 

the pilot applies a push force to the 

pitch control); and 

• The pilot can promptly recover 

from the maneuver without exceeding 

50 pounds of pull force on the pitch 

control. 

The proposed pushover maneuver 

evolved from earlier criteria developed 

shortly after a series of incidents and 

accidents highlighted the safety 

concerns related to ICTS. For example, 

early ICTS test criteria called for 

executing a pushover to a 0.3 g to 0.4 

g load factor with a pitch rate of not less 

than 10 degrees per second in an 

attempt to copy the documented ICTS 

accident conditions. An aggressive 

pushover to zero g was later found to 

result in the same combination of load 

factor and pitch rate, but with the 

advantage of not needing sophisticated 

test instrumentation to perform the test. 

In addition to the pushover maneuver, 

we propose that applicants demonstrate 

the safety of a sideslip maneuver with 

an ice-contaminated tailplane, since this 

has been shown to be a more critical 

ICTS triggering maneuver for some 

airplanes. The proposed § 25.143(i)(3) 

would require that any changes in the 

force the pilot must apply to the pitch 

control to maintain speed with 

increasing sideslip angle must steadily 

increase with no force reversals. 

Proposed § 25.143(j) would address 

airplane controllability between the 

time when the airplane first enters icing 

conditions and when the ice protection 

system is activated and performing its 

intended function. In developing the 

controllability criteria proposed in 

paragraph (j), we considered the likely 

duration of this time period and the 

means that might be used for detecting 

icing conditions and activating the ice 

protection system. The proposed 

advisory material for part 25, appendix 

C, part II(e) would provide additional 

guidance for determining the 

appropriate ice accretion for this testing 

based on the means of ice detection. 

Although activation of the ice 

protection system is expected to occur 

shortly after entering icing conditions, it 

may not occur for a relatively long time 

if the method of detecting icing 

conditions depends on the crew visually 

observing a specified amount of ice 

buildup on some reference surface (for 

example, windshield wiper, icing 

probe). To address this concern, 

proposed § 25.143(j)(1) requires 

compliance with all of the requirements 

of § 25.143 that would apply to flight in 

icing conditions for this method of 

detecting icing conditions. In this case, 

the ice accretion to be used in showing 

compliance would be the ice accretion 

that would exist before the ice 

protection system is activated and is 

performing its intended function. 

For airplanes that use other means of 

detecting icing conditions, the proposed 

requirements would be less stringent. 

This reflects the expectation that the 

airplane would fly only briefly in icing 

conditions before activation of the ice 

protection system. Instead of requiring 

compliance with all of the requirements 

of § 25.143 that apply to flight in icing 

conditions, § 25.143(j)(2) would require 

only a demonstration that the airplane 

is controllable in a pull-up maneuver up 

to 1.5 g load factor, and that there is no 

longitudinal control force reversal 

during a pushover maneuver down to a 

0.5 g load factor. 

K. Stall Warning (§ 25.207) 

We propose to revise paragraph (b) to 

require that the means for providing a 

warning of an impending stall must be 

the same for both icing and non-icing 

conditions. There would be one 

exception to this general rule. If the 

means of detecting icing conditions 

does not involve waiting until some 

specified amount of ice has accreted on 

a reference surface, then the stall 

warning may be provided by a different 

means during the time from when the 

airplane first enters icing conditions 

until the ice protection system is 

activated and is performing its intended 

function. 

We propose to add a new paragraph 

(e) to specify the stall warning margin 

that the stall warning system must 

provide in icing conditions. The stall 

Federal Register / Vol. 70, No. 213 / Friday, November 4, 2005 / Proposed Rules 67287 

warning margin is how far in advance 

the pilot is warned of a potential stall. 

We propose to evaluate the stall 

warning margin in both straight and 

turning flight while decelerating the 

airplane at rates of up to one knot per 

second. The pilot must be able to 

prevent stalling the airplane using the 

same recovery maneuver that would be 

used in non-icing conditions, starting 

the recovery maneuver not less than 3 

seconds after the stall warning begins. 

Paragraph (e) also specifies the ice 

accretions that would be used for 

showing compliance. 

We propose to revise paragraph (f) to 

consist of the existing paragraph (e), 

revised to clarify that the pilot must use 

the same maneuver to demonstrate that 

the airplane can safely recover from a 

stall in icing conditions as is used for 

non-icing conditions. 

We propose to add a new paragraph 

(h) to specify the stall warning 

requirements for the time period when 

the airplane first enters icing conditions 

until the ice protection system is 

activated and is performing its intended 

function. The proposed stall warning 

requirements would be different for 

different means of detecting icing 

conditions and whether or not the stall 

warning is provided by the same means 

for icing conditions and non-icing 

conditions. 

Currently, part 25 requires airplanes 

to provide the flightcrew an adequate 

warning of an impending stall so that 

the flightcrew can prevent the stall. The 

current requirement does not consider 

the effects of ice accretions on the 

airplane. With ice accretions on the 

airplane, the airplane may stall sooner 

(that is, at a higher speed or lower 

AOA), possibly even before the stall 

warning would occur. For an airplane to 

be approved for flight in icing 

conditions, we consider it necessary to 

provide an adequate stall warning 

margin with ice accretions on the 

airplane. For human factors reasons, we 

also consider it necessary for the means 

of providing the stall warning to be the 

same in icing conditions and non-icing 

conditions. But as discussed in the 

specific proposal for § 25.207(h), we 

would allow a limited exception to this 

general requirement. 

In most transport category airplanes, 

the stall warning is provided by a device 

called a stick shaker, which shakes the 

control column to alert the pilot when 

the airplane is close to stalling. The 

proposed addition to § 25.207(b) would 

establish the general requirement for the 

same means for the stall warning in 

icing conditions and non-icing 

conditions. Section 25.207(b) would, 

however, allow an exception to the 

general requirement. The conditions for 

the exception to the general requirement 

would be established in 

§ 25.207(h)(2)(ii). 

The general rule of § 25.207(b) may 

result in a different stick shaker 

activation point for icing conditions 

because the airplane may stall at a 

different speed or AOA with ice 

accretions. In order to maintain a safe 

margin above the stall speed and to 

provide sufficient maneuvering 

capability, an increase in the minimum 

operating speeds may be needed. 

Increasing the minimum operating 

speeds, such as takeoff and landing 

speeds, may result in a cost increase if 

operators have to reduce payload to 

comply with performance requirements 

at the higher operating speeds. 

These potential cost impacts may be 

minimized for stall warning in icing 

conditions after the ice protection 

system has been turned on. Then the 

higher settings for flight in icing 

conditions would only be used if the ice 

protection system has been activated. 

The higher operating speeds would not 

be a factor, or cost, in other operations. 

However, this design solution would 

not protect the airplane during the time 

that the airplane is in icing conditions 

before activation of the ice protection 

system. To protect the airplane during 

this time period, any changes to the stall 

warning system settings for potential ice 

accretions would need to be active at all 

times. This would mean that the 

minimum operating speeds would be 

increased for both icing and non-icing 

conditions with resulting cost 

implications. 

To minimize the potential cost 

impact, while ensuring flight safety, the 

FTHWG examined whether different 

stall warning requirements could be 

used for flight in icing conditions before 

activation of the ice protection system. 

Flight in icing conditions before 

activation of the ice protection system is 

a temporary condition. In most cases, 

this time is expected to be relatively 

short. In those cases, proposed 

paragraph (h)(2) would allow the stall 

warning to be provided by a different 

means than is used for non-icing 

conditions. For example, natural 

airplane buffeting might be used instead 

of a stick shaker. By allowing a different 

means of stall warning, the need to 

change the stall warning system setting 

would be minimized. 

However, if the stall warning is 

provided by a different means than for 

flight in non-icing conditions, the 

proposal seeks to balance this with more 

stringent flight demonstration 

requirements. The requirements would 

be more stringent for demonstrating that 

the pilot can safely recover the airplane 

after a stall warning has occurred. This 

demonstration occurs during the flight 

tests to show acceptable flight 

characteristics for stall recovery. For the 

time that the airplane is in icing 

conditions before the ice protections 

system has been activated, if stall 

warning is provided by a different 

means than for non-icing conditions, it 

may take longer for the flightcrew to 

recognize the impending stall and take 

recovery action. Therefore, instead of 

allowing a recovery maneuver to be 

started one second after the onset of 

stall warning, the recovery maneuver 

must not begin until at least 3 seconds 

after the onset of stall warning. 

Paragraph (h)(2)(i) of the proposal 

allows the recovery to start within one 

second of the stall warning. The more 

stringent three-second requirement is 

contained in the proposed paragraph 

(h)(2)(ii). 

Additionally, proposed paragraph 

(h)(2)(ii) would require the applicant to 

show that the airplane has safe handling 

qualities in case the flightcrew does not 

take suitable recovery action in time to 

prevent stalling. Compliance with the 

stall characteristics requirements of 

§ 25.203 would be required for stalls 

demonstrated using a one knot per 

second deceleration rate. 

Earlier, we stated that in most cases, 

flight in icing conditions before 

activation of the icing system is 

expected to be relatively brief. However, 

if the means of detecting icing 

conditions and activating the ice 

protection system depends on the 

flightcrew visually identifying a discrete 

amount of ice on a reference surface (for 

example, one-quarter-inch of ice on the 

wing’s leading edge), then this 

temporary condition may be of a 

relatively long duration. Therefore, we 

consider it appropriate to apply the 

same requirements for stall warning to 

this case as are applied to the case of 

flight in icing conditions after the ice 

protection system is fully active. For 

this case, we propose that the stall 

warning indication must be provided by 

the same means as in non-icing 

conditions. Proposed paragraph (h)(1) 

contains this requirement. 

The FTHWG determined that 

applying the existing stall warning 

margin requirements of § 25.207(c) and 

(d) to icing conditions would be far 

more stringent than best current 

practices and would unduly penalize 

designs that have not exhibited safety 

problems in icing conditions. The 

FTHWG examined whether the stall 

warning requirements of existing 

§ 25.207(c) and (d) could be made less 

stringent for icing conditions without 

67288 Federal Register / Vol. 70, No. 213 / Friday, November 4, 2005 / Proposed Rules 

compromising safety. The proposed 

§ 25.207(e) resulted from this effort. 

In developing the proposed 

§ 25.207(e), the FTHWG determined that 

the types of transport category airplanes 

involved in icing-related stall accidents: 

• Were equipped with deicing boots 

that operated cyclically (for example, a 

boot cycle every one to three minutes), 

and 

• Were generally very susceptible to 

large affects on stall speeds from ice 

accretions during the periods between 

boot cycles (known as intercycle ice). 

The proposed criteria of § 25.207(e), 

in combination with the proposed 

§ 25.207(b), would likely require 

different stall warning system settings 

for icing conditions and non-icing 

conditions on future airplanes with 

those characteristics. These proposals 

would have a lesser impact on airplanes 

without those characteristics. The stall 

warning settings established for the 

airplane without ice accretions may be 

retained for operation in icing 

conditions, provided they are still 

adequate to prevent stalling if the pilot 

does not take any action to recover until 

three seconds after the initiation of stall 

warning. Since all modern conventional 

transport category airplanes use some 

type of artificial stall warning system 

(stick shaker or combined aural and 

visual warning), and since three seconds 

is considered adequate time for 

response by a trained pilot, we agree 

with the FTHWG that this stall warning 

definition would be acceptable for icing 

conditions. 

The proposed revision of § 25.207(f) 

would require the pilot to use the same 

stall recovery maneuver during the 

compliance demonstration for icing 

conditions as is used for non-icing 

conditions. This proposal is based on 

human factors considerations. In 

operational service, pilots would not be 

expected to respond differently to a stall 

warning indication in icing conditions 

versus non-icing conditions. 

L. Wind Velocities (§ 25.237) 

The proposed revisions to § 25.237(a) 

would add a requirement to establish a 

safe landing crosswind component for 

use in icing conditions. The proposed 

revision to paragraph (a) also would 

state that the crosswind component 

established for takeoff without ice 

accretions may be used for takeoffs 

conducted in icing conditions. 

For taking off in crosswinds, we 

consider it unnecessary to consider the 

effect of ice accretions since these 

proposals assume that ice accretions do 

not begin until liftoff. Therefore, 

airplanes will accrete very little ice, if 

any, while close to the ground where 

crosswinds are a significant safety 

concern. Proposed § 25.237(a)(2) 

explicitly states that the takeoff 

crosswind component without icing is 

valid for icing conditions. 

However, the conditions on landing 

are different. Before landing, the 

airplane may spend a significant 

amount of time exposed to icing 

conditions. These ice accretions may 

affect directional control when 

crosswinds are encountered close to the 

ground. As a result, (a)(3)(ii) requires 

evaluation of the landing crosswind 

component with ice accretion. 

M. High-Speed Characteristics (§ 25.253) 

We propose to revise § 25.253 by 

adding a new paragraph (c) to define the 

maximum speed for stability 

characteristics, VFC/MFC, for icing 

conditions. The proposal would permit 

applicants to define a VFC/MFC for icing 

conditions that is different than the VFC/ 

MFC defined for non-icing conditions. 

Additionally, § 25.253(b) would be 

revised to refer to § 25.143(g) rather than 

§ 25.143(f) due to the proposed 

renumbering of § 25.143. 

VFC/MFC is the highest speed at which 

compliance with several airplane 

handling qualities requirements must be 

shown. The FTHWG’s review of 

historical certification data showed that 

none of the flight tests for airplane 

handling qualities performed with ice 

accretions were conducted above 300 

knots CAS. The air loads associated 

with such high speeds tend to make it 

difficult to keep either artificial or 

natural ice attached to the airframe to 

accomplish the testing. It also 

minimizes the possibility of 

encountering this condition in 

operational service. Therefore, we 

propose that the maximum speed for 

demonstrating stability characteristics 

with ice accretions is the lower of VFC, 

300 KCAS, or any other speed at which 

it can be shown that the airframe will 

be free of ice. 

N. Pilot Compartment View (§ 25.773) 

We propose to revise § 25.773(b)(1)(ii) 

to replace the phrase ‘‘if certification 

with ice protection provisions is 

requested’’ with ‘‘if certification for 

flight in icing conditions is requested.’’

The proposed change is necessary to 

be consistent with the proposed change 

to § 25.1419. As discussed in the reason 

for revising § 25.1419, compliance with 

icing-related safety of flight 

requirements should depend on 

whether the airplane would be 

approved to operate in icing conditions, 

not on whether the airplane has 

approved ice protection provisions 

installed. 

O. Inlet, Engine, and Exhaust 

Compatibility (§ 25.941) 

We propose to revise the references to 

§§ 25.143(c), (d), and (e), contained in 

paragraph (c) of § 25.941, to read 

§ 25.143(d), (e), and (f). 

The proposed changes are necessary 

to maintain references to the correct 

paragraphs of § 25.143 if the changes to 

§ 25.143 being proposed by this 

rulemaking are adopted. 

P. Ice Protection (§ 25.1419) 

We propose to revise the introductory 

text of § 25.1419 to replace the phrase, 

‘‘If certification with ice protection 

provisions is desired * * *’’ with ‘‘If 

certification for flight in icing 

conditions is desired * * *’’ The 

current rule requires an applicant to 

demonstrate an airplane’s ability to 

safely operate in icing conditions only 

when the applicant is seeking to 

certificate ice protection features. It fails 

to address certification approval for 

flight in icing conditions for airplanes 

without ice protection features. The 

proposed revision, which would adopt 

the existing wording from JAR 25.1419, 

would require an applicant to 

demonstrate the airplane’s ability to 

safely operate in icing conditions 

whenever the applicant is seeking 

approval for flight in icing conditions. 

We also propose to simplify the 

second sentence of § 25.1419 to remove 

redundant wording. This change is 

editorial in nature and is not intended 

to change the requirement in any way. 

We propose to amend § 25.1419 to 

incorporate the revised introductory text 

for the following reasons: 

• A literal reading of the current 

§ 25.1419 wording could imply that the 

applicant does not have to demonstrate 

that the airplane can be safely operated 

in icing conditions unless an ice 

protection system is installed. 

• The revised text would clarify that 

any airplane approved to fly in icing 

conditions must be capable of operating 

in the icing conditions of appendix C of 

part 25 regardless of whether or not the 

airplane has an ice protection system. 

Q. Part 25, Appendix C 

We propose to revise appendix C of 

part 25 to create two subsections: Part 

I to define the atmospheric icing 

conditions that must be considered 

when showing compliance with the 

icing-related requirements of part 25, 

and part II to define ice accretions for 

each phase of flight. We also propose to 

add a definition of the atmospheric 

icing conditions to use specifically for 

the takeoff phase of flight. 

Federal Register / Vol. 70, No. 213 / Friday, November 4, 2005 / Proposed Rules 67289 

Proposed Appendix C, Part I 

Proposed appendix C, part I would 

contain the existing appendix C 

definitions of atmospheric icing 

conditions. We propose adding a 

definition of ‘‘takeoff maximum icing,’’

which is to be used in determining ice 

accretions for the takeoff phase of flight. 

Proposed Appendix C, Part II 

Proposed appendix C, part II(a) would 

contain definitions of the ice accretions 

appropriate to each phase of flight. 

Proposed appendix C, part II(b) would 

provide options for reducing the 

number of ice accretions to be 

considered for each phase of flight. 

Proposed appendix C, part II(c) would 

permit applicants to use, for the 

airplane performance tests, the same ice 

accretion used for evaluating handling 

characteristics. Proposed appendix C, 

part II(d) would define the conditions 

for determining the ice accretions for 

the takeoff phase of flight. Proposed 

appendix C, part II(e) would define 

what ice accretion must be considered 

prior to normal ice protection system 

operation. 

One early concern with developing 

appropriate airplane performance and 

handling qualities requirements for the 

takeoff phase of flight was the 

atmospheric icing environment close to 

the ground. The FTHWG members 

expressed significant concerns with 

using the existing appendix C 

atmospheric icing envelopes for this 

purpose. The FAA meteorologists 

confirmed that the existing appendix C 

atmospheric envelopes are not generally 

representative of icing conditions close 

to the ground. 

In general, for determining the size, 

shape, location, and texture of ice 

accretions on the airplane, one needs 

information about the atmospheric icing 

environment, i.e., icing cloud size, 

cloud liquid water content, water 

droplet size, expressed in terms of the 

mean effective diameter of the droplets, 

and ambient air temperature. 

We propose to use the following 

definition of atmospheric icing 

conditions for takeoff maximum icing 

conditions in appendix C, part I(e): An 

icing cloud extending from ground level 

to a height of 1,500 feet above the 

takeoff surface with a liquid water 

content of 0.35 grams/meter 3, water 

droplets with a mean effective diameter 

of 20 microns, and an ambient 

temperature of minus 9 degrees Celsius 

(¥9° C). The following discussion 

presents the reasons for selecting these 

values. 

Since the takeoff phase of flight is 

relatively short, generally ending at a 

height of 1,500 feet above the takeoff 

surface (ref. § 25.111(a)), we consider it 

reasonable to assume that the entire 

takeoff phase could be flown within the 

same icing cloud. Therefore, we propose 

that the takeoff maximum icing 

conditions would extend from ground 

level to a height of 1,500 feet above the 

level of the takeoff surface. 

Although measured data for liquid 

water content at low altitudes are 

sparse, a comparison of data contained 

in the FAA Technical Center’s database 

on inflight icing conditions with 

theoretical predictions suggest a 

maximum liquid water content within 

the icing cloud of 0.35 grams/meter 3

from ground level up to 1,500 feet. We 

propose to use this value within the 

definition of the maximum takeoff icing 

conditions. This proposed value would 

also cover the potential for dense 

ground fog at freezing temperatures, 

which our meteorologists stated would 

expose the airplane to a liquid water 

content of approximately 0.30 grams/ 

meter 3. 

For the size of the water droplets, 

both industry and FAA icing specialists 

concurred that a mean effective 

diameter of 20 microns would be 

appropriate for icing conditions 

occurring near ground level. We 

propose to use this value within the 

definition of the maximum takeoff icing 

conditions. 

Selection of the ambient temperature 

for takeoff icing was based on 

theoretical predictions that showed the 

effect of temperature to decrease 

significantly as the temperature itself 

decreased. We propose to use an 

ambient temperature for the takeoff 

icing atmosphere of minus 9 degrees 

Celsius (¥9° C), the point at which any 

further decrease in temperature had a 

negligible effect on the resulting ice 

accretion. 

According to our meteorologists, the 

amount of water vapor that can be held 

without condensing in a given volume 

of space depends only on the 

temperature of the gas (water vapor, air, 

etc.) in that space. It does not vary with 

altitude. Therefore, the proposed takeoff 

icing atmosphere would be equally 

applicable to all airport runway 

elevations. 

Proposed part II(a) references specific 

phases of flight and defines the critical 

ice accretions associated with the 

specific phase of flight. In the main 

body of the rule, various sections 

require evaluation using the ice 

accretion defined in appendix C. 

Proposed part II(a) contains those 

definitions. For example, § 25.125(a)(1) 

requires evaluation of landing distance 

using the ice accretion defined in 

appendix C. To perform the evaluation 

required by § 25.125(a)(1), an applicant 

would use the landing ice definition 

found in paragraph (5) of this section. 

To reduce the number of artificial ice 

accretions that must be considered, 

proposed part II(b) would permit the ice 

accretion determined for one flight 

phase to be used in showing compliance 

with the flight requirements of another 

phase, provided the applicant can show 

it has a more critical effect on the flight 

parameter being evaluated. For example, 

using the ice accretion determined for 

the holding phase to show compliance 

with the requirements for the takeoff 

phase will generally have a larger effect 

on performance and therefore be more 

penalizing than using an ice accretion 

determined specifically for the takeoff 

phase. 

Proposed part II(c) clarifies that the 

ice accretion with the most adverse 

effect on handling qualities may also be 

used during the flight test 

demonstrations of performance as long 

as any performance differences are 

conservatively taken into account. This 

proposed section is consistent with the 

intent behind proposed part II(b) to 

reduce the number of ice accretions that 

must be considered. Unlike handling 

qualities, performance effects between 

relatively small differences in ice 

accretion generally can be addressed 

adequately through analysis. 

Proposed part II(d) states the 

assumptions under which the takeoff ice 

accretions are determined. Proposed 

part II(d) also states that 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. This 

requirement is consistent with the 

existing requirement of § 25.111(c)(4) 

that limits the types of configuration 

changes requiring crew action before 

reaching 400 feet above the takeoff 

surface. 

We consider it necessary to also take 

into account the effects of any ice 

accretion that may form on the airplane 

from the time the airplane enters icing 

conditions until the ice protection 

system is activated and is performing its 

intended function. The size, shape, 

location, and texture of this ice 

accretion will depend on: (1) The means 

used to identify that the airplane is in 

icing conditions (for example, the pilot 

seeing ice accreting on the airplane, an 

ice detector, a combination of freezing 

temperatures and visible moisture), (2) 

the means and procedures for activating 

the ice protection system (for example, 

the pilot manually activating the system 

after a specified amount of ice builds up 

or automatic activation), and (3) the 

67290 Federal Register / Vol. 70, No. 213 / Friday, November 4, 2005 / Proposed Rules 

system characteristics (for example, the 

time it takes to effectively remove the 

ice). We propose to define the ice 

accretion applicable to the time period 

before the ice protection system has 

been activated and is performing its 

intended function as a period of time in 

the continuous maximum icing 

conditions of proposed part I of 

appendix C, including: 

• The time for recognition, 

• A delay time appropriate to the 

means of ice detection and activation of 

the ice protection system, and 

• The time needed for the ice 

protection system to perform its 

intended function after manual or 

automatic activation. 

III. Discussion of Non-Consensus Issues 

One of the goals of the ARAC process 

is consensus on the proposed 

recommendations. Due to the variety of 

interests represented in the FTHWG, 

this goal was not fully achieved. The 

areas of non-consensus, however, were 

confined to specific details within the 

proposals, and not to the overall need to 

amend part 25 to address airplane 

performance and handling qualities in 

icing conditions. The issues for which 

full consensus was not achieved within 

the FTHWG were: 

1. The requirement that a push force 

must be needed throughout the 

pushover maneuver proposed in the 

new § 25.143(i)(2); 

2. Whether the test to evaluate 

longitudinal handling qualities during 

sideslip maneuvers should be required 

by regulation as proposed in the new 

§ 25.143(i)(3), or should only be 

included in advisory material as one 

means of showing compliance; 

3. Whether the same airplane 

performance and handling qualities 

requirements (§§ 25.143(j) and 

25.207(h)) should always apply 

whenever the means to activate the ice 

protection system depends on the pilot 

to visually identify when the airplane is 

in icing conditions; and 

4. Whether the proposed revision to 

appendix C adequately ensures that the 

full range of variables are considered in 

determining what the critical ice 

accretion is for a particular flight phase. 

Each of these non-consensus issues is 

discussed in more detail below. 

A. Non-Consensus Issue 1—

§ 25.143(i)(2) 

The FTHWG did not reach a 

consensus on the issue of requiring a 

push force throughout the maneuver 

down to a zero g load factor (or the 

lowest load factor obtainable if limited 

by elevator power). Although there was 

consensus that the test maneuver should 

be performed to zero g, the group did 

not reach a consensus on whether the 

pilot should be required to apply a push 

force to the longitudinal control system 

throughout the maneuver until a zero g 

load factor is attained. The FTHWG 

considered two alternatives. 

Alternative 1 was developed by 

FTHWG members who did not support 

our proposal of requiring a push force 

to be maintained down to zero g load 

factor in the pushover maneuver. These 

FTHWG members disagreed with the 

proposal for the following reasons: 

• Historically, the pushover test was 

performed to a 0.5 g load factor rather 

than zero g. For example, as practiced 

by Transport Canada (the Canadian 

airworthiness regulatory authority), this 

demonstration was done with a high 

pitch rate. Consequently, there was 

significant overshoot of the 0.5 g load 

factor, down to approximately 0.25 g or 

less. This maneuver was intended to be 

a controllability test beginning with the 

pilot abruptly pushing on the control 

column to achieve a high nose-down 

pitch rate, followed by a pull to recover. 

The intent was not to reach a specific 

g level below 0.5 g, but to show that the 

pilot could perform a satisfactory 

recovery. This has proven to be an 

acceptable test technique. To date, 

airplanes evaluated with this technique 

have had a satisfactory safety record in 

service. 

• Since the beginning of the 1980s, 

the practice of many certification 

authorities has been to require testing to 

lower load factors. This evolved until 

the introduction of the JAA’s NPA 25F–

219, which not only requires testing to 

zero g, but also requires a push force 

throughout the maneuver to zero g. A 

zero-g pushover is considered to be an 

improbable condition, going well 

beyond any operational maneuver, and 

does not properly represent gusts, pitch 

rate, elevator position, or other factors 

that may contribute to tailplane stalls. 

Also, since the NPA requirement was 

developed for a specific turboprop, and 

motivated by service experience on 

turboprop airplanes, other requirements 

were proposed for other types of 

airplanes. 

For the above reasons, the supporters 

of alternative 1 to § 25.143(i)(2) consider 

that requiring a push force to load 

factors as low as zero g is excessive. 

Instead, they recommend replacing 

proposed § 25.143(i)(2) with: 

The airplane must be controllable in a 

pushover maneuver down to zero g, or the 

lowest load factor obtainable if limited by 

elevator power. It must be shown that a push 

force is required throughout the maneuver 

down to 0.5 g. It must be possible to 

promptly recover from the maneuver without 

exceeding 50 pounds pull control force. 

Further supporting rationale: FAA 

Advisory Circular 25–7A, ‘‘Flight Test 

Guide for Certification of Transport 

Category Airplanes,’’ defines the 

boundaries of various flight envelopes. 

With regard to the minimum load factor 

with flaps down: 

• The normal flight envelope (NFE) 

goes to 0.8 g; 

• The operational flight envelope 

(OFE) goes to 0.5 g; and 

• The limit flight envelope (LFE) goes 

to zero g. 

Conceptually, the boundaries of the 

OFE are as far as the pilot is expected 

to go intentionally, while the LFE is 

based on structural or other limits that 

should not be exceeded. Between the 

OFE and the LFE, it is acceptable for 

degraded handling qualities, but the 

airplane must remain controllable and it 

must be possible to avoid exceeding the 

limit load factor (see § 25.143(b)). 

Although existing regulations do not 

allow force reversals (for example, from 

a push force on the control column to 

a pull force in this case) for the en route 

flight phase, in practice, the certification 

tests for these rules do not cover the full 

structural limit flight envelope. Rather, 

the certification tests cover a reasonable 

range of load factors sufficient to cover 

normal operations. For example, in the 

en route configuration, where the limit 

minimum load factor is usually negative 

1 g, the JAA’s Advisory Circular Joint 

(ACJ) No. 2 to JAR 25.143(f) states: 

‘‘* * * assessment of the characteristics 

in the normal flight envelope involving 

normal accelerations from 1 g to zero g, 

will normally be sufficient.’’

With flaps up, zero g is the midpoint 

between the limit load factor and the 

trim point. The corresponding points for 

flaps down are zero g for the limit load 

factor and 0.5 g for the midpoint 

assessment of characteristics. The 

supporters of alternative 1 to 

§ 25.143(i)(2) are concerned that 

requiring a push force to zero g means 

that this limit load factor will be 

routinely exceeded in the flight tests 

used to show compliance with the 

proposed rule. 

The zero-g pushover is not like typical 

stability tests where it is possible to 

establish steady state conditions and 

measure a repeatable control force. The 

pushover is an extremely dynamic 

maneuver lasting only a few seconds 

and involving high pitch rates in both 

directions. There will always be 

variability due to pilot technique. The 

pilot may pull slightly before reaching 

zero g to reduce the nose-down pitch 

rate and anticipate the recovery. This 

Federal Register / Vol. 70, No. 213 / Friday, November 4, 2005 / Proposed Rules 67291 

makes it impossible to distinguish 

between the force required to reach a 

given g level and the force the pilot 

applies to track the targeted pitch rate. 

At critical conditions, airplanes that 

meet the criterion suggested in the 

alternative proposal still require a 

significant pull force to recover. 

Alternative 1 to § 25.143(i)(2) would 

set a limit of 50 pounds on the total 

control force needed to recover 

promptly. This would ensure that the 

force that the pilot must exert is low 

enough so that even with only one hand 

on the pitch control (the other hand 

might be on the thrust levers or another 

control), the pilot can handle a 

combination of: 

• The force to halt the nose-down 

pitch rate, 

• The force due to any hinge moment 

reversal, and 

• The force to establish a satisfactory 

nose-up pitch rate for recovery. 

The 50-pound limit is used for a 

similar purpose in several other rules. 

The effect of data scatter and variations 

in pilot technique will cause airplanes 

that are not clearly free of ICTS 

concerns to exceed the 50-pound limit 

too often, so they will not pass this test. 

The supporters of alternative 1 to 

§ 25.143(i)(2) believe that the proposal 

contained in this rulemaking has the 

potential for adversely affecting an 

entire class of airplanes—namely light 

to medium business jets with trimmable 

stabilizers and unpowered elevators. 

Many of these airplanes exhibit a mild 

control force reversal from a push force 

to a pull force between zero g and 0.5 

g. 

Although such a characteristic will 

not comply with the proposed rule, the 

airplane remains easily controllable. 

The proposed requirement for a push 

force to be required down to a zero g 

load factor would reduce the stabilizer 

incidence available for trimming the 

airplane by two to four degrees. This 

would require either a 20 to 40 percent 

larger stabilizer or other design changes 

to compensate for the reduction in 

stabilizer trim range. The supporters of 

alternative 1 to § 25.143(i)(2) do not 

believe that the cost of these changes is 

justified by any safety benefit, as these 

airplanes are not the types having ICTS 

accidents. 

Furthermore, the proposed 

§ 25.143(i)(1) would require that 

sandpaper ice be considered if the 

elevator is unpowered, regardless of the 

ice protection system. Many of the 

current business jets are equipped with 

anti-ice systems that prevent ice 

formation on the stabilizer leading edge. 

Thus, the jets would be evaluated under 

more critical assumptions (that is, with 

the anti-ice system off) than the types 

that have had accidents. 

Ice-contaminated tailplanes retain 

normal linear characteristics until the 

onset of flow separation. The separation 

causes the hinge moment coefficient to 

slope gradually from one level to 

another over a range of 4 to 10 degrees 

AOA. With the elevator down, the hinge 

moment coefficient changes sign at an 

AOA in this range, which results in the 

control force reversal from a push to a 

pull. On a particular business jet with 

a relatively small elevator, this results in 

a gradually increasing pull force from 0 

pounds at approximately 0.4 g to 25 

pounds at zero g. 

On airplanes with large unpowered 

elevators, especially those with long 

chord lengths, the elevator control 

forces resulting from a stalled tail can be 

very high. These forces may even be too 

high for the pilots to counteract. For 

example, assume the elevator 

dimensions of the previous example are 

scaled up by a factor of 2. The elevator 

chord is then doubled, the area is 

quadrupled, and the pilot must exert 8 

times as much force on the control to 

move the elevator. If the control force in 

the previous example were 25 pounds at 

zero g, the control force for this larger 

elevator would be 200 pounds. These 

examples illustrate how the size and 

design of elevators for certain airplanes 

determine whether the control forces 

would be acceptable or hazardous. The 

test criteria recommended for showing 

compliance with the requirements 

proposed as alternative 1 to 

§ 25.143(i)(2) would identify those 

airplanes with the hazardous 

characteristics. Therefore, the 

supporters of alternative 1 to 

§ 25.143(i)(2) believe that there is no 

difference in safety between this 

alternative and our proposal. 

Results of the National Aeronautics 

and Space Administration’s (NASA) 

Tailplane Icing Program provide a basis 

for evaluating whether the proposed 

requirements adequately address the 

safety concerns. Flight tests were 

conducted in which a test airplane 

performed a series of pushovers and 

other maneuvers with and without ice 

accretions. Even without ice accretions, 

reversed control forces were sometimes 

experienced in the pushover maneuvers 

for some configurations. With the ice 

accretions, control forces exceeding 100 

pounds were experienced in some of the 

pushovers although the airplane 

remained controllable. In one test, a 

departure from controlled flight 

occurred during a power transition with 

a critical ice accretion and flaps 40 

(which is the maximum landing flap 

configuration for this airplane). This 

event involved a sudden nose-down 

pitch-over from 1-g flight like the ICTS 

accident scenarios. The same ice 

accretion had degraded pushover 

characteristics to the point that a 50- 

pound pull was required to recover from 

zero g with flaps 10, and 100 pounds 

was required with flaps 20. 

Accordingly, the criteria proposed as 

alternative 1 to § 25.143(i)(2) provide an 

adequate safety margin, and would have 

identified the aircraft as unacceptable 

before it ever got to the flaps 40 

configuration at which it lost control. 

We disagree with the position of the 

supporters of alternative 1 to 

§ 25.143(i)(2) for the following reasons: 

a. Ice contaminated tailplane stall/ 

elevator hinge moment reversal has 

been a significant factor in accidents 

occurring in icing conditions. Rapid and 

large changes in pitch, significant 

changes in control forces, pilot surprise, 

and possible disorientation in poor 

visibility that can follow from a 

tailplane stall/elevator hinge moment 

reversal can result in loss of pitch 

control. Coupled with the weather 

conditions that lead to ICTS, this loss of 

control will usually occur at low 

altitude where there is a higher 

probability of an accident. 

b. Historically, the pushover test was 

usually performed to 0.5 g load factor, 

although this was often done with a 

high pitch rate and, hence, there was 

some overshoot of the 0.5 g load factor. 

A push force on the elevator control was 

required to reach this g level. 

Certification testing and service 

experience has since shown that testing 

to only to 0.5 g is inadequate, 

considering the relatively high 

frequency of experiencing 0.5 g in 

operations. Since the beginning of the 

1980s, the practice of many certification 

authorities has been to require testing to 

lower load factors, and the JAA’s Notice 

of Proposed Amendment (NPA) 25F–

219 requires a push force throughout the 

maneuver to zero g. 

c. Reversal of elevator control force 

versus normal acceleration is not 

acceptable within the flight envelope. 

Existing requirements and advisory 

material addressing elevator control 

force characteristics (§§ 25.143(f), 

25.255(b)(2), and the guidance material 

to § 25.143(f)) do not allow force 

reversals. Furthermore, a survey of FAA, 

JAA, and other flight test personnel 

showed that a clear majority did not 

favor anything less than a push force on 

the elevator control to zero g. 

Alternative 1 to § 25.143(i)(2) would 

at least partially address the cause of 

past ICTS accidents. However, the 

method proposed for determining the 

acceptability of a control force reversal 

67292 Federal Register / Vol. 70, No. 213 / Friday, November 4, 2005 / Proposed Rules 

is subjective and would lead to 

inconsistent evaluations. We maintain 

that a push force to zero g with an icecontaminated tailplane is the minimum 

standard that can be accepted. Zero g is 

within the flight envelope of the 

airplane and this criterion addresses the 

need to have acceptable handling 

qualities for operational service when 

the pilot would not expect any control 

force reversal. Requiring a push force to 

zero g also removes subjectivity in the 

assessment of the airplane’s 

controllability and provides readily 

understood criteria of acceptability. Any 

lesser standard would not give 

confidence that the problem has been 

fully addressed. 

Transport Canada proposed the 

following alternative as a compromise 

between requiring a push force to either 

zero g or 0.5 g: 

Transport Canada advisory material 

dating back to the mid-1980s specified 

that applicants must demonstrate ± 0.5 

g applied to the longitudinal control. In 

practice, the demonstration was done in 

a fairly abrupt maneuver that generated 

a significantly higher transient pitch 

rate than that associated with a steady 

normal acceleration. The minimum 

normal acceleration obtained was 

usually around 0.25 g or less. It was 

considered that the pitch rate aspect 

was just as important as the actual 

normal acceleration in determining 

whether there were unsafe 

characteristics associated with tailplane 

stall. No pass/fail criteria were provided 

in the Transport Canada guidance 

except that the characteristics had to be 

satisfactory. 

The accident record on ice 

contaminated tailplane stall indicates 

that a significant factor was the pilot’s 

startled reaction to an abrupt hinge 

moment reversal and the magnitude of 

the control force required to recover the 

airplane to a normal 1 g condition. 

Alternative 1 to § 25.143(i)(2) would 

recognize this controllability issue by 

limiting the amount of pull force 

required to promptly recover the 

airplane from a zero g condition to a 50- 

pound pull force. In addition, 

recognizing that positive stability is also 

important, alternative 1 to § 25.143(i)(2) 

would require a push force down to 0.5 

g. 

Accident data available to Transport 

Canada indicate that aircraft involved in 

incidents and/or accidents incurred a 

tailplane stall at approximately 0.3 g to 

0.4 g. Based on this data and Transport 

Canada’s past practice, alternative 1 to 

§ 25.143(i)(2) would be acceptable, 

except that the issue of pitch rate is not 

specifically identified in the criteria. 

Transport Canada recognizes that 

combining pitch rate with a normal 

acceleration in a requirement is 

probably too complex, especially for the 

wide range of aircraft designs 

encompassed by part 25 and the parallel 

JAR–25 standards. Thus, Transport 

Canada considers that, if the 

requirement would only specify a ‘g’

level, then 0.5 g for positive stability is 

inadequate. As a compromise, Transport 

Canada proposes requiring a push force 

down to a value of 0.25 g as alternative 

2 to § 25.143(i)(2). 

While it is a compromise between the 

requirement proposed in this 

rulemaking and alternative 1 (by 

specifying 0.25 g for the push force 

requirement), we disagree with this 

alternative because it does not fully 

address the safety concerns throughout 

the flight envelope. It also does not fully 

address the cost concerns expressed 

within the FTHWG regarding 

§ 25.143(i)(2) as proposed in this 

rulemaking. 

The Transport Canada alternative 

recognizes the importance of pitch rate. 

An abrupt nose-down control input is 

required to reach zero g. We consider 

that testing to zero g, however, ensures 

that high pitch rates are adequately 

evaluated without the added 

complication of specifying a pitch rate 

requirement. 

B. Non-Consensus Issue 2—

§ 25.143(i)(3) 

The proposed new § 25.143(i)(3) 

would add a requirement that any 

changes in longitudinal control force to 

maintain speed with increasing sideslip 

angle be progressive with no reversals or 

unacceptable discontinuities. The 

FTHWG did not reach a consensus on 

whether it would be necessary to add a 

specific regulatory requirement to 

address this issue. The majority of the 

FTHWG members felt that there did not 

appear to be sufficient data to establish 

criteria specific enough to stand as a 

regulatory requirement and proposed 

that the issue be addressed through nonregulatory guidance material. 

Anomalies in longitudinal control 

force during sideslip maneuvers have 

been of concern to some accident 

investigators and regulatory specialists. 

At one time, we proposed that pushover 

maneuvers be conducted while in 

sideslips. Transport Canada considered 

that performing sideslips in a pushover 

maneuver was excessive, but 

recognizing the concern, proposed an 

additional requirement that would 

specifically assess longitudinal control 

stick forces while in sideslip 

maneuvers. 

We consider that a consensus was 

reached on the need to address this 

issue; the only difference appears to be 

whether it should be addressed in 

advisory material or in the proposed 

rule. We consider that this issue raises 

important safety concerns that must be 

addressed as a specific evaluation 

requirement. Therefore, it is appropriate 

to place it in the rule rather than in an 

AC. We recognize that AC material may 

also be needed to provide guidance on 

an acceptable means of compliance. 

C. Non-Consensus Issue 3—

§§ 25.143(j)(1) and 25.207(h) 

The proposed new §§ 25.143(j)(1) and 

25.207(h) would apply different 

requirements when different means are 

used for the pilot to visually recognize 

icing conditions. Compliance with all of 

the § 25.143 controllability requirements 

for non-icing conditions would apply if 

activation of the ice protection system 

depends on seeing a specified ice 

accretion on a reference surface (for 

example, on an ice accretion probe, or 

a wing leading edge). However, less 

stringent requirements using a lesser ice 

accretion would apply to any other 

means of identifying icing conditions, 

including seeing the first indication of 

an ice accretion on a reference surface. 

The FTHWG did not reach a 

consensus on the proposed 

§ 25.143(j)(1). The Air Line Pilots 

Association (ALPA), which was 

represented in the FTHWG, disagrees 

with the proposal. The ALPA considers 

visually recognizing the first indication 

of ice accreting on a reference surface to 

be the same situation as visually 

recognizing a specific amount of ice 

accretion on a reference surface. To the 

ALPA, both are means of visual 

recognition that require the flightcrew to 

monitor conditions outside the cockpit. 

Whenever it is necessary for the pilots 

to check outside the cockpit (which the 

ALPA does not consider to be 

equivalent to a primary instrument 

visual scan pattern), the ALPA believes 

that the same basic maneuver 

capabilities, stall protection 

requirements, and ice accretion amounts 

should apply. 

The ALPA proposes the following 

alternative text for § 25.143(j)(1): 

‘‘If normal operation of any ice 

protection system is dependent upon 

visual recognition of ice accretion, the 

requirements of § 25.143 are applicable 

with the ice accretion defined in 

proposed appendix C, part II(e).’’

The ALPA has similar concerns with 

the proposed § 25.207(h)(1) and 

proposes the following alternative text: 

‘‘If normal operation of any ice 

protection system is dependent upon 

visual recognition of ice accretion, the 

requirements of this section, except 

Federal Register / Vol. 70, No. 213 / Friday, November 4, 2005 / Proposed Rules 67293 

paragraphs (c) and (d), are applicable 

with the ice accretion defined in 

appendix C, part II(e).’’

We disagree with the alternative 

proposals for §§ 25.143(j)(1) and 

25.207(h)(1). 

The FTHWG found that there are 

significant differences in the 

aerodynamic effects on an airplane 

between the two different means of 

visual recognition of icing conditions 

identified in the ALPA alternative 

proposal discussion. The best example 

of the means covered by §§ 25.143(j)(1) 

and 25.207(h)(1), as proposed in this 

notice, are airplanes with pneumatic 

deicing boots. The operating procedures 

call for a specified amount of ice buildup before activating the ice protection 

system, a process that is repeated often 

during an icing encounter. In this case, 

the airplane is assured of being operated 

with some level of aerodynamic 

degradation before activation of the ice 

protection system. 

The best example of the second type 

of visual recognition of icing conditions 

are airplane models that are equipped 

with an ice accretion probe in the pilot’s 

field of view outside the airplane. The 

published procedure calls for activating 

the ice protection system at the first 

indication of ice buildup on the 

accretion probe. Such accretion probes, 

or an equivalent such as a windshield 

wiper post, are highly efficient ice 

collectors, and typically will accrete 

visible ice prior to ice accretion on 

aerodynamic surfaces. Under this means 

of detecting icing conditions, there may 

be little or no ice buildup on 

aerodynamic surfaces before activation 

and normal operation of the ice 

protection system, and little or no 

aerodynamic degradation. These two 

means of visually recognizing that icing 

conditions are present are distinctly 

different. 

D. Non-Consensus Issue 4—Appendix C 

The ALPA representative on the 

FTHWG did not consider that the 

combination of the proposed regulatory 

changes and associated proposed 

advisory material provided a definitive 

enough description of the required ice 

accretions, particularly with regard to 

the variables that must be considered in 

determining the critical ice accretion for 

a particular flight phase. The ALPA 

alternative proposal recommends 

adding specific references to ‘‘all flight 

conditions within the operational limits 

of the airplane’’ and ‘‘configuration 

changes’’ to the general ice accretion 

requirements of proposed part II(a) of 

appendix C to ensure that the full range 

of possible accretion locations for 

atmospheric conditions are considered. 

The alternative text would read: 

Section 25.21(g) states that if certification 

for flight in icing conditions is desired, the 

applicable requirements of subpart B must be 

met in the icing conditions of appendix C, 

unless otherwise prescribed. The most 

critical ice accretion in terms of handling 

characteristics and performance for each 

flight phase must be determined, taking into 

consideration the atmospheric conditions of 

part I of this appendix, and all flight 

conditions within the operational limits of 

the airplane (for example, configuration, 

configuration changes, speed, angle-of-attack, 

and altitude). The following ice accretions 

must be determined: 

The NASA research following the 

Model ATR–72 accident at Roselawn, 

Indiana, in 1994, observed that 

decreasing AOA causes an increase in 

aft ice accretion limit on the upper 

surface of an airfoil. Likewise, the fact 

that airflow separation on the negative 

pressure side (upper surface for a 

typical wing) is caused by ice accretions 

on the upper surface is discussed. 

Research performed by Dr. Michael B. 

Bragg and others at the University of 

Illinois has demonstrated significant 

variation in the effects on airfoil 

aerodynamics of a simulated ice 

accretion depending upon its location 

on the negative pressure side of the 

airfoil. 

Differing airspeeds and high lift 

device configurations significantly 

change the AOA and, consequently, the 

location of the stagnation point around 

which any ice accretion forms on an 

airfoil. For normal operation, this 

should make no difference on surfaces 

that are protected by the icing system. 

But for unprotected surfaces, in the 

failure case and for ice that accumulates 

prior to normal system operation, 

changing the location of ice on the 

negative pressure side of the airfoil may 

be significant. Procedural restrictions 

(that is, no holding with flaps extended, 

speed or configuration restrictions in 

case of ice system failure, etc.) could be 

used to limit the configurations 

necessary to determine the most critical 

ice accretion. However, the full range of 

possible accumulation locations must be 

considered. 

In their report on the Embraer Model 

EMB 120 accident at Monroe, Michigan, 

in 1997, the NTSB concluded that: 

The icing certification process has been 

inadequate because it has not required 

manufacturers to demonstrate the airplane’s 

flight handling and stall characteristics under 

a sufficiently realistic range of adverse 

accretion/flight handling conditions. 

(Finding #27) 

The recommendations submitted by 

the FTHWG, and this proposed rule, 

consider ice accretions for all phases of 

flight and all configurations of high lift 

devices. The proposed rule would 

require consideration of the effects of 

the ice accretion during the phases of 

flight with high lift devices extended. 

The associated proposed advisory 

material specifically recommends that 

natural icing flight testing with high lift 

devices extended in the approach and 

landing conditions be conducted. 

We do not concur with the alternative 

discussed above. The research referred 

to above determined the effect on lift 

and drag of a spoiler-like shape located 

at various chord locations of a two 

dimensional airfoil. (A two dimensional 

airfoil is a wing with an infinite 

wingspan, that is, there are no wingtips. 

It is common practice for wind tunnel 

testing to use wings that span the test 

section from one wall of the wind 

tunnel to the other. Results obtained for 

a two dimensional airfoil must usually 

be adjusted to properly represent a real 

wing.) These data do not support the 

alternative position because no data 

were presented in the references to 

connect either this shape or its location 

with airplane flight conditions or icing 

conditions, either inside or outside of 

proposed appendix C. There were no 

data showing the effect of the shape on 

an airfoil with high lift devices 

extended. 

The effect of any shape on a twodimensional airfoil is much larger than 

the effect of a similar shape on a 

complete airplane with high lift devices 

extended, and the effect of such a shape 

diminishes with increasing airplane 

size. 

The effect of ice accretions similar to 

the shapes tested in the referenced 

report were also considered by the 

FTHWG when it discussed ice accreted 

in conditions outside of proposed 

appendix C. The majority of the FTHWG 

recommended not including these 

accretions in the recommendations 

because the only icing design envelope 

available is proposed appendix C. 

IV. Rulemaking Notices and Analyses 

Paperwork Reduction Act 

The Paperwork Reduction Act of 1995 

(44 U.S.C. 3507(d)) requires that the 

FAA to consider the impact of 

paperwork and other information 

collection burdens imposed on the 

public. We have determined that there 

are no current new information 

collection requirements associated with 

this proposed rule. 

International Compatibility 

In keeping with U.S. obligations 

under the Convention on International 

67294 Federal Register / Vol. 70, No. 213 / Friday, November 4, 2005 / Proposed Rules 

Civil Aviation, it is FAA policy to 

comply with International Civil 

Aviation Organization (ICAO) Standards 

and Recommended Practices to the 

maximum extent practicable. The FAA 

has determined that there are no ICAO 

Standards and Recommended Practices 

that correspond to these proposed 

regulations. 

Executive Order 13132, Federalism 

The FAA analyzed this proposed rule 

under the principles and criteria of 

Executive Order 13132, Federalism. We 

determined that this action would not 

have a substantial direct effect on the 

States, on the relationship between the 

national Government and the States, or 

on the distribution of power and 

responsibilities among the various 

levels of government, and therefore 

would not have federalism implications. 

Regulatory Evaluation, Regulatory 

Flexibility Determination, International 

Trade Impact Assessment, and 

Unfunded Mandates Assessment 

This portion of the preamble 

summarizes the FAA’s analysis of the 

economic impacts of a proposed rule 

amending part 25 of 14 CFR to change 

the regulations applicable to transport 

category airplanes certificated for flight 

in icing conditions. It also includes 

summaries of the initial regulatory 

flexibility determination. We suggest 

readers seeking greater detail read the 

full regulatory evaluation, which is in 

the docket for this rulemaking. 

Introduction 

Changes to Federal regulations must 

undergo several economic analyses. 

First, Executive Order 12866 directs that 

each Federal agency 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 requires agencies to analyze the 

economic impact of regulatory changes 

on small entities. Third, the Trade 

Agreements Act (19 U.S.C. 2531–2533) 

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, to 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). 

In conducting these analyses, FAA 

has determined this rule (1) has benefits 

that justify its costs, (2) is not a 

‘‘significant regulatory action’’ as 

defined in section 3(f) of Executive 

Order 12866, and is not ‘‘significant’’ as 

defined in DOT’s Regulatory Policies 

and Procedures; (3) would not have a 

significant economic impact on a 

substantial number of small entities; (4) 

would have a neutral impact on 

international trade; and (5) does not 

impose an unfunded mandate on state, 

local, or tribal governments, or on the 

private sector. These analyses, available 

in the docket, are summarized below. 

Total Benefits and Costs of This 

Rulemaking 

The estimated cost of this proposed 

rule is $66.4 million ($22.0 million in 

present value at seven percent). The 

estimated potential benefits of avoiding 

13 fatalities are $89.9 million ($23.7 

million in present value at seven 

percent). 

Who Is Potentially Affected by This 

Rulemaking 

• Operators of part 25 U.S.-registered 

aircraft conducting operations under 14 

CFR parts 121, 129, 135, and 

• Manufacturers of those part 25 

aircraft. 

Our Cost Assumptions and Sources of 

Information 

This evaluation makes the following 

assumptions: 

• The base year is 2003. 

• This proposed rule is assumed to 

become a final rule in 2 years, and will 

then be effective immediately. 

• The production run for newly 

certificated airplane models is 20 years. 

• The average life of an airplane is 25 

years. 

• We analyzed the costs and benefits 

of this proposed rule over the 45-year 

period (20 + 25 = 45) 2005 through 

2049. 

• We used a 10-year certification 

compliance period. For the 10-year lifecycle period, the FAA calculated an 

average of four new certifications would 

occur. 

• We performed sensitivity analysis 

on present value discount rates of one, 

three, and the base case seven percent. 

• New airplane certifications will 

occur in year one of the analysis time 

period. 

• Value of fatality avoided—$3.0 

million (Source: ‘‘Treatment of Value of 

Life and Injury In Economic Analysis,’’

(FAA APO Bulletin, February 2002).) 

Benefits of This Rulemaking 

The benefits of this proposed rule 

consist of the value of lives saved due 

to avoiding accidents involving part 25 

airplanes operating in icing conditions. 

We estimate that a total of 13 fatalities 

could potentially be avoided by 

adopting the proposed rule. We use $3.0 

million as the value of an avoided 

fatality. Over the 45-year period of 

analysis, the potential benefit of the 

proposed rule would be $89.9 million 

($23.7 million in present value at seven 

percent). 

Cost of This Rulemaking 

We estimate the costs of this proposed 

rule to be about $66.4 million ($22.0 

million in present value at seven 

percent) over the 45-year analysis 

period. The total cost of $66.4 million 

equals the fixed certification costs of 

$6.7 million incurred in the first year 

plus the variable annual fuel burn cost 

of $59.7 million. 

Regulatory Flexibility Determination 

The Regulatory Flexibility Act of 1980 

(RFA) establishes ‘‘as a principle of 

regulatory issuance that agencies shall 

endeavor, consistent with the objective 

of the rule and of applicable statutes, to 

fit regulatory and informational 

requirements to the scale of the 

business, organizations, and 

governmental jurisdictions subject to 

regulation.’’ To achieve that principle, 

the RFA requires agencies to solicit and 

consider flexible regulatory proposals 

and to explain the rationale for their 

actions. 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 proposed or final 

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 Act. 

However, if an agency determines that 

a proposed or final rule is not expected 

to have a significant economic impact 

on a substantial number of small 

entities, section 605(b) of the 1980 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. This proposed rule would not 

have a significant economic impact on 

a substantial number of small entities. 

Federal Register / Vol. 70, No. 213 / Friday, November 4, 2005 / Proposed Rules 67295 

International Trade Impact Assessment 

The Trade Agreement Act of 1979 

prohibits Federal agencies from 

establishing any standards or engaging 

in related activities that create 

unnecessary obstacles to the foreign 

commerce of the United States. 

Legitimate domestic objectives, such as 

safety, are not considered unnecessary 

obstacles. 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 potential effect of this 

proposed rule and determined that it 

would impose the same costs on 

domestic and international entities and 

thus have a neutral trade impact. 

Unfunded Mandates Assessment 

The Unfunded Mandates Reform Act 

of 1995 (the Act) is intended, among 

other things, to curb the practice of 

imposing unfunded Federal mandates 

on State, local, and tribal governments. 

Title II of the Act 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 (adjusted 

annually for inflation) 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 inflationadjusted value of $120.7 million in lieu 

of $100 million. This proposed rule 

does not contain such a mandate. The 

requirements of Title II of the Act, 

therefore, do not apply. 

Regulations Affecting Intrastate 

Aviation in Alaska 

Section 1205 of the FAA 

Reauthorization Act of 1996 (110 Stat. 

3213) requires the Administrator, when 

modifying regulations in Title 14 of the 

CFR 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 such 

regulatory distinctions as he or she 

considers appropriate. Because this 

proposed rule would apply to the 

certification of future designs of 

transport category airplanes and their 

subsequent operation, it could, if 

adopted, affect intrastate aviation in 

Alaska. The FAA therefore specifically 

requests comments on whether there is 

justification for applying the proposed 

rule differently in intrastate operations 

in Alaska. 

Plain Language 

Executive Order 12866 (58 FR 51735, 

Oct. 4, 1993) requires each agency to 

write regulations that are simple and 

easy to understand. We invite your 

comments on how to make these 

proposed regulations easier to 

understand, including answers to 

questions such as the following: 

Are the requirements in the proposed 

regulations clearly stated? 

• Do the proposed regulations contain 

unnecessary technical language or 

jargon that interferes with their clarity? 

• Would the proposed regulations be 

easier to understand if they were 

divided into more (but shorter) sections? 

• Is the description in the NPRM 

preamble helpful in understanding the 

proposed regulations? 

Please send your comments to the 

address specified in the FOR FURTHER

INFORMATION CONTACT section. [new 

template uses ADDRESSES] 

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 proposed 

rulemaking action qualifies for the 

categorical exclusion identified in 

paragraph number 312f and involves no 

extraordinary circumstances. 

Regulations That Significantly Affect 

Energy Supply, Distribution, or Use 

The FAA has analyzed this NPRM 

under Executive Order 13211, Actions 

Concerning Regulations that 

Significantly Affect Energy Supply, 

Distribution, or Use (May 18, 2001). We 

have determined that it is not a 

‘‘significant energy action’’ under the 

executive order because it is not a 

‘‘significant regulatory action’’ under 

Executive Order 12866, and it is not 

likely to have a significant adverse effect 

on the supply, distribution, or use of 

energy. 

V. Appendixes to the Preamble 

APPENDIX I.—LIST OF ACRONYMS USED IN THIS DOCUMENT

[For your reference and ease of reading, the following list defines the acronyms that are used throughout this document. This appendix will not 

appear in the Code of Federal Regulations.] 

Acronym Definition 

AC .......................... Advisory Circular. 

ACJ ........................ Advisory Circular Joint (issued by JAA). 

AFM ....................... Airplane Flight Manual. 

ALPA ...................... Air Line Pilots Association. 

AMJ ........................ Advisory Material Joint (issued by JAA). 

AOA ....................... Angle-of-Attack. 

ARAC ..................... Aviation Rulemaking Advisory Committee. 

CAS ........................ Calibrated Airspeed. 

CS .......................... Certification Specifications (EASA airworthiness standards). 

EASA ..................... European Aviation Safety Agency. 

FAA ........................ Federal Aviation Administration. 

FTHWG .................. Flight Test Harmonization Working Group. 

ICTS ....................... Ice-Contaminated Tailplane Stall. 

IPHWG ................... Ice Protection Harmonization Working Group. 

JAA ........................ Joint Aviation Authorities. 

JAR ........................ Joint Aviation Requirements (JAA airworthiness standards). 

LFE ........................ Limit Flight Envelope. 

NASA ..................... National Aeronautics and Space Administration. 

NFE ........................ Normal Flight Envelope. 

NPA ........................ Notice of Proposed Amendment (issued by JAA or EASA). 

NPRM .................... Notice of Proposed Rulemaking. 

NTSB ..................... National Transportation Safety Board. 

OFE ........................ Operational Flight Envelope. 

67296 Federal Register / Vol. 70, No. 213 / Friday, November 4, 2005 / Proposed Rules 

APPENDIX I.—LIST OF ACRONYMS USED IN THIS DOCUMENT—Continued 

[For your reference and ease of reading, the following list defines the acronyms that are used throughout this document. This appendix will not 

appear in the Code of Federal Regulations.] 

Acronym Definition 

SLD ........................ Supercooled Large Drop. 

V1 ........................... The maximum speed in the takeoff at which the pilot must take the first action (for example, apply brakes, reduce thrust, 

deploy speed brakes) to stop the airplane within the accelerate-stop distance. V1 also means the minimum speed in the 

takeoff, following a failure of the critical engine at VEF, at which the pilot can continue the takeoff and achieve the required height above the takeoff surface within the takeoff distance. 

V2 ........................... Takeoff Safety Speed. (The target speed to be reached by the time the airplane is 35 feet above the takeoff surface.) 

VDF/MDF .................. Demonstrated Flight Diving Speed. 

VEF ......................... Engine Failure Speed. The speed at which the critical engine is assumed to fail during takeoff. 

VFC/MFC .................. Maximum Speed for Stability Characteristics. 

VFE ......................... Maximum Flaps Extended Speed. 

VFTO ....................... Final Takeoff Speed. The speed at which compliance is shown with the final takeoff climb gradient requirements of 

§ 25.121(c). 

VMC ........................ Minimum Control Speed with the critical engine inoperative. 

VMCA ...................... Air Minimum Control Speed. (Commonly used terminology for VMC.) 

VMCG ...................... Ground Minimum Control Speed. 

VMCL ....................... Landing Minimum Control Speed. 

VMO/MMO ................ Maximum Operating Limit Speed. 

VMU ........................ Minimum Unstick Speed. The minimum airspeed at and above which the airplane can safely lift off the ground and continue the takeoff. 

VR ........................... Rotation Speed. The speed at which the pilot first makes an input to the airplane controls to rotate the airplane to the 

takeoff pitch attitude. 

VREF ........................ Landing Reference Speed. 

VS 1–g ...................... 1–g Stall Speed. The calibrated airspeed at which aerodynamic forces alone can support the airplane in 1–g flight. 

VSR ......................... Reference Stall Speed. VSR may not be less than VS 1–g. For airplanes with a device that abruptly pushes the nose down 

at a selected angle of attack, (for example, a stick pusher), VSR may not be less than 2 knots or 2 percent, whichever is 

greater, above the speed at which the device operates. 

VSR0 ........................ Reference Stall Speed in the landing configuration. 

APPENDIX 2.—LIST OF TERMS USED IN THIS NPRM 

[For the reader’s reference and ease of reading, the following list defines terms that are used throughout this document. This appendix will not 

appear in the Code of Federal Regulations.] 

Term Definition 

Airfoil ......................................................... The shape of the wing when looking at its profile. 

Airplane handling qualities ........................ The response of the airplane to control inputs as assessed primarily by a pilot evaluating the ease of 

accomplishing maneuvering tasks. Airplane handling qualities refer to the stability, controllability, 

and maneuverability of the airplane. 

Airplane performance ................................ The capability of the airplane in terms of speeds, distances, weights, flight paths, etc., expressed in 

terms of characteristics like takeoff and landing distances, en route altitude capability, climb and 

descent rates, flight paths, fuel burn, payload capability, range, etc. 

En route ice ............................................... The critical ice accretion appropriate to normal operation of the ice protection system during the en 

route phase of flight. 

Final takeoff ice ......................................... The most critical ice accretion appropriate to normal operation of the ice protection system during 

the final takeoff segment. Ice accretion is assumed to start at liftoff in the takeoff maximum icing 

conditions of 14 CFR part 25, appendix C, part 1, paragraph (c). 

Force reversal ........................................... A reversal in the direction of the force that the pilot needs to apply to perform a specified maneuver 

or achieve a specified load factor. For example, in a maneuver to reduce the load factor, a push 

force on the pitch control is initially needed to begin the maneuver, but changes to a pull force as 

the load factor is reduced. 

Holding ice ................................................ The critical ice accretion appropriate to normal operation of the ice protection system during the 

holding phase of flight. 

Hinge moment ........................................... The rotational force about the hinge of a control surface. Depending on the design of the airplane’s 

flight control system, large hinge moments can result in large forces at the pilot’s control, and 

hinge moment reversals can result in forces reversals. 

Ice-contaminated tailplane stall ................ Ice accretions on the tailplane leading to either completely stalled airflow over the horizontal stabilizer, or an elevator hinge moment reversal due to separated flow on the lower surface of the 

horizontal stabilizer. 

Landing ice ................................................ The critical ice accretion appropriate to normal operation of the ice protection system during the 

landing phase of flight. This is usually the same as holding ice. 

Load factor ................................................ The lift divided by the weight, expressed in units of gravity, or ‘‘g.’’ For example, in straight and level 

flight, the lift equals the weight and the load factor is 1 g. 

Pushover maneuver .................................. A maneuver resulting from the pilot applying a push force to the airplane pitch control to pitch the 

airplane’s nose down. 

Sandpaper ice ........................................... A thin, rough layer of ice. 

Stall ........................................................... Loss of lift caused by the airflow becoming detached from the upper surface of a lifting surface such 

as a wing or tailplane. 

Federal Register / Vol. 70, No. 213 / Friday, November 4, 2005 / Proposed Rules 67297 

6United Express flight 2415 (Sundance 415), a 

British Aerospace BA–3101 Jetstream, operated by 

NPA Inc., (NPA is the name of the airline and is 

not an abbreviation). 

7 ‘‘Effect of Ice on Aircraft Handling 

Characteristics (1984 Trials),’’ Jetstream 31—G–

JSSD, British Aerospace Flight Test Report 

FTR.177/JM, dated May 13, 1985. 

8Comair flight 3272, Empresa Brasileira de 

Aeronautica, S/A (Embraer) EMB–120, operated by 

COMAIR Airlines, Inc. 

9National Transportation Safety Board, 1998. ‘‘InFlight Icing Encounter and Uncontrolled Collision 

With Terrain, Comair Flight 3272, Embraer EMB–

120RT, N265CA, Monroe, Michigan, January 9, 

1997.’’ Aircraft Accident Report NTSB/AR–98/04. 

Washington, DC. 

10 Docket No. FAA–2002–13982, published in the 

Federal Register (67 FR 70812, November 26, 2002). 

APPENDIX 2.—LIST OF TERMS USED IN THIS NPRM—Continued 

[For the reader’s reference and ease of reading, the following list defines terms that are used throughout this document. This appendix will not 

appear in the Code of Federal Regulations.] 

Term Definition 

Takeoff ice ................................................ The critical ice accretion appropriate to normal operation of the ice protection system during the 

takeoff phase of flight, assuming accretion starts at liftoff in the takeoff maximum icing conditions 

of 14 CFR part 25, appendix C, part 1, paragraph (c). 

Tailplane .................................................... The horizontal wing attached to the tail assembly of the airplane.

Appendix 3: Relevant NTSB 

Recommendations 

If adopted, this rulemaking would respond 

to the following National Transportation 

Safety Board (NTSB) Safety 

Recommendations. 

1. Safety Recommendation A–91–87. 

‘‘Amend the icing certification rules to 

require flight tests wherein ice is 

accumulated in those cruise and approach 

flap configurations in which extensive 

exposure to icing conditions can be expected, 

and require subsequent changes in 

configuration, to include landing flaps.’’

[complete text available in the docket] 

This safety recommendation resulted from 

an accident on December 26, 1989, at Pasco, 

Washington, where the airplane stalled due 

to ice-contamination on the tailplane.6 The 

radar data revealed that the airplane was in 

the clouds in icing conditions for almost 91⁄2

minutes. The NTSB determined that the 

probable cause of this accident was the 

flightcrew’s decision to continue an 

unstabilized ILS approach that led to a stall, 

most likely of the horizontal stabilizer, and 

loss of control at low altitude. Contributing 

to the stall and loss of control was the 

accumulation of airframe ice that degraded 

the aerodynamic performance of the 

airplane.7 The airplane was destroyed and 

the two pilots and all four passengers 

received fatal injuries. As discussed in more 

detail later, this notice proposes to require 

applicants to demonstrate during type 

certification that their airplane is not 

susceptible to ice-contaminated tailplane 

stall. 

2. Safety Recommendation A–98–94. 

‘‘Require manufacturers of all turbine-engine 

driven airplanes (including the EMB–120) to 

provide minimum maneuvering airspeed 

information for all airplane configurations, 

phases, and conditions of flight (icing and 

non-icing conditions); minimum airspeeds 

also should take into consideration the 

effects of various types, amounts, and 

locations of ice accumulations, including 

thin amounts of very rough ice, ice 

accumulated in supercooled large droplet 

icing conditions, and tailplane icing.’’

[complete text available on the NTSB Web 

site at: http://ntsb.gov/Recs/letters/1998/ 

A98_88_106.pdf] 

This safety recommendation resulted from 

an accident on January 9, 1997, near Monroe, 

Michigan.8 In that accident, the flightcrew 

were attempting a turning maneuver and did 

not know there was ice on the wing’s leading 

edge. With the degraded aerodynamics due to 

the ice on the wing’s leading edge, the 

airplane was at too low an airspeed to 

conduct the turning maneuver without 

stalling. This caused a rapid descent after an 

uncommanded roll excursion, resulting in a 

crash. The airplane was destroyed and the 2 

flight crewmembers, 1 flight attendant, and 

26 passengers all died. The NTSB determined 

that the probable cause of this accident was 

the FAA’s failure to establish adequate 

aircraft certification standards for flight in 

icing conditions, and to require the 

establishment of adequate minimum airspeed 

for icing conditions.9

As discussed in more detail later, this 

notice proposes to require applicants to 

demonstrate during type certification that 

their airplane has adequate maneuvering 

capabilities in icing conditions. The 

requirements added to part 25 by the 1-g stall 

rule 10 and the requirements proposed in this 

NPRM would ensure that the minimum 

operating speeds determined during the 

certification of all future transport category 

airplanes provide adequate maneuver 

capability in both non-icing and icing 

conditions. 

3. Safety Recommendation A–98–96. 

‘‘Require the manufacturers and operators of 

all airplanes that are certificated to operate 

in icing conditions to install stall warning/ 

protection systems that provide a cockpit 

warning (aural warning and/or stick shaker) 

before the onset of stall when the airplane is 

operating in icing conditions.’’ [complete text 

available on the NTSB Web site at: http:// 

ntsb.gov/Recs/letters/1998/A98_88_106.pdf] 

This safety recommendation resulted from 

the same accident discussed under Safety 

Recommendation A–98–94, above. The 

airplane stalled before either the stall 

warning system or the stall protection system 

activated. As discussed in more detail later, 

this notice proposes to require applicants to 

demonstrate during type certification that 

their airplane provides adequate warning of 

an impending stall in icing conditions. 

Although we do not currently have a part 

25 regulatory requirement for stall warning to 

be provided by a warning device in the 

cockpit, general industry design practice is to 

use a device called a stick shaker to shake the 

control column to warn the pilot of an 

impending stall. 

XIV. Proposed Amendment 

List of Subjects in 14 CFR Part 25: 

Aircraft, Aviation safety, Reporting 

and recordkeeping requirements. 

The Proposed Amendment 

In consideration of the foregoing, the 

Federal Aviation Administration 

proposes to amend part 25 of Title 14, 

Code of Federal Regulations, as follows: 

PART 25—AIRWORTHINESS 

STANDARDS: TRANSPORT 

CATEGORY AIRPLANES 

1. The authority citation for part 25 

continues to read as follows: 

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

44702, and 44704 

2. Amend § 25.21 by adding a new 

paragraph (g) to read as follows: 

§ 25.21 Proof of compliance. 

* * * * * 

(g) The requirements of this subpart 

associated with icing conditions apply 

only if certification for flight in icing 

conditions is desired. If certification for 

flight in icing conditions is desired, the 

following requirements also apply: 

(1) Each requirement of this subpart, 

except §§ 25.121(a), 25.123(c), 

25.143(b)(1) and (b)(2), 25.149, 

25.201(c)(2), 25.207(c) and (d), 25.239, 

and 25.251(b) through (e), must be met 

in icing conditions. Compliance must be 

shown using the ice accretions defined 

in appendix C, 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. 

(2) No changes in the load 

distribution limits of § 25.23, the weight 

limits of § 25.25 (except where limited 

by performance requirements of this 

67298 Federal Register / Vol. 70, No. 213 / Friday, November 4, 2005 / Proposed Rules 

subpart), and the center of gravity limits 

of § 25.27, from those for non-icing 

conditions, are allowed for flight in 

icing conditions or with ice accretion. 

3. Amend § 25.103 by revising 

paragraph (b)(3) to read as follows: 

§ 25.103 Stall speed. 

* * * * * 

(b) * * * 

(3) The airplane in other respects 

(such as flaps, landing gear, and ice 

accretions) in the condition existing in 

the test or performance standard in 

which VSR is being used; 

* * * * * 

4. Amend § 25.105 by revising 

paragraph (a) to read as follows: 

§ 25.105 Takeoff. 

(a) The takeoff speeds prescribed by 

§ 25.107, the accelerate-stop distance 

prescribed by § 25.109, the takeoff path 

prescribed by § 25.111, the takeoff 

distance and takeoff run prescribed by 

§ 25.113, and the net takeoff flight path 

prescribed by § 25.115, must be 

determined in the selected configuration 

for takeoff at each weight, altitude, and 

ambient temperature within the 

operational limits selected by the 

applicant—

(1) In non-icing conditions; and 

(2) In icing conditions, if in the 

configuration of § 25.121(b) with the 

takeoff ice accretion defined in 

appendix C: 

(i) The stall speed at maximum takeoff 

weight exceeds that in non-icing 

conditions by more than the greater of 

3 knots CAS or 3 percent of VSR; or 

(ii) The degradation of the gradient of 

climb determined in accordance with 

§ 25.121(b) is greater than one-half of 

the applicable actual-to-net takeoff flight 

path gradient reduction defined in 

§ 25.115(b). 

* * * * * 

5. Amend § 25.107 by revising 

paragraph (c)(3) and (g)(2) and adding 

new paragraph (h) to read as follows: 

§ 25.107 Takeoff speeds. 

* * * * * 

(c) * * * 

(3) A speed that provides the 

maneuvering capability specified in 

§ 25.143(h). 

* * * * * 

(g) * * * 

(2) A speed that provides the 

maneuvering capability specified in 

§ 25.143(h). 

(h) In determining the takeoff speeds 

V1, VR, and V2 for flight in icing 

conditions, the values of VMCG, VMC, 

and VMU determined for non-icing 

conditions may be used. 

6. Amend § 25.111 by revising 

paragraph (c)(3)(iii), (c)(4), and adding a 

new paragraph (c)(5) to read as follows: 

§ 25.111 Takeoff path. 

* * * * * 

(c) * * * 

(3) * * * 

(iii) 1.7 percent for four-engine 

airplanes. 

(4) The airplane configuration may 

not be changed, except for gear 

retraction and automatic propeller 

feathering, and no change in power or 

thrust that requires action by the pilot 

may be made until the airplane is 400 

feet above the takeoff surface; and 

(5) If § 25.105(a)(2) requires the 

takeoff path to be determined for flight 

in icing conditions, the airborne part of 

the takeoff must be based on the 

airplane drag: 

(i) With the takeoff ice accretion 

defined in appendix C, 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 final takeoff ice accretion 

defined in appendix C, from the point 

where the airplane is 400 feet above the 

takeoff surface to the end of the takeoff 

path. 

* * * * * 

7. Revise § 25.119 to read as follows: 

§ 25.119 Landing climb: All-enginesoperating. 

In the landing configuration, the 

steady gradient of climb may not be less 

than 3.2 percent, with the engines at the 

power or thrust that is available 8 

seconds after initiation of movement of 

the power or thrust controls from the 

minimum flight idle to the go-around 

power or thrust setting—

(a) In non-icing conditions, with a 

climb speed of VREF determined in 

accordance with § 25.125(b)(2)(i); and 

(b) In icing conditions with the 

landing ice accretion defined in 

appendix C, and with a climb speed of 

VREF determined in accordance with 

§ 25.125(b)(2)(ii). 

8. Amend § 25.121 by revising 

paragraphs (b), (c), and (d) to read as 

follows: 

§ 25.121 Climb: One-engine inoperative. 

* * * * * 

(b) Takeoff; landing gear retracted. In 

the takeoff configuration existing at the 

point of the flight path at which the 

landing gear is fully retracted, and in 

the configuration used in § 25.111 but 

without ground effect: 

(1) The steady gradient of climb may 

not be less than 2.4 percent for twoengine airplanes, 2.7 percent for threeengine airplanes, and 3.0 percent for 

four-engine airplanes, at V2 with: 

(i) The critical engine inoperative, the 

remaining engines at the takeoff power 

or thrust available at the time the 

landing gear is fully retracted, 

determined under § 25.111, unless there 

is a more critical power operating 

condition existing later along the flight 

path but before the point where the 

airplane reaches a height of 400 feet 

above the takeoff surface; and 

(ii) The weight equal to the weight 

existing when the airplane’s landing 

gear is fully retracted, determined under 

§ 25.111. 

(2) The requirements of paragraph 

(b)(1) of this section must be met: 

(i) In non-icing conditions; and 

(ii) In icing conditions with the 

takeoff ice accretion defined in 

appendix C, if in the configuration of 

§ 25.121(b) with the takeoff ice 

accretion: 

(A) The stall speed at maximum 

takeoff weight exceeds that in non-icing 

conditions by more than the greater of 

3 knots CAS or 3 percent of VSR; or 

(B) The degradation of the gradient of 

climb determined in accordance with 

§ 25.121(b) is greater than one-half of 

the applicable actual-to-net takeoff flight 

path gradient reduction defined in 

§ 25.115(b). 

(c) Final takeoff. In the en route 

configuration at the end of the takeoff 

path determined in accordance with 

§ 25.111: 

(1) The steady gradient of climb may 

not be less than 1.2 percent for twoengine airplanes, 1.5 percent for threeengine airplanes, and 1.7 percent for 

four-engine airplanes, at VFTO with—

(i) The critical engine inoperative and 

the remaining engines at the available 

maximum continuous power or thrust; 

and 

(ii) The weight equal to the weight 

existing at the end of the takeoff path, 

determined under § 25.111. 

(2) The requirements of paragraph 

(c)(1) of this section must be met: 

(i) In non-icing conditions; and 

(ii) In icing conditions with the final 

takeoff ice accretion defined in 

appendix C, if in the configuration of 

§ 25.121(b) with the takeoff ice 

accretion: 

(A) The stall speed at maximum 

takeoff weight exceeds that in non-icing 

conditions by more than the greater of 

3 knots CAS or 3 percent of VSR; or 

(B) The degradation of the gradient of 

climb determined in accordance with 

§ 25.121(b) is greater than one-half of 

the applicable actual-to-net takeoff flight 

path gradient reduction defined in 

§ 25.115(b). 

(d) Approach. In a configuration 

corresponding to the normal all-enginesoperating procedure in which VSR for 

Federal Register / Vol. 70, No. 213 / Friday, November 4, 2005 / Proposed Rules 67299 

this configuration does not exceed 110 

percent of the VSR for the related allengines-operating landing configuration: 

(1) The steady gradient of climb may 

not be less than 2.1 percent for twoengine airplanes, 2.4 percent for threeengine airplanes, and 2.7 percent for 

four-engine airplanes, with—

(i) The critical engine inoperative, the 

remaining engines at the go-around 

power or thrust setting; 

(ii) The maximum landing weight; 

(iii) A climb speed established in 

connection with normal landing 

procedures, but not exceeding 1.4 VSR; 

and 

(iv) Landing gear retracted. 

(2) The requirements of paragraph 

(d)(1) of this section must be met: 

(i) In non-icing conditions; and 

(ii) In icing conditions with the 

holding ice accretion defined in 

appendix C. 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. 

9. Amend § 25.123 by revising 

paragraphs (a) introductory text and (b) 

to read as follows: 

§ 25.123 En route flight paths. 

(a) For the en route configuration, the 

flight paths prescribed in paragraph (b) 

and (c) of this section must be 

determined at each weight, altitude, and 

ambient temperature, within the 

operating limits established for the 

airplane. The variation of weight along 

the flight path, accounting for the 

progressive consumption of fuel and oil 

by the operating engines, may be 

included in the computation. The flight 

paths must be determined at a speed not 

less than VFTO, with—

* * * * * 

(b) The one-engine-inoperative net 

flight path data must represent the 

actual climb performance diminished by 

a gradient of climb of 1.1 percent for 

two-engine airplanes, 1.4 percent for 

three-engine airplanes, and 1.6 percent 

for four-engine airplanes—

(1) In non-icing conditions; and 

(2) In icing conditions with the en 

route ice accretion defined in appendix 

C, if: 

(i) A speed of 1.18 VSR with the en 

route ice accretion exceeds the en route 

speed selected for non-icing conditions 

by more than the greater of 3 knots CAS 

or 3 percent of VSR; or 

(ii) The degradation of the gradient of 

climb is greater than one-half of the 

applicable actual-to-net flight path 

reduction defined in paragraph (b) of 

this section. 

* * * * * 

10. Revise § 25.125 to read as follows: 

§ 25.125 Landing. 

(a) The horizontal distance necessary 

to land and to come to a complete stop 

(or to a speed of approximately 3 knots 

for water landings) from a point 50 feet 

above the landing surface must be 

determined (for standard temperatures, 

at each weight, altitude, and wind 

within the operational limits established 

by the applicant for the airplane): 

(1) In non-icing conditions; and 

(2) In icing conditions with the 

landing ice accretion defined in 

appendix C if VREF for icing conditions 

exceeds VREF for non-icing conditions 

by more than 5 knots CAS. 

(b) In determining the distance in (a): 

(1) The airplane must be in the 

landing configuration. 

(2) A stabilized approach, with a 

calibrated airspeed of not less than 

VREF, must be maintained down to the 

50-foot height. 

(i) In non-icing conditions, VREF may 

not be less than: 

(A) 1.23 VSR0; 

(B) VMCL established under 

§ 25.149(f); and 

(C) A speed that provides the 

maneuvering capability specified in 

§ 25.143(h). 

(ii) In icing conditions, VREF may not 

be less than: 

(A) The speed determined in 

paragraph (b)(2)(i) of this section; 

(B) 1.23 VSR0 with the landing ice 

accretion defined in appendix C if that 

speed exceeds VREF for non-icing 

conditions by more than 5 knots CAS; 

and 

(C) A speed that provides the 

maneuvering capability specified in 

§ 25.143(h) with the landing ice 

accretion defined in appendix C. 

(3) Changes in configuration, power or 

thrust, and speed, must be made in 

accordance with the established 

procedures for service operation. 

(4) The landing must be made without 

excessive vertical acceleration, tendency 

to bounce, nose over, ground loop, 

porpoise, or water loop. 

(5) The landings may not require 

exceptional piloting skill or alertness. 

(c) For landplanes and amphibians, 

the landing distance on land must be 

determined on a level, smooth, dry, 

hard-surfaced runway. In addition—

(1) The pressures on the wheel 

braking systems may not exceed those 

specified by the brake manufacturer; 

(2) The brakes may not be used so as 

to cause excessive wear of brakes or 

tires; and 

(3) Means other than wheel brakes 

may be used if that means—

(i) Is safe and reliable; 

(ii) Is used so that consistent results 

can be expected in service; and 

(iii) Is such that exceptional skill is 

not required to control the airplane. 

(d) For seaplanes and amphibians, the 

landing distance on water must be 

determined on smooth water. 

(e) For skiplanes, the landing distance 

on snow must be determined on 

smooth, dry, snow. 

(f) The landing distance data must 

include correction factors for not more 

than 50 percent of the nominal wind 

components along the landing path 

opposite to the direction of landing, and 

not less than 150 percent of the nominal 

wind components along the landing 

path in the direction of landing. 

(g) If any device is used that depends 

on the operation of any engine, and if 

the landing distance would be 

noticeably increased when a landing is 

made with that engine inoperative, the 

landing distance must be determined 

with that engine inoperative unless the 

use of compensating means will result 

in a landing distance not more than that 

with each engine operating. 

11. Amend § 25.143 by revising 

paragraphs (c), (d), (e), (f), and (g), and 

by adding new paragraphs (h), (i), and 

(j) to read as follows: 

§ 25.143 General. 

* * * * * 

(c) The airplane must be shown to be 

safely controllable and maneuverable 

with the critical ice accretion 

appropriate to the phase of flight 

defined in appendix C, and with the 

critical engine inoperative and its 

propeller (if applicable) in the minimum 

drag position:—

(1) At the minimum V2 for takeoff; 

(2) During an approach and goaround; and 

(3) During an approach and landing. 

(d) The following table prescribes, for 

conventional wheel type controls, the 

maximum control forces permitted 

during the testing required by paragraph 

(a) through (c) of this section: 

67300 Federal Register / Vol. 70, No. 213 / Friday, November 4, 2005 / Proposed Rules 

Force, in pounds, applied to the control wheel or rudder pedals Pitch Roll Yaw 

For short term application for pitch and roll control—two hands available for control ........................... 75 50 ....................

For short term application for pitch and roll control—one hand available for control ............................. 50 25 ....................

For short term application for yaw control ............................................................................................... .................... .................... 150 

For long term application ......................................................................................................................... 10 5 20 

(e) Approved operating procedures or 

conventional operating practices must 

be followed when demonstrating 

compliance with the control force 

limitations for short term application 

that are prescribed in paragraph (d) of 

this section. The airplane must be in 

trim, or as near to being in trim as 

practical, in the preceding steady flight 

condition. For the takeoff condition, the 

airplane must be trimmed according to 

the approved operating procedures. 

(f) When demonstrating compliance 

with the control force limitations for 

long term application that are 

prescribed in paragraph (d) this section, 

the airplane must be in trim, or as near 

to being in trim as practical. 

(g) When maneuvering at a constant 

airspeed or Mach number (up VFC/MFC), 

the stick forces and the gradient of the 

stick versus maneuvering load factor 

must lie within satisfactory limits. The 

stick forces must not be so great as to 

make excessive demands on the pilot’s 

strength when maneuvering the 

airplane, and must not be so low that 

the airplane can easily be overstressed 

inadvertently. Changes of gradient that 

occur with changes of load factor must 

not cause undue difficulty maintaining 

control of the airplane, and local 

gradients must not be so low as to result 

in a danger of overcontrolling. 

(h) The maneuvering capabilities in a 

constant speed coordinated turn at 

forward center of gravity, as specified in 

the following table, must be free of stall 

warning or other characteristics that 

might interfere with normal 

maneuvering: 

Configuration Speed 

Maneuvering 

bank angle in 

a coordinated 

turn 

Thrust/power setting 

Takeoff .............................................. V2 ................ 30° Asymmetric WAT-limited.1

Takeoff .............................................. V2 + XX2 ..... 40° All-engines-operating climb.3

En route ............................................ VFTO ............ 40° Asymmetric WAT-limited.1

Landing ............................................. VREF ............. 40° Symmetric for ¥3° flight path angle. 

1A combination of weight, altitude, and temperature (WAT) such that the thrust or power setting produces the minimum climb gradient specified in § 25.121 for the flight condition. 2Airspeed approved for all-engines-operating initial climb. 

3That thrust or power setting which, in the event of failure of the critical engine and without any crew action to adjust the thrust or power of the 

remaining engines, would result in the thrust or power specified for the takeoff condition at V2, or any lesser thrust or power setting that is used 

for all-engines-operating initial climb procedures. 

(i) When demonstrating compliance 

with § 25.143 in icing conditions—

(1) Controllability must be 

demonstrated with the ice accretion 

defined in appendix C that is most 

critical for the particular flight phase; 

(2) It must be shown that a push force 

is required throughout a pushover 

maneuver down to a zero g load factor, 

or the lowest load factor obtainable if 

limited by elevator power. It must be 

possible to promptly recover from the 

maneuver without exceeding 50 pounds 

pull control force; and 

(3) Any changes in force that the pilot 

must apply to the pitch control to 

maintain speed with increasing sideslip 

angle must be steadily increasing with 

no force reversals. 

(j) For flight in icing conditions before 

the ice protection system has been 

activated and is performing its intended 

function, the following requirements 

apply: 

(1) If activating the ice protection 

system depends on the pilot seeing a 

specified ice accretion on a reference 

surface (not just the first indication of 

icing), the requirements of § 25.143 

apply with the ice accretion defined in 

appendix C, part II(e). 

(2) For other means of activating the 

ice protection system, it must be 

demonstrated in flight with the ice 

accretion defined in appendix C, part 

II(e) that: 

(i) The airplane is controllable in a 

pull-up maneuver up to 1.5 g load 

factor; and 

(ii) There is no longitudinal control 

force reversal during a pushover 

maneuver down to 0.5 g load factor. 

12. Amend § 25.207 by revising 

paragraph (b), revising paragraphs (e) 

and (f), and adding paragraphs (g) and 

(h) to read as follows: 

§ 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)(2)(ii) of this section, the 

stall warning for flight in icing 

conditions prescribed in paragraph (e) 

of this section must be provided by the 

same means as the stall warning for 

flight in non-icing conditions. 

(c) * * * 

(d) * * * 

(e) In icing conditions, the stall 

warning margin in straight and turning 

flight must be sufficient to allow the 

pilot to prevent stalling (as defined in 

§ 25.201(d)) when the pilot starts a 

recovery maneuver not less than three 

seconds after the onset of stall warning. 

When demonstrating compliance with 

this paragraph, the pilot must perform 

the recovery maneuver in the same way 

as for the airplane in non-icing 

conditions. Compliance with this 

requirement must be demonstrated in 

flight with the speed reduced at rates 

not exceeding one knot per second, 

with—

(1) The en route ice accretion defined 

in appendix C for the en route 

configuration; 

Federal Register / Vol. 70, No. 213 / Friday, November 4, 2005 / Proposed Rules 67301 

(2) The holding ice accretion defined 

in appendix C for the holding and 

approach configurations; 

(3) The landing ice accretion defined 

in appendix C for the landing and goaround configurations; and 

(4) The more critical of the takeoff ice 

and final takeoff ice accretions defined 

in appendix C for each configuration 

used in the takeoff phase of flight. 

(f) The stall warning margin must be 

sufficient in both non-icing and icing 

conditions to allow the pilot to prevent 

stalling when the pilot starts a recovery 

maneuver not less than one second after 

the onset of stall warning in slow-down 

turns with at least 1.5 g load factor 

normal to the flight path and airspeed 

deceleration rates of at least 2 knots per 

second. When demonstrating 

compliance with this paragraph for 

icing conditions, the pilot must perform 

the recovery maneuver in the same way 

as for the airplane in non-icing 

conditions. Compliance with this 

requirement must be demonstrated in 

flight with—

(1) The flaps and landing gear in any 

normal position; 

(2) The airplane trimmed for straight 

flight at a speed of 1.3 VSR; and 

(3) The power or thrust necessary to 

maintain level flight at 1.3 VSR. 

(g) Stall warning must also be 

provided in each abnormal 

configuration of the high lift devices 

that is likely to be used in flight 

following system failures (including all 

configurations covered by Airplane 

Flight Manual procedures). 

(h) For flight in icing conditions 

before the ice protection system has 

been activated and is performing its 

intended function, the following 

requirements apply, with the ice 

accretion defined in appendix C, part 

II(e): 

(1) If activating the ice protection 

system depends on the pilot seeing a 

specified ice accretion on a reference 

surface (not just the first indication of 

icing), the requirements of this section 

apply, except for paragraphs (c) and (d) 

of this section. 

(2) For other means of activating the 

ice protection system, 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 

the speed is reduced at rates not 

exceeding one knot per second and the 

pilot performs the recovery maneuver in 

the same way as for flight in non-icing 

conditions. 

(i) If stall warning is provided by the 

same means as for flight in non-icing 

conditions, the pilot may not start the 

recovery maneuver earlier than one 

second after the onset of stall warning. 

(ii) If stall warning is provided by a 

different means than for flight in nonicing conditions, the pilot may not start 

the recovery maneuver earlier than 3 

seconds after the onset of stall warning. 

Also, compliance must be shown with 

§ 25.203 using the demonstration 

prescribed by § 25.201, except that the 

deceleration rates of § 25.201(c)(2) need 

not be demonstrated. 

13. Amend § 25.237 by revising 

paragraph (a) to read as follows: 

§ 25.237 Wind velocities. 

(a) For landplanes and amphibians, 

the following applies: 

(1) A 90-degree cross component of 

wind velocity, demonstrated to be safe 

for takeoff and landing, must be 

established for dry runways and must be 

at least 20 knots or 0.2 VSRO, whichever 

is greater, except that it need not exceed 

25 knots. 

(2) The crosswind component for 

takeoff established without ice 

accretions is valid in icing conditions. 

(3) The landing crosswind component 

must be established for: 

(i) Non-icing conditions, and 

(ii) Icing conditions with the landing 

ice accretion defined in appendix C. 

* * * * * 

14. Amend § 25.253 by revising 

paragraph (b), and adding a new 

paragraph (c) to read as follows: 

§ 25.253 High-speed characteristics. 

* * * * * 

(b) Maximum speed for stability 

characteristics. VFC/MFC. VFC/MFC is the 

maximum speed at which the 

requirements of §§ 25.143(g), 25.147(e), 

25.175(b)(1), 25.177, and 25.181 must be 

met with flaps and landing gear 

retracted. Except as noted in § 25.253(c), 

VFC/MFC may not be less than a speed 

midway between VMO/MMO and VDF/ 

MDF, except that for altitudes where 

Mach number is the limiting factor, MFC

need not exceed the Mach number at 

which effective speed warning occurs. 

(c) Maximum speed for stability 

characteristics in icing conditions. The 

maximum speed for stability 

characteristics with the ice accretions 

defined in appendix C, at which the 

requirements of §§ 25.143(g), 25.147(e), 

25.175(b)(1), 25.177, and 25.181 must be 

met, is the lower of: 

(1) 300 knots CAS; 

(2) VFC; or 

(3) A speed at which it is 

demonstrated that the airframe will be 

free of ice accretion due to the effects of 

increased dynamic pressure. 

15. Amend § 25.773 by revising 

paragraph (b)(1)(ii) to read as follows: 

§ 25.773 Pilot compartment view. 

* * * * * 

(b) * * * 

(1) * * * 

(i) * * * 

(ii) The icing conditions specified in 

§ 25.1419 if certification for flight in 

icing conditions is requested. 

* * * * * 

16. Amend § 25.941 by revising 

paragraph (c) to read as follows: 

§ 25.941 Inlet, engine, and exhaust 

compatibility. 

* * * * * 

(c) In showing compliance with 

paragraph (b) of this section, the pilot 

strength required may not exceed the 

limits set forth in § 25.143(d), subject to 

the conditions set forth in paragraphs (e) 

and (f) of § 25.143. 

17. Amend § 25.1419 by revising the 

introductory text to read as follows: 

§ 25.1419 Ice protection. 

If certification for flight in icing 

conditions is desired, the airplane must 

be able to safely operate in the 

continuous maximum and intermittent 

maximum icing conditions of appendix 

C. To establish this—

* * * * * 

18. Amend appendix C of part 25 by 

adding a new part I heading and a new 

paragraph (c) to part I; and adding a new 

part II to read as follows: 

Appendix C of Part 25 

Part I—Atmospheric Icing Conditions 

(a) * * * 

(c) Takeoff maximum icing. The 

maximum intensity of atmospheric icing 

conditions for takeoff (takeoff maximum 

icing) is defined by the cloud liquid 

water content of 0.35 g/m3, the mean 

effective diameter of the cloud droplets 

of 20 microns, and the ambient air 

temperature at ground level of minus 9 

degrees Celsius (¥9°C). The takeoff 

maximum icing conditions extend from 

ground level to a height of 1,500 feet 

above the level of the takeoff surface. 

Part II—Airframe Ice Accretions for 

Showing Compliance With Subpart B 

(a) Ice accretions—General. Section 

25.21(g) states that if certification for 

flight in icing conditions is desired, the 

applicable requirements of subpart B 

must be met in the icing conditions of 

appendix C. The most critical ice 

accretion in terms of handling 

characteristics and performance for each 

flight phase must be determined, taking 

into consideration the atmospheric 

conditions of part I of this appendix, 

and the flight conditions (for example, 

configuration, speed, angle-of-attack, 

67302 Federal Register / Vol. 70, No. 213 / Friday, November 4, 2005 / Proposed Rules 

and altitude). The following ice 

accretions must be determined: 

(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 liftoff and 400 feet above the 

takeoff surface, assuming accretion 

starts at liftoff in the takeoff maximum 

icing conditions of part I, paragraph (c) 

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 1,500 feet above 

the takeoff surface, assuming accretion 

starts at liftoff in the takeoff maximum 

icing conditions of part I, paragraph (c) 

of this appendix. 

(3) En route ice is the 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 phase. 

(4) Holding ice is the critical ice 

accretion on the unprotected surfaces, 

and any ice accretion on the protected 

surfaces appropriate to normal ice 

protection system operation, during the 

holding flight phase. 

(5) Landing ice is the critical ice 

accretion on the unprotected surfaces, 

and any ice accretion on the protected 

surfaces appropriate to normal ice 

protection system operation following 

exit from the holding flight phase and 

transition to the final landing 

configuration. 

(6) Sandpaper ice is a thin, rough 

layer of ice. 

(b) In order to reduce the number of 

ice accretions to be considered when 

demonstrating compliance with the 

requirements of § 25.21(g), any of the ice 

accretions defined in paragraph (a) of 

this section may be used for any other 

flight phase if it is shown to be more 

conservative than the specific ice 

accretion defined for that flight phase. 

(c) The ice accretion that has the most 

adverse effect on handling 

characteristics may be used for airplane 

performance tests provided any 

difference in performance is 

conservatively taken into account. 

(d) Ice accretions for the takeoff 

phase. For both unprotected and 

protected parts, the ice accretion may be 

determined by calculation, assuming the 

takeoff maximum icing conditions 

defined in appendix C, and assuming 

that: 

(1) Airfoils, control surfaces and, if 

applicable, propellers are free from 

frost, snow, or ice at the start of the 

takeoff; 

(2) The ice accretion starts at liftoff; 

(3) The critical ratio of thrust/powerto-weight; 

(4) Failure of the critical engine 

occurs at VEF; and 

(5) 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. 

(e) Ice accretion before the ice 

protection system has been activated 

and is performing its intended function. 

The ice accretion before the ice 

protection system has been activated 

and is performing its intended function 

is the ice accretion formed on the 

unprotected and normally protected 

surfaces before activation and effective 

operation of the ice protection system in 

continuous maximum atmospheric icing 

conditions. 

Issued in Washington, DC, on October 24, 

2005. 

John J. Hickey, 

Director, Aircraft Certification Service. 

[FR Doc. 05–21793 Filed 11–3–05; 8:45 am] 

BILLING CODE 4910–13–P