This section of the FEDERAL REGISTER

contains notices to the public of the proposed

issuance of rules and regulations. The

purpose of these notices is to give interested

persons an opportunity to participate in the

rule making prior to the adoption of the final

rules.

Proposed Rules Federal Register

37311 

Vol. 75, No. 124 

Tuesday, June 29, 2010 

DEPARTMENT OF TRANSPORTATION 

Federal Aviation Administration 

14 CFR Parts 25 and 33 

[Docket No. FAA–2010–0636; Notice No. 10– 

10] 

RIN 2120–AJ34 

Airplane and Engine Certification 

Requirements in Supercooled Large 

Drop, Mixed Phase, and Ice Crystal 

Icing Conditions 

AGENCY: Federal Aviation 

Administration (FAA), DOT. 

ACTION: Notice of Proposed Rulemaking 

(NPRM). 

SUMMARY: The Federal Aviation 

Administration proposes to amend the 

airworthiness standards applicable to 

certain transport category airplanes 

certified for flight in icing conditions 

and the icing airworthiness standards 

applicable to certain aircraft engines. 

The proposed regulations would 

improve safety by addressing 

supercooled large drop icing conditions 

for transport category airplanes most 

affected by these icing conditions, 

mixed phase and ice crystal conditions 

for all transport category airplanes, and 

supercooled large drop, mixed phase, 

and ice crystal icing conditions for all 

turbine engines. These proposed 

regulations are the result of information 

gathered from a review of icing 

accidents and incidents. 

DATES: Send your comments on or 

before August 30, 2010. 

ADDRESSES: You may send comments 

identified by Docket Number FAA– 

2010–0636 using any of the following 

methods: 

• Federal eRulemaking Portal: Go to 

http://www.regulations.gov and follow 

the online instructions for sending your 

comments electronically. 

• Mail: Send comments to Docket 

Operations, M–30; U.S. Department of 

Transportation, 1200 New Jersey 

Avenue, SE., Room W12–140, West 

Building Ground Floor, Washington, DC 

20590–0001. 

• Hand Delivery or Courier: Bring 

comments to Docket Operations in 

Room W12–140 of the West Building 

Ground Floor at 1200 New Jersey 

Avenue, SE., Washington, DC, between 

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

Friday, except Federal holidays. 

• Fax: Fax comments to Docket 

Operations at 202–493–2251. 

For more information on the 

rulemaking process, see the 

SUPPLEMENTARY INFORMATION section of 

this document. 

Privacy: The FAA will post all 

comments we receive, without change, 

to http://www.regulations.gov, including 

any personal information you provide. 

Using the search function of our docket 

Web site, anyone can find and read the 

electronic form of all comments 

received into any of our dockets, 

including the name of the individual 

sending the comment (or signing the 

comment for 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://DocketsInfo.dot.gov. 

Docket: To read background 

documents or comments received, go to 

http://www.regulations.gov at any time 

and follow the online instructions for 

accessing the docket. Or, go to Docket 

Operations in Room W12–140 of the 

West Building Ground Floor at 1200 

New Jersey Avenue, SE., Washington, 

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

through Friday, except Federal holidays. 

FOR FURTHER INFORMATION CONTACT: For 

part 25 technical questions contact 

Robert Hettman, FAA, Propulsion/ 

Mechanical Systems Branch, ANM–112, 

Transport Airplane Directorate, Aircraft 

Certification Service, 1601 Lind 

Avenue, SW., Renton, WA 98057–3356; 

telephone (425) 227–2683; facsimile 

(425) 227–1320, e-mail 

robert.hettman@faa.gov. 

For part 33 technical questions 

contact John Fisher, FAA, Rulemaking 

and Policy Branch, ANE–111, Engine 

and Propeller Directorate Standards 

Staff, Aircraft Certification Service, 12 

New England Executive Park, 

Burlington, MA 01803; telephone (781) 

238–7149, facsimile (781) 238–7199, email john.fisher@faa.gov. 

For part 25 legal questions contact 

Douglas Anderson, FAA, Office of the 

Regional Counsel, ANM–7, Northwest 

Mountain Region, 1601 Lind Avenue, 

SW., Renton, WA 98057–3356; 

telephone (425) 227–2166; facsimile 

(425) 227–1007, e-mail 

douglas.anderson@faa.gov. 

For part 33 legal questions contact 

Vince Bennett, FAA, Office of the 

Regional Counsel, ANE–007, New 

England Region, 12 New England 

Executive Park, Burlington, MA 01803; 

telephone (781) 238–7044; facsimile 

(781) 238–7055, e-mail 

vincent.bennett@faa.gov. 

SUPPLEMENTARY INFORMATION: Later in 

this preamble under the Additional 

Information section, the FAA discusses 

how you can comment on this proposal 

and how the agency will handle your 

comments. Included in this discussion 

is related information about the docket, 

privacy, and the handling of proprietary 

or confidential business information. 

The FAA also discusses how you can 

get a copy of this proposal and related 

rulemaking documents. 

Authority for This Rulemaking 

The FAA’s authority to issue rules on 

aviation safety is found in Title 49 of the 

United States Code. Subtitle I, section 

106 describes the authority of the FAA 

Administrator. Subtitle VII, Aviation 

Programs, describes in more detail the 

scope of the agency’s authority. 

This rulemaking is proposed under 

the authority described in subtitle VII, 

part A, subpart III, section 44701, 

‘‘General requirements.’’ Under that 

section, the FAA is charged with 

promoting safe flight of civil aircraft in 

air commerce by prescribing minimum 

standards required in the interest of 

safety for the design and performance of 

aircraft; regulations and minimum 

standards in the interest of safety for 

inspecting, servicing, and overhauling 

aircraft; and regulations for other 

practices, methods, and procedures the 

Administrator finds necessary for safety 

in air commerce. This regulation is 

within the scope of that authority 

because it would prescribe— 

• New safety standards for the design 

and performance of certain transport 

category airplanes and aircraft engines; 

and 

• New safety requirements that are 

necessary for the design, production, 

and operation of those airplanes, and for 

other practices, methods, and 


wwoods2 on DSK1DXX6B1PROD with PROPOSALS
37312 Federal Register / Vol. 75, No. 124 / Tuesday, June 29, 2010 / Proposed Rules 

1Appendix 1 of this preamble contains 

definitions of certain terms used in this notice of 

proposed rulemaking (NPRM). 

procedures relating to those airplanes 

and engines. 

Summary of the Proposal 

The FAA proposes to revise certain 

regulations in Title 14, Code of Federal 

Regulations (14 CFR) part 25 

(Airworthiness Standards: Transport 

Category Airplanes) and part 33 

(Airworthiness Standards: Aircraft 

Engines) related to the certification of 

transport category airplanes and turbine 

aircraft engines in icing conditions. We 

also propose to create new regulations: 

§ 25.1324—Angle of attack systems; 

§ 25.1420 SLD icing conditions; part 25, 

appendix O (SLD icing conditions); part 

33, appendix C (this will be 

intentionally left blank as a 

placeholder); and part 33, appendix D 

(Mixed phase and ice crystal icing 

conditions). To improve the safety of 

transport category airplanes operating in 

SLD, mixed phase, and ice crystal icing 

conditions, the proposed regulations 

would: 

• Expand the certification icing 

environment to include freezing rain 

and freezing drizzle. 

• Require airplanes most affected by 

SLD icing conditions to meet certain 

safety standards in the expanded 

certification icing environment, 

including additional airplane 

performance and handling qualities 

requirements. 

• Expand the engine and engine 

installation certification, and some 

airplane component certification 

regulations (for example, angle of attack 

and airspeed indicating systems), to 

include freezing rain, freezing drizzle, 

ice crystal, and mixed phase icing 

conditions. For certain cases, a subset of 

these icing conditions is proposed. 

The benefits and costs are 

summarized below. The estimated 

benefits are $405.6 million ($99.5 

million present value). The total 

estimated costs are $71.0 million ($54.0 

million present value). On an 

annualized basis, for the time period 

2012–2064, the benefits are $7.0 

million, and the costs are $3.8 million. 

Nominal benefits PV benefits 

Benefits 

Smaller & Medium Airplanes ........................................................................................................ $249,580,915 $69,994,259 

Larger Airplanes ........................................................................................................................... 156,004,884 29,498,469 

Total Benefits ......................................................................................................................... 405,585,799 99,492,728 

(7.0 million annually) 

Costs 

Nominal cost PV cost 

Engine Cert Cost .......................................................................................................................... 7,936,000 6,931,610 

Engine Capital Cost ...................................................................................................................... 6,000,000 5,240,632 

Total Engine .......................................................................................................................... 13,936,000 12,172,242 

Smaller Airplane Certification Cost ............................................................................................... 24,999,039 21,835,129 

New Larger Airplane Certification Cost ........................................................................................ 3,154,600 2,755,350 

Derivative Larger Airplane Certification Cost ............................................................................... 10,438,800 9,117,652 

Hardware Costs ............................................................................................................................ 10,390,000 5,842,024 

Fuel Burn All ................................................................................................................................. 8,046,676 2,261,941 

Total Costs ............................................................................................................................ 70,965,115 53,984,338 

($3.8 million annually) 

Background 

In the 1990s, the FAA became aware 

that the types of icing conditions 

considered during the certification of 

transport category airplanes and turbine 

aircraft engines needed to be expanded 

to increase the level of safety during 

flight in icing. The FAA determined that 

the revised icing certification standards 

should include supercooled large drops 

(SLD), mixed phase, and ice crystals.1

Safety concerns about the adequacy of 

the icing certification standards were 

brought to the forefront of public and 

governmental attention by a 1994 

accident in Roselawn, Indiana, 

involving an Avions de Transport 

Regional ATR 72 series airplane. The 

FAA, Aerospatiale, the French Direction 

Ge ́ne ́ral de l’Aviation Civile, Bureau 

Enquete Accident, the National 

Aeronautics and Space Administration, 

the National Transportation Safety 

Board (NTSB), and others conducted an 

extensive investigation of this accident. 

These investigations led to the 

conclusion that freezing drizzle 

conditions created a ridge of ice on the 

wing’s upper surface aft of the deicing 

boots and forward of the ailerons. It was 

further concluded that this ridge of ice 

contributed to an uncommanded roll of 

the airplane. Based on its investigation, 

the NTSB recommended changes to the 

icing certification requirements. 

The certification requirements for 

icing conditions are specified in part 25, 

appendix C. The atmospheric condition 

(freezing drizzle) that contributed to the 

Roselawn accident is currently outside 

the icing envelope for certifying 

transport category airplanes. The term 

‘‘icing envelope’’ is used within part 25, 

appendix C, and this NPRM to refer to 

the environmental icing conditions 

within which the airplane must be 

shown to be able to safely operate. The 

term ‘‘transport category airplanes’’ is 

used throughout this rulemaking 

document to include all airplanes type 

certificated to part 25 regulations. 

Another atmospheric icing condition 

that is currently outside the icing 

envelope is freezing rain. The FAA has 

not required airplane manufacturers to 

show that airplanes can operate safely 

in freezing drizzle or freezing rain 

conditions. These conditions constitute 

an icing environment known as 

supercooled large drops (SLDs). 

As a result of this accident and 

consistent with related NTSB 


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2NTSB recommendations A–96–54 and A–96–56; 

available in the Docket and on the Internet at: 

http://www.ntsb.gov/Recs/letters/1996/ 

A96_48_69.pdf. 

3Published in the Federal Register, December 8, 

1997 (62 FR 64621). 

4 14 CFR 25.1419, Ice Protection. 

5For a complete discussion of the regulations see 

Amendment 25–121 (72 FR 44665, August 8, 2007), 

and Amendment 25–129 (74 FR 38328, August 3, 

2009). 

6 14 CFR 91.527, Operating in icing conditions; 

and § 135.227, Icing conditions: Operating 

limitations. 

7 14 CFR 121.629(a), Operation in icing 

conditions and § 121.341, Equipment for operations 

in icing conditions. 

8NTSB recommendation A–96–54; available in 

the Docket and on the Internet at: http:// 

www.ntsb.gov/Recs/letters/1996/A96_48_69.pdf. 

9NTSB recommendation A–96–56; available in 

the Docket and on the Internet at: http:// 

www.ntsb.gov/Recs/letters/1996/A96_48_69.pdf. 

recommendations 2 the FAA tasked the 

Aviation Rulemaking Advisory 

Committee (ARAC),3 through its Ice 

Protection Harmonization Working 

Group (IPHWG), to do the following: 

• Define an icing environment that 

includes SLDs. 

• Consider the need to define a mixed 

phase icing environment (supercooled 

liquid and ice crystals). 

• Devise requirements to assess the 

ability of an airplane to either safely 

operate without restrictions in SLD and 

mixed phase conditions or safely 

operate until it can exit these 

conditions. 

• Study the effects icing requirement 

changes could have on §§ 25.773, Pilot 

compartment view; 25.1323, Airspeed 

indicating system; and 25.1325, Static 

pressure systems. 

• Consider the need for a regulation 

on ice protection for angle of attack 

probes. 

This proposed rule is based on the 

ARAC’s recommendations to the FAA. 

Terms used in this notice of proposed 

rulemaking (NPRM) are defined in 

Appendix 1 of this preamble. 

A. Existing Regulations for Flight in 

Icing Conditions 

Currently, the certification regulations 

applicable to transport category 

airplanes for flight in icing conditions 

require that: ‘‘The airplane must be able 

to operate safely in the continuous 

maximum and intermittent maximum 

icing conditions of appendix C.’’ 4 The 

certification regulations also require 

minimum performance and handling 

qualities in these icing conditions and 

methods to detect airframe icing and to 

activate and operate ice protection 

systems.5 Icing regulations applicable to 

engines are in §§ 33.68 and 33.77. 

Operating regulations in parts 91 

(General Operating and Flight Rules) 

and 135 (Operating Requirements: 

Commuter and On Demand Operations) 

address limitations in icing conditions 

for airplanes operated under these 

parts.6 Part 121 (Operating 

Requirements: Domestic, Flag and 

Supplemental Operations) addresses 

operations in icing conditions that 

might adversely affect safety and 

requires installing certain types of ice 

protection equipment and wing 

illumination equipment.7

Some of the part 25 and 33 

regulations specify that the affected 

equipment must be able to operate in 

some or all of the icing conditions 

defined in part 25, appendix C. Other 

regulations within these parts do not 

specify the icing conditions that must be 

considered for airplane certification, 

but, historically, airplane certification 

programs have only considered icing 

conditions that are defined in appendix 

C. 

Appendix C addresses continuous 

maximum and intermittent maximum 

icing conditions within stratiform and 

cumuliform clouds ranging from sea 

level up to 30,000 feet. Appendix C 

defines icing cloud characteristics in 

terms of mean effective drop diameters, 

liquid water content, temperature, 

horizontal and vertical extent, and 

altitude. Icing conditions that contain 

drops with mean effective diameters 

that are larger than the cloud mean 

effective drop diameters defined in 

appendix C are typically referred to as 

freezing drizzle or freezing rain. Icing 

conditions containing freezing drizzle 

and freezing rain are not currently 

considered when certifying an 

airplane’s ice protection systems. 

Because the larger diameter drops 

typically impinge farther aft on the 

airfoil, exposure to these conditions can 

result in ice accretions aft of the ice 

protection area, which can negatively 

affect airplane performance and 

handling qualities. 

Likewise, mixed phase (supercooled 

liquid and ice crystals) and 100% ice 

crystal icing conditions are not 

currently considered when certifying an 

airplane’s ice protection systems. 

Exposing engines and externally 

mounted probes to these conditions 

could result in hazardous ice 

accumulations within the engine that 

may result in engine damage, power 

loss, and loss of or misleading airspeed 

indications. The certification 

regulations for transport category 

airplanes and engines do not address 

the safe operation of airplanes in SLD, 

mixed phase, or ice crystal icing 

conditions and the operating rules do 

not specifically prohibit operations in 

these conditions. 

B. National Transportation Safety Board 

Safety Recommendations 

The NTSB issued NTSB Safety 

Recommendation Numbers A–96–54 8

and A–96–56 9 as a result of the 

Roselawn accident previously 

discussed. This rulemaking activity 

partially addresses the NTSB 

recommendations because there are 

separate rulemaking activities 

associated with revisions to 14 CFR part 

23 regulations for small airplanes and 

14 CFR part 121 operational regulations. 

The NTSB recommendations are as 

follows: 

1. A–96–54 

Revise the icing criteria published in 

14 Code of Federal Regulations (CFR), 

parts 23 and 25, in light of both recent 

research into aircraft ice accretion under 

varying conditions of liquid water 

content, drop size distribution, and 

temperature, and recent developments 

in both the design and use of aircraft. 

Also, expand the appendix C icing 

certification envelope to include 

freezing drizzle/freezing rain and mixed 

water/ice crystal conditions, as 

necessary. (Class II, Priority Action) (A– 

96–54) (Supersedes A–81–116 and— 

118) 

2. A–96–56 

Revise the icing certification testing 

regulation to ensure that airplanes are 

properly tested for all conditions in 

which they are authorized to operate, or 

are otherwise shown to be capable of 

safe flight into such conditions. If safe 

operations can not be demonstrated by 

the manufacturer, operational 

limitations should be imposed to 

prohibit flight in such conditions and 

flightcrews should be provided with the 

means to positively determine when 

they are in icing conditions that exceed 

the limits for aircraft certification. (Class 

II, Priority Action) (A–96–56) 

C. Related Rulemaking Activity 

The ARAC’s Ice Protection 

Harmonization Working Group (IPHWG) 

submitted additional part 121 icing 

rulemaking recommendations to the 

FAA that may lead to future rulemaking, 

but do not directly impact this NPRM. 

Those recommendations would improve 

airplane safety when operating in icing 

conditions. The recommendations 

would: 

• Address when ice protection 

systems must be activated. 


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• Require some airplanes to exit all 

icing conditions after encountering large 

drop icing conditions conducive to ice 

accretions aft of the airframe’s protected 

area. 

D. Advisory Material 

The proposed new AC and revisions 

to existing ACs would provide guidance 

material for one acceptable means, but 

not the only means, of demonstrating 

compliance with the proposed 

regulations contained in this NPRM. 

The guidance provided in these 

documents is directed at airplane 

manufacturers, modifiers, foreign 

regulatory authorities, and FAA 

transport airplane type certification 

engineers, flight test pilots, and their 

designees. The proposed ACs will be 

posted on the ‘‘Aircraft Certification 

Draft Documents Open for Comment’’ 

Web site, http://www.faa.gov/aircraft/ 

draft_docs, after this NPRM is published 

in the Federal Register 

For advisory material related to this 

NPRM, the FAA is: 

• Developing a new AC 25–xx, 

Compliance of Transport Category 

Airplanes with Certification 

Requirements for Flight in Icing 

Conditions. 

• Revising AC 20–147, Turbojet, 

Turboprop, and Turbofan Engine 

Induction System Icing and Ice 

Ingestion. 

• Revising AC 25–25, Performance 

and Handling Characteristics in the 

Icing Conditions Specified in Part 25, 

Appendix C. 

• Revising AC 25.629–1A, Aeroelastic 

Stability Substantiation of Transport 

Category Airplanes. 

• Revising AC 25.1329–1B, Approval 

of Flight Guidance Systems. 

General Discussion of the Proposal 

The FAA proposes to revise certain 

regulations in parts 25 and 33 related to 

the certification of transport category 

airplanes and turbine aircraft engines in 

icing conditions. 

We also propose to create a new: 

§ 25.1324—Angle of attack systems; 

§ 25.1420—Supercooled large drop icing 

conditions; part 25, appendix O 

(supercooled large drop icing 

conditions; part 33, appendix C 

(intentionally left blank); and part 33, 

appendix D (Mixed phase and ice 

crystal icing conditions). Part 33, 

appendix C, is intentionally left blank 

and retained as a placeholder for nonicing related regulations so that part 33, 

appendix C, would not be confused 

with the icing conditions defined in part 

25, appendix C. 

To improve the safety of transport 

category airplanes operating in SLD, 

mixed phase, and ice crystal icing 

conditions, the proposed regulations 

would: 

• Expand the certification icing 

environment to include freezing rain 

and freezing drizzle. 

• Require airplanes most affected by 

SLD icing conditions (transport category 

airplanes with a maximum takeoff 

weight less than 60,000 pounds or with 

reversible flight controls) to meet certain 

safety standards in the expanded 

certification icing environment, 

including additional airplane 

performance and handling qualities 

requirements. 

• Expand the engine and engine 

installation certification, and some 

airplane component certification 

regulations (for example, angle of attack 

and airspeed indicating systems) to 

include freezing rain, freezing drizzle, 

ice crystal, and mixed phase icing 

conditions. For certain cases, a subset of 

these icing conditions is proposed. 

A. Safety Concern 

The ARAC’s IPHWG reviewed icing 

events involving transport category 

airplanes and found accidents and 

incidents that are believed to have 

occurred in icing conditions that are not 

addressed by the current regulations. 

The icing conditions resulted in 

flightcrews losing control of their 

aircraft and, in some cases, engine 

power loss. The review found hull 

losses and fatalities associated with SLD 

conditions, but not for ice crystal and 

mixed phase conditions. However, there 

have been 14 documented cases of ice 

crystal and mixed phase engine power 

loss events between 1988 through 2009. 

Of those events, there were 13 

occurrences of multi-engine power loss 

events. Fifty percent of those events 

were defined as ‘‘aircraft level events,’’ 

since they occurred on multiple engines 

installed on the same airplane. Two of 

these aircraft level events resulted in 

diversions. 

The incident history also indicates 

that flightcrews have experienced 

temporary loss of or misleading airspeed 

indications in icing. Airspeed 

indications on transport category 

airplanes are derived from the 

difference between two air pressures— 

the total pressure, as measured by a 

pitot tube mounted somewhere on the 

fuselage, and the ambient or static 

pressure, as measured by a static port. 

The static port may be flush mounted on 

the airplane fuselage or co-located on 

the pitot tube. When the static and pitot 

systems are co-located, the 

configuration is referred to as a pitotstatic tube. Static ports are not prone to 

collecting ice crystals, either because of 

their flush mounted locations or their 

overall shape. 

Due to the way pitot or pitot-static 

tubes are usually mounted, they are 

prone to collecting ice crystals. 

Encountering high concentrations of ice 

crystals may lead to blocked pitot or 

pitot-static tubes because the energy 

necessary to melt the ice crystals can 

exceed the tubes’ design requirements. 

Pitot or pitot-static tube blockage can 

lead to errors in measuring airspeed. 

The regulatory changes which add ice 

crystal conditions for airspeed 

indicating systems are intended to apply 

to either a pitot tube or pitot-static tube 

configuration. 

The IPHWG did not identify any 

events due to ice accumulations on 

probes that are used to measure angle of 

attack, or other angle of attack sensors. 

However, the IPHWG determined there 

are angle of attack probe designs that are 

susceptible to mixed phase conditions. 

The IPHWG concluded that the 

current regulations do not adequately 

address SLD, mixed phase, and ice 

crystal conditions. The concerns 

regarding mixed phase and ice crystal 

conditions were limited to engines, 

propulsion installations, airspeed 

indications, and angle of attack systems. 

The FAA concurs with the IPHWG’s 

conclusions. 

B. Prior FAA Actions To Address the 

Safety Concern 

The FAA has issued airworthiness 

directives (ADs) to address the unsafe 

conditions associated with operating 

certain airplanes in severe icing 

conditions, which can include SLD 

icing conditions. These ADs are 

applicable to airplanes equipped with 

both reversible flight controls in the roll 

axis and pneumatic deicing boots. The 

ADs require the flightcrews to exit icing 

when visual cues are observed that 

indicate the conditions exceed the 

capabilities of the ice protection 

equipment. In addition, for new 

certifications of airplanes equipped with 

unpowered roll axis controls and 

pneumatic deicing boots, the airplanes 

are evaluated to ensure the roll control 

forces are acceptable if the airplane 

operates in certain SLD conditions. 

However, the scope of these actions is 

limited because they do not address all 

transport category airplanes and do not 

address the underlying safety concern of 

the unknown performance and handling 

qualities safety margins for airplanes 

and engines operating in freezing 

drizzle, freezing rain, mixed phase, and 

ice crystal conditions. The IPHWG 

concluded there is a need to improve 

the regulations to ensure safe operation 


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10These requirements were recently adopted in 

Amendment 25–129 (74 FR 38328, August 3, 2009). 

Generally, that amendment requires methods to 

detect airframe icing and to activate and operate ice 

protection systems. 

of airplanes and engines in these 

conditions. 

C. Alternatives to Rulemaking 

Before proposing new rulemaking, the 

FAA considers alternative ways to solve 

the safety issue under consideration. 

Following is a brief discussion of two of 

the alternatives we considered during 

deliberations on this proposed rule. 

1. Alternative 1: Terminal Area Radar 

and Sensors 

The IPHWG considered the use of 

terminal area radar and ground-based 

sensors to identify areas of SLDs so they 

can be avoided, rather than require 

certification for operations in SLD. 

Equipment for detecting and 

characterizing icing conditions in 

holding areas is being developed. 

However, the equipment would have 

limited coverage area. For areas not 

covered by terminal area radar and 

ground-based sensors, airborne radars 

and sensors are being developed that 

would identify SLD conditions in 

sufficient time for avoidance. These 

ground-based and airborne systems are 

not mature enough to provide sufficient 

protection for all flight operations 

affected by SLD. Even if the equipment 

was mature, rulemaking would still be 

necessary to establish safety margins for 

inadvertent flight into such conditions 

and to provide an option for applicants 

to substantiate that the airplane is 

capable of safe operation in SLD 

conditions. 

2. Alternative 2: Icing Diagnostic and 

Predictive Weather Tools 

The IPHWG considered the use of 

icing diagnostic and predictive weather 

tools to avoid SLD rather than certify an 

airplane to operate in SLD conditions. 

Tools have been developed that can 

provide information on icing and SLD 

potential, but may not report all 

occurrences of SLD. These experimental 

tools are available on the Internet and 

can be used to provide flight planning 

information guidance for avoidance of 

SLD conditions. However, rulemaking 

would still be necessary to establish 

safety margins for inadvertent flight into 

such conditions and to provide an 

option for applicants to substantiate that 

the airplane is capable of safe operation 

in SLD conditions. 

Discussion of the Proposed Regulatory 

Requirements 

Appendix O to Part 25 

The proposed appendix O is 

structured like part 25, appendix C, one 

part defining icing conditions and one 

defining ice accretions. Appendix O, 

part I, would define SLD icing 

conditions and part II would define the 

ice accretions that a manufacturer must 

consider when designing an airplane. 

Supercooled Large Drop Icing 

Conditions 

Proposed § 25.1420 would add safety 

requirements that must be met in SLD 

icing conditions for certain transport 

category airplanes to be certified for 

flight in icing conditions. This change 

would require evaluating the operation 

of these airplanes in the SLD icing 

environment; developing a means to 

differentiate between different SLD 

icing conditions, if necessary; and 

developing procedures to exit all icing 

conditions. 

The proposed regulation would 

require consideration of the SLD icing 

conditions (freezing drizzle and freezing 

rain) defined in a proposed new part 25, 

appendix O, part I, in addition to the 

existing part 25, appendix C, icing 

conditions. Proposed appendix O would 

include drop sizes larger than those 

considered by current icing regulations. 

These larger drops impinge and freeze 

farther aft on airplane surfaces than the 

drops defined in appendix C and may 

affect the airplane’s performance, 

handling qualities, flutter 

characteristics, and engine and systems 

operations. The appendix O icing 

conditions, if adopted, may affect the 

design of airplane ice protection 

systems. 

The SLD icing conditions described in 

the proposed appendix O would be 

those in which the airplane must be able 

to either safely exit following the 

detection of any or specifically 

identified appendix O icing conditions, 

or safely operate without restrictions. 

Specifically, the proposed § 25.1420 

would allow three options: 

• Detect appendix O conditions and 

then operate safely while exiting all 

icing conditions (§ 25.1420(a)(1)). 

• Safely operate in a selected portion 

of appendix O conditions, detect when 

the airplane is operating in conditions 

that exceed the selected portion, and 

then operate safely while exiting all 

icing conditions (§ 25.1420(a)(2)). 

• Operate safely in all of the 

appendix O conditions (§ 25.1420(a)(3)). 

As discussed below in the section 

titled ‘‘Differences from the ARAC 

Recommendations,’’ the proposed 

§ 25.1420 would apply to airplanes with 

either: (1) a takeoff maximum gross 

weight of less than 60,000 pounds, or (2) 

reversible flight controls. 

To establish that an airplane could 

operate safely in the proposed appendix 

O conditions described above, proposed 

§ 25.1420(b) would require both analysis 

and one test, or more as found 

necessary, to establish that the ice 

protection for the various components 

of the airplane is adequate. The words 

‘‘as found necessary’’ would be applied 

in the same way as they are applied in 

§ 25.1419(b). During the certification 

process, the applicant would 

demonstrate compliance with the rule 

using a combination of analyses and 

test(s). The applicant’s means of 

compliance would consist of analyses 

and the amount and types of testing it 

finds necessary to demonstrate 

compliance with the regulation. The 

applicant would choose to use one or 

more of the tests identified in 

paragraphs § 25.1420(b)(1) through 

(b)(5). Although the applicant may 

choose the means of compliance, it is 

ultimately the FAA that determines 

whether the applicant has performed 

sufficient test(s) and analyses to 

substantiate compliance with the 

regulation. Similarly, the words ‘‘as 

necessary,’’ which appear in 

§ 25.1420(b)(3) and (b)(5), would result 

in the applicant choosing the means of 

compliance that is needed to support 

the analysis, but the FAA would make 

a finding whether the means of 

compliance is acceptable. If an 

applicant has adequate data a similarity 

analysis may be used in lieu of the 

testing required by § 25.1420(b). For an 

airplane certified to operate in at least 

a portion of proposed appendix O icing 

conditions, proposed § 25.1420(c) 

would extend the requirements of 

§ 25.1419(e), (f), (g), and (h) 10 to include 

activation and operation of airframe ice 

protection systems in the appendix O 

icing conditions for which the airplane 

is certified. Proposed § 25.1420(c) 

would not apply to airplanes certified to 

proposed § 25.1420(a)(1) because 

proposed § 25.1420(a)(1) would require 

a method to identify and safely exit all 

appendix O conditions. 

The proposed appendix O defines 

SLD conditions. It was developed by the 

ARAC IPHWG, which included 

meteorologists and icing research 

specialists from industry, FAA/FAA 

Tech Center, Meteorological Services of 

Canada, National Aeronautics and 

Space Administration (NASA), and 

Transport Canada/Transport 

Development Center. The IPHWG 

collected and analyzed airborne 

measurements of pertinent SLD 

variables, developed an engineering 

standard to be used in aircraft 

certification, and recommended that 


wwoods2 on DSK1DXX6B1PROD with PROPOSALS
37316 Federal Register / Vol. 75, No. 124 / Tuesday, June 29, 2010 / Proposed Rules 

11 14 CFR 25.21(g)(1) is proposed to be 

redesignated as § 25.21(g)(2). 

12The exceptions listed in this requirement are 

§§ 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). 

13For a complete discussion of these 

requirements, see Amendment 25–121 (72 FR 

44665, August 8, 2007). 

14 14 CFR 25.105, 25.107, 25.109, 25.111, 25.113, 

25.121, and 25.123. 

15 14 CFR 25.773, 25.929, 25.1093, 25.1323, and 

25.1325. 

standard to the FAA. The FAA concurs 

with the recommendation. 

The SLD conditions defined in 

appendix O, part I, include freezing 

drizzle and freezing rain conditions. 

The freezing drizzle and freezing rain 

environments are further divided into 

conditions in which the drop median 

volume diameters are either less than or 

greater than the 40 microns. Appendix 

O consists of measured data that was 

divided into drop distributions within 

these four icing conditions. These 

distributions were averaged to produce 

the representative distributions for each 

condition. 

The distributions of drop sizes are 

defined as part of appendix O. The need 

to include the distributions comes from 

the larger amount of mass in the larger 

drop diameters of appendix O. The 

water mass of the larger drops affects 

the amount of water that impinges on 

airplane components, the drop 

impingement, icing limits, and the ice 

buildup shape. 

Appendix O provides a liquid water 

content scale factor that would be used 

to adjust the liquid water content for 

freezing drizzle and freezing rain. The 

scale factor is based on the liquid water 

contents of continuous freezing drizzle 

and freezing rain conditions decreasing 

with increasing horizontal extents. 

Performance and Handling Qualities 

The ice accretion definitions in 

proposed appendix O, part II, and the 

proposed revisions to the performance 

and handling qualities requirements for 

flight in icing conditions are similar to 

those required for flight in appendix C 

icing conditions. The proposals address 

the three options allowed by proposed 

§ 25.1420(a). Proposed appendix O, part 

II, would contain definitions of the ice 

accretions appropriate to each phase of 

flight. The proposed appendix O, part 

II(b), would define the ice accretions 

used to show compliance with the 

performance and handling qualities 

requirements for any portion of 

appendix O in which the airplane is not 

certified to operate. The proposed 

appendix O, part II(c), would define the 

ice accretions for any portion of 

appendix O in which the airplane is 

certified to operate. 

Proposed appendix O, part II(d), 

would define the ice accretion in 

appendix O conditions before the 

airframe ice protection system is 

activated and is performing its intended 

function to reduce or eliminate ice 

accretions on protected surfaces. This 

ice accretion would be used in showing 

compliance with the controllability and 

stall warning margin requirements of 

§§ 25.143(j) and 25.207(h), respectively, 

that apply before the airframe ice 

protection system has been activated 

and is performing its intended function. 

Even if the airplane is certified to 

operate only in a portion of the 

appendix O icing conditions, the ice 

accretion used to show compliance with 

§§ 25.143(j) and 25.207(h) must consider 

all appendix O icing conditions since 

the initial entry into icing conditions 

may be into appendix O icing 

conditions in which the airplane is not 

certified to operate. 

To reduce the number of ice 

accretions needed to show compliance 

with § 25.21(g), the proposed appendix 

O, part II(e), would allow the option of 

using an ice accretion defined for one 

flight phase for any other flight phase if 

it is shown to be more critical than the 

ice accretion defined for that other flight 

phase. 

Existing § 25.21(g)(1) 11 requires that 

the performance and handling qualities 

requirements of part 25, subpart B, with 

certain exceptions,12 be met in appendix 

C icing conditions.13 Proposed 

§ 25.21(g)(3) would identify the 

performance and handling qualities 

requirements that must be met to ensure 

that an airplane certified to either the 

proposed § 25.1420(a)(1) or (a)(2) could 

safely exit icing if the icing conditions 

of proposed appendix O, for which 

certification is not sought, are 

encountered. Such an airplane would 

not be approved to take off in proposed 

appendix O icing conditions and would 

only need to be able to detect and safely 

exit those icing conditions encountered 

en route. Therefore, it is proposed that, 

in addition to the exceptions identified 

in the existing § 25.21(g)(1), such an 

airplane would not need to meet certain 

requirements 14 for appendix O icing 

conditions. 

With one exception, for an airplane 

certified under proposed § 25.1420(a)(1) 

or (a)(2), the same handling qualities 

requirements that must currently be met 

for flight in appendix C icing conditions 

are proposed for flight in appendix O 

icing conditions for which certification 

is not sought. That exception is 

§ 25.143(c)(1), which addresses 

controllability following engine failure 

during takeoff at V2. Compliance with 

that rule would not be necessary since 

the airplane would not be approved for 

takeoff in appendix O icing conditions. 

No justification for a relaxation of other 

handling qualities requirements could 

be identified. 

The requirements for safe operation in 

all or any portion of proposed appendix 

O icing conditions under proposed 

§ 25.21(g)(4) are similar to those 

currently required for appendix C icing 

conditions. With one exception, the list 

of part 25, subpart B requirements that 

currently do not have to be met for flight 

in appendix C icing conditions would 

not have to be met in proposed 

appendix O icing conditions. The 

exception is that compliance with 

§ 25.121(a), Climb: One-engineinoperative would be required for 

appendix O icing conditions because, 

unlike for appendix C icing conditions, 

the FAA cannot justify an assumption 

that the ice accretion in this flight phase 

can be assumed insignificant. In 

practice, it is expected that some 

applicants may use an operating 

limitation to prohibit takeoff in 

appendix O icing conditions. Otherwise, 

the same rationales behind the 

requirements are used for both appendix 

C and appendix O icing conditions. For 

continued operation in appendix O 

icing conditions, there should 

effectively be no degradation in 

handling qualities, and any degradation 

in performance should be no greater 

than that allowed by the regulations for 

appendix C icing conditions. 

Component Requirements for All Part 

25 Transport Category Airplanes 

In certification programs, both the 

airplane as a whole and its individual 

components are evaluated for flight in 

icing conditions. There are several rules 

in part 25 15 that contain icing related 

requirements for specific components. 

We propose to revise those rules to 

ensure the airplane can safely operate in 

the new icing conditions established in 

this proposed rule. 

Section 25.1419 requires that an 

airplane be able to safely operate in all 

of the conditions specified in appendix 

C, whereas the proposed § 25.1420 

would not require an airplane to safely 

operate in all of the appendix O icing 

conditions. Proposed § 25.1420(a)(1) 

and (a)(2) only require an airplane to be 

capable of safely exiting icing 

conditions after encountering an 

appendix O icing condition for which 

that airplane will not be certified. The 

existing regulations for pilot 

compartment view, airspeed indication 


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16 14 CFR 25.773, 25.1323, and 25.1325. 

17 Ibid. 

18See FAA report DOT/FAA/AR–09/13, 

Technical Compendium from Meetings of the 

Engine Harmonization Working Group, March 2009 

for details on appendix D and its development. 19 14 CFR 25.1323, and 25.1324. 

system, and static pressure system 16

contain requirements for operation in 

icing conditions. These sections would 

be revised to add requirements for 

operation in appendix O icing 

conditions. Section 25.1323, Airspeed 

indicating system, would also be revised 

to include and define mixed phase and 

ice crystal conditions. New proposed 

§ 25.1324 includes an icing requirement 

for angle of attack systems. This would 

be similar to the icing requirements for 

airspeed indication systems. The 

proposed section would require the 

angle of attack system to be heated to 

prevent malfunction in appendices C 

and O icing conditions and in the mixed 

phase and ice crystal conditions defined 

in § 25.1323. 

In the proposed revisions to the 

requirements for pilot compartment 

view, airspeed indication system, and 

static pressure system,17 and the new 

proposed requirements for angle of 

attack systems, an airplane certified in 

accordance with § 25.1420(a)(1) or (a)(2) 

would not be required to be evaluated 

for all of appendix O. For airplanes 

certified in accordance with 

§ 25.1420(a)(1), the icing conditions that 

the airplane is certified to safely exit 

following detection must be considered. 

For airplanes certified in accordance 

with § 25.1420(a)(2), the icing 

conditions that the airplane is certified 

to safely operate in, and to safely exit 

following detection, must be 

considered. For airplanes certified in 

accordance with § 25.1420(a)(3) and for 

airplanes not subject to § 25.1420, all 

icing conditions must be considered. 

Airplanes not certified for flight in icing 

need not consider appendix O. 

The engine induction system icing 

section (§ 25.1093) and propeller 

deicing section (§ 25.929) contain 

requirements for operation in icing 

conditions. As a conservative approach 

to ensure safe operation of an airplane 

in an inadvertent encounter with icing, 

the existing language in § 25.1093 

contains requirements for operation in 

icing conditions, even for an airplane 

that is not approved for flight in icing. 

Since proposed appendix O defines 

icing conditions that also may be 

inadvertently encountered, § 25.1093 

would be revised to reference appendix 

O in its entirety. This would maintain 

the FAA’s conservative approach for 

this section. Section 25.929 (propeller 

deicing) would also be revised to 

reference appendix O in its entirety. 

Sections 25.929 and 25.1323 

generically reference icing instead of 

specifically mentioning appendix C. 

Historically, the icing conditions 

specified in appendix C have been 

applied to these rules. For clarity, we 

are revising §§ 25.929 and 25.1323 so 

they specifically reference appendix C, 

as well as appendix O. The proposed 

revisions to icing regulations for pilot 

compartment view, propellers, engine 

induction system icing protection, 

airspeed indication system, static 

pressure system, and angle of attack 

system would be applicable to all 

transport category airplanes to ensure 

safe operation during operations in icing 

conditions. 

The proposed revisions to § 25.903 

would retain the existing regulations 

and add new subparagraphs to be 

consistent with the proposed part 33 

changes in § 33.68. These revisions 

would allow for approving new aircraft 

type certification programs with engines 

certified to earlier amendment levels. 

The proposed revisions would make it 

clear that the proposed part 33 changes 

would not be retroactively imposed on 

an already type certified engine design, 

unless service history indicated that an 

unsafe condition was present. 

The proposed revision to § 25.929 

clarifies the meaning of the words ‘‘for 

airplanes intended for use where icing 

may be expected.’’ The intent has been 

for the rule to be applicable to airplanes 

certified for flight in icing. 

Engine and Engine Installation 

Requirements 

The proposed revisions to §§ 25.1093, 

33.68, and 33.77 would change the icing 

environmental requirements used to 

evaluate engine protection and 

operation in icing conditions. The 

reason for these changes is that the 

incident history of some airplanes has 

shown that the current icing 

environmental requirements are 

inadequate. The effect of the change 

would be to require an evaluation of 

safe operation in the revised icing 

environment. The proposed revision to 

§ 25.1093 restructures paragraph (b) and 

adds a new Table 1—Icing Conditions 

for Ground Tests. The proposed rules 

would require engines and engine 

installations to operate safely 

throughout the SLD conditions defined 

in proposed new part 25, appendix O, 

and the newly defined mixed phase and 

ice crystal conditions defined in 

proposed new part 33, appendix D.18

The proposed appendix D was 

developed by the ARAC Engine 

Harmonization Working Group and the 

Power Plant Installation Harmonization 

Working Group, which included 

meteorologists and icing research 

specialists from industry, FAA/FAA 

Tech Center, Meteorological Services of 

Canada, National Aeronautics and 

Space Administration (NASA), and 

Transport Canada/Transport 

Development Center. The ARAC 

recommended appendix D and the FAA 

concurs with the recommendation. 

The proposed revision to § 25.1521 

would retain the existing regulations 

and add a new subparagraph that would 

require an additional operating 

limitation for turbine engine 

installations during ground operation in 

icing conditions defined in 

§ 25.1093(b)(2). That operating 

limitation would address the maximum 

time interval between any engine runups from idle and the minimum 

ambient temperature associated with 

that run-up interval. This limitation is 

necessary because we do not currently 

have any specific requirements for runup procedures for engine ground 

operation in icing conditions. The 

engine run-up procedure, including the 

maximum time interval between runups from idle, run-up power setting, 

duration at power, and the minimum 

ambient temperature demonstrated for 

that run-up interval proposed in 

§ 25.1521, would be included in the 

Airplane Flight Manual in accordance 

with existing § 25.1581(a)(1) and 

§ 25.1583(b)(1). 

The engine run-up procedure from 

ground idle to a moderate power or 

thrust setting is necessary to shed ice 

build-up on the fan blades before the 

quantity of ice reaches a level that could 

adversely affect engine operation if ice 

is shed into the engine. The proposed 

revision to § 25.1521 would not require 

additional testing. The ice shedding 

demonstration may be included as part 

of the § 33.68 engine icing testing. 

Operating Limitations 

The proposed revision to § 25.1533 

would establish an operating limitation 

applicable to airplanes that are not 

certified in accordance with proposed 

§ 25.1420(a)(1) or (a)(2). The flightcrews 

of these airplanes would be required to 

exit all icing conditions if they 

encounter appendix O icing conditions 

that the airplane has not been certified 

to operate in. 

Expansion of Proposed Icing 

Requirements 

The proposed regulations 19 for the 

airspeed indicating system and angle of 


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37318 Federal Register / Vol. 75, No. 124 / Tuesday, June 29, 2010 / Proposed Rules 

attack system would address the 

operation of those systems in specific 

mixed phase and ice crystal conditions, 

as defined in proposed Appendix O. 

During the drafting of this NPRM the 

FAA became aware of airspeed 

indicating system malfunctions in 

environmental conditions that may not 

be addressed by these proposed 

regulations. The FAA is reviewing the 

malfunctions and is considering the 

need to change the proposed mixed 

phase and ice crystal parameters to 

include freezing rain. The maximum 

mixed phase and ice crystal parameters 

that we are considering are those 

defined in the proposed part 33, 

appendix D. The freezing rain 

parameters that we are considering are 

based on standards some manufacturers 

have used for airdata probes. The 

maximum freezing rain parameters that 

we are considering are: 

Static air temperature Altitude range Liquid water 

content 

Horizontal extent Droplet 

MVD 

(°C) (ft) (m) (g/m3) (km) (nmiles) (μm) 

¥2 to 0 ......................................................................................................................... 0 to 10 000 0 to 3000 1 100 50 1000 

6 5 3 2000 

15 1 0.5 2000 

We consider the mixed phase and ice 

crystal parameters defined in the 

proposed part 33, appendix D, plus the 

freezing rain parameters defined above 

to be adequate to prevent potential 

airspeed indicating system malfunctions 

in these newly defined environmental 

conditions. We request technical and 

economic comments on whether the 

proposed airspeed indicating system 

and angle of attack system regulations 

should include these expanded 

parameters. Based on comments we 

receive, we may add these parameters to 

the final rule. 

Differences From the ARAC 

Recommendations 

The IPHWG recommended changes to 

parts 25 and 33 to ensure the safe 

operation of airplanes and engines in 

icing conditions. The FAA concurs with 

the recommendations, but has 

determined it is necessary to revise to 

which airplanes the new airplane icing 

certification requirements in the 

proposed § 25.1420 would apply. The 

proposed § 25.1420 in this NPRM would 

apply to airplanes with either: (1) a 

takeoff maximum gross weight of less 

than 60,000 lbs (27,000 kg), or (2) 

reversible flight controls. An airplane 

with reversible flight controls in any 

axis (pitch, roll, or yaw), even if these 

flight controls are aerodynamically 

boosted and/or power-assisted, would 

be considered to have reversible flight 

controls under this proposed rule. An 

airplane with flight controls that are 

irreversible under normal operating 

conditions, but are reversible following 

a failure, would not be considered to 

have reversible flight controls under this 

proposed rule. Reversible, 

aerodynamically boosted, and powerassisted flight controls are defined in 

Appendix 1 to the preamble of this 

NPRM. The ADs described above in 

section B. ‘‘Prior FAA Actions to address 

the Safety Concern’’ are only applicable 

to airplanes equipped with both 

reversible flight controls in the roll axis 

and pneumatic deicing boots. 

A group of IPHWG members (Boeing, 

Airbus, and Embraer, supported by 

Cessna) held a minority position in their 

belief that the applicability of the 

proposed § 25.1420 should exclude 

airplanes with certain design features. 

Their rationale for the position is that 

large transport airplanes still in 

production have not experienced any 

accidents or serious incidents as a result 

of flying in SLD icing conditions. These 

manufacturers proposed that airplanes 

having all three of the following design 

features should be excluded from 

compliance with § 25.1420: 

(1) Gross weight in excess of 60,000 

lbs (27,000 kg); 

(2) Irreversible powered flight 

controls; and 

(3) Wing leading-edge high-lift 

devices. 

These manufacturers included the 

gross weight criterion in this list, in 

part, because size has a direct bearing 

on an airplane’s susceptibility to the 

adverse effects of ice accretion. The size 

of an airplane determines the sensitivity 

of its flight characteristics to ice 

thickness and roughness. The relative 

effect of a given ice height (or ice 

roughness height) decreases as airplane 

size increases. 

The irreversible powered flight 

controls design feature was chosen, in 

part, because using irreversible powered 

flight controls reduces an airplane’s 

susceptibility to SLD conditions. The 

concern that SLD accretions can 

produce hinge moment or other 

anomalous control force/trim effects is 

not applicable to those systems. 

The wing leading-edge high-lift 

devices design feature was chosen, in 

part, because, for wings without ice 

contamination, those devices provide a 

considerable increase in the maximum 

lift coefficient (CLmax) compared to 

fixed leading edges. When wings 

equipped with those devices are 

contaminated with ice, they have 

smaller relative CLmax losses due to ice 

accretion than wings with fixed leading 

edges. 

The IPHWG majority (Air Line Pilots 

Association, International (ALPA), Civil 

Aviation Authority for the United 

Kingdom (CAA/UK), FAA/FAA Tech 

Center, Meteorological Services of 

Canada, National Aeronautics and 

Space Administration (NASA), SAAB, 

Transport Canada/Transport 

Development Center) did not accept the 

exclusion of airplanes with the three 

aforementioned design features because 

one cannot predict with confidence that 

the past service experience of airplanes 

with these specific design features will 

be applicable to future designs. The 

IPHWG majority recommended 

applying the new SLD airplane 

certification requirements proposed in 

the new § 25.1420 to all future transport 

category airplane type designs. 

The IPHWG majority opposed 

limiting the applicability of the rule 

based on airplane gross weight, in part, 

because the ratio of wing and control 

surface sizes to airplane weight varies 

between airplane designs. Therefore, 

airplane takeoff weight is not a 

consistent indicator of lifting and 

control surface size or chord, which are 

the important parameters affecting 

sensitivity to a given ice accretion. 

Excluding airplanes with irreversible 

flight controls was opposed, in part, 

because hinge moment and other 

anomalous control forces are not the 

only concern in SLD icing conditions. 

An irreversible control surface may not 

be deflected by the SLD accumulation 

but the aerodynamic efficiency of the 

control is likely to be degraded by the 

presence of SLD icing in front of the 

control surface. 

Excluding airplanes with wing 

leading edge high-lift devices was 

opposed, in part, because there are 

many different designs for such devices, 

which may not all be equally effective 


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Federal Register / Vol. 75, No. 124 / Tuesday, June 29, 2010 / Proposed Rules 37319 

20The complete IPHWG working group report is 

available on the Internet at http://regulations.gov. A 

copy will also be placed in the docket (FAA–2010– 

0636). 

21A copy of the Initial Regulatory Evaluation 

(dated October 5, 2009) can be found in the docket 

(FAA–2010–0636). 

22 14 CFR 25.773, 25.1323, 25.1324, and 25.1325. 

23 Ibid. 

in mitigating the negative effects of SLD 

ice accretions. The designs for those 

devices include: 

• Slats that may be slotted or sealed 

to the basic wing leading edge, over or 

under deflected, with deflection and 

slotting that may be automated as a 

function of stall warning or airplane 

angle of attack; 

• Krueger flaps that may be slotted or 

sealed to the wing leading edge, flexed 

to optimum curvature or conformed to 

the wing’s leading edge lower surface; 

and 

• Vortilons or some other vortex 

creating devices. 

In addition, for transport category 

airplanes with leading edge high-lift 

devices, the spanwise extent of ice 

protection varies from 100 percent for 

some early turbo-jet airplane slats, to the 

span of two slats for later airplane 

designs, to none for Krueger flaps. The 

variations in the designs lead to varying 

degrees of aerodynamic benefit. Without 

defining the specific performance 

benefits associated with the above 

designs, the potential safety margins for 

SLD conditions cannot be determined. 

The complete minority and majority 

positions are discussed in the working 

group report, which is available in the 

public docket.20

In order to propose a rule with the 

estimated costs commensurate with the 

estimated benefits, the FAA determined 

the applicability of the proposed rule 

should be limited based on service 

histories of certified airplanes, and the 

assumption that similar future designs 

will continue to not experience the 

safety problems addressed by this 

proposal. Therefore, the FAA decided to 

revise the IPHWG rulemaking 

recommendation by incorporating, in 

part, the IPHWG minority position to 

exclude airplanes with certain design 

features. 

The FAA continues to agree with the 

IPHWG majority position that the 

presence (or conversely, the absence) of 

leading edge high lift devices should not 

be used as a basis for determining the 

applicability of the proposed § 25.1420. 

There is insufficient data to conclude 

either that every type of leading edge 

high lift device, or that a specific 

leading edge high lift device design will 

affect (positively or negatively) an 

airplane’s ability to operate in SLD 

atmospheric icing conditions. Also, 

leading edge high lift devices are only 

deployed in certain phases of flight (for 

example, takeoff and landing), and their 

deployment may differ for different flap 

configurations. For example, a leading 

edge slat may be sealed in one flap 

configuration, but slotted (that is, with 

a gap opened up between the trailing 

edge of the slat and the wing) in others. 

Therefore, the applicability of the 

proposed § 25.1420 is not affected by 

the presence or absence of leading edge 

high lift devices. 

We request comment on whether this 

proposed rule, if adopted, should be 

applied to airplanes larger than 60,000 

pounds MTOW or airplanes with other 

design features whose presence or 

absence would result in the airplane 

being susceptible to safety problems 

while operating in the SLD icing 

conditions defined in the proposed 

appendix O, as well as the economic 

analysis associated with these 

decisions.21

This NPRM also differs from the 

ARAC recommendation by proposing a 

revision to § 25.1533 for airplanes not 

certified to operate in all of the SLD 

atmospheric icing conditions specified 

in the proposed new appendix O (that 

is, airplanes certified in accordance 

with proposed § 25.1420(a)(1) or (a)(2)). 

The proposal would establish an 

operating limitation that requires the 

flightcrews to exit all icing conditions if 

they encounter appendix O icing 

conditions in which the airplane has not 

been certified to operate. 

Another difference between this 

NPRM and the ARAC recommendation 

concerns an ARAC recommendation to 

establish separate stall warning margin 

and controllability requirements using 

the ice accretion associated with 

detection of appendix O icing 

conditions that require exiting all icing 

conditions. For airplanes that require 

exiting all icing conditions after 

encountering certain appendix O icing 

conditions, the ARAC recommended 

(and the FAA proposes in this NPRM) 

stall warning margin and controllability 

requirements that must be met with the 

ice accretion existing at the time the 

airplane exits all icing conditions. The 

ARAC was concerned that some future 

airplanes would be incapable of 

complying with these recommended 

requirements without including some 

means to increase the stall warning 

margin and airplane controllability 

upon detection of appendix O icing 

conditions. The ARAC recommended 

applying less stringent stall warning and 

controllability requirements with the ice 

accretion existing at the time appendix 

O icing conditions are detected, before 

the means to increase the stall warning 

margin and airplane controllability 

becomes effective. 

The FAA considers these ARAC 

recommended requirements to add 

significant complexity to the proposed 

rule to address an issue that may not 

arise. The FAA considers it unlikely 

that future airplane designs will include 

means to increase the stall warning 

margin and airplane controllability 

upon detection of appendix O icing 

conditions in addition to the means that 

are incorporated in many current 

transport category airplane designs to 

change the stall warning device 

activation point upon activation of the 

ice protection system. Therefore, these 

ARAC recommendations are not 

included in this NPRM. If needed, the 

FAA can issue special conditions, in 

accordance with § 21.16, to provide 

adequate safety standards in the 

unlikely event that such design features 

are included in a future transport 

category airplane. 

Another difference between this 

NPRM and the ARAC recommendation 

concerns the requirements for pilot 

compartment view, airspeed indication 

system, angle of attack system and static 

pressure system.22 For these rules the 

ARAC recommendation would have 

required airplanes certified in 

accordance with § 25.1420(a)(1) or (a)(2) 

to consider all appendix O icing 

conditions. However, the ARAC 

recommended advisory circular material 

allowed these airplanes to consider less 

than the full appendix O icing 

conditions. The FAA is not proposing 

that these airplanes must meet the 

performance and handling qualities 

requirements for all of the icing 

conditions specified in appendix O. 

Therefore, for pilot compartment view, 

airspeed indication system, angle of 

attack system and static pressure 

system,23 the agency concurs that it 

would only be necessary to show 

compliance under the applicable 

conditions in appendix O. 

Discussion of Working Group NonConsensus Issues 

One goal of the ARAC process is to 

have a working group achieve 

consensus on all of the 

recommendations. The IPHWG did not 

unanimously agree on the following 

issues: 

1. Whether it is necessary to flight test 

in natural SLD icing conditions. 

2. Whether airplanes with certain 

design features should be exempt from 

the recommendation for § 25.1420. 


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24The complete IPHWG working group report is 

available on the Internet at http://regulations.gov. 

The docket number is FAA–2010–0636. 

3. Whether it is acceptable to 

certificate an airplane to a portion of 

appendix O, as proposed in the 

recommendation for § 25.1420(a)(2). 

4. Whether certain icing related 

accidents might have been prevented if 

an accident airplane had complied with 

the recommendations in the IPHWG 

report. 

A detailed discussion of the IPHWG’s 

minority and majority opinions on these 

issues is included in the working group 

report. A copy of the working group 

report is in the public docket.24

The FAA predominantly concurred 

with the ARAC’s recommendations, but 

determined it was necessary to revise 

the applicability of the recommendation 

for § 25.1420, as discussed previously. 

Paperwork Reduction Act 

The Paperwork Reduction Act of 1995 

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

FAA consider the impact of paperwork 

and other information collection 

burdens imposed on the public. The 

information collection requirements 

associated with this NPRM have been 

previously approved by the Office of 

Management and Budget (OMB) under 

the provisions of the Paperwork 

Reduction Act of 1995 (44 U.S.C. 

3507(d)) and have been assigned OMB 

Control Number 2120–0018. 

International Compatibility 

In keeping with U.S. obligations 

under the Convention on International 

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. 

European Aviation Safety Agency 

The European Aviation Safety Agency 

(EASA) was established by the 

European Community to develop 

standards to ensure safety and 

environmental protection, oversee 

uniform application of those standards, 

and promote them internationally. 

EASA formally became responsible for 

certification of aircraft, engines, parts, 

and appliances on September 28, 2003. 

EASA has a project similar to SLD on 

its rulemaking inventory and our intent 

is to harmonize these regulations. 

Regulatory Evaluation, Regulatory 

Flexibility Determination, International 

Trade Analysis, and Unfunded 

Mandates 

Changes to Federal regulations must 

undergo several economic analyses. 

First, Executive Order 12866 directs that 

each Federal agency shall propose or 

adopt a regulation only upon a reasoned 

determination that the benefits of the 

intended regulation justify its costs. 

Second, the Regulatory Flexibility Act 

of 1980 (Pub. L. 96–354) requires 

agencies to analyze the economic 

impact of regulatory changes on small 

entities. Third, the Trade Agreements 

Act (Pub. L. 96–39) prohibits agencies 

from setting standards that create 

unnecessary obstacles to the foreign 

commerce of the United States. In 

developing U.S. standards, this Trade 

Act requires agencies to consider 

international standards and, where 

appropriate, that they be the basis of 

U.S. standards. Fourth, the Unfunded 

Mandates Reform Act of 1995 (Pub. L. 

104–4) requires agencies to prepare a 

written assessment of the costs, benefits, 

and other effects of proposed or final 

rules that include a Federal mandate 

likely to result in the expenditure by 

State, local, or tribal governments, in the 

aggregate, or by the private sector, of 

$100 million or more annually (adjusted 

for inflation with base year of 1995). 

This portion of the preamble 

summarizes the FAA’s analysis of the 

economic impacts of this proposed rule. 

We suggest readers seeking greater 

detail read the full regulatory 

evaluation, a copy of which we have 

placed in the docket for this rulemaking. 

In conducting these analyses, FAA 

has determined that this proposed rule: 

(1) Has benefits that justify its costs; (2) 

is not an economically ‘‘significant 

regulatory action’’ as defined in section 

3(f) of Executive Order 12866; (3) is 

‘‘significant’’ as defined in DOT’s 

Regulatory Policies and Procedures; (4) 

would not have a significant economic 

impact on a substantial number of small 

entities; (5) would not create 

unnecessary obstacles to the foreign 

commerce of the United States; and (6) 

would not impose an unfunded 

mandate on State, local, or tribal 

governments, or on the private sector by 

exceeding the threshold identified 

above. These analyses are summarized 

below. 

Total Benefits and Costs of This Rule 

This NPRM would amend the 

airworthiness standards applicable to 

certain transport category airplanes 

certified for flight in icing conditions 

and the icing airworthiness standards 

applicable to certain aircraft engines. 

The affected fleet and categories of 

benefits and costs are customized to the 

requirements contained in this proposal. 

So, depending on the category and type 

of airplane, the benefits and costs are 

analyzed over different time periods. It 

is important for the reader to focus on 

present value benefits and costs. The 

total estimated benefits are $405.6 

million ($99.5 million present value). 

The total estimated costs are $71.0 

million ($54.0 million present value). 

On an annualized basis, for the time 

period 2012–2064, the benefits are $7.0 

million, and the costs are $3.8 million. 

Therefore, the benefits of the proposed 

rule justify the costs, and the proposed 

rule is cost beneficial. 

Persons Potentially Affected by This 

Rule 

• Part 25 airplane manufacturers. 

• Engine manufacturers. 

• Operators of Affected Equipment. 

Assumptions 

• Discount rate—7%. 

• Costs and benefits are expressed in 

2009 dollars and that both costs and 

benefits start to occur in 2011. We 

conservatively assume that all 

certifications are approved one year 

after the rule is codified (2011), and that 

production/deliveries begin to occur the 

following year (2012). Airplane 

deliveries continue to accumulate until 

the airplane is out of production and 

then begin to retire in the 25th year of 

service. We have customized different 

fleet types (smaller, medium, larger) 

based upon the actual historical 

production cycles and deliveries. The 

varying periods are based on all the 

historical data that we have available. 

The production cycles for smaller 

airplanes are shorter than the 

production cycles of larger airplanes, 

thus the differing time periods. 

• Value of an Averted Fatality—$6.0 

million. 

• Fuel Cost per gallon—$1.92. 

Benefits of This Proposed Rule 

The industry, with the FAA, analyzed 

the SLD events for part 25 certified 

airplanes. We evaluated the events for 

applicability and preventability in 

context with the requirements contained 

in this proposed rule. 

First, we develop an annual risk of a 

catastrophic SLD event per aircraft and 

assume a uniform annual likelihood. 

Next, we multiply the total annual 

affected aircraft by the annual risk per 

aircraft. Lastly, we multiply the total 

annual risk by the estimated cost of an 

average SLD event. When summed over 

time, the total estimated benefits are 


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$405.6 million ($99.5 million present 

value). 

Costs of This Proposed Rule 

The total estimated costs are $71.0 

million ($54.0 million present value). 

We obtained the basis of our cost 

estimates from the industry. The 

manufacturers used accompanying 

advisory circulars (AC) describing 

acceptable means for showing 

compliance. The compliance costs are 

analyzed in context of the part 25 and 

part 33 certification requirements. 

The FAA originally asked ARAC to 

estimate other operational costs beyond 

the additional hardware and fuel 

consumption costs. The additional 

hardware costs would be for SLD ice 

detectors that manufacturers would 

install to be in compliance with the 

proposed requirements. The additional 

hardware costs would be accompanied 

by additional fuel consumption costs 

from the accompanying weight changes 

due to the SLD ice detectors. 

Accordingly, ARAC provided this data 

to the FAA. However, as we neared 

completion of our cost analysis for these 

requirements, we queried individual 

operators and they informed us that 

they were already in compliance and 

there were no additional operational 

costs beyond fuel and hardware. 

As summarized below, the cost 

categories in the regulatory evaluation 

incorporate both certification and 

operational costs. We analyze each cost 

category separately. The cost categories 

in this evaluation are the same as those 

provided by industry to comply with 

the requirements contained in this 

proposal. For this analysis, the 

estimated costs were: 

Nominal Cost PV Cost 

Engine Cert Cost ......................................................................................................................................... $7,936,000 $6,931,610 

Engine Capital Cost ..................................................................................................................................... 6,000,000 5,240,632 

Total Engine ................................................................................................................................................. 13,936,000 12,172,242 

Small Aircraft Certification Cost ................................................................................................................... 24,999,039 21,835,129 

New Large Aircraft Certification Cost .......................................................................................................... 3,154,600 2,755,350 

Amended Type Certificate Large Airplane Certification Cost ..................................................................... 10,438,800 9,117,652 

Hardware Costs ........................................................................................................................................... 10,390,000 5,842,024 

Fuel Burn All ................................................................................................................................................ 8,046,676 2,261,941 

Total ...................................................................................................................................................... 70,965,115 53,984,338 

Alternatives Considered 

Alternative 1—Make all sizes of 

aircraft applicable to the proposal. Not 

all the requirements in this proposal 

extend to larger transport category 

aircraft (those with a maximum takeoff 

weight greater than 60,000 pounds). 

Under this alternative, the proposed 

design requirements would extend to all 

transport category aircraft. This 

alternative was rejected because this 

alternative would add significant cost 

without a commensurate increase in 

benefits. 

Alternative 2—Limit the scope of 

applicability to small aircraft. Although 

this alternative would decrease the 

estimated cost, the FAA believes that 

medium airplanes have the same risk as 

small airplanes. The FAA does not want 

a significant proportion of the future 

fleet to be disproportionately at risk. 

Regulatory Flexibility Determination 

The Regulatory Flexibility Act of 1980 

(Pub. L. 96–354) (RFA) establishes ‘‘as a 

principle of regulatory issuance that 

agencies shall endeavor, consistent with 

the objectives of the rule and of 

applicable statutes, to fit regulatory and 

informational requirements to the scale 

of the businesses, organizations, and 

governmental jurisdictions subject to 

regulation. To achieve this principle, 

agencies are required to solicit and 

consider flexible regulatory proposals 

and to explain the rationale for their 

actions to assure that such proposals are 

given serious consideration.’’ The RFA 

covers a wide-range of small entities, 

including small businesses, not-forprofit organizations, and small 

governmental jurisdictions. 

Agencies must perform a review to 

determine whether a rule will have a 

significant economic impact on a 

substantial number of small entities. If 

the agency determines that it will, the 

agency must prepare a regulatory 

flexibility analysis as described in the 

RFA. 

However, if an agency determines that 

a rule is not expected to have a 

significant economic impact on a 

substantial number of small entities, 

section 605(b) of the RFA provides that 

the head of the agency may so certify 

and a regulatory flexibility analysis is 

not required. The certification must 

include a statement providing the 

factual basis for this determination, and 

the reasoning should be clear. Based on 

the analysis presented below, we 

determined there would not be a 

significant impact on a substantial 

number of small entities. 

Airplane and Engine Manufacturers 

Aircraft and Engine Manufacturers 

would be affected by the requirements 

contained in this proposal. 

For aircraft manufacturers, we use the 

size standards from the Small Business 

Administration for Air Transportation 

and Aircraft Manufacturing specifying 

companies having less than 1,500 

employees as small entities. The current 

United States part 25 airplane 

manufacturers include: Boeing, Cessna 

Aircraft, Gulfstream Aerospace, Learjet 

(owned by Bombardier), Lockheed 

Martin, McDonnell Douglas (a whollyowned subsidiary of The Boeing 

Company), Raytheon Aircraft, and 

Sabreliner Corporation. Because all U.S. 

transport-aircraft category 

manufacturers have more than 1,500 

employees, none are considered small 

entities. 

United States aircraft engine 

manufacturers include: General Electric, 

CFM International, Pratt & Whitney, 

International Aero Engines, Rolls-Royce 

Corporation, Honeywell, and Williams 

International. All but one exceeds the 

Small Business Administration smallentity criteria for aircraft engine 

manufacturers. Williams International is 

the only one of these manufacturers that 

is a U.S. small business. One small 

entity is not a substantial number. 

Operators 

In addition to the certification cost 

incurred by manufacturers, operators 

would incur fuel costs due to the 

estimated additional impact of weight 

changes from equipment on affected 

airplanes. On average, an affected 

airplane would incur additional fuel 

costs of roughly $525 per year. 

Because this proposed rule would 

apply to airplanes that have yet to be 

designed, there would be no immediate 

cost to small entities. However, as of 

2007, there are at least 54 small entity 

operators with 1,500 or fewer employees 

who would qualify as small entities. 


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According to the ‘‘Airliner Price 

Guide,’’ the average cost of a new 

aircraft that would incur such expenses 

is approximately $17 million. The 

corresponding 3-year average total 

aircraft operating expenses on an 

affected per airplane basis was 

$758,000. The estimated additional cost 

of $525 would add only 0.07% to the 

total annual operating expenses. We do 

not consider this a significant economic 

impact. 

Because this proposed rule would not 

have a significant economic impact on 

a substantial number of airplane 

manufacturers, engine manufacturers or 

operators, the FAA certifies that this 

proposed rule would not have a 

significant economic impact on a 

substantial number of small entities. 

The FAA solicits comments regarding 

this determination. 

International Trade Analysis 

The Trade Agreements Act of 1979 

(Pub. L. 96–39), as amended by the 

Uruguay Round Agreements Act (Pub. 

L. 103–465), prohibits Federal agencies 

from establishing standards or engaging 

in related activities that create 

unnecessary obstacles to the foreign 

commerce of the United States. 

Pursuant to these Acts, the 

establishment of standards is not 

considered an unnecessary obstacle to 

the foreign commerce of the United 

States, so long as the standard has a 

legitimate domestic objective, such the 

protection of safety, and does not 

operate in a manner that excludes 

imports that meet this objective. The 

statute also requires consideration of 

international standards and, where 

appropriate, that they be the basis for 

U.S. standards. 

The FAA has assessed the potential 

effect of this proposed rule and 

determined that it would impose the 

same costs on domestic and 

international entities and thus has a 

neutral trade impact. 

Unfunded Mandates Assessment 

Title II of the Unfunded Mandates 

Reform Act of 1995 (Pub. L. 104–4) 

requires each Federal agency to prepare 

a written statement assessing the effects 

of any Federal mandate in a proposed or 

final agency rule that may result in an 

expenditure of $100 million or more (in 

1995 dollars) in any one year by State, 

local, and tribal governments, in the 

aggregate, or by the private sector; such 

a mandate is deemed to be a ‘‘significant 

regulatory action.’’ The FAA currently 

uses an inflation-adjusted value of 

$143.1 million in lieu of $100 million. 

This proposed rule does not contain 

such a mandate; therefore, the 

requirements of Title II do not apply. 

Executive Order 13132, Federalism 

The FAA has 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. 

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 appropriate 

regulatory distinctions. 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. 

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 4(j) 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, while it is a 

‘‘significant regulatory action,’’ it is not 

likely to have a significant adverse effect 

on the supply, distribution, or use of 

energy. 

Plain English 

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 regulations be easier to 

understand if they were divided into 

more (but shorter) sections? 

• Is the description in the preamble 

helpful in understanding the proposed 

regulations? 

Please send your comments to the 

address specified in the ADDRESSES

section of this preamble. 

Additional 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. To ensure the docket 

does not contain duplicate comments, 

please send only one copy of written 

comments, or if you are filing comments 

electronically, please submit your 

comments only one time. 

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. 

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 after 

the comment period has closed if it is 

possible to do so without incurring 

expense or delay. We may change this 

proposal in light of the comments we 

receive. 

Proprietary or Confidential Business 

Information 

Do not file in the docket information 

that you consider to be proprietary or 

confidential business information. Send 

or deliver this information directly to 

the person identified in the FOR FURTHER

INFORMATION CONTACT section of this 

document. You must mark the 

information that you consider 


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proprietary or confidential. If you send 

the information on a disk or CD ROM, 

mark the outside of the disk or CD ROM 

and also identify electronically within 

the disk or CD ROM the specific 

information that is proprietary or 

confidential. 

Under 14 CFR 11.35(b), when we are 

aware of proprietary information filed 

with a comment, we do not place it in 

the docket. We hold it in a separate file 

to which the public does not have 

access, and we place a note in the 

docket that we have received it. If we 

receive a request to examine or copy 

this information, we treat it as any other 

request under the Freedom of 

Information Act (5 U.S.C. 552). We 

process such a request under the DOT 

procedures found in 49 CFR part 7. 

Availability of Rulemaking Documents 

You can get an electronic copy of 

rulemaking documents using the 

Internet by— 

1. Searching the Federal eRulemaking 

Portal (http://www.regulations.gov); 

2. Visiting the FAA’s Regulations and 

Policies web page at http:// 

www.faa.gov/regulations_policies/; 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 or notice 

number of this rulemaking. 

You may access all documents the 

FAA considered in developing this 

proposed rule, including economic 

analyses and technical reports, from the 

internet through the Federal 

eRulemaking Portal referenced in 

paragraph (1). 

The following appendix will not 

appear in the Code of Federal 

Regulations. 

Appendix 1 to the Preamble—Definition 

of Terms Used in This Preamble 

For the purposes of this preamble, the 

following definitions are applicable. 

These definitions of terms are intended 

for use only with this preamble: 

a. Appendix C Icing Conditions: The 

environmental conditions defined in 

appendix C of 14 CFR part 25. 

b. Appendix O Icing Conditions: The 

environmental conditions defined in 

appendix O of 14 CFR part 25. 

c. Drizzle Drop: A drop of water 

measuring 100 μm to 500 μm (0.1–0.5 

mm) in diameter. 

d. Freezing Drizzle (FZDZ): 

Supercooled drizzle drops that remain 

in liquid form and freeze upon contact 

with objects colder than 0°C. 

e. Freezing Rain (FZRA): Supercooled 

rain drops that remain in liquid form 

and freeze upon contact with objects 

colder than 0°C. 

f. Icing Conditions: The presence of 

atmospheric moisture and temperature 

conducive to airplane icing. 

g. Icing Conditions Detector: A device 

that detects the presence of atmospheric 

moisture and temperature conducive to 

airplane icing. 

h. Irreversible Flight Controls: Flight 

controls in the normal operating 

configuration that have loads generated 

at the control surfaces of an airplane 

which are reacted against the actuator 

and its mounting and cannot be 

transmitted directly back to the flight 

deck controls. This term refers to flight 

controls in which all of the force 

necessary to move the pitch, roll, or yaw 

control surfaces is provided by 

hydraulic or electric actuators, the 

motion of which is controlled by signals 

from the flight deck controls. 

i. Liquid Water Content (LWC): The 

total mass of water contained in liquid 

drops within a unit volume or mass of 

air, usually given in units of grams of 

water per cubic meter (g/m3). 

j. Mean Effective Diameter (MED): The 

calculated drop diameter that divides 

the total liquid water content present in 

the drop size distribution in half. Half 

the water volume will be in larger drops 

and half the volume in smaller drops. 

This value is calculated, as opposed to 

being arrived at by measuring actual 

drop size. The MED is based on an 

assumed Langmuir drop size 

distribution. The fact that it is a 

calculated measurement is how it differs 

from median volume diameter, which is 

based on actual drop size. 

k. Median Volume Diameter (MVD): 

The drop diameter that divides the total 

liquid water content present in the drop 

distribution in half. Half the water 

volume will be in larger drops and half 

the volume in smaller drops. The value 

is obtained by actual drop size 

measurements. 

l. Mixed Phase Icing Environment: A 

combination of supercooled liquid and 

ice crystals. 

m. Rain Drop: A drop of water greater 

than 500 μm (0.5 mm) in diameter. 

n. Reversible Flight Controls: Flight 

controls in the normal operating 

configuration that have force or motion 

originating at the airplane’s control 

surface (for example, through 

aerodynamic loads, static imbalance, or 

trim tab inputs) that is transmitted back 

to flight deck controls. This term refers 

to flight deck controls connected to the 

pitch, roll, or yaw control surfaces by 

direct mechanical linkages, cables, or 

push-pull rods in such a way that pilot 

effort produces motion or force about 

the hinge line. 

(1) Aerodynamically boosted flight 

controls: Reversible flight control 

systems that employ a movable tab on 

the trailing edge of the main control 

surface linked to the pilot’s controls or 

to the structure in such a way as to 

produce aerodynamic forces that move, 

or help to move, the surface. Among the 

various forms are flying tabs, geared or 

servo tabs, and spring tabs. 

(2) Power-assisted flight controls: 

Reversible flight control systems in 

which some means is provided, usually 

a hydraulic actuator, to apply force to a 

control surface in addition to that 

supplied by the pilot to enable large 

surface deflections to be obtained at 

high speeds. 

o. Supercooled Large Drops (SLD): 

Supercooled liquid water that includes 

freezing rain or freezing drizzle. 

p. Supercooled Water: Liquid water at 

a temperature below the freezing point 

of 0°C. 

List of Subjects 

14 CFR Part 25 

Aircraft, Aviation safety, Reporting 

and recordkeeping requirements, Safety, 

Transportation. 

14 CFR Part 33 

Aircraft, Aviation safety. 

The Proposed Amendment 

In consideration of the foregoing, the 

Federal Aviation Administration 

proposes to amend Chapter I of Title 14, 

Code of Federal Regulations parts 25 

and 33 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 revising 

paragraphs (g)(1) and (g)(2) and adding 

paragraphs (g)(3) and (g)(4) to read as 

follows: 

§ 25.21 Proof of compliance. 

* * * * * 

(g) * * * 

(1) Paragraphs (g)(3) and (g)(4) of this 

section apply only to airplanes with one 

or both of the following attributes: 

(i) Takeoff maximum gross weight is 

less than 60,000 lbs; or 

(ii) The airplane is equipped with 

reversible flight controls. 


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(2) Each requirement of this subpart, 

except §§ 25.121(a), 25.123(c), 

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

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

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

in the icing conditions specified in 

appendix C of this part. Compliance 

must be shown using the ice accretions 

defined in part II of appendix C of this 

part, assuming normal operation of the 

airplane and its ice protection system in 

accordance with the operating 

limitations and operating procedures 

established by the applicant and 

provided in the Airplane Flight Manual. 

(3) If the applicant does not seek 

certification for flight in all icing 

conditions defined in appendix O of 

this part, each requirement of this 

subpart, except §§ 25.105, 25.107, 

25.109, 25.111, 25.113, 25.115, 25.121, 

25.123, 25.143(b)(1), (b)(2), and (c)(1), 

25.149, 25.201(c)(2), 25.207(c) and (d), 

25.239, and 25.251(b) through (e), must 

be met in the appendix O icing 

conditions for which certification is not 

sought in order to allow a safe exit from 

those conditions. Compliance must be 

shown using the ice accretions defined 

in part II, paragraphs (b) and (d) of 

appendix O of this part, assuming 

normal operation of the airplane and its 

ice protection system in accordance 

with the operating limitations and 

operating procedures established by the 

applicant and provided in the Airplane 

Flight Manual. 

(4) If the applicant seeks certification 

for flight in any portion of the icing 

conditions of appendix O of this part, 

each requirement of this subpart, except 

§§ 25.123(c), 25.143(b)(1) and (2), 

25.149, 25.201(c)(2), 25.207(c) and (d), 

25.239, and 25.251(b) through (e), must 

be met in the appendix O icing 

conditions for which certification is 

sought. Compliance must be shown 

using the ice accretions defined in part 

II, paragraphs (c) and (d) of appendix O 

of this part, assuming normal operation 

of the airplane and its ice protection 

system in accordance with the operating 

limitations and operating procedures 

established by the applicant and 

provided in the Airplane Flight Manual. 

3. Amend § 25.105 by revising 

paragraph (a)(2) introductory text to 

read as follows: 

§ 25.105 Takeoff. 

(a) * * * 

(2) In icing conditions, if in the 

configuration used to show compliance 

with § 25.121(b), and with the most 

critical of the takeoff ice accretion(s) 

defined in appendices C and O of this 

part, as applicable, in accordance with 

§ 25.21(g): 

* * * * * 

4. Amend § 25.111 by revising 

paragraphs (c)(5)(i) and (c)(5)(ii) to read 

as follows: 

§ 25.111 Takeoff path. 

* * * * * 

(c) * * * 

(5) * * * 

(i) With the most critical of the takeoff 

ice accretion(s) defined in appendices C 

and O of this part, as applicable, in 

accordance with § 25.21(g), from a 

height of 35 feet above the takeoff 

surface up to the point where the 

airplane is 400 feet above the takeoff 

surface; and 

(ii) With the most critical of the final 

takeoff ice accretion(s) defined in 

appendices C and O of this part, as 

applicable, in accordance with 

§ 25.21(g), from the point where the 

airplane is 400 feet above the takeoff 

surface to the end of the takeoff path. 

* * * * * 

5. Amend § 25.119 by revising 

paragraph (b) to read as follows: 

§ 25.119 Landing climb: All-enginesoperating. 

* * * * * 

(b) In icing conditions with the most 

critical of the landing ice accretion(s) 

defined in appendices C and O of this 

part, as applicable, in accordance with 

§ 25.21(g), and with a climb speed of 

VREF determined in accordance with 

§ 25.125(b)(2)(ii). 

6. Amend § 25.121 by revising 

paragraphs (b)(2)(ii) introductory text, 

(c)(2)(ii) introductory text, and (d)(2)(ii) 

to read as follows: 

§ 25.121 Climb: One-engine-inoperative. 

* * * * * 

(b) * * * 

(2) * * * 

(ii) In icing conditions with the most 

critical of the takeoff ice accretion(s) 

defined in appendices C and O of this 

part, as applicable, in accordance with 

§ 25.21(g), if in the configuration used to 

show compliance with § 25.121(b) with 

this takeoff ice accretion: 

* * * * * 

(c) * * * 

(2) * * * 

(ii) In icing conditions with the most 

critical of the final takeoff ice 

accretion(s) defined in appendices C 

and O of this part, as applicable, in 

accordance with § 25.21(g), if in the 

configuration used to show compliance 

with § 25.121(b) with the takeoff ice 

accretion used to show compliance with 

§ 25.111(c)(5)(i): 

* * * * * 

(d) * * * 

(2) * * * 

(ii) In icing conditions with the most 

critical of the approach ice accretion(s) 

defined in appendices C and O of this 

part, as applicable, in accordance with 

§ 25.21(g). The climb speed selected for 

non-icing conditions may be used if the 

climb speed for icing conditions, 

computed in accordance with paragraph 

(d)(1)(iii) of this section, does not 

exceed that for non-icing conditions by 

more than the greater of 3 knots CAS or 

3 percent. 

7. Amend § 25.123 by revising 

paragraph (b)(2) introductory text to 

read as follows: 

§ 25.123 En-route flight paths. 

* * * * * 

(b) * * * 

(2) In icing conditions with the most 

critical of the en route ice accretion(s) 

defined in appendices C and O of this 

part, as applicable, in accordance with 

§ 25.21(g), if: 

* * * * * 

8. Amend § 25.125 by revising 

paragraphs (a)(2), (b)(2)(ii)(B), and 

(b)(2)(ii)(C) to read as follows: 

§ 25.125 Landing. 

(a) * * * 

(2) In icing conditions with the most 

critical of the landing ice accretion(s) 

defined in appendices C and O of this 

part, as applicable, in accordance with 

§ 25.21(g), if VREF for icing conditions 

exceeds VREF for non-icing conditions 

by more than 5 knots CAS at the 

maximum landing weight. 

(b) * * * 

(2) * * * 

(ii) * * * 

(B) 1.23 VSR0 with the most critical of 

the landing ice accretion(s) defined in 

appendices C and O of this part, as 

applicable, in accordance with 

§ 25.21(g), if that speed exceeds VREF

selected for non-icing conditions by 

more than 5 knots CAS; and 

(C) A speed that provides the 

maneuvering capability specified in 

§ 25.143(h) with the most critical of the 

landing ice accretion(s) defined in 

appendices C and O of this part, as 

applicable, in accordance with 

§ 25.21(g). 

* * * * * 

9. Amend § 25.143 by revising 

paragraphs (c) introductory text, (i)(1), 

and (j) introductory text to read as 

follows: 

§ 25.143 Controllability and 

maneuverability—General. 

* * * * * 

(c) The airplane must be shown to be 

safely controllable and maneuverable 

with the most critical of the ice 

accretion(s) appropriate to the phase of 

flight as defined in appendices C and O 

of this part, as applicable, in accordance 


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with § 25.21(g), and with the critical 

engine inoperative and its propeller (if 

applicable) in the minimum drag 

position: 

* * * * * 

(i) * * * 

(1) Controllability must be 

demonstrated with the most critical of 

the ice accretion(s) for the particular 

flight phase as defined in appendices C 

and O of this part, as applicable, in 

accordance with § 25.21(g); 

* * * * * 

(j) For flight in icing conditions before 

the ice protection system has been 

activated and is performing its intended 

function, it must be demonstrated in 

flight with the most critical of the ice 

accretion(s) defined in appendix C, part 

II, paragraph (e) of this part and 

appendix O, part II, paragraph (d) of this 

part, as applicable, in accordance with 

§ 25.21(g), that: 

* * * * * 

10. Amend § 25.207 by revising 

paragraphs (b), (e)(1) through (5), and 

(h) introductory text 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)(3)(ii) of this section, the 

stall warning for flight in icing 

conditions must be provided by the 

same means as the stall warning for 

flight in non-icing conditions. 

* * * * * 

(e) * * * 

(1) The most critical of the takeoff ice 

and final takeoff ice accretions defined 

in appendices C and O of this part, as 

applicable, in accordance with 

§ 25.21(g), for each configuration used 

in the takeoff phase of flight; 

(2) The most critical of the en route 

ice accretion(s) defined in appendices C 

and O of this part, as applicable, in 

accordance with § 25.21(g), for the en 

route configuration; 

(3) The most critical of the holding ice 

accretion(s) defined in appendices C 

and O of this part, as applicable, in 

accordance with § 25.21(g), for the 

holding configuration(s); 

(4) The most critical of the approach 

ice accretion(s) defined in appendices C 

and O of this part, as applicable, in 

accordance with § 25.21(g), for the 

approach configuration(s); and 

(5) The most critical of the landing ice 

accretion(s) defined in appendices C 

and O of this part, as applicable, in 

accordance with § 25.21(g), for the 

landing and go-around configuration(s). 

* * * * * 

(h) The following stall warning 

margin is required for flight in icing 

conditions before the ice protection 

system has been activated and is 

performing its intended function. 

Compliance must be shown using the 

most critical of the ice accretion(s) 

defined in appendix C, part II, 

paragraph (e) of this part and appendix 

O, part II, paragraph (d) of this part, as 

applicable, in accordance with 

§ 25.21(g). The stall warning margin in 

straight and turning flight must be 

sufficient to allow the pilot to prevent 

stalling without encountering any 

adverse flight characteristics when: 

* * * * * 

11. Amend § 25.237 by revising 

paragraph (a)(3)(ii) to read as follows: 

§ 25.237 Wind velocities. 

(a) * * * 

(3) * * * 

(ii) Icing conditions with the most 

critical of the landing ice accretion(s) 

defined in appendices C and O of this 

part, as applicable, in accordance with 

§ 25.21(g). 

* * * * * 

12. Amend § 25.253 by revising 

paragraph (c) introductory text to read 

as follows: 

§ 25.253 High-speed characteristics. 

* * * * * 

(c) Maximum speed for stability 

characteristics in icing conditions. The 

maximum speed for stability 

characteristics with the most critical of 

the ice accretions defined in appendices 

C and O of this part, as applicable, in 

accordance with § 25.21(g), 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: 

* * * * * 

13. Amend § 25.773 by revising 

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

§ 25.773 Pilot compartment view. 

* * * * * 

(b) * * * 

(1) * * * 

(ii) The icing conditions specified in 

appendix C and the following icing 

conditions specified in appendix O of 

this part, if certification for flight in 

icing conditions is sought: 

(A) For airplanes certificated in 

accordance with § 25.1420(a)(1), the 

icing conditions that the airplane is 

certified to safely exit following 

detection. 

(B) For airplanes certificated in 

accordance with § 25.1420(a)(2), the 

icing conditions that the airplane is 

certified to safely operate in and the 

icing conditions that the airplane is 

certified to safely exit following 

detection. 

(C) For airplanes certificated in 

accordance with § 25.1420(a)(3) and for 

airplanes not subject to § 25.1420, all 

icing conditions. 

* * * * * 

14. Amend § 25.903 by adding 

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

§ 25.903 Engines. 

(a) * * * 

(3) Each turbine engine must comply 

with one of the following paragraphs: 

(i) Section 33.68 of this chapter in 

effect on [effective date of final rule], or 

as subsequently amended; or 

(ii) Section 33.68 of this chapter in 

effect on February 23, 1984, or as 

subsequently amended before [effective 

date of final rule], unless that engine’s 

ice accumulation service history has 

resulted in an unsafe condition; or 

(iii) Section 33.68 of this chapter in 

effect on October 1, 1974, or as 

subsequently amended prior to February 

23, 1984, unless that engine’s ice 

accumulation service history has 

resulted in an unsafe condition; or 

(iv) Be shown to have an ice 

accumulation service history in similar 

installation locations which has not 

resulted in any unsafe conditions. 

* * * * * 

15. Amend § 25.929 by revising 

paragraph (a) to read as follows: 

§ 25.929 Propeller deicing. 

(a) If certification for flight in icing is 

sought there must be a means to prevent 

or remove hazardous ice accumulations 

that could form in the icing conditions 

defined in appendices C and O of this 

part on propellers or on accessories 

where ice accumulation would 

jeopardize engine performance. 

* * * * * 

16. Amend § 25.1093 by revising 

paragraph (b) to read as follows: 

§ 25.1093 Induction system icing 

protection. 

* * * * * 

(b) Turbine engines. Each engine, with 

all icing protection systems operating, 

must: 

(1) Operate throughout its flight 

power range, including the minimum 

descent idling speeds, in the icing 


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conditions defined in appendices C and 

O of this part, and appendix D of part 

33 of this chapter, and in falling and 

blowing snow within the limitations 

established for the airplane for such 

operation, without the accumulation of 

ice on the engine, inlet system 

components or airframe components 

that would do any of the following: 

(i) Adversely affect installed engine 

operation or cause a sustained loss of 

power or thrust; or an unacceptable 

increase in gas path operating 

temperature; or an airframe/engine 

incompatibility; or 

(ii) Result in unacceptable temporary 

power loss or engine damage; or 

(iii) Cause a stall, surge, or flameout 

or loss of engine controllability (for 

example, rollback). 

(2) Idle for a minimum of 30 minutes 

on the ground in the following icing 

conditions shown in Table 1, unless 

replaced by similar test conditions that 

are more critical. These conditions must 

be demonstrated with the available air 

bleed for icing protection at its critical 

condition, without adverse effect, 

followed by an acceleration to takeoff 

power or thrust. During the idle 

operation the engine may be run up 

periodically to a moderate power or 

thrust setting in a manner acceptable to 

the Administrator. The applicant must 

document the engine run-up procedure 

(including the maximum time interval 

between run-ups from idle, run-up 

power setting, and duration at power) 

and associated minimum ambient 

temperature demonstrated for the 

maximum time interval, and these 

conditions must be used in establishing 

the airplane operating limitations in 

accordance with § 25.1521. 

TABLE 1—ICING CONDITIONS FOR GROUND TESTS

Condition Total air temperature Water concentration 

(minimum) 

Mean effective particle 

diameter Demonstration 

(i) Rime ice condition ..... 0 to 15 °F (¥18 to ¥9 

°C).

Liquid—0.3 g/m3 ............ 15–25 microns ............... By test, analysis or combination of 

the two. 

(ii) Glaze ice condition ... 20 to 30 °F (¥7 to ¥1 

°C).

Liquid—0.3 g/m3 ............ 15–25 microns ............... By test, analysis or combination of 

the two. 

(iii) Large drop condition 15 to 30 °F (¥9 to ¥1 

°C).

Liquid—0.3 g/m3 ............ 100 microns (minimum) By test, analysis or combination of 

the two. 

* * * * * 

17. Amend § 25.1323 by revising 

paragraph (i) to read as follows: 

§ 25.1323 Airspeed indicating system. 

* * * * * 

(i) Each system must have a heated 

pitot tube or an equivalent means of 

preventing malfunction in mixed phase 

and ice crystal conditions as defined in 

Table 1 of this section, the icing 

conditions defined in appendix C of this 

part, and the following icing conditions 

specified in appendix O of this part: 

(1) For airplanes certificated in 

accordance with § 25.1420(a)(1), the 

icing conditions that the airplane is 

certified to safely exit following 

detection. 

(2) For airplanes certificated in 

accordance with § 25.1420(a)(2), the 

icing conditions that the airplane is 

certified to safely operate in and the 

icing conditions that the airplane is 

certified to safely exit following 

detection. 

(3) For airplanes certificated in 

accordance with § 25.1420(a)(3) and for 

airplanes not subject to § 25.1420, all 

icing conditions. 

TABLE 1—ICING CONDITIONS FOR AIRSPEED INDICATING SYSTEM TESTS

Air temperature Altitude range Ice water 

content 

Liquid 

water 

content 

Horizontal extent Ice median mass 

dimension 

Liquid 

water MVD 

(°C) (ft) (m) g/m3 g/m3 (km) (n miles) (μm) (μm) 

0 to ¥20 ..................... 10,000 to 30,000 ....... 3,000 to 9,000 ........... 4 

1 

0.5 

1 

1 

0.5 

5 

100 

500 

3 

50 

300 

100 to 1,000 .............. 20 

¥20 to ¥40 ................ 15,000 to 40,000 ....... 4,500 to 12,000 ......... 5 

2 

1 

0.5 

0 

0 

0 

0 

5 

20 

100 

500 

3 

10 

50 

300 

* * * * * 

18. Add § 25.1324 to read as follows: 

§ 25.1324 Angle of attack system. 

Each angle of attack system sensor 

must be heated or have an equivalent 

means of preventing malfunction in the 

mixed phase and ice crystal conditions 

as defined in § 25.1323, the icing 

conditions defined in appendix C of this 

part, and the following icing conditions 

specified in appendix O of this part: 

(a) For airplanes certificated in 

accordance with § 25.1420(a)(1), the 

icing conditions that the airplane is 

certified to safely exit following 

detection. 

(b) For airplanes certificated in 

accordance with § 25.1420(a)(2), the 

icing conditions that the airplane is 

certified to safely operate in and the 

icing conditions that the airplane is 

certified to safely exit following 

detection. 

(c) For airplanes certificated in 

accordance with § 25.1420(a)(3) and for 

airplanes not subject to § 25.1420, all 

icing conditions. 

19. Amend § 25.1325 by revising 

paragraph (b) to read as follows: 

§ 25.1325 Static pressure systems. 

* * * * * 

(b) Each static port must be designed 

and located so that: 

(1) The static pressure system 

performance is least affected by airflow 

variation, or by moisture or other 

foreign matter, and 

(2) The correlation between air 

pressure in the static pressure system 

and true ambient atmospheric static 

pressure is not changed when the 


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airplane is exposed to the icing 

conditions defined in appendix C of this 

part, and the following icing conditions 

specified in appendix O of this part: 

(i) For airplanes certificated in 

accordance with § 25.1420(a)(1), the 

icing conditions that the airplane is 

certified to safely exit following 

detection. 

(ii) For airplanes certificated in 

accordance with § 25.1420(a)(2), the 

icing conditions that the airplane is 

certified to safely operate in and the 

icing conditions that the airplane is 

certified to safely exit following 

detection. 

(iii) For airplanes certificated in 

accordance with § 25.1420(a)(3) and for 

airplanes not subject to § 25.1420, all 

icing conditions. 

* * * * * 

20. Add § 25.1420 to read as follows: 

§ 25.1420 Supercooled large drop icing 

conditions. 

(a) If certification for flight in icing 

conditions is sought, in addition to the 

requirements of § 25.1419, an airplane 

with a maximum takeoff weight less 

than 60,000 pounds or with reversible 

flight controls must be capable of 

operating in accordance with 

paragraphs (a)(1), (2), or (3), of this 

section. 

(1) Operating safely after encountering 

the icing conditions defined in 

appendix O of this part: 

(i) There must be a means provided to 

detect that the airplane is operating in 

appendix O icing conditions; and 

(ii) Following detection of appendix O 

icing conditions, the airplane must be 

capable of operating safely while exiting 

all icing conditions. 

(2) Operating safely in a portion of the 

icing conditions defined in appendix O 

of this part as selected by the applicant. 

(i) There must be a means provided to 

detect that the airplane is operating in 

conditions that exceed the selected 

portion of appendix O icing conditions; 

and 

(ii) Following detection, the airplane 

must be capable of operating safely 

while exiting all icing conditions. 

(3) Operating safely in the icing 

conditions defined in appendix O of 

this part. 

(b) To establish that the airplane can 

operate safely as required in paragraph 

(a) of this section, an analysis must be 

performed to establish that the ice 

protection for the various components 

of the airplane is adequate, taking into 

account the various airplane operational 

configurations. To verify the analysis, 

one, or more as found necessary, of the 

following methods must be used: 

(1) Laboratory dry air or simulated 

icing tests, or a combination of both, of 

the components or models of the 

components. 

(2) Laboratory dry air or simulated 

icing tests, or a combination of both, of 

models of the airplane. 

(3) Flight tests of the airplane or its 

components in simulated icing 

conditions, measured as necessary to 

support the analysis. 

(4) Flight tests of the airplane with 

simulated ice shapes. 

(5) Flight tests of the airplane in 

natural icing conditions, measured as 

necessary to support the analysis. 

(c) For an airplane certified in 

accordance with paragraph (a)(2) or 

(a)(3) of this section, the requirements of 

§ 25.1419 (e), (f), (g), and (h) must be 

met for the icing conditions defined in 

appendix O of this part in which the 

airplane is certified to operate. 

21. Amend § 25.1521 by redesignating 

paragraph (c)(3) as (c)(4) and revising it, 

and by adding new paragraph (c)(3) to 

read as follows: 

§ 25.1521 Powerplant limitations. 

* * * * * 

(c) * * * 

(3) Maximum time interval between 

engine run-ups from idle, run-up power 

setting, duration at power, and the 

associated minimum ambient 

temperature demonstrated for the 

maximum time interval, for ground 

operation in icing conditions, as defined 

in § 25.1093(b)(2). 

(4) Any other parameter for which a 

limitation has been established as part 

of the engine type certificate except that 

a limitation need not be established for 

a parameter that cannot be exceeded 

during normal operation due to the 

design of the installation or to another 

established limitation. 

* * * * * 

22. Amend § 25.1533 by adding 

paragraph (c) to read as follows: 

§ 25.1533 Additional operating limitations. 

* * * * * 

(c) For airplanes certified in 

accordance with § 25.1420(a)(1) or 

(a)(2), an operating limitation must be 

established to require exiting all icing 

conditions if icing conditions defined in 

appendix O of this part are encountered 

for which the airplane has not been 

certified to safely operate. 

23. Amend part 25 by adding 

Appendix O to part 25 to read as 

follows: 

Appendix O to Part 25—Supercooled 

Large Drop Icing Conditions 

Appendix O consists of two parts. Part I 

defines appendix O as a description of 

supercooled large drop (SLD) icing 

conditions in which the drop median volume 

diameter (MVD) is less than or greater than 

40 μm, the maximum mean effective drop 

diameter (MED) of appendix C continuous 

maximum (stratiform clouds) icing 

conditions. For appendix O, SLD icing 

conditions consist of freezing drizzle and 

freezing rain occurring in and/or below 

stratiform clouds. Part II defines ice 

accretions used to show compliance with 

part 25, subpart B, airplane performance and 

handling qualities requirements. 

Part I—Meteorology 

Appendix O icing conditions are defined 

by the parameters of altitude, vertical and 

horizontal extent, temperature, liquid water 

content, and water mass distribution as a 

function of drop diameter distribution. 

(a) Freezing Drizzle (Conditions with 

spectra maximum drop diameters from 100 

μm to 500 μm): 

(1) Pressure altitude range: 0 to 22,000 feet 

MSL. 

(2) Maximum vertical extent: 12,000 feet. 

(3) Horizontal extent: standard distance of 

17.4 nautical miles. 

(4) Total liquid water content. 

Note: Liquid water content (LWC) in grams 

per cubic meter (g/m3) based on horizontal 

extent standard distance of 17.4 nautical 

miles. 

BILLING CODE 4910–13–P 


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(5) Drop diameter distribution: 


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(6) Altitude and temperature envelope: 


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(b) Freezing Rain (Conditions with spectra 

maximum drop diameters greater than 500 

μm): 

(1) Pressure altitude range: 0 to 12,000 ft 

MSL. 

(2) Maximum vertical extent: 7,000 ft. 

(3) Horizontal extent: standard distance of 

17.4 nautical miles. 

(4) Total liquid water content. 

Note: LWC in grams per cubic meter (g/m3) 

based on horizontal extent standard distance 

of 17.4 nautical miles. 


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(5) Drop Diameter Distribution 


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(6) Altitude and temperature envelope: 


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(c) Horizontal extent. 

The liquid water content for freezing 

drizzle and freezing rain conditions for 

horizontal extents other than the standard 

17.4 nautical miles can be determined by the 

value of the liquid water content determined 

from Figure 1 or Figure 4, multiplied by the 

factor provided in Figure 7. 


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Part II—Airframe Ice Accretions for 

Showing Compliance With Subpart B 

(a) General. 

The most critical ice accretion in terms of 

airplane performance and handling qualities 

for each flight phase must be used to show 

compliance with the applicable airplane 

performance and handling qualities 

requirements for icing conditions contained 

in subpart B of this part. Applicants must 

demonstrate that the full range of 

atmospheric icing conditions specified in 

part I of this appendix have been considered, 

including drop diameter distributions, liquid 

water content, and temperature appropriate 

to the flight conditions (for example, 

configuration, speed, angle-of-attack, and 

altitude). 

(1) For an airplane certified in accordance 

with § 25.1420(a)(1), the ice accretions for 

each flight phase are defined in part II, 

paragraph (b) of this appendix. 

(2) For an airplane certified in accordance 

with § 25.1420(a)(2), the most critical ice 

accretion for each flight phase defined in part 

II, paragraphs (b) and (c) of this appendix, 

must be used. For the ice accretions defined 

in part II, paragraph (c) of this appendix, only 

the portion of part I of this appendix in 

which the airplane is capable of operating 

safely must be considered. 

(3) For an airplane certified in accordance 

with § 25.1420(a)(3), the ice accretions for 

each flight phase are defined in part II, 

paragraph (c) of this appendix. 

(b) Ice accretions for airplanes certified in 

accordance with § 25.1420(a)(1) or (a)(2). 

(1) En route ice is the en route ice as 

defined by part II, paragraph (c)(3), of this 

appendix, for an airplane certified in 

accordance with § 25.1420(a)(2), or defined 

by part II, paragraph (a)(3), of appendix C of 

this part, for an airplane certified in 

accordance with § 25.1420(a)(1), plus: 

(i) Pre-detection ice as defined by part II 

paragraph (b)(5) of this appendix; and 

(ii) The ice accumulated during the transit 

of one cloud with a horizontal extent of 17.4 

nautical miles in the most critical of the icing 

conditions defined in part I of this appendix 

and one cloud with a horizontal extent of 

17.4 nautical miles in the continuous 

maximum icing conditions defined in 

appendix C of this part. 

(2) Holding ice is the holding ice defined 

by part II, paragraph (c)(4), of this appendix, 

for an airplane certified in accordance with 

§ 25.1420(a)(2), or defined by part II, 

paragraph (a)(4) of appendix C of this part, 

for an airplane certified in accordance with 

§ 25.1420(a)(1), plus: 

(i) Pre-detection ice as defined by part II, 

paragraph (b)(5) of this appendix; and 

(ii) The ice accumulated during the transit 

of one cloud with a 17.4 nautical miles 

horizontal extent in the most critical of the 

icing conditions defined in part I of this 

appendix and one cloud with a horizontal 

extent of 17.4 nautical miles in the 

continuous maximum icing conditions 

defined in appendix C of this part. The total 

exposure to the icing conditions need not 

exceed 45 minutes. 

(3) Approach ice is the more critical of the 

holding ice defined by part II, paragraph 

(b)(2) of this appendix, or the ice calculated 

in the applicable paragraph (b)(3)(i) or (ii) of 

part II of this appendix: 

(i) For an airplane certified in accordance 

with § 25.1420(a)(2), the ice accumulated 

during descent from the maximum vertical 

extent of the icing conditions defined in part 

I of this appendix to 2,000 feet above the 

landing surface in the cruise configuration, 

plus transition to the approach configuration, 

plus: 

(A) Pre-detection ice, as defined by part II, 

paragraph (b)(5) of this appendix; and 

(B) The ice accumulated during the transit 

at 2,000 feet above the landing surface of one 

cloud with a horizontal extent of 17.4 

nautical miles in the most critical of the icing 

conditions defined in part I of this appendix 

and one cloud with a horizontal extent of 

17.4 nautical miles in the continuous 


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maximum icing conditions defined in 

appendix C of this part. 

(ii) For an airplane certified in accordance 

with § 25.1420(a)(1), the ice accumulated 

during descent from the maximum vertical 

extent of the maximum continuous icing 

conditions defined in part I of appendix C to 

2,000 feet above the landing surface in the 

cruise configuration, plus transition to the 

approach configuration, plus: 

(A) Pre-detection ice, as defined by part II, 

paragraph (b)(5) of this appendix; and 

(B) The ice accumulated during the transit 

at 2,000 feet above the landing surface of one 

cloud with a horizontal extent of 17.4 

nautical miles in the most critical of the icing 

conditions defined in part I of this appendix 

and one cloud with a horizontal extent of 

17.4 nautical miles in the continuous 

maximum icing conditions defined in 

appendix C of this part. 

(4) Landing ice is the more critical of the 

holding ice as defined by part II, paragraph 

(b)(2) of this appendix, or the ice calculated 

in the applicable paragraph (b)(4)(i) or (ii) of 

part II of this appendix: 

(i) For an airplane certified in accordance 

with § 25.1420(a)(2), the ice accretion defined 

by part II, paragraph (c)(5)(i) of this 

appendix, plus a descent from 2,000 feet 

above the landing surface to a height of 200 

feet above the landing surface with a 

transition to the landing configuration in the 

icing conditions defined in part I of this 

appendix, plus: 

(A) Pre-detection ice, as defined in part II, 

paragraph (b)(5) of this appendix; and 

(B) The ice accumulated during an exit 

maneuver, beginning with the minimum 

climb gradient required by § 25.119, from a 

height of 200 feet above the landing surface 

through one cloud with a horizontal extent 

of 17.4 nautical miles in the most critical of 

the icing conditions defined in part I of this 

appendix and one cloud with a horizontal 

extent of 17.4 nautical miles in the 

continuous maximum icing conditions 

defined in appendix C of this part. 

(ii) For an airplane certified in accordance 

with § 25.1420(a)(1), the ice accumulated in 

the maximum continuous icing conditions 

defined in appendix C of this part, during a 

descent from the maximum vertical extent of 

the icing conditions defined in appendix C 

of this part, to 2,000 feet above the landing 

surface in the cruise configuration, plus 

transition to the approach configuration and 

flying for 15 minutes at 2,000 feet above the 

landing surface, plus a descent from 2,000 

feet above the landing surface to a height of 

200 feet above the landing surface with a 

transition to the landing configuration, plus: 

(A) Pre-detection ice, as described by part 

II, paragraph (b)(5) of this appendix; and 

(B) The ice accumulated during an exit 

maneuver, beginning with the minimum 

climb gradient required by § 25.119, from a 

height of 200 feet above the landing surface 

through one cloud with a horizontal extent 

of 17.4 nautical miles in the most critical of 

the icing conditions defined in part I of this 

appendix and one cloud with a horizontal 

extent of 17.4 nautical miles in the 

continuous maximum icing conditions 

defined in appendix C of this part. 

(5) Pre-detection ice is the ice accretion 

before detection of appendix O conditions 

that require exiting per § 25.1420(a)(1) and 

(a)(2). It is the pre-existing ice accretion that 

may exist from operating in icing conditions 

in which the airplane is approved to operate 

prior to encountering the icing conditions 

requiring an exit, plus the ice accumulated 

during the time needed to detect the icing 

conditions, followed by two minutes of 

further ice accumulation to take into account 

the time for the flight crew to take action to 

exit the icing conditions, including 

coordination with air traffic control. 

(i) For an airplane certified in accordance 

with § 25.1420(a)(1), the pre-existing ice 

accretion must be based on the icing 

conditions defined in appendix C of this part. 

(ii) For an airplane certified in accordance 

with § 25.1420(a)(2), the pre-existing ice 

accretion must be based on the more critical 

of the icing conditions defined in appendix 

C of this part, or the icing conditions defined 

in part I of this appendix in which the 

airplane is capable of safely operating. The 

pre-detection ice accretion applies in 

showing compliance with §§ 25.143(k) and 

25.207(k), and as part of the ice accretion 

definitions of part II, paragraph (b)(1) through 

(b)(4) of this appendix. 

(c) Ice accretions for airplanes certified in 

accordance with §§ 25.1420(a)(2) or 

25.1420(a)(3). For an airplane certified in 

accordance with § 25.1420(a)(2), only the 

portion of the icing conditions of part I of 

this appendix in which the airplane is 

capable of operating safely must be 

considered. 

(1) Takeoff ice is the most critical ice 

accretion on unprotected surfaces, and any 

ice accretion on the protected surfaces 

appropriate to normal ice protection system 

operation, occurring between liftoff and 400 

feet above the takeoff surface, assuming 

accretion starts at liftoff in the icing 

conditions defined in part I of this appendix. 

(2) Final takeoff ice is the most critical ice 

accretion on unprotected surfaces, and any 

ice accretion on the protected surfaces 

appropriate to normal ice protection system 

operation, between 400 feet and either 1,500 

feet above the takeoff surface, or the height 

at which the transition from the takeoff to the 

en route configuration is completed and VFTO

is reached, whichever is higher. Ice accretion 

is assumed to start at liftoff in the icing 

conditions defined in part I of this appendix. 

(3) En route ice is the most critical ice 

accretion on the unprotected surfaces, and 

any ice accretion on the protected surfaces 

appropriate to normal ice protection system 

operation, during the en route flight phase in 

the icing conditions defined in part I of this 

appendix. 

(4) Holding ice is the most critical ice 

accretion on the unprotected surfaces, and 

any ice accretion on the protected surfaces 

appropriate to normal ice protection system 

operation, resulting from 45 minutes of flight 

within a cloud with a 17.4 nautical miles 

horizontal extent in the icing conditions 

defined in part I of this appendix, during the 

holding phase of flight. 

(5) Approach ice is the ice accretion on the 

unprotected surfaces, and any ice accretion 

on the protected surfaces appropriate to 

normal ice protection system operation, 

resulting from the more critical of the: 

(i) Ice accumulated in the icing conditions 

defined in part I of this appendix during a 

descent from the maximum vertical extent of 

the icing conditions defined in part I of this 

appendix, to 2,000 feet above the landing 

surface in the cruise configuration, plus 

transition to the approach configuration and 

flying for 15 minutes at 2,000 feet above the 

landing surface; or 

(ii) Holding ice as defined by part II, 

paragraph (c)(4) of this appendix. 

(6) Landing ice is the ice accretion on the 

unprotected surfaces, and any ice accretion 

on the protected surfaces appropriate to 

normal ice protection system operation, 

resulting from the more critical of the: 

(i) Ice accretion defined by part II, 

paragraph (c)(5)(i), of this appendix, plus ice 

accumulated in the icing conditions defined 

in part I of this appendix during a descent 

from 2,000 feet above the landing surface to 

a height of 200 feet above the landing surface 

with a transition to the landing configuration, 

followed by a go-around at the minimum 

climb gradient required by § 25.119, from a 

height of 200 feet above the landing surface 

to 2,000 feet above the landing surface, flying 

for 15 minutes at 2,000 feet above the landing 

surface in the approach configuration, and a 

descent to the landing surface (touchdown) 

in the landing configuration; or 

(ii) Holding ice as defined by part II 

paragraph (c)(4) of this appendix. 

(7) For both unprotected and protected 

parts, the ice accretion for the takeoff phase 

must be determined for the icing conditions 

defined in part I of this appendix, using the 

following assumptions: 

(i) The airfoils, control surfaces, and, if 

applicable, propellers are free from frost, 

snow, or ice at the start of takeoff; 

(ii) The ice accretion begins at liftoff; 

(iii) The critical ratio of thrust/power-toweight; 

(iv) Failure of the critical engine occurs at 

VEF; and 

(v) Crew activation of the ice protection 

system is in accordance with a normal 

operating procedure provided in the Airplane 

Flight Manual, except that after beginning the 

takeoff roll, it must be assumed that the crew 

takes no action to activate the ice protection 

system until the airplane is at least 400 feet 

above the takeoff surface. 

(d) The ice accretion before the ice 

protection system has been activated and is 

performing its intended function is the 

critical ice accretion formed on the 

unprotected and normally protected surfaces 

before activation and effective operation of 

the ice protection system in the icing 

conditions defined in part I of this appendix. 

This ice accretion only applies in showing 

compliance to §§ 25.143(j) and 25.207(h). 

(e) In order to reduce the number of ice 

accretions to be considered when 

demonstrating compliance with the 

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

accretions defined in this appendix may be 

used for any other flight phase if it is shown 

to be more critical than the specific ice 

accretion defined for that flight phase. 

Configuration differences and their effects on 

ice accretions must be taken into account. 

(f) The ice accretion that has the most 

adverse effect on handling qualities may be 


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used for airplane performance tests provided 

any difference in performance is 

conservatively taken into account. 

PART 33—AIRWORTHINESS 

STANDARDS: AIRCRAFT ENGINES 

24. The authority citation for part 33 

continues to read as follows: 

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

44702, 44704. 

25. Revise § 33.68 to read as follows: 

§ 33.68 Induction system icing. 

Each engine, with all icing protection 

systems operating, must: 

(a) Operate throughout its flight 

power range, including the minimum 

descent idle rotor speeds achievable in 

flight, in the icing conditions defined in 

appendices C and O of part 25 of this 

chapter, and appendix D of this part 33, 

without the accumulation of ice on the 

engine components that: 

(1) Adversely affects engine operation 

or that causes an unacceptable 

permanent loss of power or thrust or 

unacceptable increase in engine 

operating temperature; or 

(2) Results in unacceptable temporary 

power loss or engine damage; or 

(3) Causes a stall, surge, or flameout 

or loss of engine controllability (for 

example, rollback). The applicant must 

account for in-flight ram effects (for 

example; scoop factor amplification, 

water temperature, air density) in any 

critical point analysis or test 

demonstration of these flight conditions. 

(b) Operate throughout its flight 

power range, including minimum 

descent idle rotor speeds achievable in 

flight, in the icing conditions defined in 

appendices C and O of part 25 of this 

chapter. In addition, 

(1) It must be shown through Critical 

Point Analysis (CPA) that the complete 

ice envelope has been analyzed, and 

that the most critical points must be 

demonstrated by engine test, analysis or 

a combination of the two to operate 

acceptably. Extended flight in critical 

flight conditions such as hold, descent, 

approach, climb, and cruise, must be 

addressed, for the ice conditions 

defined in these appendices. 

(2) It must be shown by engine test, 

analysis or a combination of the two 

that the engine can operate acceptably 

for the following durations: 

(i) At engine powers that can sustain 

level flight: A duration that achieves 

repetitive, stabilized operation in the 

icing conditions defined in appendices 

C and O of part 25 of this chapter. 

(ii) At engine power below that which 

can sustain level flight: 

(A) Demonstration in altitude flight 

simulation test facility: A duration of 10 

minutes consistent with a simulated 

flight descent of 10,000 ft (3 km) in 

altitude while operating in Continuous 

Maximum icing conditions defined in 

appendix C of part 25 of this chapter, 

plus 40 percent liquid water content 

margin, at the critical level of airspeed 

and air temperature, or 

(B) Demonstration in ground test 

facility: A duration of 3 cycles of 

alternating icing exposure 

corresponding to the liquid water 

content levels and standard cloud 

lengths in Intermittent Maximum and 

Continuous Maximum icing conditions 

defined in appendix C of part 25 of this 

chapter, at the critical level of air 

temperature. 

(c) In addition to complying with 

§ 33.68(b), the following conditions 

shown in Table 1 of this section unless 

replaced by similar CPA test conditions 

that are more critical or produce an 

equivalent level of severity, must be 

demonstrated by an engine test: 

TABLE 1—CONDITIONS THAT MUST BE DEMONSTRATED BY AN ENGINE TEST

Condition Total air 

temperature 

Supercooled water 

concentrations 

(minimum) 

Median volume 

drop diameter 

(±3 microns) 

Duration 

1. Glaze ice conditions.21 to 25 °F (¥6 to 

¥4 °C).

2 g/m3 ................... 25 microns ............ (a) 10 minutes for power below sustainable level flight 

(idle descent). 

(b) Must show repetitive, stabilized operation for higher 

powers (50%, 75%, 100% MC). 

2. Rime ice conditions.¥10 to 0 °F (¥23 

to ¥18 °C).

1 g/m3 ................... 15 microns ............ (a) 10 minutes for power below sustainable level flight 

(idle descent). 

(b) Must show repetitive, stabilized operation for higher 

powers (50%, 75%, 100% MC). 

3. Glaze ice holding 

conditions (Turboprop and turbofan, only).

Turbofan, only: 10 

to 18 °F (¥12 to 

¥8 °C).

Turboprop, only: 2 

to 10 °F (¥17 to 

¥12 °C).

Alternating cycle: 

0.3 g/m3 (6 

minute) 1.7 g/m3

(1 minute).

20 microns ............ Must show repetitive, stabilized operation (or 45 minutes 

max). 

4. Rime ice holding 

conditions (Turboprop and turbofan, only).

Turbofan, only: 

¥10 to 0 °F 

(¥23 to ¥18 

°C) 

Turboprop, only: 2 

to 10 °F (¥17 to 

¥12 °C).

0.25 g/m3 .............. 20 microns ............ Must show repetitive, stabilized operation (or 45 minutes 

max). 

(d) The engine should be run at 

ground idle speed for a minimum of 30 

minutes at each of the following icing 

conditions shown in Table 2 of this 

section with the available air bleed for 

icing protection at its critical condition, 

without adverse effect, followed by 

acceleration to takeoff power or thrust. 

During the idle operation the engine 

may be run up periodically to a 

moderate power or thrust setting in a 

manner acceptable to the Administrator. 

The applicant must document any 

demonstrated run ups and minimum 

ambient temperature capability during 

the conduct of icing testing in the 

engine operating manual as mandatory 

in icing conditions. The applicant must 

demonstrate, with consideration of 

expected airport elevations, the 

following: 


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TABLE 2—DEMONSTRATION METHODS FOR SPECIFIC ICING CONDITIONS

Condition Total air temperature 

Supercooled water 

concentrations 

(minimum) 

Mean effective particle 

diameter Demonstration 

1. Rime ice condition ..... 0 to 15 °F (¥8 to ¥9 

°C).

Liquid—0.3 g/m3 ............ 15–25 microns ............... By engine test. 

2. Glaze ice condition .... 20 to 30 °F (¥7 to ¥1 

°C).

Liquid—0.3 g/m3 ............ 15–25 microns ............... By engine test. 

3. Snow ice condition .... 26 to 32 °F (¥3 to 0 °C) Ice—0.9 g/m3 ................ 100 microns (minimum) By test, analysis or combination of 

the two. 

4. Large drop glaze ice 

condition.

15 to 30 °F (¥9 to ¥1 

°C).

Liquid—0.3 g/m3 ............ 100 microns (minimum); 

3000 microns (maximum).

By test, analysis or combination of 

the two. 

(e) The applicant must demonstrate 

by test, analysis, or combination of the 

two, acceptable operation in ice crystals 

and mixed phase icing conditions 

throughout part 33, appendix D, icing 

envelope throughout its flight power 

range, including minimum descent 

idling speeds. 

26. Amend § 33.77 by adding 

paragraph (a) and by revising 

paragraphs (c) introductory text, (c)(1), 

(d), and (e)(1) through (4) to read as 

follows: 

§ 33.77 Foreign object ingestion—ice. 

(a) Compliance with the requirements 

of this paragraph shall be demonstrated 

by engine ice ingestion test or by 

validated analysis showing equivalence 

of other means for demonstrating soft 

body damage tolerance. 

* * * * * 

(c) Ingestion of ice under the 

conditions of this section may not — 

(1) Cause an immediate or ultimate 

unacceptable sustained power or thrust 

loss; or 

* * * * * 

(d) For an engine that incorporates a 

protection device, compliance with this 

section need not be demonstrated with 

respect to ice formed forward of the 

protection device if it is shown that— 

(1) Such ice is of a size that will not 

pass through the protective device; 

(2) The protective device will 

withstand the impact of the ice; and 

(3) The ice stopped by the protective 

device will not obstruct the flow of 

induction air into the engine with a 

resultant sustained reduction in power 

or thrust greater than those values 

defined by paragraph (c) of this section. 

(e) * * * 

(1) The minimum ice quantity and 

dimensions will be established by the 

engine size as defined in Table 1 of this 

section. 

(2) The ingested ice dimensions are 

determined by linear interpolation 

between table values, and are based on 

the actual engine’s inlet hilite area. 

(3) The ingestion velocity will 

simulate ice from the inlet being sucked 

into the engine. 

(4) Engine operation will be at the 

maximum cruise power or thrust unless 

lower power is more critical. 

TABLE 1—MINIMUM ICE SLAB DIMENSIONS BASED ON ENGINE INLET SIZE

Engine 

inlet hilite 

area 

(sq inch) 

Thickness 

(inch) 

Width 

(inch) 

Length 

(inch) 

0 .............. 0 .25 0 3.6 

80 ............ 0 .25 6 3.6 

300 .......... 0 .25 12 3.6 

700 .......... 0 .25 12 4.8 

2800 ........ 0 .35 12 8.5 

5000 ........ 0 .43 12 11.0 

7000 ........ 0 .50 12 12.7 

7900 ........ 0 .50 12 13.4 

9500 ........ 0 .50 12 14.6 

11300 ...... 0 .50 12 15.9 

13300 ...... 0 .50 12 17.1 

16500 ...... 0 .5 12 18.9 

20000 ...... 0 .5 12 20.0 

27. Amend part 33 by adding 

appendix D to read as follows: 

Appendix D to Part 33—Mixed Phase 

And Ice Crystal Icing Envelope (Deep 

Convective Clouds) 

Ice crystal conditions associated with 

convective storm cloud formations exist 

within the part 25, appendix C, Intermittent 

Maximum Icing envelope (including the 

extension to ¥40 deg C) and the Mil 

Standard 210 Hot Day envelope. This ice 

crystal icing envelope is depicted in Figure 

D1, below. 


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Within the envelope, total water content 

(TWC) in g/m3 has been determined based 

upon the adiabatic lapse defined by the 

convective rise of 90% relative humidity air 

from sea level to higher altitudes and scaled 

by a factor of 0.65 to a standard cloud length 

of 17.4 nautical miles. Figure D2 displays 

TWC for this distance over a range of ambient 

temperature within the boundaries of the ice 

crystal envelope specified in Figure D1. 


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Ice crystal size median mass dimension 

(MMD) range is 50–200 microns (equivalent 

spherical size) based upon measurements 

near convective storm cores. 

The TWC can be treated as completely 

glaciated (ice crystal) except as noted in the 

Table 1. 

TABLE 1—SUPERCOOLED LIQUID PORTION OF TWC 

Temperature 

range—deg C Horizontal cloud length LWC—g/m3

0 to ¥20 ...................................................................................... </= 50 miles ................................................................................ </=1.0 

0 to ¥20 ...................................................................................... Indefinite ...................................................................................... </=0.5 

<¥20 ........................................................................................... ..................................................................................................... 0 

The TWC levels displayed in Figure D2 

represent TWC values for a standard 

exposure distance (horizontal cloud length) 

of 17.4 nautical miles that must be adjusted 

with length of icing exposure. The 

assessment from data measurements in 

Reference 1 supports the reduction factor 

with exposure length shown in Figure D3. 

Issued in Washington, DC, on June 23, 

2010. 

KC Yanamura, 

Acting Director, Aircraft Certification Service. 

[FR Doc. 2010–15726 Filed 6–28–10; 8:45 am] 

BILLING CODE 4910–13–P 

DEPARTMENT OF TRANSPORTATION 

Federal Aviation Administration 

14 CFR Part 39 

[Docket No. FAA–2010–0640; Directorate 

Identifier 2009–NM–142–AD] 

RIN 2120–AA64 

Airworthiness Directives; EADS CASA 

(Type Certificate Previously Held by 

Construcciones Aeronauticas, S.A.) 

Model CN–235, CN–235–100, CN–235– 

200, and CN–235–300 Airplanes, and 

Model C–295 Airplanes 

AGENCY: Federal Aviation 

Administration (FAA), DOT. 

ACTION: Notice of Proposed Rulemaking 

(NPRM). 

SUMMARY: We propose to adopt a new 

airworthiness directive (AD) for the 

products listed above that would 

supersede an existing AD. This 

proposed AD results from mandatory 

continuing airworthiness information 

(MCAI) originated by an aviation 

authority of another country to identify 

and correct an unsafe condition on an 

aviation product. The MCAI describes 

the unsafe condition as: 

Prompted by [an] accident * * * the FAA 

published SFAR 88 (Special Federal Aviation 

Regulation 88) * * *. 

* * * * * 


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