Airplane Performance and Handling Qualities in Icing Conditions, 67278-67302 [05-21793]

Agencies

• Federal Aviation Administration
• DEPARTMENT OF TRANSPORTATION

[Federal Register Volume 70, Number 213 (Friday, November 4, 2005)]
[Proposed Rules]
[Pages 67278-67302]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: 05-21793]



[[Page 67277]]

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Part III





Department of Transportation





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Federal Aviation Administration



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14 CFR Part 25



Airplane Performance and Handling Qualities in Icing Conditions; 
Proposed Advisory Circular 25.21-1X, Performance and Handling 
Characteristics in the Icing Conditions Specified in Part 25, Appendix 
C; Proposed Rule and Notice

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

[[Page 67278]]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 25

[Docket No. 2005-22840; Notice No. 05-10]
RIN 2120-AI14


Airplane Performance and Handling Qualities in Icing Conditions

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Notice of proposed rulemaking (NPRM).

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SUMMARY: This action proposes to introduce new airworthiness standards 
to evaluate the performance and handling characteristics of transport 
category airplanes in icing conditions. This proposed action would 
improve the level of safety for new airplane designs when operating in 
icing conditions, and would harmonize the U.S. and European 
airworthiness standards for flight in icing conditions.

DATES: Send your comments on or before February 2, 2006.

ADDRESSES: You may send comments identified by Docket Number FAA-2005-
22840 using any of the following methods:
     DOT Docket Web site: Go to https://dms.dot.gov and follow 
the instructions for sending your comments electronically.
     Government-wide Regulations and Policies Web site: Go to 
https://www.faa.gov/regulations_policies/ and follow the instructions 
for sending your comments electronically.
     Mail: Docket Management Facility; U.S. Department of 
Transportation, 400 Seventh Street, SW., Nassif Building, Room PL-401, 
Washington, DC 20590-001.
     Fax: 1-202-493-2251.
     Hand Delivery: Room PL-401 on the plaza level of the 
Nassif Building, 400 Seventh Street, SW., Washington, DC, between 9 
a.m. and 5 p.m., Monday through Friday, except Federal holidays.
    For more information on the rulemaking process, see the 
SUPPLEMENTARY INFORMATION section of this document.
    Privacy: We will post all comments we receive, without change, to 
https://dms.dot.gov, including any personal information you provide. For 
more information, see the Privacy Act discussion in the SUPPLEMENTARY 
INFORMATION section of this document.
    Docket: To read background documents or comments received, go to 
https://dms.dot.gov at any time or to Room PL-401 on the plaza level of 
the Nassif Building, 400 Seventh Street, SW., Washington, DC, between 9 
a.m. and 5 p.m., Monday through Friday, except Federal holidays.

FOR FURTHER INFORMATION CONTACT: Don Stimson, FAA, Airplane & Flight 
Crew Interface Branch, ANM-111, Transport Airplane Directorate, 
Aircraft Certification Service, 1601 Lind Avenue SW., Renton, WA 98055-
4056; telephone: (425) 227-1129; fax: (425) 227-1149, e-mail: 
don.stimson@faa.gov.

SUPPLEMENTARY INFORMATION:

Comments Invited

    The FAA invites interested persons to participate in this 
rulemaking by submitting written comments, data, or views. We also 
invite comments relating to the economic, environmental, energy, or 
federalism impacts that might result from adopting the proposals in 
this document. The most helpful comments reference a specific portion 
of the proposal, explain the reason for any recommended change, and 
include supporting data. We ask that you send us two copies of written 
comments.
    We will file in the docket all comments we receive, as well as a 
report summarizing each substantive public contact with FAA personnel 
concerning this proposed rulemaking. The docket is available for public 
inspection before and after the comment closing date. If you wish to 
review the docket in person, go to the address in the ADDRESSES section 
of this preamble between 9 a.m. and 5 p.m., Monday through Friday, 
except Federal holidays. You may also review the docket using the 
Internet at the Web address in the ADDRESSES section.
    Privacy Act: Using the search function of our docket Web site, 
anyone can find and read the comments received into any of our dockets, 
including the name of the individual sending the comment (or signing 
the comment of behalf of an association, business, labor union, etc.). 
You may review DOT's complete Privacy Act statement in the Federal 
Register published on April 11, 2000 (65 FR 19477-78) or you may visit 
https://dms.dot.gov.
    Before acting on this proposal, we will consider all comments we 
receive on or before the closing date for comments. We will consider 
comments filed late if it is possible to do so without incurring 
expense or delay. We may change this proposal in light of the comments 
we receive.
    If you want the FAA to acknowledge receipt of your comments on this 
proposal, include with your comments a pre-addressed, stamped postcard 
on which the docket number appears. We will stamp the date on the 
postcard and mail it to you.

Availability of Rulemaking Documents

    You can get an electronic copy using the Internet by:
    (1) Searching the Department of Transportation's electronic Docket 
Management System (DMS) Web page (https://dms.dot.gov/search);
    (2) Visiting the Office of Rulemaking's Web page at https://
www.faa.gov/avr/arm/index.cfm; or
    (3) Accessing the Government Printing Office's Web page at https://
www.gpoaccess.gov/fr/.
    You can also get a copy by sending a request to the Federal 
Aviation Administration, Office of Rulemaking, ARM-1, 800 Independence 
Avenue SW., Washington, DC 20591, or by calling (202) 267-9680. Make 
sure to identify the docket number, notice number, or amendment number 
of this rulemaking.

Authority for This Rulemaking

    The FAA's authority to issue rules regarding aviation safety is 
found in Title 49 of the United States Code. Subtitle I, section 106 
describes the authority of the FAA Administrator. Subtitle VII, 
Aviation Programs, describes in more detail the scope of the agency's 
authority.
    This rulemaking is promulgated under the authority described in 
subtitle VII, part A, subpart III, section 44701, ``General 
requirements.'' Under that section, the FAA is charged with promoting 
safe flight of civil aircraft in air commerce by prescribing minimum 
standards required in the interest of safety for the design and 
performance of aircraft. This regulation is within the scope of that 
authority because it prescribes new safety standards for the design of 
transport category airplanes.

Organization of This NPRM

    Discussion of this proposal is organized under the headings listed 
below. Whenever there is a reference to a document being included in 
the docket for this NPRM, the docket referred to is Docket Number FAA-
2005-22840. A list of acronyms used is included in an appendix located 
at the end of the preamble material, between the regulatory evaluation 
and the text of the proposed amendments. Unless stated otherwise, rule 
sections referenced in this NPRM are part of Title 14, Code of Federal 
Regulations (14 CFR).

I. Executive Summary

    If adopted, this rulemaking would revise certain sections of part 
25 of Title

[[Page 67279]]

14 Code of Federal Regulations (14 CFR). Part 25 contains the 
airworthiness standards for type certification of transport category 
airplanes, but it does not currently include specific requirements for 
airplane performance or handling qualities for flight in icing 
conditions. Although part 25 requires airplanes with approved ice 
protection features to be able to operate safely in icing conditions, 
there is no standard set of criteria defining what ``to safely 
operate'' in icing conditions means in terms of airplane performance 
and handling qualities. Further, because the existing icing regulations 
only address airplanes with ice protection provisions, it is unclear 
what requirements apply in cases where the applicant is seeking to have 
an airplane without an ice protection system certificated for flight in 
icing conditions.
    This notice proposes to amend part 25 by adding a comprehensive set 
of airworthiness requirements that must be met to receive certification 
approval for flight in icing conditions, including specific performance 
and handling qualities requirements, and the ice accretion (that is, 
the size, shape, location, and texture of the ice) that must be 
considered for each phase of flight. These proposed revisions would 
ensure that minimum operating speeds determined during the 
certification of all future transport category airplanes would provide 
adequate maneuver capability in icing conditions for all phases of 
flight and all airplane configurations.
    This notice proposes to require the same airplane handling 
characteristics that apply in non-icing conditions to continue to apply 
in icing conditions. Additionally, a specific evaluation for 
susceptibility to tailplane stall in icing conditions would be added. 
This proposal, if adopted, would harmonize the U.S. and European 
airworthiness standards for flight in icing conditions. It would 
benefit the public interest while retaining or enhancing the current 
level of safety for operation in icing conditions.
    If adopted, this rulemaking would affect manufacturers, modifiers, 
and operators of transport category airplanes (but only for new designs 
or significant changes to current designs that would affect the safety 
of flight in icing conditions). Manufacturers and modifiers may need to 
develop new tests and analyses to determine ice accretions and to 
estimate performance effects for design and certification to address 
icing conditions. Operators may need to develop new or revised 
procedures regarding identification of icing conditions and the 
operation of the ice protection system.
    Service history shows that flight in icing conditions may be a 
safety risk for transport category airplanes. There have been nine 
accidents since 1983 that may have been prevented if this proposed rule 
had been in effect.\1\ The service history that we examined includes 
airplanes certificated to part 25, to its predecessor, the Civil Air 
Regulations (CAR) 4b, or to part 25 icing standards when the airplane 
was certified under part 23. In evaluating the potential for this 
rulemaking to avoid future accidents, we only considered past accidents 
involving tailplane stall or potential airframe ice accretion effects 
on drag or controllability. Accidents related to ground deicing were 
not considered.
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    \1\ These accidents were selected from the National 
Transportation Safety Board's (NTSB) accident database, and are 
discussed in Appendix 3 of this premable.
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    The NTSB has issued several safety recommendations related to 
airframe icing, some of which are addressed, at least in part, by this 
notice. If adopted, this rulemaking would require, during type 
certification, that manufacturers of transport category airplanes:
     Investigate the susceptibility of their airplanes to ice-
contaminated tailplane stall (ICTS);
     Provide for adequate warning on the flight deck of an 
impending stall in icing conditions;
     Show that their airplanes meet the same maneuvering 
capability and handling characteristics requirements in icing 
conditions as in non-icing conditions; and
     Show that their airplanes have adequate performance 
capability in icing conditions.
    As discussed in more detail later, the FAA has tentatively 
determined that this rulemaking would have the following costs and 
benefits over a 45-year analysis period. The cost of the proposed rule 
would be $22.0 million (present value). The FAA assumes the initial 
certification costs of $6.7 million for four new airplane models are 
incurred in year one of a 45-year analysis period. The future 
additional fuel burn expense is estimated to be $59.7 million and would 
be incurred over the 45-year analysis period. The benefits of this 
proposed rule consist of the value of lives saved due to avoiding 
accidents involving part 25 airplanes operating in icing conditions. 
Over the 45-year period of analysis, the potential benefit of the 
proposed rule would be $89.9 million ($23.7 million in present value at 
seven percent).

A. Past Regulatory Approach

    Currently, Sec.  25.1419, ``Ice protection,'' requires transport 
category airplanes with approved ice protection features be capable of 
operating safely within the icing conditions identified in appendix C 
of part 25. This section also requires flight testing and analyses to 
be performed to make this determination. Although an airplane's 
performance capability and handling qualities are important in 
determining whether an airplane can operate safely, part 25 does not 
have specific airplane performance or handling qualities requirements 
for flight in icing conditions, nor does the FAA have a standard set of 
criteria defining what ``to safely operate'' in icing conditions means 
in terms of airplane performance and handling qualities. The proposed 
revisions to part 25 would provide a comprehensive set of harmonized 
requirements for airplane performance and handling qualities to address 
safe operation of transport category airplanes in icing conditions.
    Further, Sec.  25.1419 requires an applicant to demonstrate that 
the airplane can operate safely in icing conditions only when the 
applicant is seeking to certificate ice protection features. It fails 
to address certification approval for flight in icing conditions for 
airplanes without ice protection features.
    In contrast, the European airworthiness standards specifically 
address certification for flight in icing conditions, independent of 
whether the airplane includes ice protection features. In addition, the 
European Joint Aviation Authorities (JAA) proposed additional guidance 
material in the early 1990s to provide criteria for determining whether 
an airplane's performance and handling qualities would allow the 
airplane to operate safely in icing conditions. The JAA's guidance 
material was proposed in draft Advisory Material--Joint (AMJ) 
25.1419.\2\ The JAA's draft AMJ was published on April 23, 1993, as a 
Notice of Proposed Amendment (NPA) 25F-219, ``Flight in Icing 
Conditions--Acceptable Handling Characteristics and Performance 
Effects.''
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    \2\ A JAA AMJ is similar to an FAA advisory circular.
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B. Harmonization of U.S. and European Regulatory Standards

1. Federal Aviation Administration
    Title 14 CFR part 25 contains the U.S. airworthiness standards for 
type certification of transport category airplanes. The part 25 
standards apply to airplanes manufactured within the

[[Page 67280]]

U.S. and to airplanes manufactured in other countries and imported to 
the U.S. under a bilateral airworthiness agreement.
2. Joint Aviation Authorities
    The JAR-25 contains the European airworthiness standards for type 
certification of transport category airplanes. Thirty-seven European 
countries accept airplanes type certificated to the JAR-25 standards, 
including airplanes manufactured in the U.S. that are type certificated 
to JAR-25 standards for export to Europe.
3. European Aviation Safety Agency (EASA)
    The European Community established a new aviation regulatory body, 
EASA, to develop standards to ensure the highest level of safety and 
environmental protection, oversee their uniform application across 
Europe, and promote them internationally. The EASA formally became 
operational for certification of aircraft, engines, parts, and 
appliances on September 28, 2003. The EASA will eventually absorb all 
of the functions and activities of the JAA, including its efforts to 
harmonize the European airworthiness certification regulations with 
those of the U.S.
    The JAR-25 standards have been incorporated into the EASA's 
``Certification Specifications for Large Aeroplanes,'' (CS)-25, in 
similar if not identical language. The EASA's CS-25 became effective 
October 17, 2003.
    The proposals contained in this notice were developed in 
coordination with the JAA. However, since the JAA's JAR-25 and the 
EASA's CS-25 are essentially the same, all of the discussions of these 
proposals relative to JAR-25 also apply to CS-25.
    The FAA's rulemaking proposal, if adopted, would parallel the JAA's 
rulemaking proposal, ``Notice of Proposed Amendment (NPA) 25B, E, F-
332,'' published on June 1, 2002.
    The EASA recently published for comment NPA 16/2004, ``Draft 
Decision of the Executive Director of the Agency on Certification 
Conditions.'' This NPA, published for comment in late 2004, is based on 
the standards that the JAA were expected to adopt.
    Although the FAA, the JAA, and EASA intend to harmonize the 
standards for airplane performance and handling qualities for flight in 
icing conditions, there are some differences between this rulemaking 
proposal and the standards proposed by the JAA and EASA. The 
differences are primarily editorial and are not intended to result in 
significant regulatory differences.

C. Proposal Development--Aviation Rulemaking Advisory Committee

    The FAA, in cooperation with the JAA and representatives of the 
American and European aerospace industries, recognized that a common 
set of standards would not only economically benefit the aviation 
industry, but also maintain a high level of safety. In 1988, the FAA 
and the JAA began a process to harmonize their respective airworthiness 
standards. To assist in the harmonization efforts, the FAA established 
the Aviation Rulemaking Advisory Committee (ARAC) in 1991,\3\ to:
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    \3\ Published in the Federal Register (56 FR 2190), on January 
22, 1991.
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    1. Provide advice and recommendations concerning the full range of 
our safety-related rulemaking activity;
    2. Develop better rules in less overall time using fewer FAA 
resources than are currently needed; and
    3. Obtain firsthand information and insight from interested parties 
regarding proposed new rules or revisions of existing rules.

There are 73 member organizations on the committee, representing a wide 
range of interests within the aviation community.
    We tasked the ARAC Flight Test Harmonization Working Group (FTHWG) 
to recommend to the ARAC new or revised requirements and compliance 
methods related to airplane performance and handling qualities in icing 
conditions.\4\
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    \4\ Published in the Federal Register (56 FR 2190), on June 10, 
1994.
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    The FTHWG reviewed in-service incidents and accidents involving 
transport category airplanes. This review revealed numerous incidents 
resulting from the effects of ice on airplane performance. The same 
review showed that the icing-related accidents resulted from a loss of 
control of the airplane due to the effect of the ice on airplane 
handling qualities. Considering this service history, the FTHWG 
determined that airplanes should generally meet the same handling 
qualities standards in icing conditions that they currently must meet 
for non-icing conditions. In certain areas, however, the FTHWG decided 
that the current handling qualities standards were inappropriate for 
flight in icing conditions. In these areas, the FTHWG developed 
alternative criteria that would apply to icing conditions.
    Since airplane performance degradation was not a causal factor in 
any of the icing-related accidents, the FTHWG concluded that the 
current performance standards already provide some safety margin to 
offset the negative effects of ice accretion. On the basis of this 
service history, the FTHWG decided that the general approach to 
airplane performance in icing conditions used by the JAA in their draft 
AMJ 25.1419 was appropriate and used this approach in its 
recommendations to the FAA. This approach allows a limited reduction in 
airplane performance capability due to ice before the effects of icing 
must be fully taken into account in the performance data provided in 
the Airplane Flight Manual (AFM). Such an approach minimizes the costs 
to manufacturers and operators while increasing the current level of 
safety for flight in icing conditions.
    This proposed rulemaking is based on the FTHWG's report, which ARAC 
approved and forwarded to the FAA, and refers to the ice accretions to 
be used in showing compliance. These ice accretions are defined in a 
new subsection of appendix C to part 25.\5\
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    \5\ The complete text of the FTHWG's report is available at 
https://www.faa.gov/avr/arm/arac/aractasks/fr0404report.pdf. The 
FTHWG preferred the term ``ice accretion'' rather than ``ice shape'' 
because it includes physical characteristics of the ice build-up 
such as texture and surface roughness in addition to its general 
size and shape.
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D. Related Rulemaking Activity

1. Amendment 25-108
    This Amendment, ``1-g Stall Speed as the Basis for Compliance With 
Part 25 of the Federal Aviation Regulations'' (referred to as the 1-g 
stall rule) (67 FR 708112, November 26, 2002) redefines the criteria 
for determining the stall speed for transport category airplanes. The 
stall speed is important because it is used as a reference speed for 
defining minimum operating speeds that provide a safety margin above 
the speed at which the airplane will stall. The previous part 25 
definition of stall speed defined it as the minimum speed reached in a 
stalling maneuver. This definition could result in a stall speed being 
defined that is too low to support the weight of the airplane in level 
flight.
    The recently adopted 1-g stall rule defines the stall speed as the 
speed at which the aerodynamic lift can support the weight of the 
airplane in 1-g flight. The 1-g stall rule also introduces a 
requirement to demonstrate adequate maneuver capability at the minimum 
operating speeds for airplane configurations associated with low speed 
operations around airports. The JAA adopted the same 1-g stall speed 
requirements in Change 15 to JAR-25.

[[Page 67281]]

2. Ice Protection Harmonization Working Group (IPHWG) Recommendations
    The FAA tasked the ARAC to consider whether airplane manufacturers 
or operators should be required to install ice detectors or provide 
some other acceptable way to warn flightcrews of potentially unsafe ice 
accumulations. The ARAC assigned this task to the IPHWG. The IPHWG 
recommended to the ARAC that the FAA adopt an operating rule for 
certain types of airplanes that would require a reliable method of 
informing pilots when to activate the ice protection system as well as 
a way of knowing when ice is accumulating aft of areas protected by the 
ice protection system. The IPHWG is also working on a recommendation 
for a type certification requirement that would identify acceptable 
ways to inform the flightcrew when to activate the ice protection 
system.
    We also tasked the ARAC to:
     Define an icing environment that includes supercooled 
large drop (SLD) icing conditions;
     Recommend requirements to assess the ability of aircraft 
to safely operate in SLD icing conditions, either for the period of 
time necessary to exit or to operate without restriction; and
     Consider mixed phase conditions (a mixture of supercooled 
water droplets and ice crystals) if such conditions are more hazardous 
than the liquid phase icing environment containing supercooled water 
droplets.
    When ARAC finishes its tasks, we expect it to forward to us a 
report containing their recommendations. These recommendations may lead 
to future rulemaking to address SLD icing conditions, but would not 
directly impact this rulemaking.

E. Advisory Material

    In addition to being tasked to recommend new or revised 
requirements related to airplane performance and handling qualities in 
icing conditions, the ARAC FTHWG was tasked to recommend advisory 
material identifying acceptable ways to comply with the proposed new or 
revised requirements. The FTHWG developed a proposed Advisory Circular, 
(AC) 25.21-1X, ``Performance and Handling Characteristics in the Icing 
Conditions Specified in Part 25, Appendix C.'' We are requesting public 
comments on this proposed advisory circular through a separate notice 
of availability in this edition of the Federal Register.

II. Discussion of the Proposals

A. Proof of Compliance (Sec.  25.21)

    We propose to add paragraph (g), to specify the requirements that 
must be met in icing conditions if an applicant seeks certification 
approval for flight in icing conditions. As discussed above, a review 
of icing-related incidents and accidents revealed loss of control to be 
the greatest threat to safety of flight in icing conditions. 
Consequently, the FTHWG identified the existing part 25 requirements 
that could prevent loss of control if they were applied to icing 
conditions. The FTHWG found, and we tentatively agree, that airplanes 
should continue to comply with most of subpart B of part 25 with ice on 
the airplane to ensure safe flight in icing conditions. The subpart B 
regulations that would be excluded by paragraph (g)(1) were determined 
to be beyond what was necessary to determine an airplane's ability to 
operate safely in icing conditions.
    Because the airplane performance and handling qualities 
requirements are flight-related requirements, it is appropriate to 
place the proposed requirements for flight in icing conditions in part 
25, subpart B (Flight) rather than in the current ice protection rule 
in Sec.  25.1419. Section 25.1419 is in subpart F (Equipment), and, 
though it is closely linked with the subpart B requirements proposed in 
this notice, it primarily applies to the ice protection equipment on 
the airplane.
    The proposed subpart B requirements would provide the minimum 
performance and handling qualities requirements corresponding to the 
Sec.  25.1419 requirement that the airplane ``be able to safely operate 
in the continuous maximum and intermittent maximum icing conditions of 
appendix C.'' Additionally, the proposed requirements would supply the 
means for determining, from a performance and handling qualities 
standpoint, whether the ice protection system and its components are 
effective, as required by Sec.  25.1419(b).
    Compliance with the proposed performance and handling qualities 
requirements may be shown by a variety of means that would be evaluated 
during the particular airplane type certification program. These means 
may include flight testing in natural icing conditions or in non-icing 
conditions using artificial ice shapes, wind tunnel testing and 
analysis, engineering simulator testing and analysis, engineering 
analysis, and comparison to previous similar airplanes.
    The proposed requirements would not specifically require 
performance and handling qualities flight testing to be conducted in 
natural icing conditions. However, we expect that for most new airplane 
designs, and for significant changes to existing designs, at least a 
limited set of tests would be flown in natural icing conditions. The 
purpose of these tests would be to confirm the airplane handling 
qualities and performance results found through other means. The 
proposed advisory material will provide guidance on an acceptable 
flight test program, including the specific tests that should be 
conducted in natural icing conditions.
    Historically, flight tests in measured natural icing conditions 
have also been conducted to verify analyses used to generate ice 
accretions for compliance with Sec.  25.1419(b), and to confirm the 
general physical characteristics and location of ice accretions used to 
evaluate airplane performance and handling qualities. This proposed 
rule is not intended to alter this practice or interpretation of Sec.  
25.1419(b). Existing AC 25.1419-1, ``Certification of Transport 
Category Airplanes for Flight in Icing Conditions,'' provides guidance 
on comparing the ice accretions used to evaluate airplane performance 
and handling qualities with those obtained in natural icing conditions.
    Proposed paragraph (g)(1) would apply the same airplane handling 
qualities requirements to flight in icing conditions as are currently 
required for non-icing conditions. Paragraph (g)(1) would also apply 
most of the airplane performance requirements currently required for 
non-icing conditions to flight in icing conditions. The icing 
conditions for showing compliance would be defined in appendix C to 
part 25. These requirements would apply to normal operations of the 
airplane and its ice protection system as specified in the AFM. By 
referencing the AFM, this paragraph would require that this manual 
include the limitations and operating procedures that are specific to 
operating in icing conditions.
    As noted in the introductory discussion, some degradation in 
airplane performance capability would be permitted when showing 
compliance with the requirements for non-icing conditions. The amount 
of performance degradation permitted in each case is identified in the 
discussion of the individual performance regulations.
    Proposed paragraph (g)(2) would prevent the use of different load, 
weight, and center-of-gravity limits for flight in icing, except where 
compliance with the applicable performance requirements impose more 
restrictive weight limits.
    The reason for these proposed requirements is that operation in 
icing

[[Page 67282]]

conditions should be essentially transparent to the flightcrew. There 
should not be any special procedures or methods used for operating in 
icing conditions other than activating ice protection systems. This 
philosophy comes from applying human factors principles to reduce 
operational complexity and flightcrew workload.

B. Stall Speed (Sec.  25.103)

    We propose to revise Sec.  25.103 to require applicants to 
determine stall speeds with ice on the airplane. The proposed Sec.  
25.103(b)(3) adds ice accretion as a variable that must be considered 
when determining stall speeds to use for the different part 25 airplane 
performance standards.
    Determining stall speeds with ice accretions is necessary to 
identify any increase in stall speeds from those determined for non-
icing conditions. The applicant would then compare any change in stall 
speed due to ice accretion with the allowable stall and operating speed 
effects contained in the proposed airplane performance standards to 
determine whether or not airplane performance data must be determined 
specifically for icing conditions.

C. Takeoff (Sec.  25.105)

    We propose to revise Sec.  25.105(a) to add the net takeoff flight 
path described in Sec.  25.115 to the list of airplane takeoff 
performance parameters that must be determined under the conditions 
specified in this paragraph. Additionally, Sec.  25.105(a) would 
specify when compliance must be shown specifically for icing 
conditions.
    We consider the proposed changes necessary to ensure the safety of 
takeoff operations in icing conditions. Ice on the wings and control 
surfaces can reduce the safety margins that currently are provided to 
prevent stalling the airplane. It can also degrade airplane climb 
performance, and cause controllability problems. We acknowledge that 
many transport category airplanes have safely operated in icing 
conditions using takeoff speeds determined for non-icing conditions. We 
agree with the FTHWG, however, that it is in the interest of safety to 
consider the effects of ice accretions on airplane takeoff performance.
    In developing this proposal, the FTHWG and the FAA considered four 
factors:
     Operating rules and practices intended to ensure that 
critical surfaces of the airplane are free of snow or ice before 
beginning a takeoff;
     The use of anti-icing fluids that provide some protection 
from icing during the takeoff;
     Increasing use of ice detectors and deicing/anti-icing 
systems on airplanes that can be operated while the airplane is still 
on the ground; and
     The icing conditions that we propose to use for the 
takeoff flight phase.
    Existing operating rules, Sec. Sec.  91.527(a), 121.629(b), and 
135.227(a), prohibit pilots from taking off with snow or ice adhering 
to the wings or other critical airplane surfaces. Additionally, 
Sec. Sec.  121.629(c) and 135.227(b) require airplane operators to have 
either an approved ground deicing/anti-icing program or conduct a pre-
takeoff contamination check within five minutes before beginning a 
takeoff to ensure that the wings, control surfaces, and other critical 
surfaces are free of frost, ice, or snow. Operators must train the 
pilots on the effects of these contaminants on airplane performance and 
controllability, on how to recognize airplane contamination, and on 
procedures intended to ensure that contamination is removed before 
takeoff.
    Ground deicing/anti-icing programs include the use of deicing/anti-
icing fluids to remove ice and snow and prevent them from reappearing 
on airplane surfaces during freezing precipitation conditions. Although 
these fluids are designed to flow off the airplane during the takeoff 
roll, we expect the fluids to continue to provide some protection 
throughout the takeoff ground run.
    On some older airplane models, the wing ice protection system was 
designed for use in flight and cannot be operated while the airplane is 
on the ground. Yet many of the current generation of airplanes have ice 
protection systems that can be operated while the airplane is on the 
ground. Some of these systems are also coupled with ice detector 
systems that will automatically activate the ice protection system in 
icing conditions. These features tend to reduce the chances that ice 
will adhere to critical airfoil surfaces during airplane ground 
operations in atmospheric icing conditions.
    As discussed later, we propose to revise appendix C of part 25 to 
define atmospheric icing conditions specifically for the takeoff phase 
of flight. These proposed atmospheric icing conditions would apply 
throughout the takeoff path, but are based on the more critical 
conditions that would be expected to occur at the end of the takeoff 
path. These conditions do not include freezing precipitation on the 
ground. At earlier points in the takeoff path, while the airplane is 
closer to the ground, the proposed takeoff icing conditions would be 
conservative, that is, they would predict larger ice accretions than 
would be likely to occur. If these conditions were to actually occur at 
ground level, they would form a freezing fog condition that would 
probably reduce visibility to the point that takeoffs could not be 
made.
    An important part of determining the effects of ice accretion on 
takeoff performance is to decide at what point in the takeoff ice 
accretion is considered to begin. For the purposes of this rulemaking, 
we consider ice accretion to begin when the airplane lifts off the 
runway surface during takeoff.
    Proposed Sec.  25.105(a) would require applicants to determine 
airplane takeoff performance for icing conditions if the ice that can 
accrete during takeoff results in increasing the reference stall speed 
(VSR) or degrading climb performance beyond specified limits. Section 
25.105(a) references all regulations related to the takeoff path. As a 
result, the performance for the entire takeoff path, including takeoff 
speeds and distances, must be determined for icing conditions if the 
stall speed or climb performance degradation limits are exceeded.
    Section 25.105(a)(2)(i) of the proposal would require applicants to 
determine takeoff path performance for icing conditions if the stall 
speed increases by more than 3 knots in calibrated airspeed or 3 
percent due to ice accretions. This proposed requirement would be more 
stringent than the guidance used by the JAA in their draft AMJ 25.1419. 
The draft AMJ allowed up to a 5 knot or 5 percent increase in stall 
speed before the takeoff performance would need to be recomputed for 
icing conditions.
    Several commenters on the AMJ, including us, expressed concern over 
allowing such a large increase in stall speed believing it would result 
in a significant reduction in safety margin between the minimum 
operating speeds and the stall speed. We agree with the FTHWG 
recommendation that a 3 knot or 3 percent increase in stall speeds is 
the maximum that should be permitted before the takeoff performance 
data should be recalculated to consider the effects of icing.
    Also, the JAA's draft AMJ 25.1419 used the effect of ice accretions 
on airplane drag rather than on climb performance to determine when the 
takeoff performance data must be provided for icing conditions. 
However, we agree with the FTHWG recommendation to consider the effect

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of ice accretions in terms of climb performance in Sec.  
25.105(a)(2)(ii) because it would cover more operating variables than 
just the effect of ice on airplane drag.
    The part 25 takeoff climb requirements include a safety margin by 
requiring applicants to determine a net flight path based on the 
airplane's actual climb performance capability reduced by a set value 
that depends on the number of engines on the airplane. Proposed Sec.  
25.105(a)(2)(ii) would require applicants to determine takeoff path 
performance specifically for icing conditions if more than half of this 
safety margin would be lost due to the effects of ice accretion.
    Part 25 divides the takeoff climb performance requirements into 
several segments. To establish the allowable limit for takeoff climb 
performance degradation in icing conditions, Sec.  25.105(a)(2)(ii) 
would consider the effect of ice accretions on just the takeoff climb 
segment defined by Sec.  25.121(b). For most transport category 
airplanes, this segment most often limits the allowable takeoff weight, 
and therefore is the most critical to safety. If the effects of ice 
accretions during the takeoff climb segment defined in Sec.  25.121(b) 
are beyond specified limits, the airplane performance for the entire 
takeoff path must be determined with ice accretions on the airplane. 
This would include from the beginning of the takeoff roll until the 
airplane is at least 1,500 feet above the takeoff surface. Thus, for 
airplanes that would be most affected by ice accretions during the 
takeoff climb, additional safety margins would also be provided for the 
takeoff ground run even though ice accretion is assumed not to begin 
until liftoff.

D. Takeoff Speeds (Sec.  25.107)

    We propose to revise Sec.  25.107(c)(3) and (g) to change the 
reference for maneuver capability considerations from Sec.  25.143(g) 
to Sec.  25.143(h). This is an editorial change due to the 
redesignation of Sec.  25.143(g) to Sec.  25.143(h) proposed below.
    We also propose to revise Sec.  25.107 by adding a new paragraph 
(h). This new paragraph would state that the minimum control speeds 
(VMCG and VMC) and minimum unstick speeds 
(VMU) determined for the airplane in non-icing conditions 
may also be used for the airplane in icing conditions. The 
VMU, VMCG, and VMC speeds are used to 
determine the takeoff speeds V1, VR, and 
V2.
    The minimum unstick speed (VMU) is defined in Sec.  
25.107(d) as the airspeed at and above which the airplane can safely 
lift off the ground and continue the takeoff. Takeoff speeds must be 
established sufficiently above this speed to assure the airplane can 
safely take off considering the variations in procedures and conditions 
that can reasonably be expected in day-to-day operations. Because these 
proposals assume that ice accretion does not begin until liftoff, this 
proposal would allow the VMU speeds for non-icing conditions 
to be used for determining takeoff speeds in icing conditions.
    The ground minimum control speed (VMCG) is used in 
determining the takeoff V1 speed. The takeoff V1 
speed is the highest speed at which the pilot must take the first 
action to be able to safely stop the airplane during a rejected takeoff 
and the lowest speed at which the takeoff can be safely continued after 
an engine failure. Since VMCG, like VMU, occurs 
before the airplane lifts off the runway, the assumption is that ice 
has not yet begun accreting on the airplane. Therefore, this proposal 
would allow the VMCG speeds determined for non-icing 
conditions to be used for determining V1 for icing 
conditions.
    The air minimum control speed, VMC (commonly referred to 
as VMCA), is defined in Sec.  25.149(b) as the airspeed at 
which it is possible to maintain control of the airplane, with no more 
than 5 degrees of bank, when the critical engine is suddenly made 
inoperative. Section 25.107 requires the rotation speed (VR) 
and the takeoff safety speed (V2) to be sufficiently higher 
than VMCA to assure that the airplane will be safely 
controllable if the critical engine fails during the takeoff. Since 
VR occurs before liftoff, like VMU and 
VMCG, this proposal would allow the VMCA speeds 
determined for non-icing conditions to be used for determining 
VR for icing conditions.
    Several concerns must be addressed if we are to allow 
VMCA speeds determined in non-icing conditions to be used to 
determine V2 in icing conditions. Unlike VR, 
V2 occurs after liftoff and ice could have begun accreting 
on the airplane. Ice may accrete at V2 because ice 
protection systems are typically not turned on until the airplane 
climbs more than 400 feet after takeoff. Also, many airplanes do not 
have any ice protection on the vertical stabilizer. These concerns 
could lead to a reduction in the airplane's directional control 
capability if ice accretion occurs. To alleviate these concerns, the 
proposed Sec.  25.143(c) would require applicants to show that 
airplanes are safely controllable and maneuverable at the minimum 
V2 speed with the critical engine inoperative and with the 
ice accretion applicable to the takeoff flight phase.

E. Takeoff Path (Sec.  25.111)

    Currently, Sec.  25.111 defines the takeoff path, describes the 
airplane configuration that applies to each portion of the takeoff 
path, and provides airplane performance requirements that must be met. 
We propose to revise Sec.  25.111 by adding a new paragraph (c)(5) 
stating that the airplane's drag used to determine the takeoff path 
after liftoff would be based on the ice accretions defined in the 
proposed revision to appendix C. To accommodate the addition of the new 
paragraph, the ``and'' at the end of Sec.  25.111(c)(3) would be moved 
to the end of Sec.  25.111(c)(4).
    The takeoff path begins at the start of the takeoff roll and ends 
when the airplane is either 1,500 feet above the takeoff surface, or at 
the altitude at which the transition from the takeoff to the en route 
configuration is completed and the final takeoff speed attained, 
whichever is higher. The takeoff path typically has two distinct climb 
segments: One from the point at which the airplane is 35 feet above the 
runway up to 400 feet, and the other from a height of 400 feet to the 
end of the takeoff path. The proposed changes to Sec.  25.111 would 
identify when the takeoff path must be determined for flight in icing 
conditions and specify the ice accretion that must be used for these 
two climb segments.
    New paragraph (c)(5) would refer back to the proposed Sec.  
25.105(a)(2) to identify when the takeoff path must be determined for 
flight in icing conditions. The ice accretions referenced in new 
paragraph (c)(5) would apply to the airborne portions of the takeoff 
path, since we are assuming that ice accretion does not begin until 
liftoff. If takeoff path performance must be determined for icing 
conditions, then the takeoff path must use the takeoff speeds of the 
proposed Sec.  25.107 for icing conditions, using the ice accretions 
specified in paragraph (c)(5).

F. Landing Climb: All-Engines-Operating (Sec.  25.119)

    We propose to revise Sec.  25.119 by requiring the airplane landing 
climb performance to be determined for both non-icing and icing 
conditions; adding references to the appropriate paragraphs of the 
proposed Sec.  25.125 revision for the landing climb speed to use for 
non-icing and icing conditions; referring to the proposed appendix C 
revision to identify the ice accretion that would be used in 
determining landing climb performance in icing conditions; and changing 
the speed used to show

[[Page 67284]]

compliance with Sec.  25.119 from a speed less than or equal to 
VREF to VREF.
    We consider the approach and landing phases of flight to be the 
flight phases most affected by icing conditions because of the 
potential for descending into and holding in icing conditions prior to 
landing. In addition, service history has shown that the majority of 
icing accidents and incidents occur in the holding, approach, and 
landing flight phases. For these reasons, our policy for the last 40 
years has been for applicants to account for the effects of airframe 
ice accretion in their airplane's approach and landing climb 
performance data provided in the Airplane Flight Manual. (Approach and 
landing climb performance refer to the airplane's climb capability in 
the approach and landing configurations during the approach and landing 
flight phases. Sections 25.121(d) and 25.119 require minimum level of 
approach and landing climb performance to ensure that airplanes can 
abort an approach or landing attempt and safely climb away.) The 
proposed changes to Sec. Sec.  25.119 and 25.121(d) (see below) serve 
to codify this policy.

G. Climb: One-Engine-Inoperative (Sec.  25.121)

    We propose to revise Sec.  25.121 by rearranging paragraphs (b), 
(c), and (d) to specify when the required climb performance must be 
determined for icing conditions; refer to the proposed appendix C 
revision to identify the ice accretion that would be used in 
calculating approach climb performance in icing conditions; and provide 
the conditions under which the approach climb speed must be increased 
to account for the effect of ice accretion.
    Sections 25.121(b) and (c) provide the climb performance 
requirements for the takeoff path segments beginning at the point the 
landing gear is fully retracted and ending at the end of the takeoff 
path. As in the proposed revision to Sec.  25.105, we propose to revise 
Sec.  25.121(b) and (c) to require takeoff climb performance to be 
determined for icing conditions if the effect of ice: (1) Increases the 
stall speed at maximum takeoff weight by more than 3 knots or 3 
percent, or (2) reduces the climb performance determined in Sec.  
25.121(b) by more than half the safety margin provided by the net 
gradient adjustment required by Sec.  25.115.
    Section 25.121(a) provides the climb performance requirements for 
the takeoff path segment beginning at liftoff and ending when the 
landing gear is fully retracted. Since we are assuming that ice 
accretion does not begin until liftoff, only a minimal amount of ice 
could be accreted during this climb segment. Therefore, the proposal 
for Sec.  25.21(g)(1) excludes compliance with Sec.  25.121(a) with ice 
accretions on the airplane.
    We propose revising Sec.  25.121(d) to state when the approach 
climb speed must be adjusted for use in icing conditions. Unlike the 
speeds used in the takeoff path, the need to adjust the approach climb 
speed would not be based on the effect of ice accretions on the 
airplane's stall speed. Instead, the measure for determining whether 
the approach climb speed needs to be adjusted for icing conditions is 
based on the effect of ice accretions on the approach climb speed. If 
the approach climb speed for icing conditions does not exceed the climb 
speed for non-icing conditions by more than the greater of 3 knots 
calibrated airspeed (CAS) or 3 percent VSR, then non-icing 
speeds may be used for calculating approach climb performance for icing 
conditions.
    The existing requirement for determining the approach climb speed 
in non-icing conditions provides applicants some flexibility by only 
specifying the maximum allowable approach climb speed. No lower limit 
is specified and we have accepted approach climb speeds as low as 1.13 
VSR (that is, 13 percent above the reference stall speeds). 
We would accept this same level of flexibility for establishing the 
approach climb speeds in icing conditions. The approach climb speeds 
for icing conditions should also be evaluated to ensure that they 
provide adequate maneuver capability.
    This proposal for the approach climb segment is less stringent than 
the 3 knots or 3 percent VSR standard used for takeoff path 
speeds. For example, if the approach climb speed is 1.25 VSR 
and VSR is 100 knots, 3 percent of the approach climb speed 
is 3.75 knots, while 3 percent of VSR would be only 3 knots. 
The approach climb speed could increase by 3.75 knots without requiring 
this increased approach climb speed to be used for calculating the 
approach climb performance in icing conditions. We consider this small 
alleviation to be acceptable since it is only relative to the need for 
increasing the approach climb speed for icing conditions. The approach 
climb performance must be recalculated with the holding ice accretion 
and presented in the AFM regardless of whether the approach climb speed 
is adjusted for operations in icing conditions.

H. En Route Flight Paths (Sec.  25.123)

    We propose to revise Sec.  25.123(a) by specifying a minimum 
allowable speed for determining en route flight paths, which would 
apply to both icing and non-icing conditions. The proposed speed, 
VFTO, is currently used as the minimum allowable speed for 
the final takeoff.
    Additionally, the proposed revision to Sec.  25.123(b) would state 
when an applicant must determine the en route flight paths specifically 
for icing conditions. Similar to the takeoff path requirements of the 
proposed revision to Sec.  25.111, en route flight path performance 
needs to be specifically determined for icing conditions if the effect 
of ice: (1) Increases the en route speed by more than 3 knots or 3 
percent, or (2) reduces climb performance by more than half the safety 
margin provided by the net gradient adjustment required by Sec.  
25.123(b). The ice accretion to be used would be specified in the 
proposed revision to appendix C.
    The reason for proposing to limit the minimum allowable en route 
climb speed to VFTO to is to prevent applicants from showing 
compliance with Sec.  25.123 by trading altitude for airspeed when 
transitioning from the final takeoff to the en route climb segment. 
This clarifying change is consistent with our original intent for Sec.  
25.123(a).
    Another reason for not allowing an en route climb speed less than 
VFTO is that VFTO is the speed at which the 
maneuver capability requirements contained in the existing Sec.  
25.143(g) must be met in the en route configuration. Allowing an en 
route climb speed lower than VFTO would not ensure that the 
airplane has adequate maneuvering capability during the en route climb 
phase of flight.
    We are not proposing any changes to the two-engine-inoperative en 
route flight path requirements contained in Sec.  25.123(c) for flight 
in icing conditions. We do not expect the pilot to stay in icing 
conditions with one engine inoperative for a long enough duration for 
the failure of a second engine in icing conditions to be an issue.
    En route and takeoff flight paths have similar safety issues. 
Therefore, we are proposing requirements for identifying when en route 
climb flight paths must be determined for icing conditions that are 
similar to those proposed for takeoff flight paths. The only 
significant difference is that for the en route climb paths, a speed of 
1.18 VSR determined with the en route ice accretion of 
proposed appendix C is compared to the en route climb speed selected 
for non-icing conditions instead of comparing stall speeds with and 
without ice accretions.
    The reason for this difference is to provide a more stringent 
requirement

[[Page 67285]]

for airplanes that use the minimum allowable en route climb speed of 
1.18 VSR. (1.18 VSR is the minimum allowable 
value of VFTO prescribed by Sec.  25.107(g)). Airplanes that 
use a higher en route climb speed have a larger speed margin to the 
stall speed and more maneuvering capability in the en route climb phase 
to help offset the negative effects of ice accumulation.
    Due to differences in their methods of generating thrust, 
propeller-driven airplanes generally have better climb performance at 
lower airspeeds than turbojet-powered airplanes. To optimize 
performance, the en route climb speed used for propeller-driven 
airplanes is usually the minimum allowable speed of 1.18 
VSR, while the en route climb speed used for turbojet-
powered airplanes is usually higher. Therefore, the proposed 
requirement would be more stringent for propeller-driven airplanes. We 
consider the increased stringency for propeller-driven airplanes to be 
desirable for the following reasons:
     Propeller-driven airplanes generally have deicing systems 
that cycle on and off, allowing ice to accrete on the protected 
surfaces before removing it. Also, these deicing systems typically do 
not remove all of the ice with each cycle, leaving some residual ice. 
Both of these effects result in drag increases that are generally not 
present on turbojet airplanes that have ice protection systems using 
hot bleed air from the engines.
     Propeller-driven airplanes will likely be subjected to 
increased exposure to icing conditions, due to their slower operating 
speeds, shorter flight lengths, and lower cruising altitudes.

I. Landing (Sec.  25.125)

    We propose to revise Sec.  25.125(a) to identify when the landing 
distance must be determined specifically for icing conditions. The 
proposed requirement would specify that the landing distance must be 
determined for icing conditions if the VREF in icing 
conditions exceeds the VREF in non-icing conditions by more 
than 5 knots CAS. For icing conditions, the landing distance would be 
determined with the landing ice accretion defined in the proposed 
revision to appendix C.
    Additionally, a new paragraph (b) would be added to include the 
landing distance requirements that would be moved from the existing 
paragraph (a). The new paragraph (b) would also set the requirements 
for determining the landing speeds to use in determining the landing 
distances for both icing and non-icing conditions. For icing 
conditions, the landing speed must not be lower than 1.23 
VSR0 with the landing ice accretion on the airplane if that 
speed exceeds the VREF for non-icing conditions by more than 
5 knots CAS.
    The existing paragraphs (b) through (f) would be redesignated as 
(c) through (g).
    Whether landing distances or landing speeds must be determined 
specifically for icing conditions depends on whether VREF 
needs to be increased by more than 5 knots CAS to counteract the effect 
of ice on airplane stall speeds. The reasons behind allowing 
VREF to increase by up to 5 knots CAS in icing conditions 
before requiring landing distance performance to be recomputed for 
icing conditions are:
     As part of the flight testing to demonstrate compliance 
with the landing distance requirements, we typically evaluate airplane 
controllability when landing at speeds lower than the normal landing 
speeds. We usually perform this evaluation at a speed 5 knots below 
VREF to cover inadvertent speed variations that may occur in 
operational service. Plus or minus five knots variation from 
VREF is frequently used as a guideline for evaluating 
expected operational variations in landing speeds.
     Normal approaches in transport category airplanes are 
typically flown at speeds above VREF to provide speed 
margins to account for wind gusts. Although the additional speed should 
be bled off by the time that the airplane is over the landing 
threshold, it may not be. Service history does not indicate any safety 
problems with the resulting longer landing distance.
     Many transport category airplanes are flown at a speed 5 
knots higher than VREF during final approach to counter any 
inadvertent speed loss. Often this additional speed has not been bled 
off before reaching the landing threshold. Again, service history does 
not indicate any safety problems with the resulting longer landing 
distance.
     A 5-knot increase above the VREF speed for non-
icing conditions equates to approximately 3 percent of the 1-g stall 
speed (slightly less than 3 percent for larger airplanes). This is 
consistent with the allowable stall speed increase proposed for the 
takeoff path requirements for icing conditions.
    As a further safety consideration for the VREF speed, 
Sec.  25.125(b)(ii)(c) would require that VREF for icing 
conditions must provide the same maneuvering capability (with ice 
accretions on the airplane) as is currently required at VREF 
for non-icing conditions. This may result in an increase to 
VREF for icing conditions even if this increase is less than 
5 knots.
    The current Sec.  25.125(a)(2), which would be redesignated as 
Sec.  25.125(b)(2)(i), requires VREF for non-icing 
conditions to be not less than the landing minimum control speed, 
VMCL. This existing requirement ensures that adequate 
directional control is available in case an engine fails during a go-
around. Under the proposed new rule, the VMCL determined for 
non-icing conditions would continue to be used for icing conditions. 
This would be similar to the takeoff flight phase, where the takeoff 
minimum control speeds, VMCG and VMCA, determined 
for non-icing conditions would continue to be used for icing 
conditions. Unlike the takeoff case; however, the continued use of the 
non-icing VMCL is not explicitly stated. We consider the 
proposed requirements to adequately address this issue without 
proposing an additional explicit requirement. Section 25.125(b)(2)(ii) 
requires VREF for icing conditions to be not less than 
VREF for non-icing conditions. Under Sec.  25.125(b)(2)(i), 
VREF for non-icing conditions must be not less than 
VMCL for non-icing conditions. Taken together, these two 
proposed requirements would allow the VMCL determined for 
non-icing conditions to continue to be used for icing conditions.
    To assure that using the VMCL determined for non-icing 
conditions will provide safe controllability and maneuverability for 
icing conditions, the proposed Sec. Sec.  25.143(c)(2) and (c)(3) would 
require the applicant to show that the airplane will be safely 
controllable and maneuverable during an approach and go-around and an 
approach and landing, both with the critical engine inoperative. For 
added safety during certification flight testing, these maneuvers may 
be accomplished with a simulated engine failure (as noted in the 
proposed advisory material associated with this proposal).

J. Controllability and Maneuverability--General (Sec.  25.143)

    We propose to revise Sec.  25.143 to add a new paragraph (c) that 
requires the applicant to show that the airplane with ice accretions 
and with the critical engine inoperative is safely controllable and 
maneuverable during takeoff, an approach and go-around, and an approach 
and landing; a new paragraph (i) to identify the ice accretions that 
must be used in showing compliance with Sec.  25.143 in icing 
conditions, and to introduce two specific controllability requirements 
that apply to flight in icing conditions; and a new paragraph (j) to 
specify tests for ensuring that the airplane has adequate 
controllability for flight in icing conditions before the ice

[[Page 67286]]

protection system is activated and performing its intended function of 
removing any ice accretions from protected surfaces.
    In addition, existing paragraphs (c) through (g) would be 
redesignated as paragraphs (d) through (h), and paragraph references in 
the newly designated paragraphs (d), (e), and (f) would be revised 
accordingly.
    The requirements proposed in new paragraph (c) are intended to 
ensure that using the minimum control speeds for non-icing conditions 
would not result in controllability and maneuverability safety concerns 
when the same speeds are used for icing conditions.
    The proposed new paragraph (i)(1) would require compliance with all 
of Sec.  25.143 in icing conditions except paragraphs (b)(1) and (2). 
Sections 25.143(b)(1) and (2) are excepted from icing analysis under 
proposed section 25.21(g).
    These proposed requirements assume a conventional empennage (that 
is, wing/fuselage/tailplane) configuration. Special conditions, issued 
in accordance with Sec.  21.16, may be necessary for certification of 
airplanes with an unconventional empennage configuration.
    Applicants can minimize the number of ice accretions to be tested 
by using one accretion that is shown to be the most critical accretion 
for several flight phases.
    In many cases, a thin, rough, layer of ice (defined as sandpaper 
ice in the proposed revision to appendix C) has been shown to have a 
more detrimental effect on handling qualities for airplanes with 
unpowered control systems than larger ice accretions. The effect of 
sandpaper ice accretions may be more significant than larger ice 
accretions on these airplanes. In some cases, such an accretion has 
resulted in control surface hinge moment reversals that required the 
flightcrew to apply extremely high forces to the controls to regain 
control of the airplane. Applicants would have to consider sandpaper 
ice in showing compliance with the proposed Sec.  25.143(i).
    The proposed paragraph (i)(2) would require applicants to conduct a 
pushover maneuver down to a zero g load factor with the critical ice 
accretion on the airplane. (If the airplane lacks enough elevator power 
to get to a zero g load factor, the maneuver may be ended at the lowest 
load factor obtainable.) The purpose of this proposed requirement is to 
evaluate an airplane's susceptibility to a phenomenon known as ice-
contaminated tailplane stall (ICTS). Ice-contaminated tailplane stall 
ca