Part 121 Activation of Ice Protection, 61055-61067 [E9-28036]

Agencies

• Federal Aviation Administration
• DEPARTMENT OF TRANSPORTATION

[Federal Register Volume 74, Number 224 (Monday, November 23, 2009)]
[Proposed Rules]
[Pages 61055-61067]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: E9-28036]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 121

[Docket No. FAA-2009-0675; Notice No. 09-07]
RIN 2120-AJ43


Part 121 Activation of Ice Protection

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Notice of proposed rulemaking (NPRM).

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SUMMARY: This action would amend the regulations applicable to 
operators of certain airplanes used in Title 14 Code of Federal 
Regulations part 121 operations and certificated for flight in icing 
conditions. The proposed standards would require either the 
installation of ice detection equipment or changes to the Airplane 
Flight Manual to ensure timely activation of the airframe ice 
protection system. This proposed regulation is the result of 
information gathered from a review of icing accidents and incidents, 
and it is intended to improve the level of safety when airplanes are 
operated in icing conditions.

DATES: Send your comments on or before February 22, 2010.

ADDRESSES: You may send comments identified by Docket Number FAA-2009-
0675 using any of the following methods:
     Federal eRulemaking Portal: Go to https://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 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 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 received, without change, 
to https://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 https://DocketsInfo.dot.gov.
    Docket: To read background documents or comments received, go to 
https://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.
    Contacts for Further Information: For operational questions about 
the proposed rule contact Jerry Ostronic, FAA, Air Carrier Operations 
Branch, AFS-220, Flight Standards Service, 800 Independence Ave., SW., 
Washington, DC 20591; telephone (202) 267-8166; facsimile (202) 267-
5229, e-mail Jerry.C.Ostronic@faa.gov.
    For aircraft certification questions about the proposed rule 
contact Robert Jones, FAA, Propulsion/Mechanical Systems Branch, ANM-
112, Transport Airplane Directorate, Aircraft Certification Service, 
1601 Lind Avenue, SW., Renton, WA 98057-3356; telephone (425) 227-1234; 
facsimile (425) 227-1149, e-mail Robert.C.Jones@faa.gov.
    For legal questions about the proposed rule contact Douglas 
Anderson, FAA, Office of Regional Counsel, Federal Aviation 
Administration, 1601 Lind Avenue, SW., Renton, Washington 98057-3356; 
telephone (425) 227-2166; fax: (425) 227-1007, e-mail 
Douglas.Anderson@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. Instructions for accessing the docket appear 
under the ADDRESSES heading of this notice of proposed rulemaking 
(NPRM). Appendix 1 of this preamble defines terms used in the preamble 
of this NPRM.

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 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; regulations and minimum standards of safety 
for inspecting, servicing, and overhauling aircraft; and regulations 
for other practices, methods, and procedures the Administrator finds 
necessary for safety in air commerce. This regulation is within the 
scope of that authority because it prescribes new safety standards for 
the operation of certain airplanes used in air carrier service.

I. Background

    On October 31, 1994, an accident involving an Avions de Transport 
Regional ATR 72 series airplane occurred in icing conditions. This 
prompted the FAA to initiate a review of aircraft safety in icing 
conditions and determine what changes could be made to increase the 
level of safety. In May 1996, the FAA sponsored the International 
Conference on Aircraft

[[Page 61056]]

Inflight Icing, where icing specialists recommended improvements to 
increase the level of safety of aircraft operating in icing conditions. 
The FAA reviewed the conference recommendations and developed a 
comprehensive, multi-year icing plan. The FAA Inflight Aircraft Icing 
Plan, dated April 1997,\1\ described various activities the FAA was 
considering to improve aircraft safety when operating in icing 
conditions. In accordance with the FAA Inflight Aircraft Icing Plan, 
the FAA tasked the Aviation Rulemaking Advisory Committee (ARAC) \2\ to 
consider the need for ice detectors or other means to warn flightcrews 
early about ice accreting on critical surfaces requiring crew action. 
The work would be carried out by ARAC's Ice Protection Harmonization 
Working Group (IPHWG). This proposed rule is based on ARAC's 
recommendations to the FAA, which may be found in the docket for this 
rulemaking, docket FAA-2009-0675.
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    \1\ FAA Inflight Aircraft Icing Plan, dated April 1997, is 
available in the Docket.
    \2\ Published in the Federal Register, December 8, 1997 (62 FR 
64621).
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A. Existing Regulations for Flight in Icing Conditions

    Currently, the certification regulations applicable to 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.\3\ Amendment 25-121 to 14 CFR part 25, 
which applies to transport category airplanes, added specific 
requirements for airplane performance and handling qualities for flight 
in icing conditions.\4\ Recently, the FAA adopted Amendment 25-129 \5\ 
to add requirements in Sec.  25.1419 to provide means to ensure timely 
activation of ice protection systems. These requirements will apply to 
airplanes type certificated in the future. The regulations for 
airplanes certificated under part 23 (non-transport) require that ``a 
means be identified or provided for determining the formation of ice on 
critical parts of the airplane * * *''
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    \3\ Section 25.1419, Ice Protection.
    \4\ 72 FR 44656 (August 8, 2007).
    \5\ 74 FR 38328 (August 3, 2009).
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    Parts 91, 121, and 135 contain regulations that apply to airplane 
operations in icing conditions. Operating regulations under parts 91 
and 135 address limitations in icing conditions for airplanes operated 
under those regulations.\6\ Part 121 addresses operations in icing 
conditions that might adversely affect safety and regulates 
installation of certain types of ice protection and wing illumination 
equipment.\7\
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    \6\ 14 CFR 91.527, Operating in icing conditions; and Sec.  
135.227, Icing conditions: Operating limitations.
    \7\ 14 CFR 121.629(a), Operation in icing conditions and Sec.  
121.341, Equipment for operations in icing conditions.
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    Neither the current operating regulations nor the certification 
regulations in effect before the recent adoption of Amendment 25-129 
require a means to ensure timely activation of ice protection systems. 
This proposed rule would provide a standard to ensure that ice 
protection systems on in-service part 121 airplanes are activated in a 
timely way to ensure safe flight in icing conditions.

B. National Transportation Safety Board Safety Recommendations

    This proposal addresses Safety Recommendation No. A-07-14 \8\ 
issued by the National Transportation Safety Board (NTSB) on the 
subject of airframe icing. That NTSB safety recommendation is a result 
of a Cessna Citation 560 series airplane accident near Pueblo, Colorado 
on February 16, 2005, in which the airplane crashed and eight people 
died. The accident airplane had been operating in icing conditions, and 
the flightcrew had not activated the airframe ice protection system 
during approach, as was required for those operating conditions by the 
Airplane Flight Manual (AFM). The NTSB recommended that manufacturers 
and operators of pneumatic-deicing-boot-equipped airplanes be required 
to revise their AFM, operating manuals, and training programs to 
emphasize that leading-edge deicing boots should be activated as soon 
as the airplane enters icing conditions.
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    \8\ NTSB recommendation A-07-14 is available in the Docket and 
on the Internet at: https://www.ntsb.gov/Recs/letters/2007/A07_12_17.pdf.
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C. Authorities

1. Federal Aviation Administration
    Title 14 CFR part 25 contains the U.S. airworthiness standards for 
type certification of transport category airplanes. These standards 
apply to airplanes manufactured within the 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 Joint Airworthiness Requirements (JAR)-25 contain the 
airworthiness standards of the Joint Aviation Authorities (JAA) of 
Europe for type certification of transport category airplanes. Thirty-
seven European countries accept airplanes type certificated to JAR-25 
standards. These countries also accept airplanes manufactured in the 
U.S. that are type certificated to JAR-25 standards for export to 
Europe.
3. 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 assumed most 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 EASA's 
``Certification Specifications for Large Aeroplanes'' (CS-25) in 
similar if not identical language. EASA's CS-25 became effective 
October 17, 2003.

D. Harmonization of U.S. Standards With Those of Other Countries

    The airworthiness standards proposed in this NPRM were developed 
before EASA began operations. They were developed in coordination with 
the JAA, United Kingdom Civil Aviation Authority, and Transport Canada. 
None of these civil aviation authorities have initiated rulemaking to 
adopt the proposed standards.

E. Related Rulemaking Activity

    A final rule titled ``Activation of Ice Protection'' was published 
on August 3, 2009.\9\ It amends Sec.  25.1419 by requiring a method to 
ensure timely activation of the airframe ice protection systems (IPS). 
It also adds requirements to reduce flightcrew workload associated with 
operation of an airframe IPS that operates cyclically, and to ensure 
that procedures for operation of an airframe IPS are included in the 
AFM. Those changes affect new airplane certification for flight in 
icing conditions. In contrast, this proposed rule is concerned with 
timely airframe IPS activation for in-service airplanes.
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    \9\ 74 FR 38328.
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F. Advisory Material

    In addition to this NPRM, the FAA has developed Advisory Circular 
(AC) 121.321, ``Compliance with the Requirements of Sec.  121.321.'' 
That proposed AC would provide guidance

[[Page 61057]]

for one acceptable means, but not the only means, of demonstrating 
compliance with this proposed rule. The draft AC has been released 
concurrently with this NPRM. It is posted on the ``Aircraft 
Certification Draft Documents Open for Comment'' Web site, https://www.faa.gov/aircraft/draft_docs. The Web site will indicate the date 
comments are due.

II. Discussion of the Proposal

A. Safety Concern

    The ARAC IPHWG, as a result of the FAA's tasking, reviewed icing 
events. The IPHWG found accidents and incidents where the flightcrew 
were either completely unaware of ice accretion on the airframe, or 
were aware of ice accretion but judged it not significant enough to 
warrant operation of the airframe IPS. The FAA agreed with the ARAC 
recommendation for rulemaking that would require that flightcrews have 
a clear means to know when to activate the airframe IPS.

B. Means To Address the Safety Concern

1. Airworthiness Directives
    The FAA has issued airworthiness directives (AD) to address when to 
activate the airframe IPS on several types of airplanes. These ADs 
require activation of pneumatic deicing boots at the first signs of ice 
accretion on the airplane. This requirement relieves the pilot of the 
responsibility for determining whether the amount of ice accumulated on 
the wing warrants airframe IPS activation. But activation of the 
pneumatic deicing boots is still subject to the flightcrew's 
observation of ice accretions, and such observations can be difficult 
during times of high workload, during operations at night, or when 
clear ice has accumulated. The difficulties associated with observing 
ice accretions are applicable to any airframe IPS that relies on the 
flightcrew's observations for activating the system, not just pneumatic 
deicing boots, so those ADs are not adequate to address the safety 
concern that is the focus of this proposed rulemaking. The FAA has 
determined, however, that because the cruise phase of flight entails a 
lower workload than other phases of flight, activation of the deicing 
boots based on flightcrew observation of ice accretions during this 
phase of flight is acceptable.
2. A Primary Ice Detection System
    The IPHWG concluded that installing a device to alert the 
flightcrew to activate the airframe IPS would be a better way to 
address the safety concern than solely relying on the flightcrew's 
observation of ice accretion to determine when to activate the IPS. The 
FAA has determined that a primary ice detection system would be one 
acceptable means to meet the objectives of this proposed rule. Such a 
system typically consists of two independent detectors (an advisory ice 
detection system typically has only one detector). A primary ice 
detection system has sufficient performance and reliability levels that 
the flightcrew does not need to monitor icing conditions. A primary ice 
detection system could either automatically activate the airframe IPS 
or indicate to the flightcrew when to activate the system. There are 
several types of airplanes currently in operation that have primary ice 
detection systems installed, and the FAA agrees with the IPHWG 
determination that these airplanes already meet the desired level of 
safety.
3. An Advisory Ice Detection System and Visual Cues
    An advisory ice detection system typically consists of one 
detector. Such a system does not have sufficient reliability to be the 
primary means of determining when the airframe IPS must be activated. 
With an advisory ice detection installed, it is still the flightcrew's 
responsibility to make the determination to activate the IPS. However, 
the advisory ice detection system would provide a much higher level of 
safety than visual cues alone and would mitigate the effects of human 
sensory limitations and inadequate attention resulting from workload.
    An advisory ice detection system, in conjunction with visual cues 
that pilots can use to identify icing accumulation, would also be an 
acceptable means of alerting the flightcrew to activate the airframe 
IPS and meet the objectives of this proposed rule. If this method is 
used, however, its acceptability would be contingent upon the 
following:
     The advisory ice detection system would indicate to the 
crew when icing conditions exist.
     The flightcrew would activate the airframe IPS based on 
either their observation of the first sign of ice accretion or an alert 
from the advisory ice detection system indicating the presence of ice, 
whichever occurs first. This activation would not depend on determining 
the thickness of the accretion.
4. Operating the Ice Protection System Continuously
    The FAA agrees with the IPHWG conclusion that an acceptable means 
of meeting the objectives of this proposed rule would be to require 
operating the airframe IPS continuously whenever the airplane is 
operating in conditions conducive to airframe icing, except in the 
cruise phase of flight (discussed below). To accomplish this, the 
flightcrew would activate the airframe IPS in response to a specific 
air temperature threshold and the presence of visible moisture. Because 
ambient temperature is indicated by flight deck instruments and the 
flightcrew can readily observe visible moisture, deciding when to 
initiate the system would require little increased effort on the part 
of the flightcrew.

C. The Proposed Rule

    The proposed rule would be applicable to airplanes with a 
certificated maximum takeoff weight (MTOW) less than 60,000 pounds. 
Proposed Sec.  121.321 would require that, 24 months after the 
effective date of the final rule, no person may operate an airplane 
with a certificated MTOW less than 60,000 pounds in conditions 
conducive to airframe icing unless the airframe IPS is operated in 
accordance with the proposed section. To address flight in icing 
conditions, proposed Sec.  121.321(a) would require one of the 
following:
    (1) A primary ice detection system and automatic or manual 
activation of the airframe IPS upon notice from the primary ice 
detection system that activation is necessary, as well as initiation of 
any other operational procedures for operating in icing conditions 
specified in the AFM; or
    (2) Both visual cues and an advisory ice detection system, either 
of which enable the flightcrew to determine when the airframe IPS must 
be activated, activation of the primary airframe IPS when either of 
those means indicate it is necessary, and initiation of any other 
operational procedures for operating in icing conditions specified in 
the AFM; or
    (3) If the airplane is not equipped to comply with either of the 
above two options, activation of the airframe IPS and initiation of 
approved procedures for operating in airframe icing conditions during 
climb, holding, maneuvering for approach and landing, and any other 
operation at approach or holding airspeeds, when in conditions 
conducive to airframe icing. However, if this option is specifically 
prohibited in the AFM, then proposed Sec.  121.321(b) would require 
either (1) or (2) above.
    Proposed Sec.  121.321(a) would also require that if option (a)(3) 
is selected, the airframe IPS must be activated and operated at the 
first sign of ice formation anywhere on the airplane during any

[[Page 61058]]

other phase of flight besides climb, holding, and maneuvering for 
approach and landing, except where the AFM specifies that the airframe 
IPS should not be used.
    Proposed Sec.  121.321(c) would require that procedures for 
operating the airframe IPS be included in the AFM for airplanes that 
comply with proposed Sec.  121.321(a)(1) or (a)(2). For airplanes that 
comply with proposed Sec.  121.321(a)(3), the procedures must be in the 
AFM or in the air carrier's operations manual required by Sec.  
121.133.
    Proposed Sec.  121.321(d) would require the AFM or the manual 
required by Sec.  121.133 to address initial activation, operation 
after initial activation, and deactivation of the airframe IPS. This 
proposed provision would allow continuous operation, automatic cycling, 
or manual cycling of the airframe IPS, depending on the design of the 
airplane's airframe IPS. For airplanes equipped with ice detection 
systems, this proposed paragraph would require cycling, either manual 
or automatic, each time ice is detected.
    Certain IPSs use fluids that lower the freezing point of water. 
Unlike other IPSs, fluid systems have a limited duration of ice 
protection that is related to the capacity of fluid that the airplane 
can carry. These systems need additional evaluation. Therefore, for 
airplanes equipped with fluid ice protection systems to comply with 
proposed Sec.  121.321, two issues must be addressed:
     System design. The system design must have adequate fluid 
capacity to ensure that the airplane/flightcrew can comply with this 
proposed rule.
     AFM Dispatch Instructions. The AFM must contain 
information to ensure that the system is serviced with the appropriate 
amount of fluid for each flight to ensure that the airplane/flightcrew 
can comply with this proposed rule.
    For airplanes without ice detection systems, this proposed rule 
also allows manual cycling based on time intervals. Recently adopted 14 
CFR 25.1419(g) requires transport category airplanes to be equipped 
with an ice detection system that alerts the pilot when to activate the 
airframe IPS if the ice protection is not either operated continuously 
in icing conditions or automatically activated. However, it does not 
allow manual cycling of the IPS based on time intervals. Therefore, 
manual cycling based on time intervals would be allowed only for 
airplanes without Sec.  25.1419(g) in their certification basis. This 
would allow the existing airplane fleet to comply with this proposed 
rule without modifying the airframe IPS.
    The modifications to airplanes to install ice detection systems to 
comply with this proposed rule would likely be complex. They would 
require thorough testing and analysis to ensure that the ice detection 
systems perform their intended function when installed on the airplane. 
Therefore, the FAA proposes in Sec.  121.321(e) that these 
modifications would require approval through an amended or supplemental 
type certificate in accordance with 14 CFR part 21. In the normal 
course of equipment approval, any revised procedures and/or limitations 
associated with such modifications would also need to be addressed in 
the AFM under Sec. Sec.  23.1581 or 25.1581.

D. Affected Airplanes

    The ARAC's recommendation was limited to airplanes with a 
certificated MTOW of less than 60,000 lbs. A limited analysis of past 
icing events revealed that airplanes with certificated MTOWs greater 
than 60,000 lbs. have not experienced accidents due to in-flight icing, 
while airplanes with lower certificated MTOWs have an event history. 
Since certificated MTOW is simple to discern, well-understood, and will 
address airplanes that have had an event history, the IPHWG recommended 
it be adopted as the discriminating parameter and the FAA agrees.
    The FAA requests comment on whether this proposed rule, if adopted, 
should be applied to airplanes larger than 60,000 pounds MTOW. For 
example, initial indications were that icing may have been implicated 
in a recent accident near Buffalo, New York, involving an airplane with 
a MTOW slightly greater than 60,000 pounds. While subsequent 
investigation indicates that icing was not implicated in this accident, 
if this rule applied to airplanes with a MTOW of 66,000 pounds, the 
accident airplane would have been subject to its requirements.\10\
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    \10\ The accident airplane was equipped with an ice detection 
system that would enable an operator to comply with this proposed 
rule. Preliminary reports indicate that the ice protection system 
was operating at the time of the accident.
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E. Phase of Flight Considerations

1. Approach, Landing, Go-Around and Holding Phases of Flight
    The IPHWG accident and incident review revealed that the phases of 
flight that presented the greatest risk from airframe icing were those 
associated with low speed and relatively high angle-of-attack operation 
(that is, approach, landing, go-around, and holding). With respect to 
these phases of flight, for airplanes not equipped with primary or 
advisory ice detection systems, the IPHWG determined that the following 
factors substantiated the need for requiring activation of the airframe 
IPS while in conditions conducive to icing:
     An overall majority of events which originated in these 
phases of flight;
     A sufficient number of events in which the flightcrew was 
confirmed to be unaware of ice accretion, supplemented by a substantial 
number of events in which flightcrew awareness of ice accretion was 
unknown;
     High cockpit workload resulting in low residual flightcrew 
attention;
     Frequent maneuvering, resulting in little opportunity for 
the flightcrew to detect aerodynamic degradations due to icing; and
     Maneuvering at relatively high angles of attack.
    The FAA concurred with this analysis.
2. Cruise Phase
    In contrast with the phases of flight discussed previously, for the 
cruise phase of flight in airplanes not equipped with primary or 
advisory ice detection systems, the IPHWG determined that it would not 
be appropriate to require activation of the airframe IPS while in 
conditions conducive to icing. Rather, the IPHWG recommended that the 
airframe IPS be activated at the first sign of ice accretion, and 
operated thereafter, using an automatic system or manually based on 
time, until after the airplane departs the conditions conducive to 
icing.
    The IPHWG reviewed accidents and incidents that originated during 
the cruise phase of flight.\11\ For the events with sufficient data 
available for analysis, the IPHWG found that flightcrews were aware of 
the ice accretion, but did not activate the IPS. Waiting for a specific 
thickness of ice to accrete before activating the IPS was consistent 
with the common activation procedure at that time.
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    \11\ Cruise is the phase in which an altitude or flight level is 
maintained during en route level flight.
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    Flightcrew workload is lighter during the cruise phase of flight. 
This may account for the flightcrews of the cruise phase accident and 
incident airplanes being aware of the ice accretion, as compared to 
events which have occurred in other phases of flight, when workload was 
high and flightcrews were not aware of ice accretions.
    The IPHWG also considered the human factors aspect of requiring

[[Page 61059]]

flightcrews to activate the IPS during the cruise phase of flight. 
Activation of the IPS based on conditions conducive to ice accretion, 
even if ice is not actually accreting, is a conservative way to ensure 
that the IPS is operated in a timely manner. For the cruise phase of 
flight, however, the IPHWG considered that flightcrews would more 
reliably activate the airframe IPS at the first sign of icing than they 
would if required to activate the system and keep operating it for long 
periods without any indication of ice accretion.
    The IPHWG determined the following factors substantiated the 
acceptability of requiring activation of the airframe IPS based on 
flightcrew observation of airframe ice accretions during the cruise 
phase of flight:
     No accidents or incidents during cruise where the 
flightcrew were unaware of ice accretions on the airframe;
     Low cockpit workload, resulting in sufficient residual 
flightcrew attention to detect ice accretions;
     Infrequent maneuvering, resulting in opportunity for the 
flightcrew to detect aerodynamic degradations due to icing; and
     Human factors concerns about requiring flightcrews to 
operate the IPS for extended periods of time when there may not be any 
ice on the airframe.
    The FAA agrees with this analysis. Therefore, for the cruise phase 
of flight, this proposed rule is written to require IPS activation and 
use at the first sign of ice on the airplane and thereafter, according 
to the procedures in the AFM or in the manual required by Sec.  
121.133. This may be accomplished with an automatic system, or the IPS 
may be cycled manually based on time.
3. Takeoff Phase of Flight
    The IPHWG excluded the takeoff phase of flight from its 
recommendation for rulemaking because the accidents related to that 
phase of flight were caused by improper ground deicing/anti-icing 
procedures. Ground deicing and anti-icing procedures have been 
addressed by Amendment 121-253 to 14 CFR (121.629(b) and (c), 
``Operating in icing conditions''). Again, the FAA agreed with this 
recommendation.

F. Temperature

    In some cases, airframe manufacturers have specified definitions of 
icing conditions for some airplane types. In the absence of type-
specific information, the IPHWG concluded that conditions conducive to 
airframe icing would exist in flight at an outside air temperature at 
or below 2 [deg]C in clouds or precipitation.
    Engine IPSs are commonly operated at or below a static air 
temperature of 5 [deg]C or a total air temperature of 10 [deg]C. This 
temperature is different from the 2 [deg]C recommended by ARAC for this 
proposal. The FAA believes that using a common temperature for 
activation of both the engine and the airframe IPSs would reduce crew 
workload and decrease the probability of the flightcrew not noticing 
when the temperature has dropped to 2 [deg]C. The FAA therefore 
proposes to identify conditions conducive to airframe icing in this 
proposed rule as visible moisture at or below a static air temperature 
of 5 [deg]C or a total air temperature of 10 [deg]C.
    The FAA agrees with the IPHWG that flightcrews must be given a 
clear means to know when to activate the airframe IPS. In the past, 
many airplanes have had procedures requiring activation only after a 
substantial accumulation of ice. This proposed rule would require that 
ice detection systems be installed, or that ice protection systems be 
manually activated in conditions conducive to icing in most phases of 
flight. In the cruise phase, the airframe IPS would be activated at the 
first sign of ice accumulation anywhere on the airplane. To ensure 
timely activation of the airframe IPS, the FAA proposes to amend the 
current part 121 regulations as recommended by the IPHWG, except for 
the change to the temperature considered conducive to airframe icing, 
as discussed above.

G. Technology Available To Comply With Proposed Rule

    The FAA and IPHWG reviewed the current state of ice detector 
technology and found viable means of compliance with the proposed rule. 
There are several methods available to reliably alert the flightcrew to 
activate the airframe IPS. This technology has been approved for use on 
airplanes to alert or advise the pilot of ice accretion, or as the 
primary means of determining when the airframe IPS should be activated.

H. Differences From the ARAC Recommendation

    Besides the change in the air temperatures proposed for defining 
conditions conducive to icing, which is discussed earlier in this 
document, the FAA made several other changes to the rule recommended by 
ARAC through the IPHWG. One change was a rewording of the ARAC-
recommended rule to clarify its applicability to the airframe IPS. The 
rule language recommended by ARAC did not specify applicability only to 
airframe IPSs.
    The FAA made another change because, although the ARAC 
recommendation provided three ways to ensure that the flightcrew would 
know when to activate the airframe IPS, for at least one of them it did 
not specify when the flightcrew must activate the airframe IPS. The 
agency has revised the ARAC wording to clarify when the flightcrew must 
activate the airframe IPS. The FAA also revised the ARAC-recommended 
rule to specify items that must be included in the AFM or the manual 
required by Sec.  121.133. These revisions are considered minor changes 
to the ARAC's recommendation.

I. Airworthiness Directives

    The requirements proposed in this NPRM to some extent overlap and 
duplicate existing requirements in certain airworthiness directives 
(ADs). As discussed above, these ADs require revisions to the AFM for 
certain airplanes to provide information and instructions to pilots for 
operating in icing conditions. This proposed rule would also require 
AFM revisions to provide information for operating in icing conditions 
for those same airplanes, among others. However, the operating 
information required by this proposal would be more detailed and 
specific to the individual airplane models than the information 
required by the ADs and, in some cases, the proposed instructions to 
the pilots would be more stringent than those required by the ADs.
    If this proposed rule is adopted, the FAA will revise those ADs to 
incorporate the new requirements. It is necessary to retain those ADs 
because this proposed rule would apply only to part 121 operations. The 
ADs, on the other hand, apply to all operations of the subject 
airplanes. Rescinding the ADs would allow reintroduction of the unsafe 
condition (that is, delayed activation of IPSs) into operations 
conducted under other parts.
    The list of those ADs appears in Appendix 2 of the preamble of this 
NPRM.

J. Level of Approval

    For an amended or supplemental type certificate used to comply with 
this proposed rule, among the pertinent rules that apply to any 
modification are Sec. Sec.  23.1301 or 25.1301 (``Equipment--Function 
and installation''). Paragraph (a) of these rules requires that the 
equipment ``be of a kind and design appropriate to its intended 
function.'' This proposed rule would not by itself impose new 
airworthiness standards. However, to meet this ``intended function'' 
requirement, an applicant seeking approval of design changes to enable 
operators to comply with this

[[Page 61060]]

proposed rule would have to show that the airplane, as modified, would, 
in fact, comply with this proposed rule. This requirement is consistent 
with the FAA's practice of compliance findings for the digital flight 
data recorder requirements of Sec.  121.343 (Amendment No. 121-238, 
``Extension of Compliance Data for Installation of Digital Flight Data 
Recorders on Stage 2 Airplanes'').\12\
---------------------------------------------------------------------------

    \12\ Docket No. 27532, published in the Federal Register on May 
24, 1994 (59 FR 26896).
---------------------------------------------------------------------------

    This proposed rule is not intended to disapprove an existing part 
23 or part 25 approval for flight in icing conditions. It would not 
require re-certification of an airplane for flight in conditions 
conducive to airframe icing.

K. Compliance Time

    This notice proposes a two-year compliance time after the effective 
date of the final rule. That compliance time is based on the time 
required to approve new designs and install new equipment. For some 
airplanes, it may be possible to comply through AFM revisions alone, 
which could be accomplished quickly. However, some airplanes may need 
to go through a more involved certification process, so the longer 
compliance time of two years was chosen.

L. Reasons for Not Proposing Part 91 and Part 135 Operating Rules

    Part 121 covers all scheduled air carrier operations of airplanes 
with ten or more passenger seats and scheduled air carrier operations 
of all turbojets regardless of size. The ``hub and spoke'' route 
network of many air carriers can concentrate large numbers of part 121 
operations within a single weather system. With occasional exceptions 
under Sec.  121.590, part 121 operators are constrained to using only 
airports certificated under 14 CFR part 139. A given part 121 operator 
is generally further constrained to use of only those part 139 airports 
listed in its Operations Specifications.
    Flightcrews of part 121 operators generally do not carry approach 
charts for airports not listed in their Operations Specifications. 
During busy traffic periods, lengthy vectoring or holding for landing 
sequencing is common at these airports. When this vectoring results in 
exposure to undesirable conditions such as icing, the flightcrews' 
options (except in case of emergency) are generally limited to 
tolerating the exposure or diverting to a pre-planned part 139 
alternate airport listed in their Operations Specifications.
    The FAA considered 14 CFR part 91 and part 135 operations. Most 
aircraft operated under parts 91 and 135 have been subjected to the ADs 
discussed above regarding activation of their de-icing boots at first 
signs of ice accretion. Those ADs apply to all aircraft with pneumatic 
de-icing boots that are certificated for flight in known icing 
conditions. The ADs addressing boot activation resulted from an FAA 
review of operating procedures and certification bases on the affected 
aircraft. As a result of this aircraft review and issuance of ADs, a 
level of safety for initial ice accretions has been established.
    Part 91 and part 135 aircraft are typically smaller-scale aircraft 
than those operated under part 121. This smaller scale provides easier 
monitoring of ice accretions. Part 91 and part 135 operators are also 
not limited to part 139 airports only, and in fact, often avoid them 
because of the factors discussed above. Even when such operations 
include part 139 airports, operators may divert to any of a number of 
suitable airports near the scheduled part 139 airport. Consequently, 
part 91 and part 135 operators often operate in a lower air traffic 
density that results in fewer holding delays and significantly more 
routing options in icing conditions.
    The level of safety provided by the combination of the ADs, the 
review of the operating procedures, the ability to more readily 
evaluate ice accretions, and tactical flexibility provide a level of 
safety comparable to other part 91 and part 135 operational 
requirements. The proposed part 121 rule change will enhance the level 
of safety for the segment of the traveling public that has the greatest 
exposure and subsequent risk associated with flight in icing 
conditions. Therefore, the IPHWG concluded that rules for parts 91 and 
135 are not required at this time, and the FAA agrees.

M. Applicability to Part 23 and Part 25 Airplanes

    The icing accident and incident database developed by the IPHWG 
showed that all the relevant accidents and incidents occurred on 
airplanes with a certificated MTOW of less than 60,000 pounds. Based on 
this finding, the FAA is proposing a part 121 rule that is applicable 
to those airplanes. Since the proposed rule addresses the safety 
concerns of flight in icing conditions for smaller airplanes (those 
with a certificated MTOW less than 60,000 pounds), the rule would be 
applicable to both part 23 and part 25 airplanes that are operated 
under part 121.

N. Discussion of Working Group Non-Consensus Issues

    The IPHWG did not reach consensus on several issues related to this 
rulemaking proposal. A summary of these issues can be found in the 
docket. The complete working group discussion of the dissenting 
opinions is also available in the docket for this rulemaking.

O. Related ARAC Recommendations

    The ARAC has submitted the following additional rulemaking 
recommendations to the FAA to improve the safety of operations in icing 
conditions. The FAA has not yet completed deliberations on these 
recommendations, but they may lead to future rulemaking.
     A part 121 recommendation to require certain airplanes to 
exit icing conditions.
     Parts 25 and 33 recommendations to address ice protection 
activation and operations in supercooled large droplet, mixed phase, 
and glaciated icing conditions.

Rulemaking Notices and Analyses

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 FAA has determined that 
there are no new information collection requirements associated with 
this proposed rule.

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 
determined that there are no ICAO Standards and Recommended Practices 
that correspond to these proposed regulations.

Economic Evaluation, Regulatory Flexibility Determination, Trade Impact 
Assessment, and Unfunded Mandates Assessment

    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

[[Page 61061]]

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. The FAA suggests readers 
seeking greater detail read the full regulatory evaluation, a copy of 
which the agency has placed in the docket for this rulemaking.
    In conducting these analyses, the 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) has been designated as a 
``significant regulatory action'' by the Office of Management and 
Budget, because it harmonizes U.S. and international standards, and is 
therefore ``significant'' under 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

    The estimated cost of this proposed rule is about $5.5 million 
($2.9 million in seven percent present value terms). The estimated 
potential benefits of averting one accident and four fatalities are 
about $17.3 million ($12.6 million in seven percent present value 
terms).

Who Is Potentially Affected by This Rule?

    Operators of transport category airplanes with a maximum take-off 
weight under 60,000 pounds operating under 14 CFR part 121.

Assumptions

    (1) The base year is 2008.
    (2) The proposal will become final in December 2010.
    (3) The compliance date of the rule is 24 months from the effective 
date of the final rule.
    (4) The analysis period is 20 years.
    (5) The value of an averted fatality is $5.8 million.\13\
---------------------------------------------------------------------------

    \13\ ``Treatment of the Economic Value of a Statistical Life in 
Departmental Analysis'', February 5, 2008, U.S. Department of 
Transportation Memorandum.
---------------------------------------------------------------------------

    (6) The FAA used $79.93 hourly rate for a mechanic/technician 
working for an airplane manufacturer or modifier and the $76.01 hourly 
rate for an engineer working for an airplane manufacturer or modifier. 
These hourly rates include overhead costs.
    (7) The FAA assumed whenever various compliance options are 
available to the operators, the minimal cost option will always be 
chosen.

Benefits of This Rule

    The benefits of this proposed rule consist of the value of 
fatalities, loss of airplanes, and investigation cost averted from 
avoiding accidents involving transport category airplanes with a 
maximum take-off weight under 60,000 pounds operating under 14 CFR part 
121. The FAA estimates that one accident and four fatalities could 
potentially be avoided, over the analysis period, by adopting the 
proposed rule. The value of an averted fatality is assumed to be $5.8 
million. A series of airworthiness directives (AD) were issued for 
airplanes with pneumatic de-icing boots to activate the systems at the 
first sign of ice accretion. Due to the similarity of requirements 
between the ADs and this proposal, the FAA accounted for the effects of 
recent ADs by reducing the estimated benefits. Over the analysis 
period, the potential benefits of the proposed rule would be $17.3 
million ($12.6 million in seven percent present value terms).

Estimated Costs of This Proposal

    Using Ice Protection Harmonization Working Group (IPHWG) airplane 
compliance costs, the FAA estimates the total undiscounted cost of the 
proposed rule, over the analysis period, to be about $5.5 million. The 
seven percent present value cost of this proposed rule over the 
analysis period is about $2.9 million. The agency estimates the initial 
costs for a new certification program to operate the deicing boots 
based on visible moisture and temperature are about $385,000. The FAA 
estimates the operating and training costs are about $5.1 million.

Alternatives Considered

Alternative One
    The alternative of maintaining the status quo would not address the 
NTSB recommendations and the FAA's In-flight Icing Plan. The FAA 
rejected this alternative because the proposed rule would enhance 
passenger safety and prevent icing-related accidents for airplanes with 
a certificated MTOW less than 60,000 pounds. As it stands, the proposed 
rule is the reasoned result of the FAA Administrator carrying out the 
FAA's In-flight Aircraft Icing Plan.
Alternative Two
    Alternative Two would be to issue more ADs requiring a means to 
know when to activate the airframe IPS. The FAA has already issued ADs 
to address the activation of airframe IPSs.
    An evaluation of accidents and incidents led to the conclusion that 
the ADs do not provide adequate assurance that the flightcrew will be 
made aware of when to activate the airframe IPS. Because this problem 
is not unique to particular airplane designs, but exists for all 
airplanes that are susceptible to the icing hazards described 
previously, it is appropriate to address this problem through an 
operational rule, rather than by ADs.
Alternative Three
    Alternative Three is the proposed rule. The FAA's judgment is that 
this is the most viable option, since the proposed rule will increase 
the safety of the flying public by reducing icing-related accidents in 
the future in the least costly way.

Regulatory Flexibility Determination

    The Regulatory Flexibility Act of 1980 (Pub. L. 96-354) (RFA) 
establishes ``as a principle of regulatory issuance that agencies shall 
endeavor, consistent with the objectives of the rule and of applicable 
statutes, to fit regulatory and informational requirements to the scale 
of the businesses, organizations, and governmental jurisdictions 
subject to regulation. To achieve this principle, agencies are required 
to solicit and consider flexible regulatory proposals and to explain 
the rationale for their actions to assure that such proposals are given 
serious consideration.'' The RFA covers a wide range of small entities, 
including small businesses, not-for-profit organizations, and small 
governmental jurisdictions.
    Agencies must perform a review to determine whether a rule will 
have a significant economic impact on a substantial number of small 
entities. If the agency determines that it will, the

[[Page 61062]]

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.
    The FAA believes that this proposed rule would not have a 
significant impact on a substantial number of small entities for the 
following reasons.
    On October 31, 1994, at 1559 Central Standard Time, an Avions de 
Transport Regional Model ATR 72, operated by Simmons Airlines, 
Incorporated, and doing business as American Eagle flight 4184, crashed 
during a rapid descent after an uncommanded roll excursion. The FAA, 
Aerospatiale, the French Direction G[eacute]n[eacute]rale de l'Aviation 
Civile, Bureau Enquete Accident, National Aeronautics and Space 
Administration (NASA), National Transportation Safety Board, and others 
have conducted an extensive investigation of this accident.
    This accident and the investigation prompted the FAA to initiate a 
review of aircraft in-flight icing safety and determine changes that 
could be made to increase the level of safety. The proposed rule 
addresses NTSB recommendation A-07-14. The proposed rule is also one of 
the items listed in the FAA's In-flight Aircraft Icing Plan, April 
1997. The Icing Plan details the FAA's plans for improving the safety 
of airplanes when they are operated in icing conditions.
    This NPRM specifically applies to 14 CFR part 121 operators of 
airplanes that have a certificated MTOW of less than 60,000 pounds. The 
FAA determined which small entities could be affected by associating 
airplanes with a certificated MTOW of less than 60,000 pounds with part 
121 operators. For this section of the analysis, the agency considered 
only those operators meeting the above criteria that have 1,500 or 
fewer employees.
    To estimate the number of affected airplanes, the FAA analyzed the 
current active fleet of airplanes, a forecast of airplanes affected by 
the proposed rule entering the fleet, and a forecast of the retired 
affected airplanes exiting the fleet during the analysis period.
    The FAA also generated a list of all U.S. operated civilian 
airplanes operating under 14 CFR part 121. Each airplane group was 
matched with its current (as of September 2008) MTOW and average age 
through the use of the BACK FleetPCTM database. All airplanes with an 
MTOW greater than 60,000 pounds were eliminated.
    Using industry sources, the FAA determined which airplanes 
currently had primary or advisory icing detection systems. Airplanes 
equipped with either a primary or advisory ice detection systems are in 
compliance, and this proposal would impose no costs to operators of 
these airplanes. All turbojets affected by this proposal are in 
compliance, as these airplanes are equipped with either an approved 
primary ice detection system or advisory ice detection systems.
    For the base case, the FAA used the FAA Aerospace Forecast, 2008-
2025 (Table 26) for the part 121 regional turboprop retirement forecast 
and determined the number of turboprop airplanes that would retire over 
the analysis interval. The report does not forecast turboprop airplanes 
by equipment type. In estimating the costs, the FAA retires the older 
active airplanes affected by the proposal first.
    Using information provided by the World Aviation Directory, SEC 
filings, and the Internet, scheduled and non-scheduled commercial 
operators that are subsidiary businesses of larger businesses were 
eliminated from the database. An example of a subsidiary business is 
Continental Express, Inc., which is a subsidiary of Continental 
Airlines. Using information provided by the U.S. Department of 
Transportation Form 41 filings, the World Aviation Directory, Winter 
2000, and Dunn and Bradstreet's company databases, all businesses with 
more than 1,500 employees were eliminated. For the remaining 
businesses, the FAA obtained company revenue from these sources when 
the operator's revenue was public. Following this approach, six small 
entities operate airplanes that would be affected by this proposal.
    The FAA estimated the cost of compliance per airplane and 
multiplied this cost by the total fleet of affected airplanes per 
operator, over the analysis period, to obtain the total compliance cost 
by small entity. The non-recurring costs, for updating the AFM for each 
major airplane group, were distributed equally among the airplanes in 
each major airplane group. These non-recurring costs occurred in year 
four of the analysis period. Note the more airplanes in a major 
airplane group, the less expensive, per airplane, the non-recurring 
costs are to the operators of those airplanes. In addition to the AFM 
cost, the additional incremental recurring costs include boot 
maintenance, replacement, and installation labor. These recurring costs 
started in year five and continued either until the airplane retired or 
through the end of the analysis period.
    The degree to which small air operator entities can ``afford'' the 
cost of compliance is determined by the availability of financial 
resources. The initial implementation costs of the proposed rule may be 
financed, paid for using existing company assets, or borrowed. As a 
proxy for the firm's ability to afford the cost of compliance, the FAA 
calculated the ratio of the total annualized cost of the proposed rule 
as a percentage of annual revenue. This ratio is a conservative measure 
as the annualized value of the 20-year total compliance cost is divided 
by one year of annual revenue (no growth in revenues is assumed). No 
small business operator potentially affected by this proposed rule 
incurred costs greater that one percent of their annual revenue. The 
following table shows the base case economic impact on the small entity 
air operators affected by this proposed rule.

                                              Table 1--Economic Impact on Small Entity Operators--Base Case
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                          Small operator  Small operator  Small operator  Small operator  Small operator  Small operator
                          Year                                   A               B               C               D               E               F
--------------------------------------------------------------------------------------------------------------------------------------------------------
1.......................................................              $0              $0              $0              $0              $0              $0
2.......................................................               0               0               0               0               0               0
3.......................................................               0               0               0               0               0               0
4.......................................................          59,717         302,084         302,084          37,540          15,591          92,992
5.......................................................          58,617          87,925          87,925           7,327               0          29,308
6.......................................................          58,617          73,271          80,598           7,327               0          29,308
7.......................................................          58,617          65,944          65,944               0               0          21,981
8.......................................................          58,617          51,290          51,290               0               0          14,654

[[Page 61063]]

 
9.......................................................          58,617          36,636          36,636               0               0           7,327
10......................................................          58,617          29,308          29,308               0               0               0
11......................................................          58,617          21,981          21,981               0               0               0
12......................................................          58,617          14,654          14,654               0               0               0
13......................................................          58,617           7,327          14,654               0               0               0
14......................................................          58,617           7,327           7,327               0               0               0
15......................................................          58,617               0           7,327               0               0               0
16......................................................          58,617               0           7,327               0               0               0
17......................................................          58,617               0               0               0               0               0
18......................................................          51,290               0               0               0               0               0
19......................................................          43,963               0               0               0               0               0
20......................................................          36,636               0               0               0               0               0
                                                         -----------------------------------------------------------------------------------------------
    Total...............................................         953,623         697,748         727,056          52,194          15,591         195,571
                                                         ===============================================================================================
Annualized Costs........................................          90,012          65,860          68,627           4,927           1,472          18,460
Annual Revenue..........................................      30,000,000      76,348,000     100,000,000      78,148,212     141,000,000      18,200,000
Percentage..............................................           0.30%           0.09%           0.07%           0.01%           0.00%           0.10%
--------------------------------------------------------------------------------------------------------------------------------------------------------

    The FAA conducted a sensitivity analysis \14\ where the agency 
relaxed the retirement assumption from the base case. For this 
sensitivity analysis, the FAA used the FleetPCTM database and 
determined turboprops are retired from U.S. certificated service at an 
average age (mean) of 26.4. In the base case, the FAA assumes the 
active affected airplanes start retiring in year one and continue to 
retire at the annual turboprop retirement rate estimated by the FAA 
forecasting group.\15\ In the sensitivity analysis, the agency assumes 
each of the small operator's airplanes are retired when the average age 
for the fleet of this airplane type reaches the average retirement age 
of 26.4 years. For all but one operator, the sensitivity analysis 
results in slightly higher costs. The following table shows the results 
of the sensitivity analysis the FAA performed for the economic impact 
on the small entity air operators affected by this proposed rule.
---------------------------------------------------------------------------

    \14\ A sensitivity analysis is the study of how the variation 
(uncertainty) in the output of a mathematical model can be 
apportioned, qualitatively or quantitatively, to different sources 
of variation in the input of a model.
    \15\ FAA Statistical and Forecast Branch, APO-110--FAA Aerospace 
Forecast, 2008-2025, Table 26.

                    Table 2--Sensitivity Analysis Economic Impact on Small Entity Operators When Airplanes Are Retired at 26.4 Years
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                          Small operator  Small operator  Small operator  Small operator  Small operator  Small operator
                          Year                                   A               B               C               D               E               F
--------------------------------------------------------------------------------------------------------------------------------------------------------
1.......................................................              $0              $0              $0              $0              $0              $0
2.......................................................               0               0               0               0               0               0
3......................................................