[Federal Register Volume 59, Number 57 (Thursday, March 24, 1994)]
[Unknown Section]
[Page 0]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 94-6961]


[[Page Unknown]]

[Federal Register: March 24, 1994]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 25

[Docket No. NM-92; Final Special Conditions No. 25-ANM-81]

 

Special Conditions: Learjet, Inc., Model 45 Airplane, High 
Altitude Operation

AGENCY: Federal Aviation Administration, DOT.

ACTION: Final special conditions.

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SUMMARY: These special conditions are issued to Learjet Inc. of 
Wichita, KS, for the Learjet Inc., Model 45 airplane. This new airplane 
has an unusual design feature associated with an unusually high 
operating altitude (51,000 feet), for which the applicable 
airworthiness regulations do not contain adequate or appropriate safety 
standards. These special conditions contain the additional safety 
standards that the Administrator considers necessary to establish a 
level of safety equivalent to that established by the existing 
airworthiness standards.

EFFECTIVE DATE: April 25, 1994.

FOR FURTHER INFORMATION CONTACT:
Mark Quam, FAA, Standardization Branch, ANM-113, Transport Airplane 
Directorate, Aircraft Certification Service, 1601 Lind Avenue SW., 
Renton, Washington, 98055-4056; telephone (206) 227-2145.

SUPPLEMENTARY INFORMATION: 

Background

    On January 27, 1992, Learjet Inc., (Learjet), 8220 West Harry 
Street, Wichita, KS 67209-2942, or P.O. Box 7707, Wichita, KS 67277-
7707, applied for a new type certificate in the transport airplane 
category for the Model 45 airplane. The Learjet Model 45 is a T-tail, 
low wing, medium sized business jet powered by two Garrett TFE 731-20 
turbofan engines mounted on pylons extending from the aft fuselage. 
Each engine will be capable of delivering 3,500 pounds thrust, with 
auto performance reserve 3,650 pounds thrust. The airplane will be 
capable of operating with two flight crewmembers and a maximum of ten 
passengers (standard is eight passengers). The type design of the 
Learjet Model 45 series airplanes contains a number of novel and 
unusual design features for an airplane type certificated under the 
applicable provisions of part 25 of the Federal Aviation Regulations 
(FAR). Those features include the relatively small passenger cabin 
volume and a high operating altitude. The applicable airworthiness 
requirements do not contain adequate or appropriate safety standards 
for the Learjet 45 series airplanes; therefore, special conditions are 
necessary to establish a level of safety equivalent to that established 
in the regulations.

Type Certification Basis

    Under the provisions of Sec. 21.17 of the FAR, Learjet must show, 
except as provided in Sec. 25.2, that the Model 45 meets the applicable 
provisions of part 25, effective February 1, 1965, as amended by 
Amendments 25-1 through 25-75. In addition, the proposed certification 
basis for the Model 45 includes part 34, effective September 10, 1990, 
plus any amendments in effect at the time of certification; and part 
36, effective December 1, 1969, as amended by Amendments 36-1 through 
the amendment in effect at the time of certification. These special 
conditions will form an additional part of the type certification 
basis. In addition, the certification basis may include other special 
conditions that are not relevant to these special conditions.
    If the Administrator finds that the applicable airworthiness 
regulations (i.e., part 25, as amended) do not contain adequate or 
appropriate safety standards for the Learjet Model 45 because of a 
novel or unusual design feature, special conditions are prescribed 
under the provisions of Sec. 21.16 to establish a level of safety 
equivalent to that established in the regulations.
    Special conditions, as appropriate, are issued in accordance with 
Sec. 11.49 of the FAR after public notice, as required by Secs. 11.28 
and 11.29, and become part of the type certification basis in 
accordance with Sec. 21.17(a)(2).

Novel or Unusual Design Feature

    The Learjet Model 45 will incorporate an unusual design feature in 
that it will be certified to operate up to an altitude of 51,000 feet.
    The FAA considers certification of transport category airplanes for 
operation at altitudes greater than 41,000 feet to be a novel or 
unusual feature because current part 25 does not contain standards to 
ensure the same level of safety as that provided during operation at 
lower altitudes. Special conditions have therefore been adopted to 
provide adequate standards for transport category airplanes previously 
approved for operation at these high altitudes, including certain 
Learjet models, the Boeing Model 747, Dassault-Breguet Falcon 900, 
Canadair Model 600, Cessna Model 650, Israel Aircraft Industries Model 
1125, and Cessna Model 560. The special conditions for the Cessna Model 
650 or previously certified Learjet models are considered the most 
applicable to the Model 45 and its proposed operation and are therefore 
used as the basis for the special conditions described below.
    Damage tolerance methods are proposed to be used to assure pressure 
vessel integrity while operating at the higher altitudes, in lieu of 
the \1/2\-bay crack criterion used in some previous special conditions. 
Crack growth data are used to prescribe an inspection program that 
should detect cracks before an opening in the pressure vessel would 
allow rapid depressurization. Initial crack sizes for detection are 
determined under Sec. 25.571, as amended by Amendment 25-72. The 
maximum extent of failure and pressure vessel opening determined from 
the above analysis must be demonstrated to comply with the 
pressurization section of the proposed special conditions, which state 
that the cabin altitude after failure must not exceed the cabin 
altitude/time curve limits shown in Figures 3 and 4.
    In order to ensure that there is adequate fresh air for crewmembers 
to perform their duties, to provide reasonable passenger comfort, and 
to enable occupants to better withstand the effects of decompression at 
high altitudes, the ventilation system must be designed to provide 10 
cubic feet of fresh air per minute per person during normal operations. 
Therefore, these special conditions require that crewmembers and 
passengers be provided with 10 cubic feet of fresh air per minute per 
person. In addition, during the development of the supersonic transport 
special conditions, it was noted that certain pressurization failures 
resulted in hot ram or bleed air being used to maintain pressurization. 
Such a measure can lead to cabin temperatures that exceed human 
tolerance. Therefore, these special conditions require airplane 
interior temperature limits following probable and improbable failures.
    Continuous flow passenger oxygen equipment is certificated for use 
up to 40,000 feet; however, for rapid decompressions above 34,000 feet, 
reverse diffusion leads to low oxygen partial pressures in the lungs, 
to the extent that a small percentage of passengers may lose useful 
consciousness at 35,000 feet. The percentage increases to an estimated 
60 percent at 40,000 feet, even with the use of the continuous flow 
system. Therefore, to prevent permanent physiological damage, the cabin 
altitude must not exceed 25,000 feet for more than 2 minutes, or 40,000 
feet for any time period. The maximum peak cabin altitude of 40,000 
feet is consistent with the standards established for previous 
certification programs. In addition, at high altitudes the other 
aspects of decompression sickness have a significant, detrimental 
effect on pilot performance (for example, a pilot can be incapacitated 
by internal expanding gases).
    Decompression resulting in cabin altitudes above the 37,000-foot 
limit depicted in Figure 4 approaches the physiological limits of the 
average person; therefore, every effort must be made to provide the 
pilots with adequate oxygen equipment to withstand these severe 
decompressions. Reducing the time interval between pressurization 
failure and the time the pilots receive oxygen will provide a safety 
margin against being incapacitated and can be accomplished by the use 
of mask-mounted regulators. These special conditions therefore require 
pressure demand masks with mask-mounted regulators for the flightcrew. 
This combination of equipment will provide the best practical 
protection for the failures covered by the special conditions and for 
improbably failures not covered by the special conditions, provided the 
cabin altitude is limited.

Discussion of Comments

    Notice of proposed special conditions No. SC-93-8-NM was published 
in the Federal Register on December 22, 1993 (58 FR 67716). No comments 
were received, and the special conditions are adopted as proposed.

Conclusion

    This action affects only certain unusual or novel design features 
on one model of airplane. It is not a rule of general applicability and 
affects only the manufacturer who applied to the FAA for approval of 
these features on the airplane.

List of Subjects in 14 CFR Part 25

    Aircraft, Aviation safety, Reporting and recordkeeping 
requirements.

    The authority citation for these special conditions is as follows: 
Authority: 49 U.S.C. app. 1344, 1348(c), 1352, 1354(a), 1355, 1421 
through 1431, 1502, 1651(b)(2), 42 U.S.C. 1857f-10, 4321 et seq.; E.O. 
11514; and 49 U.S.C. 106(g).

The Special Conditions

    Accordingly, the following special conditions are issued as part of 
the type certification basis for the Learjet Model 45 series airplanes:

Operation to 51,000 Feet

    1. Pressure vessel integrity. (a) The maximum extent of failure and 
pressure vessel opening that can be demonstrated to comply with 
paragraph 4 (Pressurization) of this special condition must be 
determined. It must be demonstrated by crack propagation and damage 
tolerance analysis supported by testing that a larger opening or a more 
severe failure than demonstrated will not occur in normal operations.
    (b) Inspection schedules and procedures must be established to 
assure that cracks and normal fuselage leak rates will not deteriorate 
to the extent that an unsafe condition could exist during normal 
operation.
    (c) With regard to the fuselage structural design for cabin 
pressure capability above 45,000 feet altitude, the pressure vessel 
structure, including doors and windows, must comply with 
Sec. 25.365(d), using a factor of 1.67 instead of the 1.33 factor 
described.
    2. Ventilation. In lieu of the requirements of Sec. 25.831(a), the 
ventilation system must be designed to provide a sufficient amount of 
uncontaminated air to enable the crewmembers to perform their duties 
without undue discomfort or fatigue, and to provide reasonable 
passenger comfort during normal operating conditions and also in the 
event of any probable failure to any system that could adversely affect 
the cabin ventilating air. For normal operations, crewmembers and 
passengers must be provided with at least 10 cubic feet of fresh air 
per minute per person, or the equivalent in filtered, recirculated air 
based on the volume and composition at the corresponding cabin pressure 
altitude of not more than 8,000 feet.
    3. Air conditioning. In addition to the requirements of 
Sec. 25.831, paragraphs (b) through (e), the cabin cooling system must 
be designed to meet the following conditions during flight above 15,000 
feet mean sea level (MSL): (a) After any probably failure, the cabin 
temperature-time history may not exceed the values shown in Figure 1.
    (b) After any improbable failure, the cabin temperature-time 
history may not exceed the values shown in Figure 2.
    4. Pressurization. In addition to the requirements of Sec. 25.841, 
the following apply: (a) The pressurization system, which includes for 
this purpose bleed air, air conditioning, and pressure control systems, 
must prevent the cabin altitude from exceeding the cabin altitude-time 
history shown in Figure 3 after each of the following: (1) Any probable 
malfunction or failure of the pressurization system. The existence of 
undetected, latent malfunctions or failures in conjunction with 
probable failures must be considered.
    (2) Any single failure in the pressurization system, combined with 
the occurrence of a leak produced by a complete loss of a door seal 
element, or a fuselage leak through an opening having an effective area 
2.0 times the effective area that produces the maximum permissible 
fuselage leak rate approved for normal operation, whichever produces a 
more severe leak.
    (b) The cabin altitude-time history may not exceed that shown in 
Figure 4 after each of the following: (1) The maximum pressure vessel 
opening resulting from an initially detectable crack propagating for a 
period encompassing four normal inspection intervals. Mid-panel cracks 
and cracks through skin-stringer and skin-frame combinations must be 
considered.
    (2) The pressure vessel opening or duct failure resulting from 
probable damage (failure effect) while under maximum operating cabin 
pressure differential due to a tire burst, engine rotor burst, loss of 
antennas or stall warning vanes, or any probable equipment failure 
(bleed air, pressure control, air conditioning, electrical source(s), 
etc.) that affects pressurization.
    (3) Complete loss of thrust from all engines.
    (c) In showing compliance with paragraphs 4(a) and 4(b) of these 
special conditions (Pressurization), it may be assumed that an 
emergency descent is made by approved emergency procedure. A 17-second 
crew recognition and reaction time must be applied between cabin 
altitude warning and the initiation of an emergency descent.

    Note: For the flight evaluation of the rapid descent, the test 
article must have the cabin volume representative of what is 
expected to be normal, such that Cessna must reduce the total cabin 
volume by that which would be occupied by the furnishings and total 
number of people.

    5. Oxygen equipment and supply. (a) A continuous flow oxygen system 
must be provided for the passengers.
    (b) A quick-donning pressure demand mask with mask-mounted 
regulator must be provided for each pilot. Quick-donning from the 
stowed position must be demonstrated to show that the mask can be 
withdrawn from stowage and donned within 5 seconds.

BILLING CODE 4910-13-M

TR24MR94.000


TR24MR94.001


TR24MR94.002


TR24MR94.003


BILLING CODE 4910-13-C
    Issued in Renton, Washington, on March 9, 1994.
Darrell M. Pederson,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service, ANM-100.
[FR Doc. 94-6961 Filed 3-23-94; 8:45 am]
BILLING CODE 4910-13-M