94-6961. Special Conditions: Learjet, Inc., Model 45 Airplane, High Altitude Operation  

  • [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
    
    
    

Document Information

Published:
03/24/1994
Department:
Federal Aviation Administration
Entry Type:
Uncategorized Document
Action:
Final special conditions.
Document Number:
94-6961
Dates:
April 25, 1994.
Pages:
0-0 (1 pages)
Docket Numbers:
Federal Register: March 24, 1994, Docket No. NM-92, Final Special Conditions No. 25-ANM-81
CFR: (3)
14 CFR 25.365(d)
14 CFR 11.49
14 CFR 25.831