[Federal Register Volume 59, Number 31 (Tuesday, February 15, 1994)]
[Unknown Section]
[Page 0]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 94-3449]


[[Page Unknown]]

[Federal Register: February 15, 1994]


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DEPARTMENT OF TRANSPORTATION
14 CFR Part 25

[Docket No. NM-89; Special Conditions No. 25-ANM-80]

 

Special Conditions; Cessna Aircraft Company, Model 750 (Citation 
X) Airplane, High Altitude Operation

AGENCY: Federal Aviation Administration, DOT.

ACTION: Final special conditions.

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SUMMARY: These special conditions are issued for the Cessna Aircraft 
Company (Cessna), Model 750 (Citation X) airplane. This new airplane 
will have a novel and 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: March 17, 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 October 15, 1991, Cessna Aircraft Company (Cessna), 6030 Cessna 
Blvd., P.O. Box 7704, Wichita, KS 67277-7704, applied for a new type 
certificate in the transport airplane category for the Model 750 
(Citation X) airplane. The Cessna Model 750 is a T-tail, low swept 
wing, medium sized business jet powered by two GMA-3007C turbofan 
engines mounted on pylons extending from the aft fuselage. Each engine 
will be capable of delivering 6,000 pounds thrust. The flight controls 
will be powered and capable of manual reversion. The type design of the 
Cessna Model 750 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 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 Cessna 750 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, Cessna must show, 
except as provided in Sec. 25.2, that the Model 750 (Citation X) meets 
the applicable provisions of part 25, effective February 1, 1965, as 
amended by Amendments 25-1 through 25-74. In addition, the 
certification basis for the Model 750 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. No exemptions are anticipated. 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 Cessna Model 750 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 Cessna Model 750 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 are considered the most applicable to the Model 750 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 cabin 
altitude after failure must not exceed the cabin altitude/time curve 
limits shown in Figures 3 and 4.
    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. To prevent permanent physiological damage, the cabin altitude 
must not exceed 25,000 feet for more than 2 minutes. 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 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. This special 
condition therefore requires 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 improbable failures not covered by the 
special conditions, provided the cabin altitude is limited.

Discussion of Comments

    Notice of proposed special conditions No. SC-93-5-NM was published 
in the Federal Register on November 10, 1993 (14 CFR 59689). No 
comments were received.

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, Federal Aviation Administration, 
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, pursuant to the authority delegated to me by the 
Administrator, the following special conditions are issued as part of 
the type certification basis for the Cessna Model 750 (Citation X) 
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 
prescribed.
    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 of 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 probable 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.

TR15FE94.085


TR15FE94.086


TR15FE94.087


TR15FE94.088

    Issued in Renton, Washington, on January 31, 1994.
Darrell M. Pederson,
Acting Manager, Transport Airplane Directorate Aircraft Certification 
Service, ANM-100.
[FR Doc. 94-3449 Filed 2-14-94; 8:45 am]
BILLING CODE 4910-13-M