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

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]

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