00-3301. Special Conditions: Cessna Aircraft Company, Model 525A, High Altitude Operation

AGENCY:

Federal Aviation Administration (FAA), DOT.

ACTION:

Final special conditions.

SUMMARY:

These special conditions are issued for the Cessna Aircraft Company Model 525A airplane. This airplane will have novel or unusual design features associated with high altitude operation. The applicable airworthiness regulations do not contain adequate or appropriate safety standards for this design feature. 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 15, 2000.

FOR FURTHER INFORMATION CONTACT:

Lowell Foster, Federal Aviation Administration, Aircraft Certification Service, Small Airplane Directorate, ACE-111, DOT Building, 901 Locust, Kansas City, MO 64106; 816-329-4125, fax [phone].

SUPPLEMENTARY INFORMATION:

Background

On May 14, 1998, Cessna Aircraft Company applied to amend the Model 525 Type Certificate to add a new Model 525A. The Model 525A is a derivative of the Model 525 currently approved under Type Certificate Data Sheet A1WI.

The Cessna Model 525A, a derivative of the Model 525, will be certified for operation to a maximum altitude of 45,000 feet. This will be the first of this series to be approved above 41,000 feet. The certification basis of the Model 525 was primarily 14 CFR part 23, as amended by Amendments 23-1 through 23-40, plus special conditions. This unusually high operating altitude constitutes a novel or unusual design feature for which the applicable airworthiness regulations do not contain adequate or appropriate safety standards. Therefore, it is necessary to prescribe special conditions that provide the level of safety to that established by the regulations.

The FAA has previously issued Special Conditions No. 23-ACE-87, to another small turbojet airplane model with requested approval for operation up to 49,000 feet.

The FAA policy is to apply special conditions to part 23 airplanes when the certified altitude exceeds the capability of the oxygen system (in this case, the passenger system). This was the situation for a part 23 turbojet airplane. Thus, the special conditions were deemed to be appropriate for the Cessna Model 525A and provide the basis for formulating the special conditions described below:

Damage tolerance methods are prescribed to assure pressure vessel integrity while operating at the higher altitudes. Crack growth data is used to prescribe an inspection program, which should detect cracks before an opening in the pressure vessel would allow rapid depressurization. Initial crack sizes for detection are determined under § 23.571 as amended by Amendment 23-48.

The cabin altitude after failure may not exceed the cabin altitude/time history curve limits shown in Figures 3 and 4.

Continuous flow passenger oxygen equipment is certified 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 these 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 of Figure 4 approaches the physiological limits of the average person; therefore, every effort must be made to provide the pilot with adequate oxygen equipment to withstand these severe decompressions. Reducing the time interval between pressurization failure and the time the pilot receives oxygen will provide a safety margin against being incapacitated and can be accomplished by the use of mask-mounted regulators. The 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.

Type Certification Basis

Under the provisions of § 21.101, Cessna Aircraft Company must show that the Cessna Model 525A meets the applicable provisions of the regulations incorporated by reference in Type Certificate Data Sheet A1WI or the applicable regulations in effect on the date of application for the change to the Cessna Model 525A. The regulations incorporated by reference in the type certificate are commonly referred to as the “original type certification basis.” The regulations incorporated by reference in Type Certificate Data Sheet A1WI are as follows:

(1) Part 23 of the Federal Aviation Regulations effective February 1, 1965, as amended by Amendments 23-1 through 23-40;

(a) In addition, if the regulations incorporated by reference do not provide adequate standards with respect to the change, the applicant must comply with certain regulations in effect on the date of application for the change. The FAA has determined that the Cessna Model 525A must also be shown to comply with the following sections of part 23:

Federal Aviation Regulations §§ 23.331, 23.351, 23.421, 23.423, 23.425, 23.427, 23.939, and 23.1163 as amended by Amendments 23-1 through 23-42;

Federal Aviation Regulations §§ 23.943, 23.951, 23.957, 23.961, 23.967, 23.991, 23.993, 23.997, 23.999, 23.1001, 23.1011, 23.1019, 23.1041, 23.1061, 23.1189, 23.1322, 23.1357, 23.1391, 23.1393, 23.1395, and 23.1445 as amended by Amendments 23-1 through 23-43;

Federal Aviation Regulations §§ 23.305, 23.321, 23.361, 23.397, 23.479, 23.485, 23.613, 23.615, 23.621, 23.731 and 23.1549 as amended by Amendments 23-1 through 23-45;

Federal Aviation Regulations §§ 23.335, 23.337, 23.341, 23.343, 23.345, 23.347, 23.371, 23.393, 23.399, 23.415, 23.441, 23.443, 23.455, 23.457, 23.473, 23.499, 23.561, 23.571, 23.572, 23.611, 23.629, 23.673, and 23.725 as amended by Amendments 23-1 through 23-48;

Federal Aviation Regulations §§ 23.677, 23.723, 23.785, 23.787, 23.791, 23.853, 23.855, 23.1303, 23.1307, 23.1321, 23.1351, 23.1353, 23.1361, and 23.1401 as amended by Amendments 23-1 through 23-49;

Federal Aviation Regulations §§ 23.233, 23.235, 23.1555, and 23.1589 as amended by Amendments 23-1 through 23-50;

Federal Aviation Regulations §§ 23.901, 23.903, 23.929, 23.963, 23.965, 23.1013, 23.1043, 23.1143, 23.1183, 23.1191, and 23.1337 as amended by Amendments 23-1 through 23-51;

(2) Federal Aviation Regulations part 36 effective December 1, 1969, as amended by Amendments 36-1 through the amendment in effect at the time of TC issuance.

(3) Federal Aviation Regulations part 34 effective September 10, 1990, as amended by Amendment 34-1, Fuel Venting and Exhaust Emission Requirements for Turbine Engine Powered Airplanes.

(4) Special Conditions as follows:

(a) 23-ACE-55, additional requirements for engine location, performance, characteristics, and protection of electronic systems from lightning and high intensity radiated electromagnetic fields (HIRF).

(b) Special conditions adopted by this rulemaking action.

(5) Exemption: Exemption number 5759 granted. Model 525A to use Federal Aviation Regulations § 25.181 in lieu of damping criteria of Federal Aviation Regulations § 23.181(b).

(6) Compliance with ice protection will be demonstrated in accordance with Federal Aviation Regulations § 23.1419.

Because the Administrator has found that the applicable airworthiness regulations (i.e., part 23) do not contain adequate or appropriate safety standards for the Cessna Model 525A because of a novel or unusual design feature, special conditions are prescribed under the provisions of § 21.16.

In addition to the applicable airworthiness regulations and special conditions, the Model 525A must comply with the part 23 fuel vent and exhaust emission requirements of 14 CFR part 34 and the part 23 noise certification requirements of 14 CFR part 36, and the FAA must issue a finding of regulatory adequacy pursuant to § 611 of Public Law 92-574, the “Noise Control Act of 1972.”

Special conditions, as appropriate, are issued in accordance with § 11.49 after public notice, as required by § § 11.28 and 11.29(b), and become part of the type certification basis in accordance with § 21.101(b)(2).

Special conditions are initially applicable to the model for which they are issued. Should the type certificate for that model be amended later to include any other model that incorporates the same novel or unusual design feature, or should any other model already included on the same type certificate be modified to incorporate the same novel or unusual design feature, the special conditions would also apply to the other model under the provisions of § 21.101(a)(1).

Novel or Unusual Design Features

The Model 525A will incorporate the following novel or unusual design feature: The methods used to ensure pressure vessel integrity and to provide ventilation, air conditioning, and pressurization will be unique due to the operating altitude of this airplane.

Discussion of Comments

A notice of proposed special conditions No. 23-99-01-SC for the Cessna Aircraft Company Model 525A airplanes was published in the Federal Register on September 13, 1999 (64 FR 49413). No comments were received.

Applicability

As discussed above, these special conditions are applicable to the Cessna Model 525A. Should the Cessna Aircraft Company apply at a later date for a change to the type certificate to include another model incorporating the same novel or unusual design feature, the special conditions would apply to that model as well under the provisions of § 21.101(a)(1).

Conclusion

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

List of Subjects in 14 CFR Part 23

• Aircraft
• Aviation safety
• Signs and symbols

Citation

The authority citation for these special conditions is as follows:

Authority: 49 U.S.C. 106(g), 40113 and 44701; 14 CFR 21.16 and 21.17; and 14 CFR 11.28 and 11.49.

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 Aircraft Company Model 525A airplane.

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.

2. Ventilation

In addition to the requirements of § 23.831(b), 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 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 no more than 8,000 feet.

3. Air Conditioning

In addition to the requirements of § 23.831, 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 § 23.841, 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, in conjunction with any undetected, latent malfunctions or 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 4a and 4b of these special conditions (Pressurization), it may be assumed that an emergency descent is made by an 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) In addition to the requirements of § 23.1441(d), the following applies: A quick-donning oxygen mask system with a pressure-demand, mask mounted regulator must be provided for the flightcrew. It must be shown that each quick-donning mask can, with one hand and within 5 seconds, be placed on the face from its ready position, properly secured, sealed, and supplying oxygen upon demand.

(b) In addition to the requirements of § 23.1443, the following applies: A continuous flow oxygen system must be provided for each passenger.

(c) In addition to the requirements of § 23.1445, the following applies: If the flightcrew and passengers share a common source of oxygen, a means to separately reserve the minimum supply required by the flightcrew must be provided.

Issued in Kansas City, Missouri on January 28, 2000.

Michael Gallagher,

Manager, Small Airplane Directorate, Aircraft Certification Service.