E7-15973. Special Conditions: Adam Aircraft, Model A700; Fire Extinguishing for Aft Fuselage Mounted Engines

AGENCY:

Federal Aviation Administration (FAA), DOT.

ACTION:

Final special conditions.

SUMMARY:

These special conditions are issued for the Adam Aircraft, Model A700 airplane. This airplane will have a novel or unusual design feature(s) associated with aft mounted engine fire protection. 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.

DATES:

Effective Date: August 6, 2007

FOR FURTHER INFORMATION CONTACT:

Leslie B. Taylor, Regulations & Policy Branch, ACE-111, Federal Aviation Administration, Small Airplane Directorate, Aircraft Certification Service, 901 Locust, Kansas City, MO 64106; telephone [phone]; facsimile [phone], e-mail at [e-mail].

SUPPLEMENTARY INFORMATION:

Background

On April 12, 2004, Adam Aircraft applied for a type certificate for their new Model A700. The Model A700 is a 6 to 8 seat, pressurized, retractable-gear, composite structure airplane with two turbofan engines mounted on pylons on either side of the aft fuselage.

14 CFR part 23 has historically addressed fire protection through prevention, identification, and containment. Prevention has been provided through minimizing the potential for ignition of flammable fluids and vapors. Identification has been provided by locating engines within the pilots' primary field of view and/or with the incorporation of fire detection systems. This has provided both rapid detection of a fire and confirmation when it was extinguished. Containment has been provided through the isolation of designated fire zones, through flammable fluid shutoff valves, and firewalls. This containment philosophy also ensures that components of the engine control system will function effectively to permit a safe shutdown of an engine. However, containment has only been demonstrated for 15 minutes. If a fire occurs in traditional part 23 airplanes, the appropriate corrective action is to land as soon as possible. For a small, simple airplane originally envisioned by part 23, it is possible to descend and land within 15 minutes; thus, the occupants can safely exit the airplane before the firewall is breached. These simple airplanes normally have the engine located away from critical flight control systems and primary structure. This has ensured that, throughout a fire event, a pilot can continue safe flight, and it has made the prediction of fire effects relatively easy. Other design features of these simple aircraft, such as low stall speeds and short landing distances, ensure that even in the event of an off-field landing, the potential for the outcome being catastrophic has been minimized.

Title 14 CFR part 23 did not envision the type of configuration of the Model A700 airplane. The Model A700 incorporates two turbofan engines located on pylons on either side of the aft fuselage. These engines are not in the pilots' field of view. With the location in the aft fuselage, the ability to visually detect a fire is minimal.

Type Certification Basis

Under 14 CFR part 21, § 21.17, Adam Aircraft must show that the Model A700 meets the applicable provisions of part 23, as amended by Amendments 23-1 through 23-55, thereto.

If the Administrator finds that the applicable airworthiness regulations in 14 CFR part 23 do not contain adequate or appropriate safety standards for the Model A700 because of a novel or unusual design feature, special conditions are prescribed under § 21.16.

In addition to the applicable airworthiness regulations and special conditions, the Model A700 must comply with the fuel vent and exhaust emission requirements of 14 CFR part 34 and the noise certification requirements of 14 CFR part 36, and the FAA must issue a finding of regulatory adequacy under section 611 of Public Law 92-574, the “Noise Control Act of 1972.”

Discussion

The FAA issues special conditions, as defined in § 11.19, under § 11.38, and they become part of the type certification basis under § 21.17(a)(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 or similar novel or unusual design feature, the special conditions would also apply to the other model under § 21.101.

Novel or Unusual Design Features

The Model A700 will incorporate the following novel or unusual design features: The Model A700 incorporates two turbofan engines located on pylons on either side of the aft fuselage. These engines are not in the pilots' field of view. The effects of a fire in such a compartment are more varied and adverse than the typical engine fire in a simple part 23 airplane. With the location in the aft fuselage, the ability to visually detect a fire is minimal. However, the ability to extinguish an engine fire becomes extremely critical with the Model A700 engine location.

While the certification basis for the Model A700 requires that a fire detection system be installed due to the engine location, fire extinguishing is also considered a requirement. A sustained fire could result in loss of control of the airplane and damage to primary structure before an emergency landing could be made. Because of the location of critical structures and flight controls, a means to minimize the probability of re-ignition from occurring is necessary. One acceptable method to minimize re-ignition is to install a two-shot system. The effects of a fire emanating from an enclosed engine installation are more varied, adverse, and more difficult to predict than an engine fire envisioned for typical part 23 airplanes.

Discussion of Comments

A notice of proposed special conditions, Notice No. 23-07-02-SC, for the Adam Aircraft Model A700 was published in the Federal Register on June 25, 2007 (72 FR 34644). No comments were received, and the special conditions are adopted as proposed.

Applicability

As discussed above, these special conditions are applicable to the Model A700. Should Adam Aircraft apply later 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.

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 11.38 and 11.19.

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 Adam Aircraft, Model A700 airplanes.

Aft fuselage mounted engines need to protect the airplane from fires that were not envisioned in the development of part 23. Therefore, special conditions for a fire extinguishing system are required for airplanes with this engine configuration.

Regulations requiring and defining engine compartment fire extinguishing systems already exist for part 23 commuter category airplanes. These regulations will provide an adequate level of safety for the normal category Model A700 aircraft with its aft pylon mounted engines.

As the extinguishing agent is subject to change during the service life of the airplane, the certification basis needs to include 14 CFR part 23, § 23.1197 in its entirety.

Each fire zone should be ventilated to prevent the accumulation of flammable vapors. It must also be designed such that it will not allow entry of flammable fluids, vapors, or flames from other fire zones. It must be designed such that it does not create an additional fire hazard from the discharge of vapors or fluids.

1. SC 23.1195—Add the requirements of § 23.1195 while deleting “For commuter category airplanes.”

23.1195, Fire Extinguishing Systems

(a) Fire extinguishing systems must be installed and compliance shown with the following:

(1) Except for combustor, turbine, and tailpipe sections of turbine-engine installations that contain lines or components carrying flammable fluids or gases for which a fire originating in these sections is shown to be controllable, a fire extinguisher system must serve each engine compartment;

(2) The fire extinguishing system, the quantity of extinguishing agent, the rate of discharge, and the discharge distribution must be adequate to extinguish fires. An individual “one-shot” system may be used except for embedded engines where a “two-shot” system is required.

(3) The fire extinguishing system for a nacelle must be able to simultaneously protect each compartment of the nacelle for which protection is provided.

(b) If an auxiliary power unit is installed in any airplane certificated to this part, that auxiliary power unit compartment must be served by a fire extinguishing system meeting the requirements of paragraph (a)(2) of this section.

2. SC 23.1197—Add the requirements of § 23.1197 while deleting “For commuter category airplanes.”

23.1197, Fire Extinguishing Agents

The following applies:

(a) Fire extinguishing agents must—

(1) Be capable of extinguishing flames emanating from any burning fluids or other combustible materials in the area protected by the fire extinguishing system; and

(2) Have thermal stability over the temperature range likely to be experienced in the compartment in which they are stored.

(b) If any toxic extinguishing agent is used, provisions must be made to prevent harmful concentrations of fluid or fluid vapors (from leakage during normal operation of the airplane or as a result of discharging the fire extinguisher on the ground or in flight) from entering any personnel compartment, even though a defect may exist in the extinguishing system. This must be shown by test except for built-in carbon dioxide fuselage compartment fire extinguishing systems for which—

(1) Five pounds or less of carbon dioxide will be discharged under established fire control procedures into any fuselage compartment; or

(2) Protective breathing equipment is available for each flight crewmember on flight deck duty.

3. SC 23.1199—Add the requirements of § 23.1199 while deleting “For commuter category airplanes.”

23.1199, Extinguishing Agent Containers

The following applies:

(a) Each extinguishing agent container must have a pressure relief to prevent bursting of the container by excessive internal pressures.

(b) The discharge end of each discharge line from a pressure relief connection must be located so that discharge of the fire-extinguishing agent would not damage the airplane. The line must also be located or protected to prevent clogging caused by ice or other foreign matter.

(c) A means must be provided for each fire extinguishing agent container to indicate that the container has discharged or that the charging pressure is below the established minimum necessary for proper functioning.

(d) The temperature of each container must be maintained, under intended operating conditions, to prevent the pressure in the container from—

(1) Falling below that necessary to provide an adequate rate of discharge; or

(2) Rising high enough to cause premature discharge.

(e) If a pyrotechnic capsule is used to discharge the fire extinguishing agent, each container must be installed so that temperature conditions will not cause hazardous deterioration of the pyrotechnic capsule.

4. SC 23.1201—Add the requirements of § 23.1201 while deleting “For commuter category airplanes.”

23.1201, Fire Extinguishing System Materials

The following apply:

(a) No material in any fire extinguishing system may react chemically with any extinguishing agent so as to create a hazard.

(b) Each system component in an engine compartment must be fireproof. Issued in Kansas City, Missouri on August 6, 2007.

Kim Smith,

Manager, Small Airplane Directorate, Aircraft Certification Service.