Waives Flammability Requirements For A Period Of Five Years

The FAA has granted a temporary exemption from flammability requirements to Textron Aviation for the fuel system in its new Longitude business jet (Model 700), which will expire five years after the airplane receives type certification.

According to the FAA, The Textron Model 700 fuel system stores fuel in the wing with the center portion covered by an aerodynamic fairing. While Textron considers the entire fuel tank to be in a conventional unheated aluminum wing, which could be shown to meet the flammability requirement via qualitative analysis, the FAA determined that the portion of the fuel tank covered by the aerodynamic fairing is not a conventional unheated aluminum wing tank. With this FAA determination, the Model 700 does not comply with the requirements of 14 CFR 25.981(b), amendment 25-125.

Textron requested a permanent exemption for the Model 700 based on the excellent safety record, pertaining to the requirement, of other aircraft in the Textron fleet which have similar fuel system configurations.

Textron argued that among other things, the fuel systems:

• Consist of two integral aluminum wing tanks that extend into the fuselage contour where they are separated by, and symmetric about, BL 0.00. The wing is mounted entirely beneath the fuselage with no portion of the fuel tank penetrating the fuselage cylinder. The wing tank structure is conventional structure with aluminum ribs, spars, stringers, and skins.
• The portion of the fuel tank located below the fuselage contour is isolated from the external airflow by the fuselage and associated aerodynamic fairings; however, the wing skin area covered by fairings is very small relative to the externally exposed aerodynamic surface area, and it is ventilated in flight by outside air, which enters the forward fairing through National Advisory Committee for Aeronautics (NACA) scoops and flows aft, over and above the fuel tank before being exhausted overboard at the aft fairing.
• There are no significant heat sources external to the fuel tank (such as air conditioning equipment or heat exchangers) in the portion of the wing covered by aerodynamic fairings.

Subsequent to the original request for relief, Textron determined that there are potential design solutions which could allow the Model 700 to be compliant with the requirements, and requested a time-limited exemption from compliance for the Model 700 for 5 years after the date of initial type certification instead of the full exemption originally requested.

Textron will commit to providing a design solution that will allow direct compliance to the regulation before the expiration of the requested exemption. The proposed design change will be available within 5 years of receipt of the Model 700 type certificate. This will allow Textron time to develop, install, test, and certify the optimum design solution. This duration also aligns with the typical program schedule which has significant early experimental and development testing completed prior to application for certification, which in this case that early time has not been applicable.

Based on its analysis of the request and justifications, the FAA granted the temporary relief to Textron for the Longitude. The company must submit a compliance plan by October 1, and the airplane remains on track for certification in the third quarter of this year, Textron said.

(Images from file)

FMI: Exemption document