The FAA recently granted Textron Aviation an exemption for the Cessna Citation Longitude's fuel tank, which is expected to resolve at least one issue that has held up certification of the super-midsize jet originally expected two years ago. Company officials anticipate Longitude type certification by the end of next month.
“We are pleased that the FAA has affirmed the permanent fuel tank exemption for the Citation Longitude,” Textron Aviation said in a statement to AIN. “The purpose of the exemption is to align the Longitude’s fuel system compliant design with the regulation, which did not anticipate the type of solution used. This is the permanent means of full compliance with the regulation.” All Longitude deliveries will have a compliant fuel system, the company added.
It largely puts to rest a process that began more than a year-and-a-half ago and a requirement by the FAA that Textron Aviation asserted at one point “would result in the disruption of production deliveries of the Model 700, causing [the compny] to experience a significant loss of revenue.”
Textron Aviation’s initial appeal for exemption in February 2018 centered around a difference in interpretation between the FAA and the company on what constitutes a center fuel tank. The Longitude is designed with the fuel tank in a conventional unheated aluminum wing, but includes a portion covered by aerodynamic fairings. The company considers the entire fuel tank to be in a conventional unheated aluminum wing (CUAW) that meets flammability requirements.
But the FAA disagreed, determining that the portion covered by the aerodynamic fairings is not a conventional unheated aluminum wing tank, which means the aircraft doesn’t meet the requirements of FAR 25.981(b), amendment 25-125.
In its earlier exemption request, Textron pointed to the safety records of other jets in its fleet with similar fuel systems such as the Citation Sovereign and M2, as well as the Hawker 4000. A temporary exemption issued in August 2018 accepted an interim modification and called for a long-term solution.
A second appeal made by Textron Aviation in December 2018 was more narrowly focused on the more extensive requirements that apply to the use of the flammability reduction means (FRM) in fuel tanks. The FAA has determined that the aircraft's dedicated electric recirculation pump is an FRM and therefore the aircraft must meet those requirements.
In its June 26 decision granting the exemption, the FAA said: “the design modification that Textron has incorporated in the Model 700, in order to cool the fuel tanks and reduce fuel heating, improves the overall tank flammability to a level equivalent to a CUAW tank.”