The US Air Force believes that ten modifications, costing an estimated $6.2 million, will be required before its 110 Slingsby T-3A Firefly flight-screener aircraft can be returned to flight status by the the middle of 1998.

The single-engined, two-seat light aircraft made by the UK's Slingsby Aviation, which replaced the USAF's ageing fleet of T-41 (Cessna 172) trainers, was grounded by the USAF in July 1997 after a series of engine shutdowns, including nine with the aircraft airborne.

Six people have died in three accidents since 1995, when the Firefly was introduced to screen pilot candidates. Each crash killed a flight instructor and a USAF Academy cadet, although none of the fatal incidents is believed to have been caused by engine shutdowns.

Gen Lloyd Newton, commander of the Air Education and Training Command, says that an investigation has concluded that the $300,000 aircraft, powered by a 195kW (260hp) Textron Lycoming AEIO-540-D4A5 piston engine suffers from "a fuel- vapourisation problem."

He thinks that the ten proposed modifications, which include increasing the diameter of the fuel lines, moving the fuel-boost pump on the engine, and rerouting some of the fuel lines on the powerplant, will "cure" the problem.

The US Federal Aviation Administration says that the USAF is the only Firefly operator in the USA. It notes that the modifications must be approved by the FAA through a supplemental type certificate (STC) because the aircraft was certificated by civil-aviation authorities. The STC will follow flight testing of the planned modifications scheduled to take place this year, says the FAA.

Newton says that the modifications, the responsibility of the USAF, will be made by the AF Air Logistics Center at Tinker AFB, Oklahoma. Although concerned about the number of fatal accidents, he stands by the USAF's decision to purchase the Firefly.

Jeff Bevan, Slingsby managing director, says that the company "-has complete confidence in the ability of the Firefly and its safety record". He notes that the USAF has "-generally expressed satisfaction with its performance".

Source: Flight International