Owners of more than 500 Honeywell TFE731-family turbofan engines are being called upon by the US Federal Aviation Administration to return their engines to the factory to check for improperly machined high-pressure turbine disks, an error the regulator expects will cost more than $13 million to correct.

The powerplants are used on a wide variety of business jets, including the Dassault Falcon 20, 50 and 900EX, Cessna Citation II, VI and VII, Learjet 40, 45 and 55, and the Hawker 800 and 850.

In a proposed airworthiness directive (AD) issued last week, the FAA says that it "became aware of a manufacturing audit" in June 2006 indicating that some high-pressure turbine rotor disks had received "improperly machined radii in the root of the forward and aft curvic teeth". Honeywell issued a service bulletin on the problem in July 2006.

Left unfixed, the issue could cause "higher stress in the curvic area" of the high-pressure turbine rotor disk than originally calculated by the manufacturer, says the FAA, possibly causing an uncontained engine failure. The agency says it has not received any reports of cracked high-pressure turbine rotor disks due to the faulty machining, but says the higher stress "reduces the calculated low-cycle fatigue life limit to below the current published life limit".

The FAA expects that half of the engines inspected will display the problem, leading to fixes that will cost roughly $50,000 per engine.

Honeywell says it has instituted a special programme along with the service bulletin that will provide the inspection free of charge if done during a major periodic inspection for maintenance service plan participants, and a prorated discount on the work for all others based on the number of hours the disks have been in service.

According to the company, more than 30% of the engines have already been inspected, though no data was provided on how many disks had to be replaced.

Source: Flight International