The US Federal Aviation Administration has issued an emergency airworthiness directive (AD) after a third in-flight engine shutdown involving a General Electric GE90-115B with a transfer gearbox failure.
The emergency AD expands the population of GE90-115Bs covered by a previous AD to all engines built between September 2012 and June, raising the total number of engines involved to 132.
GE says it is still working to understand why the manufacturing process used by supplier Avio started producing a number of defective transfer gearboxes beginning in September last year.
Avio uses a heat-treatment process that suddenly after September appears to create stress points on the surface of the gear, GE says.
While Avio and GE continue investigating the cause of the problem, Avio is shot-peening all of the gears produced from early June to reduce the surface stresses on the part.
The FAA initially issued an AD earlier this year after two in-flight engine shutdowns were reported. The issue involved a population of 118 engines, and the immediate concern was addressing Boeing 777-300ERs flying with two engines in the suspect population.
On 2 July, a Korean Air Lines 777-300ER flying with two engines delivered in early June encountered an in-flight shutdown that was traced back to a transfer gearbox failure. Engines delivered in June were previously considered as outside the suspect engine population, but the new emergency AD adds them to the pool.