The US Federal Aviation Administration has issued an airworthiness directive (AD) to operators of General Electric CF6-80A engines, mandating the inspection and reworking where necessary of all high-pressure turbine (HPT) rotor disks before the end of 2008, writes Guy Norris.
The action comes in the wake of a 2 June incident at Los Angeles International airport - when an engine on an American Airlines Boeing 767-200 suffered an uncontained failure during a ground run - and effectively accelerates compliance times issued under a previous AD published in 2004.
The 2004 AD was prompted by virtually identical failures experienced on a USAir 767 in 2000 and an Air New Zealand 767 in 2002.
The FAA says the "incident with an American 767 at Los Angeles prompted us to take a closer look to see if there was a pattern among that failure and two previous incidents". In the meantime, it adds, "it is prudent to act even before determining the root cause of that incident to reduce the risk of another such event. The agency will not hesitate to take further action if additional information from the investigation warrants."
The AD is intended to "detect and prevent cracks that could spread and cause the disk to fail", adds the agency. According to the FAA, almost 4,500 CF6-80 engines are in worldwide service, but GE says that in practice, the AD affects fewer than 800 engines of the 3,400 units in service made before 2001, when the design of the HPT rotor disk was changed to alleviate the problem.
Of the affected engines, GE says that around 175 are yet to be inspected, while 600 still need to be reworked. This involves smoothing out the slot bottom where all sharp edges now have to be worked out.
Source: Flight International