The US FAA is proposing that operators of nearly 500 US-registered Boeing 737 Next Generation (NG) aircraft inspect the twin-jet's aft engine mounts to determine if the centre link assembly mechanism is reversed, a problem originally thought to apply only to aircraft after having an engine removed and improperly reinstalled during maintenance.
The new airworthiness directive (AD) would replace a 2003 AD requiring operators of 737NGs with serial number 1 - 1,277 to review maintenance records to determine whether an engine had been removed since the original manufacturing date, and if it had, to perform an inspection of the aft mount for correct installation.
"Since we issued (the AD), the manufacturer informed us that it is possible that some centre links were incorrectly installed in an aft engine mount before the airplane was delivered," says the FAA. In fact, the agency says operators had reported that the centre link assemblies were found to be reversed on "several airplanes" that had never been removed.
According to a Boeing spokeswoman, the airframer has received "a couple of reports" of the link being installed incorrectly.
The company says it recently revised instructions for installing the part, including the correct orientation. "We have also sent a service bulletin to all operators of 737NG, recommending an inspection of the link for proper orientation, including a decal with illustration of correct orientation of the engine strut upper link," says the spokeswoman.
Left unchecked, the FAA says a reversed link assembly increases structural loads on the aft mount, which could cause the mechanism to fail with "consequent separation of the engine from the airplane".
Though no 737NG aircraft have experienced engine separation incidents to date, several 737-200 models have shed right-side engines due to fatigue in the aft cone bolts holding the engines to the wing structure, the most recent being the Nationwide Airlines 737-200 in November 2007.
To date, Boeing has delivered 2,722 737NG aircraft.
Source: Air Transport Intelligence news
