U.S. aviation regulators have ordered airlines to inspect certain Pratt & Whitney engines on Boeing jets for invisible cracks before the planes fly again.
The United States Federal Aviation Administration on Tuesday issued an emergency airworthiness directive for the PW4000-112, an engine used in about 8% of Boeing’s 777s. The order came three days after a engine on a broken 777 four minutes after takeoff, scattering debris over a Denver suburb.
No one on United Airlines Flight 328 or on the ground was injured, but the aircraft powered by P&W, a division of Raytheon Technologies, were effectively grounded as a result of the incident.
National Transportation Safety Board investigators said Monday that a fan blade in the turbine was showing signs of “metal fatigue”, which seems to have caused it at the root. The cut blade struck a second blade, cutting it in half.
The order required aircraft operators to perform a thermal-acoustic imaging inspection of the titanium fan blades on the front of each engine. The “technology can detect cracks on the inner surfaces of hollow fan blades or in areas that cannot be seen on visual inspection,” the FAA said.
Regulations currently require the engine to be inspected every 6,500 flight cycles – defined as one take off and one landing. The FAA said it could establish a shorter inspection interval based on the results of initial checks of airlines’ engines.
The PW4000-112 debuted in 1995 as the launch engine for the 777, but the engine has not been used in widebody Boeing jets since the mid-2000s.
Saturday’s incident in the skies over Colorado was not the first alarming episode involving the engine. The fan blades broke from a turbine in December on a Japan Airlines flight and in 2018 on a United flight to Hawaii.
NTSB investigators discovered during the Hawaii incident – where no one was injured – that fatigue had made a small crack inside the hollow-core fan blade. The crack was found during an inspection in 2010 and again in 2015, when it was larger.
“The inspectors attributed the indication to a defect in the paint used during the [thermal acoustic imaging] and allowed the blade to continue the overhaul process and be put back into service ”, NTSB report mentionned.
The report found that inspectors mainly received on-the-job training, which “could have a negative impact on the inspection. P&W has indicated that it is working to correct these problems ”.