The Federal Aviation Administration (FAA) of the United States announced Tuesday that it had issued an emergency airworthiness directive regarding certain Pratt & Whitney PW4000 engines. The directive requires Thermal Acoustic Imagery of fan blades to detect any hidden cracks before the planes equipped with them are allowed to take off again.
Titanium blades to be inspected
Following this weekend’s spectacular engine failure resulting in someone’s Colorado-garden becoming a modern art installation (thankfully without injury to life or limb), the FAA has issued an emergency airworthiness directive (AD) related to certain Pratt & Whitney engines.
The directive requires operators with airplanes equipped with these engines to inspect them before further flight. The FAA said it had reviewed all the data from Saturday’s incident, where a United Boeing 777-200 suffered an engine failure shortly after take-off from Denver.
The PW4000 number two engine’s fan-blade failure mere minutes after United’s flight took off for Honolulu resulted in a damaged engine, an in-flight engine fire, and damage to the airplane.
Combined with other safety factors, the agency has determined that carriers have to conduct a thermal acoustic image (TAI) inspection of the large titanium blades at the front of the engine.
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Most operators have already grounded the plane
Boeing recommended the grounding of 777s equipped with PW4000 engines almost immediately following the incident. The specific type of engine is fitted on 128 earlier generation Boeing 777s. Many of these – 52 – are operated by United Airlines, with close to half already parked due to the ongoing crisis.
The rest are with All Nippon Airways (22, half of which are stored), Korean Air (16, nine already parked), Japan Airlines (13, four parked), Asiana Airlines (nine, two in storage), and low-cost Korean carrier Jin Air (four). All carriers apart from Jin Air have voluntarily grounded the aircraft in question.
Engines included in the emergency AD are Pratt & Whitney Division PW4074, PW4074D, PW4077, PW4077D, PW4084D, PW4090, and PW4090-3 model turbofans with specific types of low-pressure compressor blades installed.
Results to be reviews on a rolling basis
The AD is effective immediately upon release. The FAA says that it will review the results on a rolling basis. The usual inspection interval for these engines is every 6,500 flight cycles, meaning one take-off and landing.
Thermal acoustic imagery can reveal cracks on the blades’ interior surfaces, which would not be detected during a visual inspection. It uses a short burst of high-power ultrasonic energy in the 20KHz range to excite a part and then monitor it with a thermal camera. The method ‘heats up’ potential cracks and makes them visible in the infrared range.
What do you make of the FAA’s airworthiness directive? Have you heard of thermal acoustic imagery as a means of inspecting aircraft engines? Leave a comment below and let us know.