The US Federal Aviation Administration (FAA) has issued an Emergency Airworthiness Directive that requires US operators to conduct an immediate inspection on certain Boeing 777 aircraft equipped with Pratt & Whitney PW4000 engines.

This directive was issued after United flight UA328 departing from Denver International Airport to Honolulu suffered engine failure and shed debris over Denver on 20 February.

In a statement, the FAA said: “After reviewing the available data and considering other safety factors, the FAA determined that operators must conduct a thermal acoustic image (TAI) inspection of the large titanium fan blades located at the front of each engine. TAI technology can detect cracks on the interior surfaces of the hollow fan blades, or in areas that cannot be seen during a visual inspection.”

In response to the engine failure, airlines in the US, Japan and South Korea grounded several Boeing 777 aircraft equipped with Pratt & Whitney 4000-112 engines.

Boeing installed the engine on 128 planes, or less than 10%, of the global fleet of more than 1,600 delivered 777 widebody jets.

The engine manufacturer immediately reacted by recommending airlines to ground the aircraft with this engine type.

Meanwhile, Pratt & Whitney owner Raytheon Technologies announced that fan blades need to undergo thermal acoustic imaging (TAI) inspections before returning to service.

The inspection will be performed by Pratt & Whitney’s FAA-authorised repair station in East Hartford, Connecticut.