Pratt & Whitney Contained Engine Failure
On the 20th of February 2021, a Boeing 777-200, flying as United Airlines flight UA328, suffered an engine failure shortly after take off from Denver International Airport for a scheduled domestic flight to Honolulu, Hawaii. There were 229 passengers and ten crew on board.
United Airlines was the launch customer for the Boeing 777 when the company placed an order for 34 Pratt & Whitney-powered aircraft in 1990 to replace its aging DC-10s. The accident aircraft, registration N772UA, was the fifth Boeing 777 ever produced, built in 1994. It is powered by two Pratt & Whitney engines model PW4077.
About four minutes after take off from Denver, climbing through 12,500 feet, the number two engine failed. The aircraft was being flown manually and the flight crew immediately declared an emergency and requested a left turn back to Denver (as an NTSB representative put it, so “as to not turn right over the ‘dead’ engine”.)
Two of the fan blades fractured within the engine. A portion of one of the blades was embedded in the fan blade containment ring. The remaining fan blades had damage on the tips and leading edges. The inlet and cowling separated from the engine and fell to the ground.
A passenger took a video of the engine which immediately became a viral sensation.
The incident is frequently being referred to as an uncontained engine failure, which I suspect is because of this video showing the engine with no cowling. However, this was a contained engine failure, which means that the failed engine pieces (in this case the fan blades) are contained within the engine case or exit via the tail pipe. Much development has been put into aviation technology to contain the fan blades of an engine in the case of a failure, as the potential hazard of high speed debris acting as shrapnel would put the aircraft and the passengers at much more risk than the engine failure itself.
An NTSB representative confirmed that the video made the failure look “not as contained as it actually was”. He said that both fire suppression tanks were deployed into the #2 engine, the thrust was neutralised and the fuel was cut. The fire was likely residual flames from a damaged fuel line.
The debris on the ground was not from the engine, but the inlet and cowling which separated from the engine and fell to the ground over Broomfield, Colorado, a city northwest of the airport. Local news quickly reported that the Broomfield police had received reports of a plane falling from the sky when the debris began to land. A senior FAA investigator who lives in the Denver area immediately started working with local law enforcement to recover the components for the investigation.
This footage shows the debris falling in the distance:
— Nicole Fierro (@FierroNicole) February 21, 2021
Resident Kieran Cain took this photograph of a piece of cowling which landed on his neighbour’s porch:
— Kieran Cain (@KieranCain) February 20, 2021
He reported that he both heard and saw the debris dropping and that there was property damage to houses but no injuries.
The inlet and cowling which separated were manufactured by Boeing, not Pratt & Whitney. According to the Wall Street Journal, Boeing has been in discussions with the FAA to replace all of the casing from its 777 jets after a similar incident in 2018.
The NTSB has posted photographs of the aircraft in the hangar, including this one showing the damage to the fan blades:
and this one showing the missing inlet and cowling:
The naked engine looks a lot less frightening on the ground, I have to admit.
On the 23rd of February, three days after the incident, the FAA released an emergency airworthiness directive:
…prompted by the in-flight failure of a 1st-stage low-pressure compressor (LPC) blade on a PW40077 model turbofan engine resulting in an engine fire during flight. This condition, if not addressed, could result in a 1st-stage LPC blade release, damage to the engine, and damage to the airplane.
The FAA is issuing this AD because the agency has determined the unsafe condition described previously is likely to exist or develop in other products of the same type design.
(1) Before further flight, perform a thermal acoustic image (TAI) inspection of the 1st-stage LPC blades for cracks using a method by the FAA
(2) If any 1st-stage LPC blade fails the inspection required by paragraph (g)(1) of this AD, remove the blade from service and replace with a part eligible for installation before further flight.
High cycle fatigue is a primary cause of fan blade failures, which is why the inspection to search for fatigue cracks is required on a list of Pratt & Whitney engines before the 777 can go back into service.
Pratt & Whitney have confirmed that they will carry out Thermal Acoustic Imaging inspections on all fan blades on the Pratt & Whitney PW4000-112 engines to confirm their airworthiness. They also commended the flight crew operating United Airlines flight 328 for their professionalism.
Boeing’s media release says that this affects 69 PW4000-powered 777s in service and 59 in storage, while Pratt & Whitney’s statement says that their PW-4000-112” engine powers approximately 125 Boeing 777 aircraft.
United Airlines is the only affected US operator, with 24 in service. Japan’s regulator ordered all PW4000-powered 777s grounded, affecting 13 aircraft from Japan Airlines and 19 from All Nippon Airways. The UK CAA has banned flights by aircraft with PW-4000-112 engines, although there are no airlines that currently operate that type to destinations in the UK or indeed anywhere near UK airspace.
On the same day, a Boeing 747-412 flying as Longtail Aviation flight 5504 from Maastrict, NL to NYC, US, suffered an uncontained engine failure in their number one engine. The engine was coincidentally also Pratt & Whitney engine, the PW4056, which is not one of the engines listed in the FAA’s airworthiness directive. The flight was passing through 1,400 feet with the number one engine failed. This was an uncontained failure. Pieces of the fan blades fell over the village of Meerseen, causing two injuries and stabbing one poor car through the heart.
The flight crew declared an emergency and then entered a holding pattern to dump fuel before diverting to Liege Airport in Belgium, making a safe landing an hour after its departure from Maastricht.
The engine which failed over the Netherlands was also a Pratt & Whitney, the PW4056, however the failure appears to be unrelated; the PW4056 does not have the same fan blades. Both aircraft went into service over a quarter of a century ago (1991 and 1994), making them older than some of the readers of this website. It appears to be a coincidence that both failed on the same day.