Grounding of Small Portion of Boeing 777 Fleet Unlikely to Cause Significant Passenger Disruptions
On February 20, a United Airlines (UA) Boeing 777 operating flight UA-328 from Denver (DEN) to Honolulu (HNL) experienced an engine failure shortly after takeoff from DEN, which caused parts of the engine nacelle and cowling to fall off the aircraft onto a residential area below. The aircraft returned to DEN and landed safely. Nobody onboard the aircraft or on the ground suffered injuries.
In response, all airlines operating Boeing 777s equipped with certain variants of the Pratt & Whitney PW4000 engine grounded the aircraft at Boeing’s request. The US Federal Aviation Administration (FAA) later formally grounded the aircraft until airlines and Pratt & Whitney can inspect the engines’ fan blades for invisible cracks. The groundings are unlikely to have a major impact on global airline travel, as they affect a relatively small number of aircraft. While many media outlets have exaggerated the safety threats associated with the United Airlines incident, some aspects of the incident do present safety concerns. However, the Boeing 777 remains an exceptionally safe aircraft.
Are All Boeing 777s Grounded?
No. Only a small portion of the global Boeing 777 fleet is grounded. According to Boeing, there are 69 777s in service with affected engines and a further 59 in storage. By comparison, Boeing has built over 1,600 777s, the vast majority of which are still in service.
The only airlines operating Boeing 777s with PW4000 engines are United, Japanese carrier All Nippon Airways (NK), South Korean carrier Asiana (OZ), Japan Airlines (JL), Korean Air (KE), and Korean Air’s subsidiary Jin Air (LJ). All the airlines have grounded the affected aircraft until further notice. Ukraine International Airlines (PS) also has one aircraft in its fleet, but the aircraft was already in storage due to the COVID-19 pandemic.
All these airlines except for Asiana and Jin Air also operate 777s powered by different engines, so passengers may still find themselves flying on 777s with these airlines while the PW4000-powered 777s are grounded.
How Will Groundings Impact Passengers?
The groundings are unlikely to have a major impact on passengers. Of the six airlines operating PW4000-powered Boeing 777s, only United had more than 10 active in its fleet. The ongoing COVID-19 pandemic means that airlines have ample extra capacity to accommodate passengers who were scheduled to fly on the affected aircraft, either by swapping in other aircraft or by moving passengers onto other flights. United’s PW4000-powered 777s were mostly used on domestic routes that were relatively short for a 777, making it easier for the airline to use other aircraft to operate the routes.
What Happened in the Denver Incident?
Investigators say that one of the blades on the large fan at the front of the engine broke, causing the engine to fail. Investigators have not determined why the fan blade failed. There are a number of potential causes of a fan blade failure, including metal fatigue, undetected manufacturing flaws, faulty maintenance, or an external object striking the fan blade. The fan blade itself appears to have stayed inside the engine, but the impact of the failure and subsequent heavy vibrations likely caused the nacelle and cowling to separate from the aircraft.
The incident on flight UA-328 is not the first time a fan blade failure on a PW4000 engine has caused a serious incident on a 777. In Feb. 2018, a United Airlines 777 experienced a very similar failure over the Pacific Ocean, which also saw the engine cowling separate from the aircraft. Investigators found that the 2018 incident was caused by a crack in a fan blade, which went undetected due to the inadequate training of inspectors at Pratt & Whitney. A fan blade failure also likely caused a PW4000 engine failure on a Japan Airlines 777 in Dec. 2020, although investigators have not published a final report on the incident.
Does the Incident Represent a Major Safety Concern?
Many media outlets have exaggerated the threat posed by the engine failure on flight UA-328, but the incident did highlight some legitimate safety concerns. While a Boeing 777 is safe to fly on one engine, the parts falling off the engine could pose a serious hazard to the aircraft and to people on the ground.
An engine failure alone on a Boeing 777 is not a major safety threat. All modern airliners can take off, fly, and land safely with one engine failed, and the 777, in particular, is certified to fly for over three hours on one engine. Airline pilots are also generally well prepared for an engine failure. Pilots routinely train for engine failures in simulators, including failures at the worst possible parts of a flight, and pilots’ pre-flight briefing includes a discussion of what procedures they will follow in the event of an engine failure.
The bigger concern about what happened on flight UA-328 and in similar incidents is that large engine nacelle and cowling parts fell off the aircraft. These large parts could pose a serious threat to the aircraft’s safety if they hit certain parts of the wing, fuselage, or tail after they separate from the engine. On flight UA-328 a piece of the cowling appears to have ripped a hole in the underside of the aircraft’s fuselage, although it did not cause any critical damage. In April 2018, an engine cowling on a Southwest Airlines (WN) Boeing 737 came off the engine and struck a passenger window after a fan blade failure, causing an explosive decompression that killed a passenger. The parts also pose a serious threat to any people or property below the aircraft’s flight path. Flight UA-328, together with previous incidents, may push regulators to require stronger cowling and nacelle attachments for future aircraft to ensure that the parts do not separate in the event of an engine failure.
Could Other Aircraft be Affected?
The February 20 failure of a PW4000 engine on a Boeing 747 freighter in the Netherlands has led some media outlets to speculate that authorities may ground Boeing 747 and Boeing 767 aircraft that are also powered by the PW4000 engine. Such a scenario is unlikely, however. The fan blade design of the PW4000s used on the Boeing 777 is unique to that variant of the engine, so authorities are unlikely to ground other aircraft models with PW4000 engines. Initial reports of the incident in the Netherlands also suggest that the failure occurred in a different part of the engine than the failure on flight UA-328 did. However, conclusions will have to wait until the investigation is complete. Authorities are also highly unlikely to ground Boeing 777s powered by different engine models, as there are no current significant safety concerns for those engines.
Is the Boeing 777 Safe?
The Boeing 777 is an exceptionally safe aircraft, even by the modern airline industry's extremely high standards. The aircraft has been in service for over 25 years and has only had three accidents with passenger fatalities, giving it one of the lowest accident rates in the history of aviation. None of these fatal accidents have been linked to design or technical flaws with the 777. Crisis24 does not see any reason to avoid flying on Boeing 777s that remain in service.
