The geek with a cynical view: United Airlines Flight 328

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United Airlines Flight 328 was a scheduled domestic passenger flight from Denver to Honolulu, Hawaii on February 20, 2021; the Boeing 777-222 operating the route on that date suffered an apparently contained engine failure shortly after takeoff,[1] that nevertheless resulted in a debris field at least 1 mile (1.6 km) wide over the Commons Park suburb of Broomfield, Colorado and surrounding area.[2][3][4][5][6] Falling debris from the affected engine cowling was recorded by eyewitnesses using smartphone cameras and a dash cam.[7][8][9]

The flight landed safely with no injuries or loss of life to those in the aircraft or on the ground.[10] Although the aircraft landed safely, the engine failure resulted in damage to the engine, an in-flight engine fire, and damage to the airplane.[11] The failed engine was a Pratt & Whitney model PW4077 turbofan.[12] The U.S. Federal Aviation Administration immediately issued an Emergency Airworthiness Directive requiring U.S. operators of airplanes equipped with similar Pratt & Whitney PW4000 series engines to inspect these engines' fan blades before further flight.[11] The U.S. National Transportation Safety Board is investigating the aircraft engine incident.

Contents

Aircraft

The aircraft involved was a Boeing 777-222 registered as N772UA (c/n 26930/Line no.5).[13] The aircraft was built in November 1994[14] and delivered to United in September 1995. The aircraft is fitted with two Pratt & Whitney PW4077 engines.[13]

Originally the aircraft started out as WA005, one of the original Boeing 777-200s that took part in the flight test certification program prior to its entry into commercial service.[15][14]

On the day of the incident the aircraft had arrived in Denver from Chicago O'Hare International Airport (ORD) as UA flight 2465, departing at 9:37 a.m. CST and arriving at 10:50 a.m. MST.[16]

Incident

United 328 departed from Denver International Airport's Runway 25 uneventfully at 12:15 local time,[17] but while climbing through 13,000 feet (4,000 m), there was an internal failure within the right engine. This resulted in some of the engine cowling becoming detached, causing it to fall to the ground, along with other engine parts. The pilots contacted air traffic control and the airliner subsequently landed safely at Runway 26 at 13:37 local time. No one on the ground or in the aircraft was injured, though flying debris resulted in a large hole in the wing to body fairing.[18][19]

Passengers were re-booked on UA flight 3025 – operated by a different Boeing 777, N773UA, a sister ship to N772UA immediately ahead of it on the production line[20] – that took off from DEN to HNL hours later. On February 13, 2018, originating from San Francisco as United Airlines Flight 1175, N773UA had a similar engine failure and loss of the engine cowling 120 miles from its destination of Honolulu, where it made a safe emergency landing.[21] Boeing has been working on a redesign for a replacement fan cowl as a result of that incident, according to documents reviewed by the Wall Street Journal.[22]

Another 777-289, JA8978, operated as Japan Air Lines Flight 904 from Okinawa-Naha Airport (OKA) on December 4, 2020, also experienced a similar fan blade out failure and partial loss of the fan cowl six minutes after takeoff;[23] it returned to OKA and landed safely, but the Japan Transport Safety Board considered it a “serious incident” and launched an investigation.[24]

Investigation

Photograph showing damage to the right engine cowling, including the loss of the inlet fairing and fan doors (NTSB photo)

The National Transportation Safety Board (NTSB) is investigating the incident.[9] A senior investigator living in the Denver area immediately coordinated with first responders. Three other investigators from the NTSB's Denver regional office are assisting. It was noted upon initial inspection that the inlet and the cowling had separated from the engine and that two fan blades had fractured, one near its root and an adjacent one about mid-span; a portion of one blade was embedded in the containment ring. The remainder of the fan blades exhibited damage to the tips and leading edges.[1]

On February 22, 2021, National Transportation Safety Board Chairman Robert Sumwalt announced that the damage to the fan blade is consistent with metal fatigue, according to a preliminary assessment.[25][26] It is unclear whether the failure is consistent with other failures attributed to metal fatigue in a fan blade in a February 2018 United Airlines flight and a December 2020 Japan Airlines flight.[25] Sumwalt also said that "by our strictest definition"[27] NTSB did not consider the incident an uncontained engine failure because "the containment ring contained the parts as they were flying out."[28] The NTSB will look into why the engine cowling separated from the aircraft and why there was a fire, despite indications that the fuel supply to the engine had been turned off.[25]

Pratt & Whitney PW4000

Damage to PW4000 hollow fan blades from UA328 (NTSB photo)

There have been previous reports of PW4000 engine failures. In December 2020, Japan Airlines Flight JL904 operating a Boeing 777 suffered a failure of the same engine type at around 16,000 to 17,000 feet.[29]

On February 13, 2018, United 1175 en route from San Francisco to Honolulu suffered from an engine failure over the Pacific. The aircraft was also a Boeing 777-222, N773UA, with an identical configuration to N772UA operating United 328. The aircraft subsequently landed safely in Honolulu with no injuries or loss of life. The NTSB eventually determined that the fan blade inside the engine fractured, leading to the failure.[21] The investigation faulted Pratt & Whitney for not doing more stringent inspections.[30] The aircraft was eventually repaired and returned to service.[21]

On the same day as United 328, a Boeing 747-400BCF belonging to Longtail Aviation experienced an uncontained engine failure, shortly after departing Maastricht Airport in the Netherlands.[31] Two people were injured by the falling debris.[32] The 747-400BCF was powered by PW4056 engines, an earlier version of the PW4000 engine.[31]

Reactions

After the accident of UA328, the Japanese Ministry of Land, Infrastructure, Transport and Tourism ordered the grounding of 32 Boeing 777 aircraft operated by Japan Airlines and All Nippon Airways.[33] The Federal Aviation Administration (FAA) ordered increased inspections of Boeing 777 aircraft with PW4000 engines;[34] United Airlines had preemptively removed all such airliners (of which it has 28 in storage, and 24 in use) from active service.[34][35]

On February 22, 2021, following an Emergency Airworthiness Directive, Boeing confirmed that it had grounded worldwide all 128 of its Boeing 777 aircraft equipped with certain Pratt & Whitney PW4000 engines because of the UA328 incident.[36] Later that day, the British Civil Aviation Authority also banned Boeing 777s powered by Pratt & Whitney PW4000-112 engines from entering UK airspace.[37][38]

On February 23, 2021, Pratt & Whitney released a statement that the company was cooperating with federal investigators and coordinating with operators and regulators to support a revised inspection interval of the PW4000 engines.[30]

Groundings by operator

As of 24 February 2021[39]

Airline In service In storage Total

United Airlines 24 28 52

All Nippon Airways 10 14 24

Japan Airlines 7 13 20

Korean Air 7 10 17

Asiana Airlines 6 1 7

Jin Air 4 0 4

Total 58 66 124

The geek with a cynical view

Friday, February 26, 2021

United Airlines Flight 328

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