[1][3] Parts departing from the engine cowling of the Boeing 777-222[a] aircraft resulted in a debris field at least 1 mile (1.6 km) long over suburban residential areas of Broomfield, Colorado.

Similar 777-200 series aircraft were quickly grounded by several national aviation authorities, including the U.S. Federal Aviation Administration, which issued an Emergency Airworthiness Directive requiring U.S. operators of airplanes equipped with similar Pratt & Whitney PW4000-112 series engines to inspect these engines' fan blades before further flight.

[11] Japan Air Lines, which had a similar incident in December 2020, retired all of its P&W-equipped Boeing 777-200s a year earlier than planned in March 2021.

United Airlines, which also had a similar incident in 2018, grounded their Pratt & Whitney powered 777-200s from early to mid 2021 until July 2022 (with the exception of the accident aircraft.)

[22] The hollow-core fan blade that experienced metal fatigue failure in this incident had only undergone 2,979 cycles since its last trip to the P&W factory for nondestructive testing using thermal acoustic imaging (TAI) to find hidden internal defects.

This interval is less than half of the 6,500 cycle test frequency established in 2019 after a similar engine failure on a previous United Airlines 777-222 flight to Honolulu (UA1175) in 2018.

[26][27] At 13:04 local time it departed normally from Runway 25 en route to Daniel K. Inouye International Airport (HNL) as flight UA328.

[28] No one on the ground or in the aircraft was injured,[29] although flying debris resulted in a hole in the wing to body fairing, a non-critical composite part designed to reduce aerodynamic drag.

[30] The flight crew contacted air traffic control to declare an emergency and request a left turn to return to the airport.

They elected not to dump fuel for safety and time reasons and determined that the excess landing weight was not significant enough to outweigh other considerations.

Airport Rescue and Firefighting (ARFF) met the airplane as soon as it stopped on the runway and applied water and foaming agent to the right engine.

[24] Passengers were re-booked on flight UA3025 – operated by a different Boeing 777, N773UA, a sister ship to N772UA immediately ahead of it on the production line[27] – that took off hours later.

N773UA had previously experienced an extremely similar engine failure in 2018 as United Airlines Flight 1175 from San Francisco to Hawaii.

The flight descended continuously from 36,000 feet (11,000 m) and landed at HNL approximately 40 minutes later with no reported injuries or loss of life.

The NTSB determined that a fan blade fractured from a pre-existing metal fatigue crack that had been slowly propagating since 2010, leading to the failure.

[36] The investigation faulted Pratt & Whitney for not identifying the crack in two previous inspections due to a lack of training in Pratt & Whitney's thermal acoustic image (TAI) inspection process, resulting in "an incorrect evaluation of an indication that resulted in a blade with a crack being returned to service where it eventually fractured.

"[37][38] Boeing had 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.

[44] Coincidentally, on the same day as the United 328 incident, a Boeing 747-400BCF operating as Longtail Aviation flight LGT-5504, experienced an uncontained engine failure shortly after departing Maastricht Airport in the Netherlands, and two people were injured by debris that also fell in a residential area.

[30] 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.

Examination of the engine accessories showed multiple broken fuel, oil, and hydraulic lines and that the gearbox was fractured.

[50] The following operators grounded their 777-200 series aircraft within a week of the incident:[65] This article incorporates public domain material from websites or documents of the National Transportation Safety Board.