On February 13, 2018, around noon local time, a Boeing 777-222[a] operating as United Airlines Flight 1175 (UA1175), experienced an in-flight separation of a fan blade in the No.

The flight crew shut down the failed engine, declared an emergency, and began a drift-down descent, proceeding direct to HNL where they made a single-engine landing without further incident at 12:37 local time.

Its installed set of hollow-core fan blades had undergone two previous overhauls at P&W that included a thermal acoustic imaging (TAI) internal inspection that is intended to prevent this type of failure.

Two small punctures were found in the right side fuselage just below the window belt with material transfer consistent with impact from pieces of an engine fan blade.

The aircraft involved was a Boeing 777-222, the United Airlines specific variant of the original 777-200 series, registered as N773UA, (c/n 26929) and line number 4.

[3] At the time of the fan blade out engine failure event, 11:58 Hawaiian standard time (HST), the flight was about 120 miles (100 nmi; 190 km) from HNL at flight level (FL) 360 (roughly 36,000 feet or 11,000 meters) when there was a violent jolt and very loud bang that both pilots stated was followed by extreme airframe vibrations.

Subsequent laboratory examination of the skin surrounding the puncture found embedded particles of largely titanium and vanadium, which along with aluminum are the alloying elements of the fan blade material.

The location of the maximum deformation of the wrap was coincident with the approximately 34-inch (86 cm) long crack on the inside of the fan case.

11 revealed a low cycle fatigue (LCF) fracture that originated on the interior cavity wall directly below the surface.

[3] The metallurgical examination of the fractured fan blade was accomplished at P&W's Materials Laboratory in the presence of members of the Powerplants Group as well as an NTSB metallurgist.

The examination revealed a fatigue fracture that had initiated from a subsurface origin on the interior surface of the hollow core fan blade.

The origin of the crack was in an area where the basal planes of the crystals were all similarly aligned and were almost perpendicular the localized stress field when the fan blade was formed.

The Federal Aviation Administration (FAA) engine certification office issued a Notice of Proposed Rulemaking that would mandate the accomplishment of initial and repetitive TAI inspections on PW4000 112-inch fan blades.

[11] The inlet is a cantilevered structure that directs the airflow into the engine fan case in a controlled and uniform manner.

The inlet consists of two concentric cylinders (the inner and outer barrels) joined by forward and aft bulkheads and a lip skin.

During engine fan blade out (FBO) certification testing the inlet cowl construction consisted of an aluminum bulkhead.

On June 30, 2020, more than two years after the incident, the NTSB determined the probable cause(s) of this incident to be:[3] The fracture of a fan blade due to P&W's continued classification of the Thermal Acoustic Imaging (TAI) inspection process as a new and emerging technology that permitted them to continue accomplishing the inspection without having to develop a formal, defined initial and recurrent training program or an inspector certification program.

[16] In 2019 the FAA issued an airworthiness directive mandating recurring engine inspections based on usage cycles, and at that time stated "these thresholds provide an acceptable level of safety".

[17] The 6500 flight cycle fan blade inspection interval adopted by the FAA was also adopted and used by other national authorities, until Japan's transport ministry ordered increased inspection frequency after the similar JAL 777-200/PW4000 engine failure incident at Naha Airport (OKA) in Japan on December 4, 2020.

[9] On February 12, 2020, a resident of California and Guam who was a passenger on the flight filed suit in the Superior Court of Guam seeking over $1 million each from United, the Boeing Company and Pratt & Whitney for severe mental and emotional injuries, including post-traumatic stress disorder, in addition to physical injuries.

The lawsuit cites statements made by the captain to the press including a description of the sensation after the engine failure as, "the aircraft experiencing what felt like 'hit[ting] a brick wall at 500 miles an hour'".

The manufacturer told regulators it had decided to redesign and make replacement covers with which airlines could retrofit their fleets, according to the FAA document.

"[21][22] This article incorporates public domain material from websites or documents of the National Transportation Safety Board.