United Airlines flight UA328 suffered an engine failure shortly after departing Denver International Airport on 20 February 2020. The 777-200 (MSN 26930 | L/N 5) was operating from Denver to Honolulu with 231 passengers and 10 crew and returned safely to Denver. Parts of the right-hand engine were scattered near Broomfield, west of the airport. The NTSB is investigating the incident.

Updates on this incident

United flight 328 flight path

UA328 speed and altitude graph

The aircraft suffered a failure of its right hand engine (engine number 2) about 4 minutes after take off and landed back at Denver 23 minutes after take off.

Photos and video from the area

Photos and video posted to social media indicate the aircraft’s engine cowling detached.

Flight 328 @united engine caught fire. my parents are on this flight 🙃🙃 everyone’s okay though! pic.twitter.com/cBt82nIkqb

— michaela🦋 (@michaelagiulia) February 20, 2021

The engine inlet cowling landed in a neighborhood in Broomfield, Colorado.

BREAKING: Giant metal engine piece just landed in this Broomfield person's yard after plane flying over experienced explosion @9NEWS pic.twitter.com/ZpZkXClFlr

— Kieran Cain (@KieranCain) February 20, 2021

UA328 aircraft information

UA328 was operated by 777-200 registered N772UA. It is the fifth 777 ever produced by Boeing and powered by two Pratt & Whitney PW4000 series engines.

Download Flightradar24 data

You may view playback from UA328 here, or download CSV and KML files below.

• CSV file
• KML file

Updates

21 February 2021

In the wake of UA328’s engine failure, regulators and investigators have acted to ground aircraft operated by the same engines and require an accelerated inspection timeline. The following updates were issued on 21 February 2021.

• Japan grounded 777s with the same Pratt and Whitney PW4000 engines as UA328, affecting 13 Japan Airlines 777s and 19 ANA 777s.
• The United States Federal Aviation Administration is in the process of issuing an Emergency Airworthiness Directive ‘that would require immediate or stepped-up inspections of Boeing 777 airplanes equipped with certain Pratt & Whitney PW4000 engines.’
• United Airlines released a statement:
  • Starting immediately and out of an abundance of caution, we are voluntarily and temporarily removing 24 Boeing 777 aircraft powered by Pratt & Whitney 4000 series engines from our schedule. Since yesterday, we’ve been in touch with regulators at the NTSB and FAA and will continue to work closely with them to determine any additional steps that are needed to ensure these aircraft meet our rigorous safety standards and can return to service.
• Boeing released a statement supporting the suspension of operations for the 69 in-service and 59 in-storage Pratt & Whitney 4000-112 powered 777s until the ‘FAA identifies the appropriate inspection protocol.’
• Pratt & Whitney released a statement that they are ‘actively coordinating with operators and regulators to support the revised inspection interval of the Pratt & Whitney PW4000 engines that power Boeing 777 aircraft.’
• The NTSB released a preliminary investigative update noting that the inlet and cowling separated from the engine of UA328 and that inspection of the fan revealed that two fan blades were fractured, one near the root and the other about mid-span. Additionally, ‘a portion of one blade was imbedded [sic] in the containment ring’ and the ‘remainder of the fan blades exhibited damage to the tips and leading edges’
• The UK CAA also banned flights by aircraft with PW4000-112 engines, though no airlines currently operate that type to destinations in the UK or near UK airspace.

22 February 2021

As part of its preliminary update on 22 February, the NTSB released photos of the damage to the PW4077 engine on N772UA.

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Damage to N772UA near the wing root and right side of the fuselage

23 February

The US FAA has now issued its Emergency Airworthiness Directive. The directive requires thermal acoustic image (TAI) inspection of all 1st-stage low pressure compressor section blades on specific Pratt & Whitney PW4000 series engines before next flight. Previously, this inspection was required every 6,500 flight cycles. This airworthiness directive was prompted by initial findings from the investigation into UA328’s engine failure. Read the full airworthiness directive.

Following the FAA’s issuance of the EAD, Pratt & Whitney issued a statement:

The U.S. Federal Aviation Administration has issued an Airworthiness Directive requiring inspection of fan blades on the Pratt & Whitney PW4000-112” engines prior to their return to service.

The process requires the shipment of fan blades to Pratt & Whitney where Thermal Acoustic Imaging (TAI) inspection will be used to confirm airworthiness. The inspection is performed by Pratt & Whitney’s FAA-authorized repair station.

Pratt & Whitney powers approximately 125 Boeing 777 aircraft with its PW4000-112” engine. The directive applies only to the PW4000-112” model, and the fan blades that are unique to this engine type.

5 March

The NTSB issued an investigative update on 5 March, providing additional information on the sequence of events that led to the failure of the PW4077 on UA328. According to the NTSB, the pilots reported that they increased the engine power four minutes after take off to climb more quickly through expected turbulence, and ‘immediately after the throttles were advanced a loud bang was recorded on the CVR. FDR data indicate the engine made an uncommanded shutdown and the engine fire warning activated shortly after.’

8 September 2023

The NTSB has issued its final report on the fan blade out (FBO) event suffered by UA328. The agency finds the probable cause of the incident to be simply, “fatigue failure of the right engine fan blade.” The NTSB however continues to follow the thread:

Contributing to the fan blade failure was the inadequate inspection of the blades, which failed to identify low-level indications of cracking, and the insufficient frequency of the manufacturer’s inspection intervals, which permitted the low-level crack indications to propagate undetected and ultimately resulted in the fatigue failure. Contributing to the severity of the engine damage following the fan blade failure was the design and testing of the engine inlet, which failed to ensure that the inlet could adequately dissipate the energy of, and therefore limit further damage from, an in-flight fan blade out event. Contributing to the severity of the engine fire was the failure of the “K” flange following the fan blade out, which allowed hot ignition gases to enter the nacelle and imparted damage to several components that fed flammable fluids to the nacelle, which allowed the fire to propagate past the undercowl area and into the thrust reversers, where it could not be extinguished.

Featured image © Positive Rate Photography