A Boeing 777-200 engine fire following an engine failure last month was not fed by fuel and burned outside the core of the Pratt & Whitney PW4077 turbofan. That is according to the National Transportation Safety Board (NTSB), which on 5 March says the pilots were successful in shutting off fuel to the badly damaged engine. In an investigation update, the NTSB also reveals more details about the incident and says investigators found evidence of metal fatigue on the engine’s failed fan blade. The 20 February incident involved a United Airlines 777 (registration N772UA) operating flight 328 from Denver to Honolulu. “Initial examination of the right engine fire damage… found it was primarily contained to the engine’s accessory components, thrust reverser skin and composite honeycomb structure of the inboard and outboard thrust reversers,” the NTSB says. Early after the accident, the agency said it was seeking both to understand why the engine failed and why it remained on fire following the failure. “The spar valve, which stops fuel flow to the engine when the fire switch is pulled in the cockpit, was found closed. There was no evidence of a fuel-fed fire,” the NTSB says. “Examination of the engine accessories showed multiple broken fuel, oil and hydraulic lines, and the gearbox was fractured.” The engine’s aft cowling “appeared to be intact and undamaged, and all four pressure relief doors were found in the open position”. Shortly after taking off from Denver, at about 12,500ft altitude and travelling at about 280kt (519km/h), the pilots of United flight 328 “advanced power” to limit the amount of time the aircraft would be flying through turbulence. “Immediately after the throttles were advanced a loud bang was recorded on the [cockpit voice recorder],” the NTSB says. Information from the flight data recorder indicates “the engine made an uncommanded shutdown”. The pilots declared an emergency and “discharged both fire bottles into the engine”. Needing to get on the ground quick, they did not dump fuel, the NTSB says. On the power of a single engine, the captain piloted the aircraft back to Denver, landing without injuries to any passengers or crew. Examining the engine, investigators found one blade “was fractured transversely across the airfoil about 5in above the base of the blade at the leading edge and about 7.5in above the base of the blade at the trailing edge”. “Preliminary findings from the scanning electron microscope examination have identified multiple fatigue fracture origins on the interior surface of a cavity within the blade,” the NTSB says. “The blade’s fracture surface was consistent with fatigue.” When the blade failed, the engine had been in service for 2,979 flight cycles since its previous inspection. It had undergone thermal acoustic image (TAI) inspections in 2014 and 2016, and the 2016 data had been re-examined in 2018 following a similar inflight failure that year of a 777’s PW4000, the NTSB notes. On 22 February, P&W issued a “special instruction” that calls for affected engines’ fan blades to undergo TAI inspections at 1,000-cycle intervals. The following day, the US Federal Aviation Administration issued an emergency order requiring airliners to complete the inspections before further flight.

Airbus A320-family operators are set to be instructed to carry out repetitive inspections of windshield components after a main cockpit window on a Chinese A319 blew out in cruise nearly three years ago. About 40min after taking off from Chongqing for Lhasa, the Sichuan Airlines aircraft had been flying at 9,800m (32,100ft) when the first officer’s window began to crack and was then blasted from its cockpit frame. The aircraft, about 2.2nm west of waypoint MIKOS on airway B213, depressurised from its cabin altitude of 6,272ft. Inquiries by the Civil Aviation Administration of China concluded that external water vapour probably infiltrated the windshield’s seal, as a result of damage, and over time affected the insulation of electrical wiring located at the bottom edge. This eventually led to continuous electrical discharge arcing in the lower left windshield corner, resulting in localised high temperatures which caused the glass to fracture, weakening it until it could not withstand the differential air pressure between the cockpit interior and the external atmosphere. The European Union Aviation Safety Agency says such a situation would require “exceptional piloting skill” to maintain control of the aircraft, and would inflict damage to systems and injuries on the crew. Airbus has drawn up a service bulletin containing instructions for repetitive detailed inspection and electrical test measurement of left- and right-hand windshields. EASA is proposing differing inspection and test regimes depending on the specific windshield part numbers involved. Certain windshield require these checks to be undertaken within 750h, 750 cycles or four months, while intervals for other parts depend on the windshield age and utilisation as well as its maintenance history – including whether ‘windshield sensor’ fault messages have been recorded. The Sichuan aircraft involved in the blow-out event (B-6419) on 14 May 2018 was seven years old at the time. No prior fault had been recorded on the right-hand windshield, which was the one originally installed during the A319’s manufacture. Multiple circuit-breakers popped as the windshield failed and several aircraft systems failed. The captain and first officer were both wearing seatbelts, says the CAAC. Of the 128 occupants, the first officer and a member of the cabin crew were the only ones to sustain injuries. The aircraft, which received minor external damage, landed at Chengdu about 35min after the incident.

The innovation-finance arm of American Express is the latest company to invest in Denver-based supersonic aircraft maker Boom Supersonic. Boom says it received an investment of undisclosed sum from American Express Ventures, which has helped fund dozens of start ups in several industries. American Express Ventures joins several firms that have helped fund Boom’s plan to develop Overture, a supersonic airliner that it hopes will enter passenger service by 2029. Harshul Sanghi, the head of American Express Ventures, describes Boom’s ambitions as a nice fit for American Express, which has long aligned itself with the travel industry. Other Boom investors have included US firms Emerson Collective, Y Combinator Continuity, Caffeinated Capital and SV Angel. Last year Boom rolled out a supersonic demonstrator called XB-1, which it intends to start flying this year. The company is meanwhile developing Overture, a supersonic jet that will carry 65-88 passengers and be rolled out in 2025, Boom says. The company has received “pre-orders” from Japan Airlines for 20 Overture jets, and from Virgin Group for 10.