Two blades broke with great force on one of the engines on Flight UA328. Something similar may have happened twice before with the same type of aircraft.
The images, quickly spreading on social media, are spectacular. From the cabin, filmed by a passenger, a burning engine can be seen, the fairing of which is missing. Photos are taken from the ground that show the aircraft pulling a long plume of smoke behind it at low altitude. And then there’s a piece of metal that drills into the roof of a parked car. Two engine blades of the machine broke under almost full load shortly after take-off with such great force that they tore off the engine casing.
In the end there were no injuries, and the United Airlines Boeing 777-200 returned to Denver, Colorado Airport on Saturday. Nevertheless, the major engine failure was not without consequences: On Sunday evening, the American Federal Aviation Administration (FAA) first ordered detailed examinations of all aircraft that use the same type of engine. Then even the manufacturer Boeing recommended that customers take the machines out of circulation for the time being until the FAA has issued new inspection rules. And the National Transportation Safety Board (NTSB) Aircraft Accident Investigation Board began a formal investigation into the incident.
128 older Boeing 777s equipped with Pratt & Whitney PW4000 engines are affected by the temporary flight ban. Due to the corona pandemic, only 69 of the planes are currently flying.The Pratt-777s from United, Japan Airlines, All Nippon Airways, Korean Air and Asiana are used. Since 2004, Boeing has only installed engines from Pratt competitor General Electric on the more modern versions of the 777.
According to a spokesman, the Lufthansa Group only uses General Electric engines that are not affected by the companies Lufthansa Cargo, Swiss and Austrian.
The current flight ban therefore only affects a relatively small sub-fleet of the long-haul model and relates to a cause that is comparatively easy to identify and can be eliminated. It is therefore not even close to the extent and importance of the recently lifted flight ban on the Boeing 737 Max, which was not allowed to take off for almost two years. Nevertheless, the case shows how difficult it is often to draw the right conclusions from knowledge gained over decades in aircraft maintenance. And what can happen if corrections are not made in time.
Three accidents of the same type
The fact that Boeing is about to withdraw its sub-fleet is due to the fact that the same error may not only have happened on flight UA328 on Saturday, but already twice before: in February 2018 on another United plane on the flight from San Francisco to Honolulu and in December 2020 on a Japan Airlines 777 en route from Naha to Tokyo. Even with these two equally minor damage, it had dismantled engines from the same Pratt series.
The first United flight (UA1175) is particularly interesting: in 2010, eight years before the engine failure, during a routine inspection of an engine blade, technicians discovered something that looked like a crack. But they thought this was a test error and the matter was harmless. Five years later, the engine was noticed again during maintenance: the crack had enlarged in the meantime, but the employees again came to the conclusion that the test was not correct and the blade was OK. The engine flew for another three years until the blade on the Honolulu flight finally burst at the exact spot that had been identified as a weak point years earlier.
The subsequent investigation showed that the training of the technicians had to be improved so that they can differentiate between real material defects and false alarms in the future. The FAA also ordered shorter maintenance intervals in order to better monitor the relevant aircraft.
Almost three years later, there have now been two other, very similar incidents. In both cases, a shovel broke off at the root and then cut through an adjacent one at about half the height. The NTSB will submit a first investigation report in accordance with the international protocol within one month. The circumstances and evidence suggest a case of material fatigue. The machines in the series should only be used again when all blades have been checked and defective parts have been replaced. It will also have to be clarified why the shortened intervals and new training content obviously could not have prevented the spectacular breakdowns.
These and similar problems with engines are not entirely uncommon. They also affect other manufacturers and engines. Most recently, Rolls-Royce had massive quality issues with their Trent 1000 engines, which are used on the Boeing 787. In November 2010, a blade broke inside a Trent 900 engine on a Qantas Airbus A380. The exploding engine also damaged other systems such as the hydraulics. The repairs took over a year and cost nearly $ 150 million (read the article from the time): Engines at the absolute limit).
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