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. Shortly after take-off, two of the machine’s engine blades broke under almost full load with such force that they tore off the engine casing.
In the end there were no injuries, and so was Boeing 777-200 United Airlines 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 aircraft worldwide are affected by the temporary flight ban 777equipped with Pratt & Whitney PW4000 engines. Because of the corona pandemic, only 69 of the machines are currently flying.777s from United and Japan Airlines, All Nippon Airways, Korean Air and Asiana. Boeing has been using the more modern versions of the 777 only engines from the Pratt competitor General Electric.
The 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 from the world. It is therefore not even close to the extent and importance of the Boeing flight ban, which was recently lifted 737 Maxthat 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.
It may be the third incident of the same pattern
The fact that Boeing is about to withdraw its sub-fleet is due to the fact that the same error may have happened not only on flight UA328 on Saturday, but twice before: in February 2018 on another United machine on the flight from San Francisco to Honolulu and in December 2020 with a Japan Airlines777 on the way 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, technicians during a routine inspection of an engine blade 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 incorrect and the blade was okay. The engine flew for another three years until the blade finally burst on the Honolulu flight at exactly the point 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 distinguish real material defects from 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 about halfway up. The NTSB will submit an initial investigation report according to 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 problems with their Trent 1000 engines that were on the Boeing 787 be used. In November 2010, a Trent 900 engine on a Qantas Airbus broke A380 a shovel inside the engine. The exploding engine also damaged other systems such as the hydraulics. The repairs took over a year and cost nearly $ 150 million.
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