Photo: Jason Paur/Wired.com
The National Transportation Safety Board is recommending inspections for all new Boeing 787 and 747-8 aircraft with General Electric engines. The NTSB made the recommendation to the Federal Aviation Administration after two of GE's newest engines experienced failures in the past few months. Three separate incidents all point to a similar cause for the failures in the engines.
"The parties to our investigation – the FAA, GE and Boeing – have taken many important steps and additional efforts are in progress to ensure that the fleet is inspected properly," NTSB Chairman Deborah A.P. Hersman said in a statement on Friday. "We are issuing this recommendation today because of the potential for multiple engine failures on a single aircraft and the urgent need for the FAA to act immediately."
The first failure of one of General Electric's new GEnx-1B occurred in July at Boeing's 787 facility in South Carolina. During a routine engine run-up of a new 787 during a taxi test, metal debris was ejected out of the back of the engine, igniting a small grass fire. An initial inspection points to the failure of a shaft in the engine.
At the end of August an inspection of a GEnx-1B on a different 787 that had yet to run showed a similar crack in the same area of the fan midshaft. That engine was inspected to help investigators determine the cause of the cracks.
Then, last week the pilot of a new Boeing 747-8F cargo airplane rejected a takeoff in Shanghai after losing power in one of the four GEnx-2B engines while accelerating down the runway. Initial inspections of the engine show similar damage in the low pressure turbine section of the nearly identical engine to those found in Boeing's 787s. The 747-8F had flown around 1,200 hours since being delivered.
In recent decades it's been rare for a new turbofan engine to have any significant problems beyond design phase according to Richard Aboulafia of the Teal Group.
"It's been a long time since an engine entered service and had an actual out of the box problem." Aboulafia told Wired.
A General Electric GEnx-2B engine being installed on a Boeing 747-8 at a factory in Everett, Washington. The low-pressure turbine area can be seen near the center of photo, just to the left of the cone at the back of the engine. The crack occurred in a section of the midshaft hidden from view, approximately where the large black fan is to the left of center in the photo. Photo: Jason Paur/Wired.com
Aboulafia added that the investigation and cooperation between the government agencies along with Boeing and General Electric shows the necessary steps are in place to deal with such issues, "the system is working admirably." he says.
According to the NTSB, GE has developed an ultrasonic inspection method for the fan midshaft that can be used while the engine is still on the airplane. All of the GEnx-1B engines used on 787 Dreamliners as well as spare engines have been inspected. All of the GEnx-2B engines on passenger versions of the 747-8 have also been inspected. There are more than 40 General Electric engines on freighter versions of the new jumbo jet that still await engine inspections and are expected to be completed this week.
The engine maker believes it has found the cause of the cracks and has changed the way the shafts are coated during the manufacturing and assembly process.
The NTSB is recommending the ultrasonic inspection be performed on all engines before flight. And it is adding that repeat inspections be made of the fan midshaft at relatively regular intervals so any potential crack could be detected before it grows to a length that could cause an engine failure.
Engine failures in modern airliners are very rare and twin engine aircraft such as the 787 are capable of flying to a runway on a single engine in the case of an emergency from any point during a normal airline flight. Much of that capability comes from the high powered engines available to airplane makers today and is demonstrated during ultra-long endurance flights in flight testing.
"There's a lot more margin built in," says Aboulafia. "Losing an engine means you still have plenty of thrust." He points to the Boeing 727 developed in the 1960s when four engines were the norm and three engines were thought to be a minimum to have enough thrust should an engine fail at a critical point.
Boeing's new 787 Dreamliner can be ordered with either the General Electric or Rolls-Royce engines. Both of the new engines are responsible for a significant portion of the fuel efficiency improvements of the new airplane. And the Rolls-Royce engines haven't been trouble free. Earlier in the summer the launch customer fo the 787, All Nippon Airways, temporarily grounded its fleet of Dreamliners after premature corrosion was found in the gearboxes of the Rolls Royce Trent 1000 engines.
The gearboxes were replaced before any incident occurred.
Christina Bonnington 18 Sep, 2012
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Source: http://feeds.wired.com/~r/wired/index/~3/MMrRF0lUGVA/
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