SEATTLE -- The Federal Aviation Administration late Friday notified operators of 82 twin-engine Boeing 767s, powered by General Electric and Rolls-Royce engines, that they can resume using thrust reversers, which help slow jetliners after landing.
Planes equipped with Pratt & Whitney engines, like those on the Lauda Air 767 that crashed May 26 in Thailand, must continue to keep their thrust reversers pinned closed while additional investigation and testing continue. Investigators are searching to find possible malfunctions that could cause the thrusters to deploy in flight.
The system used by Pratt & Whitney engines was found in recent tests by Boeing to be susceptible to bits of failed O-ring seals -- material that could cause the reverser system to &L malfunction.
David Duff, FAA spokesman in Seattle, said that the GE and Rolls-Royce engines have pneumatic, rather than hydraulic, systems to operate the thrusters and have been found unlikely to be contaminated by other material in the system.
However, sources close to the Lauda crash have said that a flawed electronically controlled valve, which can cause uncommanded reverser deployment in flight, operates the same both the pneumatic and hydraulic systems.
Officials still don't know whether contamination, a stray electrical signal, vibration or some other phenomenon can cause the valve to accidentally deploy the reversers using either pneumatic or hydraulic systems.
Even as the FAA removed the lockout order for 767s with pneumatic reversers, Boeing was preparing to recommend inspection of the flawed valve in both pneumatic and hydraulic reverser systems on more than 1,400 late-model 747s, 757s and 737s.
On Aug. 15, the FAA told all Boeing 767 operators to stop using their thrust reversers while the investigation in the wake of the Lauda crash continued. That order covered 168 planes worldwide and 39 in the United States. The FAA has authority over only U.S. operators, but its counterparts worldwide generally follow its lead.
Following the issuance of an airworthiness directive Friday, 26 Boeing planes in the United States can resume use of thrust reversers.
Putting them back into service involves removing locking pins and takes about an hour, said Elizabeth Reese, spokeswoman for the Boeing Commercial Airplane Group.
Boeing and the FAA are continuing to study potential problems that could cause thrust reversers to malfunction on all Boeing jets, Ms. Reese and Mr. Duff said.
A thrust reverser has not been pinpointed as a cause of the Lauda crash. But the wreckage showed that the system had allowed the left engine to go into reverse while in flight, which likely made the aircraft momentarily difficult to control.
In July, the FAA asked operators to inspect their thrust reversers and report any problems. The carriers have until today to report back.