PHILADELPHIA — The manufacturer of the jet that crashed on takeoff in Massachusetts last year, killing the co-owner of The Philadelphia Inquirer and six other people, has reported a problem with a fail-safe system that can allow the planes to reach high speeds on the runway even if they are prevented from taking off.
Gulfstream Aerospace Corp. said in a document released by the National Transportation Safety Board that the Gulfstream IV has an interlock system that is supposed to keep the plane's throttle from being moved past 6 degrees, thereby limiting acceleration, while hinged tail sections, called elevators, are immobilized.
But the company told the National Transportation Safety Board last spring that the interlock system actually allows the throttle to be moved to an average 21 degrees. The company said the issue "remained undiscovered on more than 500 aircraft over 25 years and more than 2 million takeoffs."
Still, Gulfstream contends the crash was due to the flight crew's failure to check if the gust lock system, which locks the tail sections, was engaged and to immediately abort the flight once it was clear there was a problem. The May 2014 crash at Hanscom Field killed all on board, including businessman and philanthropist Lewis Katz.
Gulfstream said tests done after the crash led company officials to believe that the interlock system "achieved its safety intent of limiting the operation of the aircraft," but the crew "improperly responded" by trying to disengage the gust lock "instead of immediately aborting the takeoff."
The Philadelphia Inquirer reported Saturday that in response to its questions, the Federal Aviation Administration announced Friday that it was working with Gulfstream on "design changes" to the nearly 500 Gulfstream IV aircraft still in service.
According to documents released by the NTSB, Gulfstream told officials that it is "actively working" to make improvements in the gust lock system, including "additional restrictions to throttle movement," better materials and recurring compliance checks. But the company said even with those improvements, checks must always be done "to ensure that there are no locks, jams or failures in the flight control system prior to takeoff."
The NTSB has not yet ruled on a cause of the crash, but in their preliminary report investigators pointed to the gust lock system, which is designed to steady parked aircraft in winds and protect them from damage, as a possible factor in the crash.
Aviation analysts say the plane would have been unable to take off had the lock been engaged, but the crew might not have been aware of the issue without a flight check — and documents released in April indicate that pilots employed by Katz rarely conducted full preflight checks.
Gulfstream said it notified operators after the accident that despite the interlock design, "if proper procedures are not followed, movement of the throttle to a position capable of providing sufficient engine power for autothrottle engagement and takeoff power may be possible for GIV models." Operators were urged to ensure that the lock was off prior to starting engines, to check flight control movements and to confirm that elevators were free.