Air safety investigators said yesterday it is possible that one of the four engines on the charter jet that crashed in Gander, Newfoundland, last Thursday was thrown into reverse as the plane was lifting off the runway, a condition that would be difficult for a pilot to control. A total of 256 people including 248 Army soldiers died in the crash.
Further, a spokesman for McDonnell Douglas Corp., manufacturer of the DC8 jetliner operated by Arrow Air Inc., said there is one 1971 incident in the 26-year history of that type of plane during which an engine accidentally went into reverse in flight, the result of a broken hydraulic fluid line. The crew was able to recover and land safely, the spokesman said.
Jet engines do not actually reverse themselves. Instead, a set of shutters, which when fully deployed looks much like a bucket, surrounds the exhaust of the jet engine and redirects the thrust of the engine forward. Reversers are most often used to aid in braking after landing, and can be intentionally deployed only after the throttles have been retarded to idle.
The chief investigator for the Canadian Aviation Safety Board, Peter Boag, said in Gander yesterday, "It is too early to attach any significance to these observations," a position shared by U.S. officials close to the investigation.
They stressed that several possibilities, including ice on the wings or the unplanned deployment of the airplane's spoilers (which destroy the lift of the wing) could also explain the crash. There are three recorded incidents of unplanned spoiler deployment in DC8 history.
"I wouldn't hang my hat on the thrust reverser theory yet, but it's the best thing we have so far," an expert said. He said that data from the flight data recorder, one of the plane's "black boxes" would be cranked into a DC8 flight simulator to test the thrust reverser theory.
Specialists agreed that if the thrust reversers were deployed, it was not done intentionally by the crew. Parts of the airplane recovered from the crash site show that the hydraulic actuator -- a cylinder containing a hydraulic-driven piston -- was found in a position that would indicate full deployment of the reversers.
That was on the right outboard engine. All four engines were developing high power at the time of impact, according to preliminary examinations.
The plane reached a top speed of 165 knots, slightly above liftoff speed of about 158 knots. It climbed only slightly; the exact height was not recorded. The speed deteriorated rapidly to 144 knots before impact. At impact the aircraft was in a right-wing-low attitude and had veered about 20 degrees to the right of its intended takeoff path.
That is consistent with three engines developing forward thrust and the outboard right-wing engine attempting to drag the plane in the opposite direction.
Charles E. Beatley, former mayor of Alexandria and a retired DC8 captain for United Airlines, said, "I would say the odds are he lost power; the deviation to the right tells you something is wrong with the right-side engines. He was close to maximum weight [within 25,000 pounds or so], so he had very little room to correct."
Andy Yates, another former DC8 captain at United, said, "It's very possible that [the reverse thrusters] are what could have caused it. But until after they tear that engine down, we won't know whether those thrusters were deployed before or after impact."
Meanwhile, officials said they have no plans to suspend flights on Arrow. "This is the first accident involving a charter aircraft in something like 15 years," said Pentagon spokesman Robert B. Sims. "Tragic as it is, it is not necessarily indicative of a major problem."
An Air Force official, saying the Air Force was not "technically responsible" for chartering the jetliner, noted the flight was arranged by the Multinational Force Organization in Rome from a list of commercial carriers certified by the Federal Aviation Administration. Arrow also has a $13.8 million contract with the Air Force to carry personnel and cargo this year.
"As long as the FAA certifies them, we use them," the official said.