Pitch-control mechanisms apparently were improperly adjusted just two days before a commuter plane climbed too steeply, nosed over and crashed in North Carolina, federal officials said Tuesday.
Moments after taking off from Charlotte-Douglas International Airport on Jan. 8, US Airways Express Flight 5481 plunged into a hangar and burst into flames, killing the 19 passengers and two crew members on board.
The pilot of the twin turboprop Beech 1900, Katie Leslie, reported an emergency as the plane lifted off, but her radio transmission was cut off before she could explain the problem, the National Transportation Safety Board said.
Data from the Beech's "black box" flight data recorder, which was recovered from the wreckage, show that the plane was pitched up at a normal 7-degree angle as it lifted off, but that angle increased sharply to an abnormal 52 degrees by the time the aircraft reached 1,200 feet.
Unable to sustain flight at such a steep pitch, the plane stalled, rolled to the right and dived into the hangar.
The NTSB's attention immediately focused on the plane's elevators -- the two flaps that swing up and down at the rear of the wing-like horizontal stabilizer on the tail, increasing and decreasing pitch.
The data recorder showed the pitch had been "moving up and down a lot" since Jan. 6, when the tail assembly of the Beech 1900 underwent maintenance at the Raytheon Aerospace repair facility at Ceredo, W.Va., said John Goglia, the NTSB member heading the investigation.
The board said Tuesday that apparent improper adjustments during the maintenance caused instruments in the cockpit to indicate that the elevator was pitched down 10 degrees when, in fact, the elevator was level.
Furthermore, the two elevator control cables, normally the same length, had been tightened so that one was 1.8 inches longer than the other. The NTSB did not comment further, and Barry Schiff, a retired pilot and a consultant in numerous other air crash investigations, said the effect of the unequal cable lengths was not immediately clear.
The NTSB said further investigation is needed before it can determine whether any of the maintenance adjustments were major factors in the crash.
The crew involved in the accident had flown the plane five times after the maintenance without incident. Other pilots who flew the plane three times after the maintenance said they had no problems.
The Beech 1900 was carrying a load close to the allowable weight limit, and a Federal Aviation Administration directive issued Monday questioned whether the assumption that passengers weigh an average of 165 pounds may be too low.
Airlines that fly small commuter planes now must survey passengers' weight, and may put some people on scales.
Questions have arisen whether the Beech 1900's cargo may have shifted to the rear as the plane lifted off, causing the nose to pitch abnormally high.
However, Schiff pointed out, the plane climbed out for several seconds at a 7-degree angle before the pitch suddenly increased. A cargo shift, he said, would have caused the nose to pitch up immediately on liftoff.
"Something happened after that 7-degree climb," he said.