Faulty maintenance work on the pitch control rigging caused the Colgan Air Raytheon Beech 1900D crash just after take-off from Hyannis, Massachusetts, on 26 August 2003, according to the US National Transportation Safety Board (NTSB) report.
Both pilots were killed when the aircraft went out of control because the pitch trim was working in the opposite sense to normal, say the investigators.
The fatal flight was the first after maintenance had been carried out on the aircraft. Causal factors cited by the NTSB include: a short-cut in working practices by the mechanics who were replacing the forward elevator trim cable; ambiguity in a trim control system diagram in the airliner maintenance manual (AMM) ; the crew's failure to note in the maintenance log before take-off the nature of the work that had just been carried out; and their omission of the "first flight of the day" checklist, which includes an elevator trim check that would have revealed the error.
After determining what appeared to have happened, the NTSB rigged a serviceable 1900D pitch trim the way it had been done in the Colgan Air aircraft and carried out a ground test to check what the results would be. The mistake had been to route the trim cable the wrong way around the elevator trim drum. When this had been done in the test airframe, the NTSB operated the electric trim switch and found that the trim tabs moved in the correct sense, but the manual trim wheel rotated in the opposite sense. Correspondingly, when the investigators operated the manual pitch trim wheel, the pitch trim tabs moved in the reverse sense to the rotation.
On the fatal flight, the crew reported a runaway trim in the nose-down sense and rotated the manual trim wheel fully nose-up. But because the rigging was reversed, the crew were faced with a 113kg (250lb) nose-down control column load and lost control.
This was the second 1900D fatal accident of the year in the USA in which a pitch control system rigging error was a causal factor, according to the NTSB.
On 8 January 2003 an Air Midwest 1900D had gone out of control after pitching steeply nose-up just after take-off from Charlotte/Douglas airport, South Carolina, and all 21 people on board were killed.
The NTSB said the Air Midwest mistake was in the elevator control runs rather than the trim system, and the pitch-up was worsened because the full load had given the aircraft an aft centre of gravity.
DAVID LEARMOUNT / LONDON
Source: Flight International