Investigation Summary
The accident occurred during a deadhead repositioning flight following a Detail Six (D6) maintenance check. During this check, technicians replaced both elevator trim tab actuators and the forward elevator trim cable. Investigators found that the maintenance crew skipped 19 steps required by the Beechcraft 1900D maintenance manual, including the removal of the elevators, which would have provided better access for cable routing. Instead, they attempted a shortcut and failed to use a lead wire to ensure correct cable orientation. Crucially, the Beechcraft maintenance manual contained a diagram (Figure 201) that incorrectly depicted the elevator trim drum. This ambiguity, combined with the skipped steps, led to the cables being wound in a way that reversed the system's logic. When the pilots attempted to set nose-up trim for takeoff, they unknowingly set the tabs to full nose-down. Upon liftoff, the aircraft exhibited a severe nose-up pitch. As the pilots applied nose-down column pressure and attempted to use the trim to relieve the force, the reversed system actually increased the nose-down aerodynamic force. The NTSB determined that maintaining level flight would have required 250 pounds of force on the control yoke, a physical load that made recovery nearly impossible.
Final Conclusions
The National Transportation Safety Board determined the probable cause was the improper replacement of the forward elevator trim cable and the subsequent inadequate functional check by maintenance personnel. Contributing to the accident were the flight crew's failure to follow checklist procedures (specifically the preflight trim check) and the aircraft manufacturer's erroneous depiction of the elevator trim drum in the maintenance manual.
Video Analysis
A Critical Error in the Skies #aircrashinvestigation #flightrisk — Colgan Air Flight 9446 crashed into Hyannis Harbor shortly after takeoff, claiming the lives of its two pilots. What caused this devastating accident?
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Airframe & Maintenance
Crew Experience
Captain
Aged 39; with Colgan Air for two years.
First Officer
Aged 38; with Colgan Air for less than a year.
Systems & Failure Modes
Elevator Trim System
A system of cables, drums, and actuators that moves small tabs on the elevator to reduce the physical force a pilot must exert on the yoke to maintain a pitch attitude.
Elevator Trim Tab Actuators
Mechanical units that physically move the trim tabs; both were replaced during the maintenance check preceding the accident.
Interesting Facts
- 01The flight was the first after a major maintenance check involving the elevator trim system.
- 02Maintenance technicians skipped 19 steps in the manufacturer's manual to save time.
- 03The Beechcraft 1900D maintenance manual incorrectly depicted the elevator trim drum backwards.
- 04The captain failed to perform the 'first flight of the day' checklist, which included a trim movement check.
- 05Flight simulations showed that the physical force required to counter the mis-rigged trim was approximately 250 pounds.
Safety Actions & Advisories
Maintenance Manual Correction
Source ↗Following the accident, Raytheon issued a Temporary Revision (TR 27-7) to the Beechcraft 1900D Maintenance Manual on September 12, 2003, to correct the erroneous and misleading depiction of the elevator trim drum and cable orientation in Figure 201.