Cessna 560XL N662QS incident near Debary, Florida

Probable cause

An accumulation of debris in the airplane’s bilge drain holes that prevented accumulated moisture from properly draining; the accumulated moisture subsequently froze around the elevator control components, which resulted in the flight control stiffness. Contributing to the accident was maintenance personnel’s improper installation of seals in the airplane’s tailcone, which allowed water to enter the tailcone.

NTSB analysis

The flight departed uneventfully and was climbing to their planned cruise altitude. As the airplane climbed through FL350 at a rate of 1,000 feet per minute (fpm) and with the autopilot engaged, the airplane pitched nose-down and entered a 400-fpm descent. The flight crew then disconnected the autopilot, assumed manual control of the airplane, and leveled at FL350. Both crewmembers noted that "excessive" force was required to change the pitch of the airplane, and subsequently notified air traffic control of the situation. The crew then requested a descent, and noted that both trim and manual elevator control inputs would result in an exaggerated pitch response from the airplane. Upon descending through FL180, the crew felt that something "broke loose" and the elevator controls began to respond normally. The crew subsequently re-engaged the autopilot and continued to the planned destination uneventfully.

Post-incident examination of the airplane revealed that several of the fuselage bilge drain holes were partially or totally obstructed, allowing water to accumulate within the bilge and in areas adjacent to elevator control cables and pulleys. Several of the pulleys exhibited evidence of saturation with moisture, and two of the pulleys' bearings had seized completely and displayed evidence that the control cable had subsequently worn their grooves. Additionally, seals designed to limit the entry of moisture within the tail area were not trimmed according to the published installation procedure. As a result of the findings of the investigation, the airframe manufacturer and operator each implemented a revised inspection and cleaning program to ensure the proper drainage of moisture from the tailcone and fuselage bilge areas.

Text from the NTSB. Open the NTSB docket for ERA13IA114 for the full record.