NTSB recommends FAA address CitationJet trim

AINonline
September 27, 2007, 8:35 AM

The NTSB has recommended that the FAA require an aural trim-in-motion warning in the Cessna CitationJet 525 to alert pilots of a runaway trim. The Safety Board made the recommendation, along with three others that address runaway trim, last month in response to the 2003 Citation 525 crash in Coupeville, Wash., in which the pilot was forced to ditch the aircraft in the waters near Whidbey Island following a runaway trim.

The other recommendations include requiring contrasting color bands on the pitch trim wheel, requiring Cessna to replace the pitch-trim circuit breaker with a collared circuit breaker, and requiring the manufacturer to demonstrate that the maximum control forces in a Citation 525 meet the certification requirements of 14 Code of Federal regulations Part 23 during a pitch trim runaway.

The CitationJet pilot told Safety Board investigators that he noticed a decrease in the rate of climb at around 14,000 feet msl after departing from Victoria International Airport in Victoria, British Columbia. He disengaged the autopilot/trim switch, which caused the airplane to “immediately pitch down to an attitude approximately 10 degrees below the horizon,” according to the Safety Board. “Within seconds it was apparent that level flight was not possible,” he told investigators.

The pilot attempted to retrim the airplane using the electric trim switch and the manual trim wheel, but he was unable to do so. The pilot and the passenger, who was seated in the cockpit, then applied “maximum yoke back pressure,” but the nose-down pitch attitude increased and the airplane approached its maximum indicated speed of 263 knots. The pilot said that because of the control forces, he “could not safely remove either hand from the control yoke for more than a few seconds at a time.” He determined that he could not safely land at any nearby airports and opted to ditch the airplane in the waters of Penn Cove. Both the pilot and the passenger survived the crash.

Post-accident investigation revealed that the autopilot trim down (K6) relay on the pitch trim circuit board had failed in the “power on” position. The NTSB also found that the autopilot/disengage switch did not disengage the electric trim switch due to the failure in the circuit board.

The Safety Board determined the cause of the crash to be “failure in the airplane’s electric pitch trim system” and “the manufacturer’s inadequate design of the pitch trim circuitry that allowed for a single-point failure mode and the absence of an adequate failure warning system to clearly alert the pilot to the pitch trim runaway condition.”

“The pilot had only indirect indications to assist in identifying the condition,” the Safety Board noted, adding that the manual trim wheel’s solid dark color makes it difficult to discern the movement of the trim tab position indicator, especially if the pilot is focused on other tasks. Contrasting color bands on the pitch trim wheel would “provide more timely recognition of a trim runaway condition before control forces become unmanageable.”

The Safety Board also noted that the situation could have been corrected if the pilot had disabled the pitch trim circuit breaker; however, because of the control forces involved, “it is unlikely that [the pilot] would have been able to quickly locate and pull the appropriate circuit breaker while maintaining control of the airplane.” A collared circuit breaker, according to the Safety Board, would “aid the pilot in quickly identifying it.”

A spokeswoman for Cessna said she couldn’t comment on the recommendations. “It’s really a matter between the FAA and the NTSB at this point,” she said.

According to the NTSB, the recommendations were not made in response to the June 4 crash of a Cessna Citation II into Lake Michigan, in which six people died. The pilots reported a runaway trim to air traffic controllers, and at one point one of the pilots attempted to pull the circuit breakers. “Recommendations are accident specific,” a spokesman said, adding that the NTSB had made no formal recommendations regarding the Citation II crash.

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