The National Transportation Safety Board determined today that the February 2005 crash of a Cessna Citation owned by Circuit City Stores, Inc., was caused by the flight crew's failure to effectively monitor and maintain airspeed and comply with procedures for deice boot activation on their approach to Pueblo, Colorado, which led to an aerodynamic stall. Contributing to the accident was the FAA's failure to establish adequate certification requirements for flight into icing conditions, which led to the inadequate stall warning margin provided by the airplane's stall warning system.
The accident occurred on February 16, 2005, when the first of two Cessna Citation aircraft carrying Circuit City employees to a meeting in California crashed just east of the Pueblo Memorial Airport. All six passengers and the two flight crewmembers were killed in the crash.
"This accident underscores the importance of flight crews carefully monitoring and cross checking flight instruments during approach," stated NTSB Chairman Mark V. Rosenker. "We would also like to see more progress from the Federal Aviation Administration on major icing recommendations we issued a decade ago."
The Board's investigation determined that the aircraft encountered icing conditions during the flight resulting in an accumulation of thin, rough ice on the wing leading edges that degraded the aircraft's performance. According to the Cessna 560 airplane flight manual (AFM), pilots are trained to increase the landing reference airspeed whenever any residual ice is present or can be expected during approach and landing. An examination of the cockpit voice recorder (CVR) did not record either pilot mention increasing the airspeed during the approach.
Additionally, company and AFM procedures for approach and landing in icing conditions required pilots to activate the deice system when any ice accumulation, regardless of thickness, was visible and to continue to monitor the wing leading edges for ice. Despite this guidance, there is no evidence that the accident flight crew activated the deice boots during the approach. The flight crew of the trailing Circuit City "sister ship" did cycle the deice boots numerous times and maintained increased airspeed during the approach and subsequently landed safely.
As a result, the Board recommended that the Federal Aviation Administration require that operational training for the Cessna 560 (Citation) aircraft emphasize the AFM requirements to increase airspeed and operate the deice boots during approaches when ice is present on the wings. The Board also recommended that the FAA require that all airplanes equipped with pneumatic deice boots have a mode that will automatically continue to cycle the deice boots once the system has been activated.
The investigation also determined that the airplane's stall warning system did not activate until after the aerodynamic stall occurred. The warning system is intended to provide flight crews with adequate warning of an impending stall in time to take preventative action. Because of the higher stall speeds that occur in icing conditions, the margin between the warning and the stall occurrence can be diminished. The Board recommended that the FAA require modification of the Cessna 560's stall warning system to provide an adequate warning margin in icing conditions that existed on this approach.
The Board further concluded that ice bridging does not occur on modern airplanes; therefore, there is no reason for flight crews to delay activation of the deice boots. The Board recommended that the FAA require that guidance for aircraft with pneumatic deice boots be revised to indicate that the leading edge deice boots should be activated as soon as the aircraft enters icing conditions.
The Board also called on the FAA to develop pilot training programs to emphasize monitoring skills and workload management.
Additionally, the Board reiterated two recommendations issued in 1996 and 1998 to the FAA calling for revised certification standards for aircraft operating in icing conditions. The Board has classified the FAA's response to these recommendations as unacceptable.
A synopsis of the Board's report, including the probable cause and safety recommendations, is available on the Board's Web site, www.ntsb.gov, under "Board Meetings." The Board's full report will be available on the Web site in several weeks.