Cessna Citation CJ2+ experiences loss of control due to AOA vane failure and pilot distraction

Casualties unknown • 5.7 nm north-west of Coventry, Warwickshire, GB

A private Cessna 525A Citation CJ2+, registration N380CR, entered a series of rolls and departed from controlled flight after an angle of attack sensing error and pilot distraction.

What happened

On 31 December 2013, a Cessna 525A Citation CJ2+, registration N380CR, was climbing through FL420 toward its cruising altitude of FL430 during a private flight from Leeds Bradford Airport to Spain. The pilot was utilizing the autopilot in vertical speed mode. During the climb, the pilot briefly diverted his attention to a portable electronic device to check wind forecasts.

While the pilot was looking down, the aircraft's airspeed decayed significantly. The aircraft then experienced a sudden, severe nose-down pitch and a right roll of 57 degrees, which caused the autopilot to disengage. The aircraft entered a period of uncontrolled flight, performing five 360-degree rolls to the right. During this sequence, the aircraft encountered high cirrus clouds, obscuring the horizon and causing the flight display to enter a 'declutter' mode. The pilot eventually regained control once the aircraft descended into clearer air and a visible horizon was established. The aircraft subsequently landed safely at Leeds Bradford Airport with no fatalities and no injuries to the crew or passenger, though the airframe sustained structural damage to the wings and antenna.

The investigation

Investigators examined the aircraft's AReS recording system, which provided critical data regarding the aircraft's parameters. The investigation focused on why the stall warning system failed to activate and why the aircraft was able to reach such low airspeeds without intervention.

Technical analysis of the angle of attack (AOA) vane revealed a significant defect. CT scans showed that an internal PTFE seal had become displaced, creating a gap that allowed moisture to enter the vane case. This moisture likely froze, causing the AOA vane to 'stick' at a fixed position. Because the system continued to report this static value as 'valid,' the pilot was not alerted to the true angle of an approaching stall. Furthermore, the investigation looked into the pilot's use of vertical speed mode and the impact of the 'declutter' mode on the pilot's ability to recover the aircraft.

Probable cause

The loss of control was caused by the pilot operating the aircraft in a vertical speed mode that allowed the airspeed to decay to a stall, compounded by a lack of monitoring due to distraction by a portable electronic device. This was made critical by the failure of the stall warning system, which failed to alert the pilot because the angle of attack vane was stuck due to moisture ingress and subsequent freezing.

Frequently asked questions

What happened in the 2013-12-31 Cessna 525A Citation CJ2+ accident near 5.7 nm north-west of Coventry, Warwickshire, GB?

A private Cessna 525A Citation CJ2+, registration N380CR, entered a series of rolls and departed from controlled flight after an angle of attack sensing error and pilot distraction.

What aircraft was involved and where did it happen?

The accident on 2013-12-31 involved a Cessna 525A Citation CJ2+, registration N380CR, at 5.7 nm north-west of Coventry, Warwickshire, GB.

What was the probable cause of the accident?

The loss of control was caused by the pilot operating the aircraft in a vertical speed mode that allowed the airspeed to decay to a stall, compounded by a lack of monitoring due to distraction by a portable electronic device. This was made critical by the failure of the stall warning system, which failed to alert the…

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