Boeing 717-200 N935AT accident near Pleasant Grove, North Carolina

Probable cause

The captain's excessive maneuver in response to a traffic alert and collision avoidance system (TCAS) alert, which resulted in a serious injury to a flight attendant. Contributing to the accident was the operator's inadequate TCAS training and guidance.

NTSB analysis

During cruise descent the captain of the scheduled airline flight handed over control of the airplane to the first officer to make a public address announcement regarding turbulence. He had just turned on the fasten seatbelt sign when they received a resolution advisory (RA) from the onboard traffic alert and collision avoidance system (TCAS). The captain then took back control of the airplane and initiated an avoidance maneuver. During the avoidance maneuver, a flight attendant sustained serious injuries and a child passenger sustained a minor injury.

Review of air traffic control radar data and data from the onboard flight data recorder revealed that 1.5 seconds after the TCAS RA occurred, the captain initiated a series of excessive control inputs which resulted in a positive vertical acceleration of approximately 1.6g. One second after the positive vertical acceleration the airplane sustained a maximum negative vertical acceleration of approximately .2g. A second after the negative vertical acceleration the airplane sustained another positive load of 1.4g after which the acceleration was dampened out. According to the TCAS manufacturer's published guidance, a flight crew should "promptly but smoothly" follow a TCAS RA and since the maneuvers are coordinated between aircraft, the crew should never maneuver in the opposite direction of the advisory. The advisories are always based on the "least amount of deviation from the flight path" while providing safe vertical separation. Typical RAs that would require a maneuver by a flightcrew only requires crew response within 5 seconds and g-forces of ±.25g. Review of the airline's training and guidance materials for the two different types of airplanes the airline operated revealed that this information was included in the training and guidance material for one of the airplane types in their fleet but was not included in the training and guidance materials for the accident airplane type.

Text from the NTSB. Open the NTSB docket for ERA10LA041 for the full record.