BOEING 717-200 near Pleasant Grove, NC — 2009-10-26

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.

Contributing factors

Contributing to the accident was the operator's inadequate TCAS training and guidance.

NTSB narrative

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.

Analysis

Primary failure mode

Automation / mode confusion

First missed decision gate

Captain could have engaged autopilot earlier to stabilize descent before TCAS alert.

NTSB coding

• Abrupt maneuver · Enroute-descent
• Decision Making / Judgment

Evidence available

• FDR / data
• ADS-B / radar
• 12 docket documents

Docket documents12

• Flight Data Recorder 10 - Attachment 1 - Tabular Data (Zipped CSV File)fdr
• Flight Data Recorder 10 - Specialist's Factual Reportfdr
• Pilot/Operator Aircraft Accident Report, NTSB Form 6120.1form
• Statement of Party Representatives to NTSB Investigationinterview
• Witness Statments and Interview Summariesinterview
• B-717 TCAS Bulletin (Post-Accident)other
• Excerpts from Airtran B-717 Aircraft Operations Manual (TCAS Guidance Post-Accident)other
• Excerpts from Airtran B-717 Aircraft Operations Manual (TCAS)other
• Excerpts from Airtran B737 Aircraft Operations Manual (TCAS)other
• Excerpts from B-717 Aircraft Operations Manual (TCAS Guidance Pre-Accident)other
• Excerpts from Honeywell Collision Avoidance System Pilot's Guideother
• TRS 669 Radar Dataradar

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