ATR ATR72 near Dallas, TX — 2009-12-26

Probable cause

A fatigue failure of an elevator stop bracket, which resulted in a partial jam of the elevator control. Contributing to the failure was the improper installation of shim stacks, poor alignment of the brackets, and cyclic stresses acting on the lower stop, generated by the repeated improper use of the gust lock system.

NTSB narrative

The flight crew reported that, while in level flight, they discovered that both control columns were jammed and they could only move the control column fore and aft a maximum of about 1 inch. After running checklist procedures without success, the flight crew slowed the airplane to 180 knots and were able to regain full control of the elevator. On final approach and after configuring for landing, the elevators again seemed to be jammed. The flight crew conducted a go-around and declared an emergency. During the second approach, with both control columns partially jammed, the flight crew performed a shallow approach to a smooth landing. A postincident examination revealed that brackets holding an elevator stop had fractured, causing the elevator movement to partially jam. The fractures were consistent with fatigue failure and were caused by a combination of improperly installed shim stacks, poor alignment of the L-brackets, and cyclic stresses acting on the lower stop, which were generated by the repeated improper use of the gust lock system.

Analysis

Primary failure mode

Mechanical failure

First missed decision gate

Properly engaging the gust lock before takeoff could have prevented the issue.

NTSB coding

• Flight control sys malf/fail · Enroute-descent

Evidence available

• CVR
• FDR / data
• Photos
• 25 docket documents

Docket documents25

• ATC 3 - ATC Specialist Reportatc
• ATC 3 - Attachment 1 - ATC Summary of Eventatc
• ATC 3 - Attachment 2 - ATCT Tower Logatc
• ATC 3 - Attachment 3 - FAA Form 8020-9, ATC Incident Preliminary Noticeatc
• ATC 3 - Attachment 4 - ATC Quality Assurance Reviewatc
• Dispatchers Statementatc
• Cockpit Voice Recorder 12 - Summary Factual Report of Investigationcvr
• Flight Data Recorder 10 - Attachment 1 (FDR tabular data for figures 1 to 24)fdr
• Flight Data Recorder 10 - Attachment 2 (FDR tabular data for figures 25 to 32; file is zipped)fdr
• Flight Data Recorder 10 - Specialist's Factual Reportfdr
• Pilot/Operator Aircraft Accident Report, NTSB Form 6120.1 - received 1-8-2010form
• Pilot/Operator Aircraft Accident Report, NTSB Form 6120.1 - received 12-30-2009form
• Release of Aircraft Wreckage, NTSB Form 6120.15form
• Crewmember Interview - Captaininterview
• Statement of Party Representatives to NTSB Investigationinterview
• Airport - KDFW ILS or LOC Runway 36Lother
• Crewmember Inverview - First Officerother
• European Aviation Safety Agency (EASA) Airworthiness Directive 2010-0138 for all ATR 42 and 72 Airplanesother
• Federal Aviation Administration (FAA) Airworthiness Directive 2010-NM-AD for all ATR 42 and 72 Airplanesother
• Manufacturer's Flight Manual Requirements for Engagement of the Gust Lockother
• Operator's "HI6 Message" Sent to All Pilotsother
• Operator's Aircraft Operating Manual (AOM) Description of the Gust Lockother
• Materials Laboratory Factual Report 10-056 (With 22 Embedded Photos)photos
• Operator's Safety Bulletin Alert 2010-05 (with 2 embedded photos)photos
• Photo of N494AE (Internet Photo from www.flickr.com)photos

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