Gust lock
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A gust lock on an aircraft is a mechanism that locks control surfaces and open aircraft doors in place while the aircraft is parked on the ground and non-operational. Gust locks prevent wind from causing unexpected movements of the control surfaces and their linked controls inside the aircraft, as well as aircraft doors on some aircraft. Otherwise wind gusts could cause possible damage to the control surfaces and systems, or nearby people, cargo, or machinery. Some gust locks are external devices attached directly to the aircraft's control surfaces, while others are attached to the flight controls inside the cockpit.
Safety
A gust lock can pose a serious safety hazard if its removal is omitted before an aircraft's takeoff, because it renders the flight control inoperative. Many internal gust locks have a safety feature that locks out the aircraft's throttle or engine-start controls until removed and stowed. External-only gust locks typically lack this safety feature, and must be tagged with a large red Remove before flight streamer.
The very first example built of the Boeing B-17 Flying Fortress, the initial Model 299 aircraft, was lost in just this way on October 30, 1935, when its self-contained gust locks were left engaged, with the resulting crash killing Boeing chief test pilot Leslie Tower, and United States Army Air Corps test pilot Ployer Peter Hill. Less than a year later, Nazi German Luftwaffe Generalleutnant Walter Wever lost his life in a similar accident from gust lock neglect, when his Heinkel He 70 Blitz monoplane crashed on June 3, 1936, from the Blitz's aileron gust locks not being disengaged before takeoff. Prince Gustaf Adolf of Sweden, the American singer and actress Grace Moore and 21 others were killed in 1947 during the crash of a KLM flight at Copenhagen Airport due to the flight crew forgetting to disengage the gust lock on the tail fin of the aircraft. The crash of Air Indiana Flight 216 occurred due to failure to remove the gust locks.
A C-124 transport carrying US servicemen home for Christmas crashed in 1952 due to engagement of gust locks.
One recent example of a tragedy involving a gust lock left in place was a crash of a Gulfstream IV at Hanscom Field on May 31, 2014. This crash killed Philadelphia Inquirer co-owner Lewis Katz as well as 6 others.[1]
As these many tragedies (and this is far from a complete list) illustrate, when a gust lock is used, its disengagement is a very important step on the preflight checklist.
References
"Gust lock". The Illustrated Encyclopedia of Aviation and Space. 6. Los Angeles: A.F.E. Press. 1971. p. 1043. LCCN 68014013.