Death by Control Lock

Posted October 29th 2005 at 5:26 pm by Ron

Why is it that so many pilots seem to neglect to remove the control lock before takeoff? I just don’t get it. This is the one thing that’s 100% guaranteed to kill you in an aircraft.

Take, for example, this DeHavilland DH4 Caribou. In 1992, this aircraft was being used as a testbed for the Pratt & Whitney PT-6 turboprop conversion. The pilots failed to remove the control lock before a flight, with predictable results.

It is supposed to be physically impossible to advance the throttles with the lock on. But this aircraft was being modified and was operating in the restricted category. The throttle quadrant was not properly rigged to accommodate the throttle levers for the turbine engines. Three people were on board; two test pilots and an engineer.

These sorts of accidents are especially noteworthy when you consider that it took more than just a lazy preflight. The pilot(s) also had to ignore the control check, fail to see the lock installed, and neglect to put in any sort of crosswind correction during taxi. They’d also have to exhibit a general lack of checklist discipline. In fact, they’d have to basically not touch the controls at all until rotation.

For those of you who are not pilots, the control lock is usually painted red, very visible, and located in the cockpit right in front of the pilot.

(hat tip: John Pappas at Dreamflight)

Posted in Mishaps
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6 Responses to “Death by Control Lock”


  • Comment from Graeme
    Posted at: November 2, 2005 at 6:33 pm

    Looks like a W and B issue to me..not a control lock isuse

  • Comment from Mike E.
    Posted at: November 8, 2005 at 1:45 am

    The pilot was able to make a BIG elevator movement for rotation, but seemingly unable to make a nose down movement. Are you sure this was a control lock issue? I think I have to agree with Graeme, it sure looks like a weight & balance problem, perhaps a cargo shift?

  • Comment from Joel
    Posted at: November 8, 2005 at 11:14 am

    For us none-pilots, can you explain what the control lock actually locks down? Is is sort of like on your car the steering wheel will lock when you are in ‘park?’

  • Comment from Ron
    Posted at: November 8, 2005 at 5:14 pm

    Joel: it’s more akin to one of those anti-theft steering wheel clubs in that it physically prevents the controls from being moved.

    The control lock physically holds the flight controls in one place so that they are immovable. On some aircraft, it’s a pin that goes through the control column to keep it from moving.

    The purpose of using a control lock is to prevent damage to the aileron, rudder, and elevator if the winds should kick up. Such winds could cause these control surfaces to “flutter” back and forth in the gusts, hitting the mechanical stops with enough force to cause damage to the control system.

    There are many different types of control locks. Some go on the yoke or stick inside the cockpit, while others are external locks that are physically placed on the control surfaces.

    An internal lock looks like what you’ll see at http://www.gustlock.com.

    An external lock (in this case, for a rudder) looks like this.

  • Comment from Ron
    Posted at: November 8, 2005 at 5:41 pm

    Regarding the issue of whether this was a W&B problem or a control lock problem, I did some digging via Google and found an analysis of this accident by Bombardier Aerospace product safety manager James Donnelly. Here’s part of what he wrote:

    The accident investigation used this videotape and some 35mm photographs as a key resource in determining what went wrong at Gimli.

    With the exception of a slightly higher-than-normal nose attitude at lift-off, the aircraft’s initial climb appeared normal. At about 35 feet AGL, the aircraft made a noticeable pitch-up movement.

    When I tell you that the photography revealed that the elevator control surfaces were observed to pitch trailing-edge-up for rotation, neutralize and then remain in the neutral position through the balance of that short flight, I expect most of you will come to the same conclusion as the Transportation Safety Board of Canada. The aircraft’s control gust locks were at least partly engaged.

    A very close examination of the video does indicate rudder movement and minimal elevator movement, during the start of the takeoff roll. On the standard Caribou, the gust lock control handle is located forward of the power quadrant, and it has two positions — forward for Unlocked, and aft for Locked. If the control surfaces are not in the neutral position when the lock is engaged, any movement of the surfaces through the neutral position will cause the lock to engage.

    In addition, on the factory-standard Caribou, the control handle is designed so that when it is in the aft-Locked position, the power levers cannot be fully advanced. This is intended to prevent power application and takeoff when the gust lock system is engaged. The accident investigation further revealed that the aircraft’s takeoff distance was approximately 20 per cent longer than anticipated for the conditions. This may provide further evidence that the gust locks played a part in this event.

    Analysis of the recovered debris indicated that, although the aileron and elevator locking mechanisms were in their respective Disengaged positions, the rudder locking mechanism was found to have been in the fully engaged position at impact. Further investigation revealed that in fact, it had been jammed there by the forces of the impact. In addition, the analysis determined from the damage evidence that the aileron control lock had been dis-engaged at the time of impact.

    In its synopsis of the accident, the Transportation Safety Board concluded that the control gust lock system had not been fully disengaged prior to flight and that one or more of the locking pins had become re-engaged after lift-off.

    What could have prevented this accident? The most obvious solution was that a complete six-point control check prior to takeoff would have revealed that free and proper movement of the control system was compromised. No control check was seen by witnesses on the ground, nor was one recorded on video or still photography. As noted earlier, some rudder and elevator movement was observed, at the end of the runway at the start of the takeoff roll. The Caribou’s standard procedures do allow for locking the control surfaces for ground operation, but the aircraft flight manual also requires a six-point control check prior to takeoff.

    Another point — although not one addressed by the TSB in its review — concerns the crew. We understand that shortly before the flight, the scheduled co-pilot — a very experienced piston-Caribou captain — was replaced by another pilot with considerably less total time and experience on type. He was, in fact, the aircraft owner’s son.

    We therefore speculate whether a more experienced co-pilot might have caught the missed six-point control check, or might have been more aware that the aircraft was not responding as it should have.

    During the post-accident autopsy, a knob from the gust lock handle was found embedded in the captain’s right wrist. The TSB concluded that the captain was attempting to operate the gust lock handle when the aircraft hit the ground.

  • Comment from Dennis M
    Posted at: December 27, 2005 at 8:13 pm

    I was only ever a student pilot, but everything I climbed into had control locks that could dismay Godzilla. Even finding the ignitions while being hit in the face with all those red aluminum flags and nylon streamers was difficult. The only thing missing from the locks was a red barbed-wire barrier between the pilot and the seat. Not a bad system. As one of my instructors made her students memorize, ’90% of the problems a pilot encounters in the air, he chose to take into the air with him’.



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