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.

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.