Caribou crash discussion

[poteroo]

Saw a circuit flown in a C182, with the contol pin still in, by an instructor, who successfully used trim,rudder, and power to fly the circuit. After he had successfully landed the thing, his ticket was 'lifted' by the then CASA, and I doubt he ever flew again. It was actually a good bit of reactive flying....but we won't mention everything else!

 

happy days,

 

 

[Guest ozzie]

remember a story on our dropzone of ol'harry trying to remove a bent nail from the lock on the C182 as he barrelled down the strip.

 

 

[facthunter]

Caribou.

 

The aircraft is turbine powered, which introduces another possibility.

 

A turbo-prop normally has auto feather which is needed for,the reason that a windmilling propeller, still connected to a flamed out turbine can actually creat drag equal to TWICE the normal forward thrust,

 

The definition on my screen has not allowed me to establish the control positions, but if the right engine suffered a power loss, especially with a low climb speed, the aircraft would do exactly what it did there. The only way to stop the uncommanded roll would be to close the other throttle quickly, but the immediate effect of this is not always helpfull, as closing the throttle coarsens off the prop pitch and the flywheel effect can produce a thrust incease MOMENTARILY.

 

This phenomenon was very marked on the Fokker F-27 Friendship, where a too rapid response to a close-the-throttle engine failure would mis-identify the failed engine, and cause a trigger-happy pilot to apply the rudder on the wrong side causing some very unhelpful antics, directionally.

 

If someone here who can get a better picture then I, can determine the position of the rudder, (It should be hard over to the left) ,that might throw some light on the picture.

 

If a conversion from piston to turbo-props was being undertaken, invariably that would require a greater rudder capability, to cope with the situation that I have described.

 

IF ( as Matt suggests) the gust lock was engaged, ( and we would be talking of an internal one I presume) They are usually located in a very noticeable ( prominent) position , but MAY be left engaged during taxi, in normal ops. IF that fact has been established then there is no need to consider the matter further, but HAS it been established? There was not much left of that aircraft, and not all military aircraft were fitted with Flight Data Recorders. Bloody awful prang Nev..

 

 

[Ben Longden]

Anyone have a copy of the crash report?

 

Make a good comparison to the possibilities we have come up with..

 

Ben

 

 

[Guest Andys@coffs]

.... IF that fact has been established then there is no need to consider the matter further, but HAS it been established?

Nev. Cant find anything that I consider to be definitive, however the same video at Youtube, submitted by a different poster has the following info:-

 

Results Of A Poor (or no) Preflight: Two test pilots on board, and no one checked the controls free and clear before starting t/o roll. It hurts to watch this video, but it's a dramatic reminder that there really are good reasons to do a thorough preflight and to make sure the controls are free.

 

This happened just north of Winnipeg, and the aircraft was the first version with PT-6-67 Turboprops. ('Modernized' Caribou.) The Canadian DOT concluded that the control locks were still locked when the aircraft took off. You who have flown the Caribou wonder how that could have happened when it is physically impossible to advance the throttles (past 1800 RPM) with the gust-lock in -- but this aircraft had been modified (still Restricted Category) and the throttle quadrant was not properly rigged to accommodate the throttle levers for the turbine engines.

 

The URL for that one is

 

 

However in the comments for that video someone concludes that the problem was the load shifting during take off. Spoken with authority... but nothing to back the assertion so I dont know?

 

Either seem improbable to me....... but the flames are real enough

 

Andy

 

 

[vme]

Mr James Donnelly

 

Manager, Product Safety

 

Bombardier Aerospace, Regional Aircraft

 

2001 Australasian Air Safety Seminar

 

June 2 - 3, 2001

 

.....

 

The final example I'd like to bring before you today also deals with a modified aircraft.

 

Like the first event I described, it's unusual because virtually the entire accident sequence

 

is captured on videotape.

 

The accident occurred in August 1992 at the Gimli Industrial Park in Manitoba - a

 

famous site in Canadian aviation history, where an Air Canada Boeing 767 known as the

 

Gimli Glider was dead-sticked onto a drag racing strip, following fuel exhaustion.

 

The accident aircraft is a highly modified de Havilland aircraft. In this case a Caribou had

 

been converted to turbine power and was operated under the EXPERIMENTAL category

 

of CAR 4b.

 

The conversion was accomplished at Gimli, and the aircraft first flew in mid-November

 

1991, before accumulating about 23 hours on 12 flights by month end.

 

These preliminary tests revealed the need for the replacement of the aircraft's mechanical

 

vacuum pumps with a Bendix suction system, the addition of in-line fuel boost pumps

 

and the installation of a newly designed hydraulic pump.

 

The accident occurred on August 27, 1992 on the first of several planned trips to flight-

 

check the fuel and hydraulic systems. The aircraft had been hangared in a partially dis-

 

assembled state over the winter, and had only recently been re-assembled, including the

 

re-installation of the complete tail section.

 

I'll let the video show you what happened - and I will caution you right now that this

 

footage is extremely graphic -

 

[Video]

 

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 aircraftÃŒs 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 CaribouÃŒs 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 pointÛalthough not one addressed by the TSB in its reviewÛconcerns 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.

 

Our expectation was that the pilot flying would have had his hand on the power lever

 

quadrant, which is located immediately aft of the gust lock handle. It is therefore

 

conceivable that, during the impact sequence, his hand might have moved forward, and

 

that this might account for the autopsy finding.

 

This accident investigation was problematic for us as the aircraft's original manufacturer,

 

as we had not been involved in the turbine conversion, system modifications, or

 

subsequent flight testing.

 

As I noted earlier, the conversion required extensive modification of a large number of

 

the aircraft's systems, and we know from the investigation that these included a re-

 

designed throttle quadrant.

 

The TSB report concludes that the newly designed system did not interfere with the

 

positional relationship between the throttle levers and the gust lock control handle, as full

 

power could not be obtained with the lock handle in the engaged position.

 

However, in our minds, since we did not design or participate in the modification

 

process, we cannot conclusively rule-out interference with normal operation of the

 

aircraft's original systems.

 

In this accident investigation our contribution was therefore essentially limited to the

 

identification of components familiar to us, confirming the operation of the original gust

 

lock system, and confirming the deflection of the control surfaces' spring tabs when

 

operation is attempted against the locks.

 

We had not reviewed the turbine aircraft flight manual but here again, we suspect it was

 

substantially similar to the original aircraft flight manual.

 

... full paper: http://www.asasi.org/papers/2001/Four%20Unrelated%20Accidents.pdf