Interesting Single Otter Accident

[pelmet]

From TSB.....

C-GLMT, a de Havilland DHC-3T operated by Kississing Lake Lodge Ltd. (dba Wings Over
Kississing), was conducting a flight from Wollaston Lake Airport (CZWL), SK to Points North
Landing Airport (CYNL), SK. After takeoff from CZWL, the pilot was unable to reduce the engine
(Pratt & Whitney Canada PT6A-34) power setting to climb power. All further attempts to reduce
power had no effect. The pilot activated the emergency power lever, but it also had no effect. The
pilot initiated a climb in an attempt to manage the airspeed. The aircraft then proceeded to CYNL;
however, the airspeed increased to over 140 MPH and the pilot's side window shattered. When in
range of CYNL, the pilot shut down the engine at approximately 4000 feet ASL with the condition
lever. The aircraft decelerated more quickly than anticipated and the aircraft struck trees on final
approach and the aircraft came to a stop beside the runway. The aircraft sustained substantial
damage to the left wing, nose, and landing gear. There were no injuries.

I wonder if he was able to feather the prop. Been a long time since I was at Points North(about the time of their DC-3 crash). How long is the runway again.

[172DDriver]

IIRC is a 5800 foot strip, a pretty good landing surface.


Those guys have been doing the freight between Walloston and Points for the last 10 months or so, going pretty hard. At first, we speculated that it was fuel starvation but it seems otherwise.

[Capt. Underpants]

I wonder if he was able to feather the prop.

I can't see any reason why the prop would not feather. This has happened a few times on different variants of the PT6. Usually something awry in the FCU forces it to "think" more fuel is required.

[itsgrosswhatinet]

After coming up short more than once on (simulated) engine out approaches in single engine turbines it's probably a good idea to come in way too steep and lose altitude with forward slipping on final.

[nobody23]

How is the window shattering at 140 relevant? Vne is 144

[sunk]

Was this a recent accident?

[digits_]

How is the window shattering at 140 relevant? Vne is 144

It would affect the pilot's visibility and affect his choice of landing strip. It might give us a hint as to what could have caused the technical problems (or could be completely unrelated). A window shattering below VNE, or even slightly above it, is not normal.

[Meatservo]

How is the window shattering at 140 relevant? Vne is 144

Maybe they meant knots, which would be 165 mph or so. I wish people would stop using statute miles in aviation.

Also I thought VMo in a PT6 Otter was 118 knots. They stick a red line at the bottom of the old yellow arc. Or at least they used to.

[nobody23]

How is the window shattering at 140 relevant? Vne is 144

Maybe they meant knots, which would be 165 mph or so. I wish people would stop using statute miles in aviation.

Also I thought VMo in a PT6 Otter was 118 knots. They stick a red line at the bottom of the old yellow arc. Or at least they used to.

VMO is 125 knots = 144mph on wheels/skis. I also dislike SM

[nobody23]

How is the window shattering at 140 relevant? Vne is 144

Maybe they meant knots, which would be 165 mph or so. I wish people would stop using statute miles in aviation.

Also I thought VMo in a PT6 Otter was 118 knots. They stick a red line at the bottom of the old yellow arc. Or at least they used to.

VMO is 125 knots = 144mph on wheels/skis. I also dislike SM. I’m curious with the stuck power and likelihood of over-speeding once in cruise why not just land back where they took off, 3800’ paved?

[phillyfan]

Very strange. An FCU failure usually leaves the engine at low power. I have had to use Emergency power a couple times. Not sure why that would not work in this case?

[sunk]

Was it the side window, or the left side windscreen?

[scdriver]

Very strange. An FCU failure usually leaves the engine at low power. I have had to use Emergency power a couple times. Not sure why that would not work in this case?

All the emergency power lever does is bypass the fcu and dump raw fuel into the engine so there’s no way to use it in the scenario where you’re already getting too much fuel. I’ve heard of different versions of the pt6 basically cooking themselves from some internal fcu issue that opens the taps on fuel flow.

[scdriver]

I wonder if he was able to feather the prop.

I can't see any reason why the prop would not feather. This has happened a few times on different variants of the PT6. Usually something awry in the FCU forces it to "think" more fuel is required.

It would have feathered itself as soon as he shut it down with condition. Whether you’d want to try and feather at full power, I’m not sure… but it would do it

[C-FDPB]

Does anyone have intel on when this event occured? Was it recently with the "polar vortex" conditions? I had trouble with a -34 last winter in -30 where it was doing some funny things. In my case it was a little different with the prop gov "sticking", wasn't allowing the prop to reach full rpm. Maybe cold related issues?

[TailwheelPilot]

It occurred January 10.

[groncher]

Shouldn't really be cold related. PT6's have been running in the north for a long time.

I did have one in the arctic, a long time ago, that decided to accelerate on start to near max. Was probably -35 or so.
It had been on floats prior to the ferry north and likely had moisture in the FCU. A new FCU fixed it.

[Posthumane]

While not exactly the same engine, the fuel control unit on a Bell 412 with the PT6T twin pac had some issues with runaway engines in cold weather due to moisture in one of the lines freezing, if memory serves correctly. I recall the procedure was to switch to manual fuel governing right after engine start and let the engine warm up for several minutes before switching back to auto governing.

[cncpc]

How is the window shattering at 140 relevant? Vne is 144

[co-joe]

It would have feathered itself as soon as he shut it down with condition. Whether you’d want to try and feather at full power, I’m not sure… but it would do it

Not necessarily, if the prop stays in fine pitch, the wind milling of it would produce enough oil pressure to counteract the spring and counterweights in the prop governor. If it had a float plane kit it could also have blade locks preventing feathering on shutdown. If it really was a torque runaway I can understand being reluctant to feather the engine while the torque is going up, driving the blades to feather at full power the engine would likely tear itself apart, then once the condition lever is brought to cut off there may be a small window in time to disengage the blade locks. Will definitely be an interesting read once the full report comes out.

[scdriver]

It would have feathered itself as soon as he shut it down with condition. Whether you’d want to try and feather at full power, I’m not sure… but it would do it

Not necessarily, if the prop stays in fine pitch, the wind milling of it would produce enough oil pressure to counteract the spring and counterweights in the prop governor. If it had a float plane kit it could also have blade locks preventing feathering on shutdown. If it really was a torque runaway I can understand being reluctant to feather the engine while the torque is going up, driving the blades to feather at full power the engine would likely tear itself apart, then once the condition lever is brought to cut off there may be a small window in time to disengage the blade locks. Will definitely be an interesting read once the full report comes out.

The blade latches only catch if it’s shutdown with the prop angle aft of the latch angle, about -1 degree. In other words it only latches if you shut it down in reverse. The otter has an internal oil pump that provides oil pressure, so you’d have nothing left when you shut it down in flight regardless of the prop angle at the time

[Level@3000]

A few Winters ago while flying a -34 Turbo Otter in the mid - 30s I had the linkage hang up and torque would not reduce below 20 lbs. Power lever traveled normally. Once back at the base and on approach to the ice, I pulled condition lever off and feathered the prop. The thing really didn’t want to land but stopped 150 yard from the trees. Maintenance came out and sprayed LPS on the linkage. Good to go! Perhaps something similar to this happened?

[itsgrosswhatinet]

A few Winters ago while flying a -34 Turbo Otter in the mid - 30s I had the linkage hang up and torque would not reduce below 20 lbs. Power lever traveled normally. Once back at the base and on approach to the ice, I pulled condition lever off and feathered the prop. The thing really didn’t want to land but stopped 150 yard from the trees. Maintenance came out and sprayed LPS on the linkage. Good to go! Perhaps something similar to this happened?

You feathered the prop.