Bearskin Metro 3 CYRL accident - Speculation thread

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cncpc
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Re: Bearskin Metro 3 CYRL accident - Speculation thread

Post by cncpc »

burst plenum.jpg
burst plenum.jpg (22.5 KiB) Viewed 3547 times
2.5milefinal wrote:If there is a serious discussion/speculation on any accident even if later we find out it was completely out in left field I say its worth it. If it gets pilots back into the books and thinking about how they can do things safer its worth it... that's what makes forums a good thing.
For example I just finished reading an article about 'Plenum Failure'. It may have nothing to do with this crash. But now I remember what it is and what it is all about.
I assume that's the article I linked in the other thread. I came in the context of asking whether this might be a plenum failure cause. Call it speculation if you wish, but it is very well informed speculation. I called a very experienced crash investigator, and very smart person, and I gave him the three facts (yes, facts, not "facts"). He thought for a bit, and said the most likely cause was a plenum explosion. Not the only possible cause. Likely may mean only 10% chance if the other causes are all less than 10%.

That lead to my post raising the plenum issue. Which led to a STFU request? Which lead to a thread in an Accident forum being unilaterally declared by some to be a Condolences thread, and this one started as a Speculation thread.

WTF is wrong with us? Is this a gathering of deaf, dumb and blind kids who can do nothing but play a mean foosball, and who have a pathological compulsion to forever express condolences to people they never knew and who don't have the remotest idea that AvCanada even exists? And then get all arsewise with people who have an immediate professional interest in gaining information of what happened in order that they may at the first opportunity know if there is some risk in their own operations and how they may immediately act to deal with that risk.

Plenum failures come in varying degrees of seriousness. This above is likely the most serious, the failure on the Terrace MU-2. I've spoken with an operator that had a failure with a 4 inch crack opened up an inch at its widest.

The MU-2 failure was violent and resulted in serious deformation of the cowling. Somehow the prop did not get feathered, but the T handle was pulled. In an MU-2, it seems the feather is accomplished by bringing the condition lever to emergency stop. Jetstreams have stop feather T handles, and apparently Metros have stop feather knobs.

On the Jetstream rig, there are certain types of plenum rupture which can disable the stop feather mechanism.

In the case of the 4 inch crack, the engine lost power and would only produce 35% torque and there were temp spikes. I don't know how the crew handled it, but the aircraft landed safely.

It would seem that a catastrophic failure and flameout might be preferable in that if the feather mechanism is damaged, then the loss of oil pressure in the dome would lead to the springs moving the blades to feather. That may not always be what happens.
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cncpc
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Re: Bearskin Metro 3 CYRL accident - Speculation thread

Post by cncpc »

Transferred from the Condolences thread...
CID wrote:
It's news evidence (verified) that they were descending on a beeline course to the Airport, while still on the exact same course as en-route and not even attempting any other approach procedure yet not quite reaching it on that 'shortest trajectory possible'.
According to additional information released, the airplane appears to have been on an IFR approach and the crew reported passing ULOTU which is 3 DME east for the approach to 26. Not on a beeline course to the airport and on an approach contrary to what is stated above.
That seems to be an accurate account of that phase of the flight. Somehow the aircraft turned left and hit the ground about 2 miles south of the field, or more likely southeast, as 2 miles directly south does not come all that close to Hwy 125.

This happened in good VFR weather.
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casey
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Re: Bearskin Metro 3 CYRL accident - Speculation thread

Post by casey »

I am more of a PT6 guy but i assume the above pic is the combustion can on a Garret i can see how if it blew you would be in a pickle.My condolences to the Bear community worked next door to them in the Austin days
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olddirtyloud
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Re: Bearskin Metro 3 CYRL accident - Speculation thread

Post by olddirtyloud »

Where did this 10 minute out emergency theory come from? I don't believe they've even heard the CVR yet...if things were normal until 3 miles, and then the engine problems occur, assuming on the extremity of it, it would make sense that they yawed left and ended up where they did.
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Re: Accident in YRL Nov 10, 2013

Post by HighBypass »

Thanks old timer. I've done a few NTS in flight shutdowns as well for training and after a new engine install but not with those engine models and it really does work quite well. That why I'm puzzled as to how there was an accident and not a single engine landing. I suppose we will have to wait for more facts from the cvr/fdr.
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cncpc
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Re: Bearskin Metro 3 CYRL accident - Speculation thread

Post by cncpc »

olddirtyloud wrote:Where did this 10 minute out emergency theory come from? I don't believe they've even heard the CVR yet...if things were normal until 3 miles, and then the engine problems occur, assuming on the extremity of it, it would make sense that they yawed left and ended up where they did.
It came from press reports of what the TSB said. "some kind of emergency 10 minutes before landing".

The Bearskin copilot in the back is quoted as saying there was some kind of engine problem.

It would not be uncommon for a plenum failure to be preceded by a fire warning light. Little crack developing to rapid fatigue failure.

Yes, it makes sense. More sense if there was a problem feathering.
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Ki-ll
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Re: Bearskin Metro 3 CYRL accident - Speculation thread

Post by Ki-ll »

The fact that they were on approach over ULOTU indicates that they were on the extended runway centerline. The fact that they ended up to the south of the field indicates that something turned them that way. The fact that they declared an emergency indicates that it likely was not a CFIT in its classical sense, the crew was aware of some problem.
If in fact the problem was with the left engine, then the airplane will turn around to the left (into the dead engine), which it did. Had it not been turning to the left, they would have ended up on the runway or close to it. So there might have been a difficulty controlling the direction.
Difficulty controlling direction on a turboprop engine would come from a windmilling propeller. How bad it would windmill would depend on several factors, the main factor is whether the NTS system was working. With NTS working about 70% of the drag would be reduced, without it the drag would be bad (how bad depends on other things such as airspeed, blade angle, density altitude). So even with the exploded plenum I would imagine the NTS system should take care of the drag. However the situation of loosing an engine at night, in turbulent air with gear down and flaps at half close to the ground makes for a very bad recipe. It would probably be fairly difficult to recognize the failure right away since the airspeed and direction are fluctuating masking the onset of airspeed loss and direction change. But a fast recognition is what the crew needs at this point. In addition to that an exploded plenum (if it did) would likely sever the cable which controls the feather valve via the STOP&FEATHER knob. So if you are able to pull the control out, it might not work, which adds to confusion even more... If it does not work, then NTS system is your best bet. If that does not work, then the maximum blade angle the prop would go to (due to beta follow up system) on a -11 engine is 20 degrees with the Power Lever all the way forward, which it probably won't be on approach. If the Power Lever is around the approach setting, then it would be more likely around 10 degrees, which is a lot of drag at first a (large force (abnormally large) required on the rudder pedals and yoke).
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Re: Bearskin Metro 3 CYRL accident - Speculation thread

Post by Ki-ll »

cncpc wrote:
olddirtyloud wrote:Where did this 10 minute out emergency theory come from? I don't believe they've even heard the CVR yet...if things were normal until 3 miles, and then the engine problems occur, assuming on the extremity of it, it would make sense that they yawed left and ended up where they did.
It came from press reports of what the TSB said. "some kind of emergency 10 minutes before landing".

The Bearskin copilot in the back is quoted as saying there was some kind of engine problem.

It would not be uncommon for a plenum failure to be preceded by a fire warning light. Little crack developing to rapid fatigue failure.

Yes, it makes sense. More sense if there was a problem feathering.
It does not look like 10 minutes is an accurate figure, the CADORS has the following narrative
A Bearskin Lake Air Fairchild SA227-AC (C-FFZN/ BLS311) from Sioux Lookout, ON (CYXL) to Red Lake, ON (CYRL) was conducting an area navigation (RNAV) runway 26 approach into CYRL and reported ULOTU final at approximately 0027Z. Shortly thereafter, the aircraft declared an emergency, followed by a Mayday. Airport staff vehicle reported to have observed the aircraft crash south of the airfield in the vicinity of the non-directional beacon (NDB) striking a power line. Ambulance, Fire and Police all dispatched to crash site.
So it looks like things happened really fast.
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Re: Bearskin Metro 3 CYRL accident - Speculation thread

Post by cncpc »

Ki-ll wrote:The fact that they were on approach over ULOTU indicates that they were on the extended runway centerline. The fact that they ended up to the south of the field indicates that something turned them that way. The fact that they declared an emergency indicates that it likely was not a CFIT in its classical sense, the crew was aware of some problem.
If in fact the problem was with the left engine, then the airplane will turn around to the left (into the dead engine), which it did. Had it not been turning to the left, they would have ended up on the runway or close to it. So there might have been a difficulty controlling the direction.
Difficulty controlling direction on a turboprop engine would come from a windmilling propeller. How bad it would windmill would depend on several factors, the main factor is whether the NTS system was working. With NTS working about 70% of the drag would be reduced, without it the drag would be bad (how bad depends on other things such as airspeed, blade angle, density altitude). So even with the exploded plenum I would imagine the NTS system should take care of the drag. However the situation of loosing an engine at night, in turbulent air with gear down and flaps at half close to the ground makes for a very bad recipe. It would probably be fairly difficult to recognize the failure right away since the airspeed and direction are fluctuating masking the onset of airspeed loss and direction change. But a fast recognition is what the crew needs at this point. In addition to that an exploded plenum (if it did) would likely sever the cable which controls the feather valve via the STOP&FEATHER knob. So if you are able to pull the control out, it might not work, which adds to confusion even more... If it does not work, then NTS system is your best bet. If that does not work, then the maximum blade angle the prop would go to (due to beta follow up system) on a -11 engine is 20 degrees with the Power Lever all the way forward, which it probably won't be on approach. If the Power Lever is around the approach setting, then it would be more likely around 10 degrees, which is a lot of drag at first a (large force (abnormally large) required on the rudder pedals and yoke).
That is the best of all posts in both threads about this accident.

Not that it couldn't have used a couple more paragraphs?
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Re: Bearskin Metro 3 CYRL accident - Speculation thread

Post by olddirtyloud »

cncpc wrote:
It would not be uncommon for a plenum failure to be preceded by a fire warning light. Little crack developing to rapid fatigue failure.
A fire light 10 minutes away would have meant an engine shut down 10 minutes away, and notification to either centre or Kenora FSS. Like the cadors says, things went bad and fast.
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Re: Bearskin Metro 3 CYRL accident - Speculation thread

Post by Ki-ll »

cncpc wrote:
That is the best of all posts in both threads about this accident.

Not that it couldn't have used a couple more paragraphs?
I don't really know what else to add without going into the realm of science fiction...
Engine failure on a direct drive engine without some kind of limiter not allowing the pitch to go to low is not fun during the day in smooth air at altitude, it has taken airplanes out of the sky on numerous occasions. If that happens at night, in MVFR and turbulent air then it is an extremely tough task for the crew to handle. The worst thing is that there is no guidance on such situation anywhere, neither in a flight manual nor any circulars. All the certification is done with the NTS system operational.
I read that these 331 engines are also prone to cracks in gearbox, but I have not reviewed that information yet.
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Re: Bearskin Metro 3 CYRL accident - Speculation thread

Post by cncpc »

Ki-ll wrote:
cncpc wrote:
That is the best of all posts in both threads about this accident.

Not that it couldn't have used a couple more paragraphs?
I don't really know what else to add without going into the realm of science fiction...
Engine failure on a direct drive engine without some kind of limiter not allowing the pitch to go to low is not fun during the day in smooth air at altitude, it has taken airplanes out of the sky on numerous occasions. If that happens at night, in MVFR and turbulent air then it is an extremely tough task for the crew to handle. The worst thing is that there is no guidance on such situation anywhere, neither in a flight manual nor any circulars. All the certification is done with the NTS system operational.
I read that these 331 engines are also prone to cracks in gearbox, but I have not reviewed that information yet.
There is a post here about gearbox cracks as well.
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Re: Bearskin Metro 3 CYRL accident - Speculation thread

Post by cncpc »

Ki-ll wrote:
cncpc wrote:
olddirtyloud wrote:Where did this 10 minute out emergency theory come from? I don't believe they've even heard the CVR yet...if things were normal until 3 miles, and then the engine problems occur, assuming on the extremity of it, it would make sense that they yawed left and ended up where they did.
It came from press reports of what the TSB said. "some kind of emergency 10 minutes before landing".

The Bearskin copilot in the back is quoted as saying there was some kind of engine problem.

It would not be uncommon for a plenum failure to be preceded by a fire warning light. Little crack developing to rapid fatigue failure.

Yes, it makes sense. More sense if there was a problem feathering.
It does not look like 10 minutes is an accurate figure, the CADORS has the following narrative
A Bearskin Lake Air Fairchild SA227-AC (C-FFZN/ BLS311) from Sioux Lookout, ON (CYXL) to Red Lake, ON (CYRL) was conducting an area navigation (RNAV) runway 26 approach into CYRL and reported ULOTU final at approximately 0027Z. Shortly thereafter, the aircraft declared an emergency, followed by a Mayday. Airport staff vehicle reported to have observed the aircraft crash south of the airfield in the vicinity of the non-directional beacon (NDB) striking a power line. Ambulance, Fire and Police all dispatched to crash site.
So it looks like things happened really fast.
Yes. However, they may have reported some problem a way back, but not formally declared an emergency.
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Re: Bearskin Metro 3 CYRL accident - Speculation thread

Post by cncpc »

olddirtyloud wrote:
cncpc wrote:
It would not be uncommon for a plenum failure to be preceded by a fire warning light. Little crack developing to rapid fatigue failure.
A fire light 10 minutes away would have meant an engine shut down 10 minutes away, and notification to either centre or Kenora FSS. Like the cadors says, things went bad and fast.
Yes, that makes sense. However, if that aircraft has a history of seemingly false fire warnings, then your scenario, which is the SOP scenario, may not have been what the crew actually did.

It's an odd thing, whatever it was.
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Re: Bearskin Metro 3 CYRL accident - Speculation thread

Post by Ki-ll »

cncpc wrote: Yes. However, they may have reported some problem a way back, but not formally declared an emergency.
Very true. If only they would release a bit more factual information...
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Re: Bearskin Metro 3 CYRL accident - Speculation thread

Post by pdw »

raven54 wrote:I just have to ask, pdw...what is with your fascination with winds? Variable this and that/unexpected this or that...In all seriousness I am wondering.
Sure, thanks for asking. No fascination at all, just watching out for real facts.

Hard to believe ... we're about to find out they actually may have landed in an opposite direction from whence they came, if the dead engine pulled them left off their final heading for rwy 26 ? The southerly direction would produce a VERY high crash-speed when settling it into the trees there.
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Re: Bearskin Metro 3 CYRL accident - Speculation thread

Post by GUMPS »

pdw wrote:
raven54 wrote:I just have to ask, pdw...what is with your fascination with winds? Variable this and that/unexpected this or that...In all seriousness I am wondering.
Sure, thanks for asking. No fascination at all, just watching out for real facts.

Hard to believe ... we're about to find out they actually may have landed in an opposite direction from whence they came, if the dead engine pulled them left off their final heading for rwy 26 ? The southerly direction would produce a VERY high crash-speed when settling it into the trees there.
Case Closed...
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Re: Bearskin Metro 3 CYRL accident - Speculation thread

Post by nottellin »

pdw wrote:
raven54 wrote:I just have to ask, pdw...what is with your fascination with winds? Variable this and that/unexpected this or that...In all seriousness I am wondering.
Sure, thanks for asking. No fascination at all, just watching out for real facts.

Hard to believe ... we're about to find out they actually may have landed in an opposite direction from whence they came, if the dead engine pulled them left off their final heading for rwy 26 ? The southerly direction would produce a VERY high crash-speed when settling it into the trees there.
Yikes :?
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Re: Bearskin Metro 3 CYRL accident - Speculation thread

Post by BTD »

I have had an engine failure with an nts fail as well. I will say that I am grateful we were very lightly loaded.

In our case it did not prevent feathering.

I have no idea what happened in this case.
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Re: Bearskin Metro 3 CYRL accident - Speculation thread

Post by Ki-ll »

BTD wrote:I have had an engine failure with an nts fail as well. I will say that I am grateful we were very lightly loaded.

In our case it did not prevent feathering.

I have no idea what happened in this case.
Could you please elaborate on specifics? How bad were the forces on the controls (rudder pedals/control column)? What was the airspeed loss? How long did it take you to feather the engine? Was there an associated altitude loss? If you don't mind of course...
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Re: Bearskin Metro 3 CYRL accident - Speculation thread

Post by DonutHole »

Its been awhile since 331 class but cant the prop get hung up on the locks if it isnt feathered before a certain rpm. Something about locks and centrifugal force is ringing a bell
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Re: Bearskin Metro 3 CYRL accident - Speculation thread

Post by boeingboy »

Its been awhile since 331 class but cant the prop get hung up on the locks if it isnt feathered before a certain rpm. Something about locks and centrifugal force is ringing a bell
No. The only way to get the prop on the locks is to have the blades go into reverse.

Sometimes you can miss the locks on shutdown if you don't pull it into reverse soon enough.
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Re: Bearskin Metro 3 CYRL accident - Speculation thread

Post by Liquid Charlie »

Would the failure of NTS and Feather systems not be covered in sim -- we know multiple failures are not allowed for assessment but it can be demonstrated or is it covered with a statement that it "won't be controllable" if the NTS is not working and the engine won't feather.
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Re: Bearskin Metro 3 CYRL accident - Speculation thread

Post by triplese7en »

DonutHole... the prop won't get hung up on the locks because it needs to be held in reverse to get the prop behind the locks. What you're probably thinking of is the engine has a range of 18-28% where there are harmonic vibrations that can cause damage if the engine is allowed to 'hover' in that range. You're only allowed combustion assisted acceleration through that range. If you don't have light off on start by 10 seconds after 10% or by 20% you have to abort the start. As for feathering, the AFM recommends you feather prior to 30% to avoid this RPM range.

LiquidCharlie... the chances that you have an engine failure, NTS failure, and feathering failure in combination are extremely small. It isn't that uncommon to have an engine failure in combination with an NTS failure though. One poster above has said to have experienced that.

If you did have that triple failure I can pretty much guarantee you will be descending no matter how well you fly the airplane. Basically keep your speed up and do a nice flare before you smack the ground.
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Re: Bearskin Metro 3 CYRL accident - Speculation thread

Post by DonutHole »

Its ben awhile but in the 331 what prevents spring pressure from driving the prop to feather when the engine is shut down?
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