- burst plenum.jpg (22.5 KiB) Viewed 3548 times
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%.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.
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.
