S-92 questions

[mulligan]

I used to fly Jetrangers many years ago and have forgotten most of what I knew. So I have a few questions for the experts.
Reading today's National Post was pretty chilling. What else could have gone wrong I wonder?
Allowing for the fact that this IS a newspaper article, a few things have me scratching my head:
It says that the FDR stopped recording "as the helicopter descended to 240 metres". It goes on to say that "at 150 metres the tail rotor drive was lost". If the recorder had stopped then how do they know when the tail rotor failed? I seem to recall that the tail rotor has it's own gearbox with a seperate oil supply so what caused the TR to fail? Main gearbox failure? Also, I think the Globe and Mail referred to an electrical failure on top of everything else! Any thoughts on what caused that?
The more I learn about this accident the more I conclude that it was simply non-surviveable. If someone pulled all that stuff on you in a simulator I think you'd be justified in getting up and walking away!

[carholme]

Mulligan;

No expert but here is a link to the TSB photos showing the drive pinion in the Main Gear Box. If you scroll down to the bottom you will see from the teeth damage that the tail rotor drive became completely disconnected. This damage is at the Main Gear Box (transmission) end of the drive train, not the T/R gear box end.

http://www.tsb.gc.ca/eng/medias-media/p ... 9A0016.asp

Electrical power on the S92 is provided by Main Gear Box driven alternators which are oil cooled from the MGB oil supply. Only conjecture at this point but loss of oil pressure, overheating and resultant electrical failure seems probable.

The S92 is equipped with HUMS (Health Unit Monitoring/Management System) and though the TSB have not released any HUMS information as yet, it has to be presumed that any retrievable information was also used to deduce the timeline.

http://www.tsb.gc.ca/eng/medias-media/c ... 090618.asp

carholme

[sky's the limit]

The more I learn about this accident the more I conclude that it was simply non-surviveable. If someone pulled all that stuff on you in a simulator I think you'd be justified in getting up and walking away!

I agree 100%. This was a very unfortunate string of events starting on the drawing board.

stl

[kingeddie]

They were able to piece together most of the last 800 feet with the hums data including the rolling off of the engines and attitude changes in the flare as well as the impact . I have it in email somewhere . i ll post it if i can find it later

KE

[mulligan]

Thanks very much for this. I wasn't aware of the HUMS. The picture of the TR takeoff unit is amazing! What kind of heat could have done that!
I fly in and out of YYT quite a lot and it's good to hear the Cougar machines again. Must be a fairly tense atmosphere though.

[carholme]

Mulligan;

Very difficult to say at this point whether it was heat related or possible mechanical damage/interference in the gear train. TSB has not related any information concerning the interior condition of the MGB, therefore not much to go on.

The photo of the damaged gear teeth would make for some good discussion but it only shows a portion of the gear and therefore would only be unfounded speculation.

carholme

[2R]

A picture is worth a thousand words.
Having so many things go wrong on one aircraft seems more than bad luck.

[sky's the limit]

A picture is worth a thousand words.
Having so many things go wrong on one aircraft seems more than bad luck.

This more a case of one thing leading to another, not a myriad of separate issues converging at once.

stl