Weststar AW139 Hyd failure and RH MLG Collapse

[industry insider]

On 23rd December, one of Weststar's AW139 suffered in flight #2 HYD system failure while on an offshore flight. Durng the RTB Landing, the RH MLG Collapsed.

Initial findings show the No.2 Hydraulic System PCM fluid level was non-existent and the upper deck area around the No.2 PCM wet with hydraulic fluid. The leak appeared to come from an apparent failure on the PCM end of the No. 2 hydraulic hose assembly (PN A494AE3E00E0930X per IETP IPD Ref. 39-A-29-12-00-040-941A-A, item 2) connecting the No. 2 Hydraulic Pump to the No. 2 PCM.

Investigation into why the MLG collapsed is ongoing.

[212man]

The landing gear is operated from the number 2 system and it freefalls when the reservoir level falls below 50%, although the Emergency Down button should then be pushed, which uses the number 1 system to hydraulically force it down.

[malabo]

212man, thought you were true blue 92. Get typed on the 139? Ground school was a while ago, but I dimly remember that with a loss of #2 hyd fluid taking out the utility system the gear can still be extended by pushing the emerg button and then lever down to match the switch/position logic. If it doesn't lock, the #1 pressure will hold it down until the rotor decays to about 20%. It would be bad luck to lose the #2 system and have have the gear not lock down at the same time, but Weststar seems to have more than their share of bad luck with landing gear. Training fodder for next year.

[Outwest]

212man is mostly correct, but just to clarify that at 50% on sys #2 the utility (landing gear) SOV closes and since the only thing holding the gear up is the hyd pressure (no up-locks), the gear will free fall. However, when the fluid level drops to 28% then the utility re-opens and the TR SOV closes. The correct action would be to use the EMERG landing gear (hyd sys #1) button before landing.

[HLCPTR]

But don't forget that at 22%, the utility SOV2 closes once again.

The speed (rate) of the fluid loss and the status of the valves at the time of pilot intervention affects the indications in the CAS window.

Ultimately however, use of the emergency down is called for if you do not have positive downlocks (three green) after placing the landing gear lever to the down position.

If all three legs were not down and locked, the "LANDING GEAR" aural warning should have sounded at 150 ft AGL.

:ok:

[Outwest]

Oh I didn't forget it, the point I was trying to make was that the SOV closure causes the gear to freefall, not total loss of fluid.

Anyway, we all agree that the Emerg Down should have been used (and maybe it was).

[noooby]

And if all 3 gear weren't down and locked, you also wouldn't have 3 greens. Recommended practice is to hover and have ground crew try to manually pull the gear into the locked position.
Having said that, if the emergency button was pushed, I can't see a reason for the gear to not lock down. That is what the button is for!!!
Also, why was the leaking hose not found before? There have been a few cases of hydraulic hoses leaking/sweating, sometimes being monitored for weeks before being replaced. They don't just suddenly fail.......
Seems like there could be a bit more to this story.

[spinwing]

Mmmmm ....

..... They don't just suddenly fail .......


Actually at 3000+ PSI (207 Bar) they can and do!


:uhoh:

[noooby]

Mmmmm... Actually they don't. Hoses of this type are stressed to at least 6000 psi. Usual failure points are where the fittings are installed on each end and that will usually weep for a while before failing.

[rapman]

Unfortunately the hydraulic pressure hoses, especially on the #2 system do fail suddenly! Asked any experienced operator running a high time machine:ugh:

Whilst the hoses are rated at 6000psi, they have a design flaw which causes them to fracture and burst where the union is Joined to hose. These hoses are covered in rubber so cannot be inspected for cracks/fractures. At 3000 psi these hoses let go without warning!

Agusta are fully aware of this problem as Operators have reported multiple failures:eek:

[alouette]

If Agusta is fully aware of this problem, and other discrepancies then why don't they respond in a professional manner, and get these issues rectified? If I'd be looking to tender aircraft for a contract then I would seriously having doubts of putting up with this "horseplay".

[malabo]

I think Agusta had already issued a BT, maybe the problem is the slacker operators being slow to comply. And the even slacker operator training departments that waste time training the improbable instead of focussing on known current problems. Some eventually falls on the pilots, two on board, either one of them remember to push the Emerg Gear button, and check for the green lock lights? Good scenario requiring practical and useful application of CRM, or was their CRM training a droning PowerPoint taught by a retired airline pilot? Lots of operator holes between the OEM and the passengers.

[spinwing]

Mmmm ...

Malabo .... quite correct as you say ... also Agusta in their wisdom supply a QRH which actually lays down the procedure to follow after such an event ...

I know this because a similar failure has happened to me ... happily everything worked as advertised and the recovery to base was otherwise un-eventual ... but as you say ... CRM etc etc ...

Having said all that ... why don't we all wait and see what the officious investigation of the facts comes up with ... eh?


Cheers

[212man]

Having said all that ... why don't we all wait and see what the officious investigation of the facts comes up with

Yes, I'm sure the report will be easy to find online, along with all the other freely available reports :E

[spinwing]

Mmmm ..

Oh the cynicism ..... :ugh: (but your most probably right :hmm:)