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GA Aircraft ditching - Irish Sea - 16th Dec

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GA Aircraft ditching - Irish Sea - 16th Dec

Old 18th Dec 2009, 15:49
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Mystery solved and what can I say but "Bravo" and very well done.
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Old 18th Dec 2009, 15:55
  #62 (permalink)  
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Edited thread title

I have taken the liberty of editing the thread title to reflect the successful outcome of the episode.

Good job, glad you're safe ManxLadybird!

And thanks for sharing your experience on here.

SD
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Old 18th Dec 2009, 16:02
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Timothy said:
It does seem that both sides may be CSU related (overspeed (ie too fine) on one, underspeed (ie too coarse) on the other)
It is difficult to see how any CSU failure could cause the manifold pressure on an engine with the throttle well open to drop to 17". Surely that could only be caused by an induction blockage?
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Old 18th Dec 2009, 16:25
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It looks like both engines had low MP.
Anyone got any idea what could cause this?
and I would also be interested to know if the plane had just been in for maintenance.

Eddieheli
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Old 18th Dec 2009, 16:45
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Eddie, could you please explain to me how you consider that low MP can cause an uncontrollable prop overspeed?
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Old 18th Dec 2009, 17:12
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MLB

what a fantastic outcome for you and your family.
I just hope that if anything a fraction as risky as your problem, ever happend to me ,that I react with your courage and calmness.
It probably didn't feel all that calm at the time
A lady flight instructor who flies from our strip recently had a canopy smashed,possibly bird impact but not known.
She was covered in blood and could only see properly from one eye,but managed to land in a field unhurt and aircraft undamaged apart from what happened in the air.
Perhaps ladies are better at it than us chaps when the chips are down?
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Old 18th Dec 2009, 17:46
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Liferaft not much good unless you can get into it

MLB did very well and her husband likely saved her life by insisting on her wearing an immersion suit, especially when she was unable to board the liferaft.

Without the immersion suit she may not have remained able to hold onto the liferaft until rescue, although in this case her rescuers were exceedingly prompt

To those flying overwater: Does your liferaft have effective boarding steps?
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Old 18th Dec 2009, 17:48
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Originally Posted by Captain Stable Eddie
, could you please explain to me how you consider that low MP can cause an uncontrollable prop overspeed?
Originally Posted by ManxLadybird
...[right engine] overspeeding in excess of 2800 rpm and I could not stabilise it. The MP was low as well so I did not have much to play with.

... my left engine lost power. My MP was down to 17 inches.
would sort of suggest a low MP problem developed on both engines and an overspeed on one.

It would seem to suggest a general induction problem (snow packing, induction ice???) as both engines appear to have been affected. Is there a reasonable CSU failure mode that could have the same root cause?

--------
I am not aware of an engine failure mode that results in less than atmospheric MP other than 'induction blockage' or a 'stuck' throttle cable (indirectly causing an induction blockage)
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Old 18th Dec 2009, 18:49
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Anyone who has seen the construction of a CSU will know that low MP cannot cause a prop overspeed. The only thing that can cause a prop overspeed is a failure of both governors within the CSU.

As I read her post, MLB was between cloud layers and not in icing conditions. She talks about completely different symptoms for each engine failure. It is possible that the second failure was caused by intake icing descending through cloud layers, but I won't bet much on that - MLB was there - she could probably tell you whether it was likely given the conditions at the time.

As for the first engine failure, my money is on some mechanical failure within the CSU.
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Old 18th Dec 2009, 19:02
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induction air filter icing

Will cause a low MP indication, having the same effect at closing the throttle.
Selecting alternate air would provide unobstructed air supply to the engine restoring power. No info is this is catered for on this aircraft.
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Old 18th Dec 2009, 19:44
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MLB, what have you written in your logbook for the landing point? I have an entry in mine from years ago that says take off point Belize International and landing point 'A Swamp... Ouch'.
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Old 18th Dec 2009, 20:03
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I guess her log book may be a little damp and out of reach.
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Old 19th Dec 2009, 09:36
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As a flying diver,( or a diving flier), I can tell you that there is little difference in the sea temperature in that area between winter and summer. You will chill through very quickly any time of the year without protective clothing. Heat is leeched from the body 20 times faster in water than air. The average temperature recorded on dives is only 7Celcius.
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Old 19th Dec 2009, 10:31
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Congratulations to MLB for a successful outcome to a double emergency,and to the rescue crews for their prompt reaction.
I don`t know what the Comanche POH , but it may well be worth thinking about that in other larger pistons ,in extremely cold weather,one should cycle the props several times,maybe every 45min-1hr,to circulate fresher ,warm oil through the governors,as the viscosity would /could change ,leading to poor/ degraded control,especially in a long constant power cruise.
It is only a thought ,and no way reflects the events .
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Old 19th Dec 2009, 11:02
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Originally Posted by Flyingmac
As a flying diver,( or a diving flier), I can tell you that there is little difference in the sea temperature in that area between winter and summer. You will chill through very quickly any time of the year without protective clothing. Heat is leeched from the body 20 times faster in water than air. The average temperature recorded on dives is only 7Celcius.
Found a URL for surface temperatures, and whilst I agree the deeper water won't vary much at all, the surface seems to by up to 10C. But it took a lot of time & swearing to get that far with the site - it seems very slow.

Coastal Observatory, Liverpool Bay, Irish Sea (UK) | Satellite

But even if the water was at it's warmest, MLB should keep wearing her immersion suite.
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Old 19th Dec 2009, 15:20
  #76 (permalink)  
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I am a cynical soul and consider the chances of the two failures being completely unconnected too low to consider seriously.
I agree. However, the evidence is at the bottom of the sea and the AAIB are unlikely to recover it.

UV
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Old 19th Dec 2009, 15:52
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Interesting read from MLB, well done.

I "ditched" 50 times in the summer - but I had floats on

Regarding a double engine failure in a Multi, purely for interest sake - One way which could cause a DEF on many types is to crossfeed only one engine and forget about it. If you do this, both engines feed off one tank, BUT the fuel return of the crossfed engine goes back into the tank on the side of that engine. The result is that you have a huge fuel flow from one tank (~whatever, say 30 gals/hr) with the other tank starting to fill up from the fuel retun. When full of course the excess fuel will be dumped overboard. So eventually both engines stop - as the tank they are running off is empty, but you still have full fuel in the other wing...
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Old 19th Dec 2009, 18:15
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This is the second time a Comanche has ditched near to these rigs:

http://www.aaib.gov.uk/cms_resources...pdf_500979.pdf

The last one was G-ASRH in 2001.

Last edited by robbo; 19th Dec 2009 at 18:38.
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Old 19th Dec 2009, 19:17
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Congratulations to MLB for excellent handling and also for reporting to the rest of us so we might learn.
The technique for getting into a liferaft without steps involves submerging oneself by pushing against the liferaft and then using inertia from bouyancy to propell oneself into the liferaft. It's not easy in a training pool so I can only guess how hard it is for real!
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Old 19th Dec 2009, 20:09
  #80 (permalink)  
 
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The only thing that can cause a prop overspeed is a failure of both governors within the CSU.
Not quite true, lose of pressure (Nitrogen/air) in the prop dome will cause and over speed as well.

If you do this, both engines feed off one tank, BUT the fuel return of the crossfed engine goes back into the tank on the side of that engine.
Not in the case of engines fitted with the Bendix fuel injection system as fitted to Lycomings, of which the Comanche is one type with these engines.

Induction icing is unlikely to cause a power lose due to the location of the intake plus the Comanche is fitted with automatically opening alternate air doors which can be also opened manually.
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