Go Back  PPRuNe Forums > Non-Airline Forums > Private Flying
Reload this Page >

GA Aircraft ditching - Irish Sea - 16th Dec

Private Flying The forum for discussion and questions about any form of flying where you are doing it for the sheer pleasure of flight, rather than being paid!

GA Aircraft ditching - Irish Sea - 16th Dec

Old 19th Dec 2009, 21:17
  #81 (permalink)  
 
Join Date: Jan 2006
Location: An island somewhere
Posts: 423
Likes: 0
Received 0 Likes on 0 Posts
KeepItStraight said:

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.
You may well be right, and this could well have no bearing at all on the accident in question.

However, it is certainly interesting to note that the alternate air door design in the the PA30 is poor and has been responsible for engine failures (and, I understand, double engine failures) through air inlet blockage in the past. From an air accident report:

The original design of the alternate air door on the normally aspirated PA30's and PA39's puts the door downstream of the air filter and in an area of high vibration. A failure of the door hinge or shaft will lead to an immediate engine failure. A modification exists to move this door to a lower vibration area on the lid of the air filter. If not modified, this door should be inspected thoroughly and frequently (we have had an Australian fatality due to this).
And from a separate Twin Comanche incident arising from alternate air door failure:

I was flying my PA-30 over water together with my friend Michael in his PA-39. My position was some 200 ft behind and to his right side (we flew many thousands of miles that way, with the leading aircraft calling for both as "Comanche Formation"). All of a sudden it looked like he applied brakes: His aircraft slowed down and in a second I was at his level. I throttled back and we exchanged ideas about what went wrong, as all gauges were normal. All of a sudden he started to accelerate and soon operation was normal. This repeated itself several times to our amazement. However, he was able to make it safely to destination. After landing we started to look for a possible cause and it did not take long to find that one of these doors got loose and partially blocked the air passage. When it moved back and forth the size of the free passage was changed. Fortunately, there was never a full block.
Thus the lack of prop RPM stability through a wildly fluctuating manifold pressure could be explained! Of course, as I said, this could well have no bearing at all on the accident in question.

Last edited by Islander2; 19th Dec 2009 at 21:41.
Islander2 is offline  
Old 20th Dec 2009, 07:28
  #82 (permalink)  
 
Join Date: Aug 2003
Location: Surrey
Posts: 1,217
Likes: 0
Received 0 Likes on 0 Posts
Islander2 and I threw 'induction blockage' out as an idea to explain low MP on one (or depending on how you read MLB's post both) engine(s). There have been several answers of how common forms of intake blockage shouldn't effect this aircraft. Moving away from this particular case - are there any system failures that can result in less than atmospheric MP other than an induction blockage? (ignoring the case of a faulty gauge)? Are there any sources of inflight induction problems other than, icing/snow, broken alt air door, others??

Last edited by mm_flynn; 20th Dec 2009 at 07:41.
mm_flynn is offline  
Old 20th Dec 2009, 16:55
  #83 (permalink)  
 
Join Date: Sep 2002
Location: The South
Posts: 98
Likes: 0
Received 0 Likes on 0 Posts
Moving away from this particular case - are there any system failures that can result in less than atmospheric MP other than an induction blockage?
To see the MP reduce, I believe you must either have an increased intake restriction (e.g. throttle closure, intake blockage/icing etc.) or increased engine RPM (effectively causing increased suction from the engine and hence increased pressure difference across any existing intake restriction, intentional or otherwise).

So I can see how a failure of a CSU would show up as reduced MP as well as increased RPM. But a failure that just results in decreasing MP (and no RPM change) can't, to my mind, be caused by anything other than an intake restriction of some kind.

Mark
mark147 is offline  
Old 20th Dec 2009, 17:41
  #84 (permalink)  
 
Join Date: Jun 2003
Location: EuroGA.org
Posts: 13,787
Likes: 0
Received 0 Likes on 0 Posts
You would need a helluva RPM increase to drop MP really significantly.

On my TB20 (IO-540-C4 engine) I see about 1/3 inch MP change from 2300rpm to 2500rpm.

However, we don't know anything about ManxLadybird's flight conditions.
IO540 is offline  
Old 20th Dec 2009, 18:32
  #85 (permalink)  
 
Join Date: Jan 2006
Location: An island somewhere
Posts: 423
Likes: 0
Received 0 Likes on 0 Posts
You would need a helluva RPM increase to drop MP really significantly.
True, but it's the converse that is more interesting. If it were a failed alternate air door, the MP could have been fluctuating between 17" and, say, 22" ... which, presumably, would put the prop on and off its fine pitch stops and present a fluctuating or 'unstable' RPM!
Islander2 is offline  
Old 20th Dec 2009, 19:26
  #86 (permalink)  
 
Join Date: Jun 2003
Location: EuroGA.org
Posts: 13,787
Likes: 0
Received 0 Likes on 0 Posts
Yes, very much so. At the low MP end the governor would drop out of regulation, and at the top MP end it would overshoot a bit.

So a messy/intermittent intake blockage could manifest itself as wildly varying RPM.

Metars for 16/12/09 around 1200:

METAR EGNH 161250Z 32009KT 9999 -RA FEW023 SCT038 06/04 Q1011
METAR EGNH 161220Z 32008KT 9999 -RA FEW022 SCT033 06/04 Q1011
METAR EGNH 161150Z 32009KT 9999 -RA FEW022 SCT033 06/04 Q1012

For some reason can't get the skew-t from Wyoming Univ. Some from here for the general area suggest solid IMC from a low level (which the metars don't support) to c. 15000ft with 0C around 3000ft. Meteox.com shows strong scattered returns for the area.

Could it have been snowing?

Last edited by IO540; 20th Dec 2009 at 19:42.
IO540 is offline  
Old 21st Dec 2009, 08:33
  #87 (permalink)  
 
Join Date: Sep 2009
Location: N.YORKSHIRE
Posts: 891
Received 22 Likes on 10 Posts
Can anyone tell me what depth of water the aircraft sank in?
Flyingmac is offline  
Old 21st Dec 2009, 10:20
  #88 (permalink)  
Thread Starter
 
Join Date: Dec 2009
Location: uk
Posts: 5
Likes: 0
Received 0 Likes on 0 Posts
MLB,

Congratulations on a fantastic outcome and thank you for posting on this thread.

A lot of different emergency agencies where alerted and on standby for you - and I would just like to thank them all.

Have a great Christmas and I hope your back in the air very soon.
icantfindagoodname is offline  
Old 21st Dec 2009, 12:47
  #89 (permalink)  
 
Join Date: Jul 2007
Location: Lincolnshire
Posts: 365
Likes: 0
Received 0 Likes on 0 Posts
The Irish sea is not particularly deep.

I would think around 20 metres or so, where the ditching occurred.
Oldpilot55 is offline  
Old 21st Dec 2009, 13:42
  #90 (permalink)  
 
Join Date: Sep 2009
Location: N.YORKSHIRE
Posts: 891
Received 22 Likes on 10 Posts
If it's only in 20mtrs it would be fairly easy to bring it to the surface, but doubt it would be worth the effort. Easy dive though.
Flyingmac is offline  
Old 22nd Dec 2009, 09:16
  #91 (permalink)  
 
Join Date: May 2002
Location: Who can say?
Posts: 1,700
Likes: 0
Received 0 Likes on 0 Posts
Easy dive though.
I think not. Poor visibility, strong current, BLOODY FREEZING even in a drysuit, and a relatively very small thing to find as well as quite light so it could have drifted for quite a distance. The expense of mounting a dive to locate it would far exceed the replacement value of the airframe.
Captain Stable is offline  
Old 22nd Dec 2009, 10:40
  #92 (permalink)  

 
Join Date: May 2001
Location: 75N 16E
Age: 54
Posts: 4,729
Likes: 0
Received 0 Likes on 0 Posts
Perhaps there is an ROV vessel in the area already due to the oil and gas ops which can salvage it? Not cheap of course but it depends if it has to be salvaged for any reason....
englishal is offline  
Old 22nd Dec 2009, 13:06
  #93 (permalink)  
 
Join Date: Jan 2008
Location: Hants
Posts: 42
Likes: 0
Received 0 Likes on 0 Posts
Quote:
Easy dive though.
I think not. Poor visibility, strong current, BLOODY FREEZING even in a drysuit, and a relatively very small thing to find as well as quite light so it could have drifted for quite a distance. The expense of mounting a dive to locate it would far exceed the replacement value of the airframe.
Not difficult to dive on the slack although vis may be an issue. Site would need to surveyed by decent side scan sonar to locate and/or a form of magnetic detector. Not sure it would be worthwhile going to the effort.
rocco16 is offline  
Old 22nd Dec 2009, 16:10
  #94 (permalink)  
 
Join Date: Aug 2003
Location: Surrey
Posts: 1,217
Likes: 0
Received 0 Likes on 0 Posts
Neither insurance nor the AAIB appears to have pulled out the previous Twin Comanche that went down in the area. The salvage value of the airframe will be pretty much nil (how much for a light twin with no engines or avionics ??)

The AAIB report will probably be a factual description of the events of the flight, ending with
The pilot was unharmed but was later flown to a mainland hospital as a precaution.
Further investigation as to the cause of the total power loss could not be carried out as the wreckage was not recovered from the sea.
(From the AAIB report of 8 years ago - same type, same place).
mm_flynn is offline  
Old 22nd Dec 2009, 18:19
  #95 (permalink)  
 
Join Date: Sep 2009
Location: N.YORKSHIRE
Posts: 891
Received 22 Likes on 10 Posts
Had vis of 20mtrs plus in UK waters at 60mtrs depth. Cold not an issue if properly equipped. Current is rarely a problem at slack on a neap tide. Sidescan sonar much cheaper these days and very good when used with GPS. Our RHIB can run a search pattern at 40 knots. Still not worth it though. Price of Aluminium too low. Fuel too high. Won't bother.
Flyingmac is offline  
Old 23rd Dec 2009, 14:38
  #96 (permalink)  
 
Join Date: May 1999
Location: Quite near 'An aerodrome somewhere in England'
Posts: 26,903
Received 351 Likes on 124 Posts
ManxLadybird, my warmest congratulations on an excellent piece of flying. Whilst the cause of the double engine failure is a mystery still, the description you provided of your descent and pre-ditching drills was quite outstanding. Were you taught all those things you described, or was it instinct? Either way, that was a 'copybook' ditching.

I'm sending you a PM as I think that your account needs a wider audience - many of us have already learned a lot from your post and I thank you for that!

Congratulations again; enjoy a relaxing Christmas!
BEagle is online now  
Old 23rd Dec 2009, 20:25
  #97 (permalink)  
 
Join Date: Sep 2007
Location: here
Posts: 220
Likes: 0
Received 0 Likes on 0 Posts
40 kts? How do you stop the 'fish' from coming out of the water at that speed? And I would think the data is unusable too - we struggle much above 4 or 5 kts to get quality usuable data.

HTC
herman the crab is offline  
Old 24th Dec 2009, 09:24
  #98 (permalink)  
 
Join Date: Sep 2009
Location: N.YORKSHIRE
Posts: 891
Received 22 Likes on 10 Posts
Fairly flat sea bed. Find target at decent speed with a good sounder and mark with M.O.B button on GPS. Positively ID target with slow speed sidescan pass. Job's a good'un.
Flyingmac is offline  
Old 25th Dec 2009, 08:00
  #99 (permalink)  
 
Join Date: Dec 2009
Location: Singapore
Age: 63
Posts: 1
Likes: 0
Received 0 Likes on 0 Posts
Perhaps there is an ROV vessel in the area already due to the oil and gas ops which can salvage it? Not cheap of course but it depends if it has to be salvaged for any reason....
There is! It is the Northern Canyon, on contract to Centrica. Operator Hallin Marine ( www.hallinmarine.com ). Vessel has both ROVs and diving spread onboard. Operating in Morecombe Bay area now until approx beginning of February 2010.

Operating cost per day of the Northern Canyon > Hull value of of a PA30 so unlikely to be worthwhile. I need to declare personal interest - but happy to help if someone wants it back
Tropical John is offline  
Old 26th Dec 2009, 19:35
  #100 (permalink)  
 
Join Date: Sep 2007
Location: here
Posts: 220
Likes: 0
Received 0 Likes on 0 Posts
Well your RIB must have some pretty fancy equipment on board as I've not come across an echo sounder that gives usuable data at that speed in a RIB either!

HTC
herman the crab is offline  

Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service

Copyright © 2024 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.