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Police helicopter crashes onto Glasgow pub

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Police helicopter crashes onto Glasgow pub

Old 19th Dec 2013, 03:59
  #1361 (permalink)  
 
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and the pilot responded by shutting down one, it's possible that he shut down the good one
A sensible theory at last and very relevant in a single pilot operation.

I have seen two pilots in the sim analyse an engine problem and then jointly agree to shut down the wrong engine and do so when they were under no particular stress. This happened in the 1988 BM 737 accident too.
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Old 19th Dec 2013, 05:50
  #1362 (permalink)  
 
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I admit I'm a little out of my depth with this question, but unlike an airplane, both engines in a twin helicopter are coupled by the same load. So if one engine starts surging and generally misbehaving then what does the FADEC do to the other engine good engine that doesn't know about it's twin brother's indecisiveness at providing the necessary power to the MGB?

What would the engine indicators be showing in such a condition on the 135?
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Old 19th Dec 2013, 07:54
  #1363 (permalink)  
 
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I admit I'm a little out of my depth with this question, but unlike an airplane, both engines in a twin helicopter are coupled by the same load. So if one engine starts surging and generally misbehaving then what does the FADEC do to the other engine good engine that doesn't know about it's twin brother's indecisiveness at providing the necessary power to the MGB?

What would the engine indicators be showing in such a condition on the 135?
The good engine will take over. F. e. if you fly with 2 x 55% TQ, when in OEI you will get ~110% TQ on the good engine unless you lower the collective ( powerlever ) and get the approbiate indications on your engine instruments, split needles ( N2, TQ etc )

skadi
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Old 19th Dec 2013, 07:59
  #1364 (permalink)  
 
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Police helicopter crashes onto Glasgow pub

Cattle truck, that's a good question. Also, the anecdotal incidence of pilots shutting down perfectly serviceable engines is higher than the accidents stats would suggest. However, there are a number of high profile accidents where this occurred. The various reasons for this type of error are well documented. It would be interesting to know what the FADEC reaction is to one engine malfunctioning when twin engines operate through a common drive. Presumably, if one starts to go offline, the other spools up to compensate to maintain the required power setting? Given earlier comments about fuel feed and the potential for one engine to flame out due to fuel starvation 2 mins before the other what would happen if the 'critical' engine (I.e.first to go on a low fuel ) was operating normally when no 2 went off line?
Thanks Skadi!
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Old 19th Dec 2013, 08:05
  #1365 (permalink)  
 
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I would suggest shutting down the wrong engine in a modern EC product is a little harder to do as all digital indications of failure are clearly indicated against the offending engine. Of course this would not rule out a cognitive failure to place the hand on the correct switch or lever.

Would current EC135 pilots agree or not?
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Old 19th Dec 2013, 08:57
  #1366 (permalink)  
 
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Difficult to answer, however we are taught to select engine to idle, check correct, then shutdown. I am sure that the switch positions have been noted, that would make the enquiry easier, if they have actually been moved.
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Old 19th Dec 2013, 08:57
  #1367 (permalink)  
 
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Not an EC135 driver but I do have a few thousand hours in DA42s. For those not familiar with the aircraft it is a simple twin with ECU controlled engines managed by a single power lever for each engine. Additionally each engine has ECU AUTO/B switch which allows for the manual selection of ECU B. Fiddling with ECUs is not part of the immediate action drill on engine failure. Engine instrumentation comes via a Garmin G1000 display.



One 'advantage' of an engine failure in a twin aeroplane is that you get significant yaw in the direction of the failed engine. Indeed, first recognition of failure will probably come through the rudder pedals.

In about 800hrs of DA42 instructing, of which probably half that time has been spent in engine failure modes I have twice encountered pilots, one of whom was a qualified twin driver who was undergoing differences training, who have attempted to secure the wrong engine. On both occasions they correctly followed the identification and rectification drills right to the point they went to retard the 'correct' throttle.

It happens.

Last edited by Cows getting bigger; 19th Dec 2013 at 09:12.
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Old 19th Dec 2013, 09:19
  #1368 (permalink)  
 
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Originally Posted by skadi View Post
The good engine will take over. F. e. if you fly with 2 x 55% TQ, when in OEI you will get ~110% TQ on the good engine ...
Thanks skadi, I understand that occurs when the bad engine stops completely, but what if it's surging, banging and up to all sorts of bad behaviour on it's way out, can anyone hazard a guess what the engine indicators would show as the FADEC of the good engine fights the FADEC of the bad engine until the bad engine finally stops turning?

The old hydro mechanical FCUs were relatively slow to react to transient demand - which depending on the circumstances could be a good thing. New electronic metering systems are quite capable of responding in milliseconds which under non-normal conditions could cause more problems than good.
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Old 19th Dec 2013, 10:25
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ref post 1026 fuel tank layout.

The EC-135 has three fuel tanks. Main and two supply. The engines are supplied from the supply tanks by suction and can easy run on either engine driven driven fuel pump (accessory part of engine).
The FWD and AFT Transfer pumps job is to transfer fuel from Main tank to Supply. To help out the job there are also two overflow holes too allow for free overflow to the supply tank.

As a lot of the flying PD does is hover, it is not uncommen to turn of the aft pump when light appears. But what if the FWD transf. is us? No fuel is then transfered to supply tanks.
The overflow holes are quite high and not at any help at such low level. This means that there are no fuel transfer from Main to supply tanks. The main fuel level in main is still showing reasonable fuel amount and can easily be mistaken for not starting on final reserve fuel, while Supply tanks are nearing empty. This may explain why amber caution light never comes on (inside Main tank), while they probably got Warning Low Level at very late stage.

That said, there are warning light on us pumps, if the system worked..
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Old 19th Dec 2013, 11:13
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Quote "To help out the job there are also two overflow holes too allow for free overflow to the supply tank."

these 'holes' are incorporated to allow fuel to spill back from the supply tanks into the main tank. The Transfer pumps have a rate of flow greater than the the engine driven pumps to deliberately prevent the supply tanks from emptying whilst the main is transfering. There is a 'trick' where a nose high attitude will spill fuel from the main (at certain levels) into the supply tanks without transfer pumps on.

Not sure what amber caution from the main tanks you are on about, the only caution from the main tank sensors will be quantity discrepancy driven, loss of sensing, and transfer pump dry or inoperative. Certainly nothing to do with low fuel quantity...that is from the supply tank systems.

Should both transfer pumps become inoperative due to failure, lack of fuel to transfer, or switch selection/CB failure. the engines will continue to draw fuel from the supply tanks. Should an engine driven pump fail, the supply tanks prime pump should be selected on to feed the engine.

Others have explained the supply tank low fuel warning systems very well....there are 2 independant systems....both have had their problems in the past but the likleyhood of 4 cautions and warnings failling in the same sortie at the same time as the pilot misreading 3 seperate fuel qty indications or taking no action would seem unlikely. I certainly included fuel as part of my regular scan procedure.

As aircraft and units have been withdrawn from the new National service fuel has become a critical factor in task profiles, it is burning a hole in the mind of all police pilots during the sortie. 95 ltrs of fuel was drained from this aircraft, if it is being suggested that it was 'stuck' in the main tank, the pilot and crew would have had to ignore so many visual and audio warnings unless again it is suggested that all of these systems failed on the same flight.
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Old 19th Dec 2013, 11:22
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Each supply tank supplies one of the engines.
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Old 19th Dec 2013, 11:44
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As a lot of the flying PD does is hover, it is not uncommen to turn of the aft pump when light appears.
Are you really sure? Hover means noseup attitude, so the light would first appear at the FWD pump.
BTW, its not uncommon to turn the relevant pump off, its procedure according to ECL.

But after departure and commencing cruise attitude, the aft pump will illuminate ( assuming main tank is almost empty ) , because the fuel will then be in the forward section.
And now you forget to switch on the FWD pump again. Guess what happpens....

skadi
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Old 19th Dec 2013, 12:52
  #1373 (permalink)  
 
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I'll guess. Fuel doesn't transfer to the supply tanks.
Close?
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Old 19th Dec 2013, 12:55
  #1374 (permalink)  
 
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SKADI - could you complete your story.......both main tank pump have now been switched off. What would then happen? Is it:

1. Supply tank content indications start to decrease......
2. Time ?.....AMBER FUEL LOW Illuminates for each Supply Tank....Time??
3. .....RED FUEL LOW illuminates for each Supply Tank...........Aproximatley 8 minutes (?) to first flame-out.
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Old 19th Dec 2013, 12:59
  #1375 (permalink)  
 
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Transfer Pumps

Page 56 post 1102 questioned the use of the transfer pumps and changes in pitch with speed change. I am fixed wing only but sensed a great deal of unease regarding tranfer pumps.
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Old 19th Dec 2013, 13:11
  #1376 (permalink)  
 
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Robin 400,

Helicopters tend to have more attitude changes than fixed wing especially those with rigid type rotorheads.

The system on the EC135 is well proven and employed on many similar types. One big longitudinal placed tank feeding two independant supply tanks using a "Full-Feeder" tank principle incorporating "overflow" connections at the top of the suplly tanks feeding back into the main tank.

As the fuel level gets down to the lower levels, significant changes in longitudinal attitude require some carefull management of the fuel transfer system. This is normal and ussually the pilots that fly these types are fully appraised of the system operation and limitations and how to manage the situations as they arise from say, prolonged hovering.

Failures create warnings. Low Level indications are nearly always independant from contents indications (as in the case of the RED LOW FUEL caption in the EC135).

Ultimatley, providing the crew are alert and the checklist is correctly formatted, a landing should take place as soon as possible (nearest safe site) if the backstop (RED) LOW FUEL warning illuminates, regardless of any other contradictory or misunderstood indications.

I would go as far to say that the system is as robust and simple as it can be while employing more than sufficient redundancy in indications and warnings to enable a safe landing to be made under all conditions provided the RFM actions are complied with.

Of course in the case of this accident we do not yet know if any of this is relevant or significant but it is noticeable that the 95 Litres recovered from the fuel system so stated in the AAIB report is similar to the KG value that could get trapped in the main tank as unuseable fuel under certain failure/switch selections.

It is also worth noting that the EC135 worldwide fleet has completed over 2.8m flight hours.
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Old 19th Dec 2013, 13:24
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Totally agree with you that is why after reading the 135 training manual many days ago my interest in the failure of the Nrv valves or a loose connection caused me concern.
The supply tanks ceased being refilled with fuel remaing in the main tank.
Engines have different fuel flow depending on many things, is is remotely possible that both supply tanks exhausted at approximately the same time.
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Old 19th Dec 2013, 13:27
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SKADI - could you complete your story.......both main tank pump have now been switched off. What would then happen? Is it:

1. Supply tank content indications start to decrease......
2. Time ?.....AMBER FUEL LOW Illuminates for each Supply Tank....Time??
3. .....RED FUEL LOW illuminates for each Supply Tank...........Aproximatley 8 minutes (?) to first flame-out.
1. right
2. normally yes, but according to the published SIN could be after #3 in the worst case
3. RED FUEL LOW on, ECL says to be on the ground within 8 or 10 min ( depends on the installed fuel tanks ), so first flameout after that time.

skadi
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Old 19th Dec 2013, 13:39
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Thanks Skadi!
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Old 19th Dec 2013, 13:42
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Many things are remotely possible, however 3 crew ignoring 4 warnings and 3 fuel quantity readings doesn't find its way onto my radar. Now, this might be remotely possible.....an undiagnosed TR control or drive problem occurring in cruise flight, that only manifests itself when AS reduces on approach to landing (the fin becomes much less effective at around 65/70 kts). Those that fly 135 will attest to the large pedal movement required at around that speed. IF, and it's a big IF, this occurred whilst AS is reducing and landing checks are being carried out, COULD result in an undemanded rotation and nose high attitude with further rapid reduction in AS leaving little if any time to get the thing into auto whilst getting rid of the power.
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