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Police helicopter crashes onto Glasgow pub

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Police helicopter crashes onto Glasgow pub

Old 25th Feb 2014, 13:39
  #2421 (permalink)  

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What is the fuel endurance of an EC-135 if the Transfer Pumps are not turned on during the Start....and left off during the flight. Start with the assumed 400KG of Fuel they had at the start. How long would you have been able to fly?
400 - 76 = 324 kgs

From the report, "Using an average fuel consumption of 200 kg/hr" (3.33 kg/min)

… about 97 minutes!

20:45 to 22:22 = 1hr 37 minutes!
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Old 25th Feb 2014, 13:44
  #2422 (permalink)  
 
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So....Transfer Pumps serve no function?

Why the concern about the Transfer Pump Switches?
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Old 25th Feb 2014, 13:48
  #2423 (permalink)  

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Of course they do, thats why with the transfer pumps off, there was still 76 kgs (23 minutes worth) of fuel left in the main tank!
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Old 25th Feb 2014, 14:04
  #2424 (permalink)  
 
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400 - 76 = 324 kgs

From the report, "Using an average fuel consumption of 200 kg/hr" (3.33 kg/min)

… about 97 minutes!

20:45 to 22:22 = 1hr 37 minutes!
I think you have to recalculate that. With the XFER pumps OFF from starting engines you cant get as low as 74kg in the main tank.
Just remember your groundrun after the ASB ( supplytank fuel sensor check )

skadi
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Old 25th Feb 2014, 14:07
  #2425 (permalink)  

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I think you have to recalculate that. With the XFER pumps OFF from starting engines you cant get as low as 74kg in the main tank.
Hows that then? How low do you think the main tank goes without the tx pumps on?
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Old 25th Feb 2014, 14:12
  #2426 (permalink)  
 
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"How low do you think the main tank goes without the tx pumps"

138 Kgs when we tried it - on the ground.
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Old 25th Feb 2014, 14:21
  #2427 (permalink)  
 
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SS, remember the discussions here in the EC135 thread about the required groundruns around christmas?

http://www.pprune.org/rotorheads/189...ml#post8236717

http://www.pprune.org/rotorheads/189...ml#post8255341

skadi
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Old 25th Feb 2014, 14:25
  #2428 (permalink)  
 
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Hows that then? How low do you think the main tank goes without the tx pumps on?
Is there a reason why the supply tanks aren't designed to be physically lower than the main tank and so could be fed by gravity in the event of pump failures?


Mickjoebill
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Old 25th Feb 2014, 14:34
  #2429 (permalink)  

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skadi;
SS, remember the discussions here in the EC135 thread about the required groundruns around christmas?
Yes I do, and in your links that I'm sure you must have read, you would have read;

"I did two runs yesterday on one we started with 100KG in the main and this burned off with the xfer pumps de-selected until 52kg only then the supply tanks started to show a reduction. We then did the second aircraft where we drained the main tank to 60kg before we started the test thinking it will take 10kg before we start to see the supply tanks dropping except we didn't. We had 12kg left in the main before the supply showed any signs of dropping."
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Old 25th Feb 2014, 15:31
  #2430 (permalink)  
 
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Originally Posted by mickjoebill View Post
Is there a reason why the supply tanks aren't designed to be physically lower than the main tank and so could be fed by gravity in the event of pump failures? Mickjoebill
The answer to that is probably resident somewhere in Eurocopter/Airbus Helicopters, or among the old hands from Messerschmitt-Bölkow-Blohm (if anywhere). If you look at the original spec/requirements documents for the various versions of this model's predecessor(Bo105, etc) I suspect the answer will lie there. The weight and cost of two internal transfer pumps added where purely gravity feed would require ... zero suggests to me that a particular requirement was being met.
I'll hazard a guess: an issue in design that some call a "graceful degradation" feature. If one tank has a leak, you don't necessarily lose all of your fuel ... but that's a general not a specific answer.

I'd need to go back a few dozen pages, or maybe in the EC-135 thread, but there was quite a bit of discussion on that point in the weeks after the crash.
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Old 25th Feb 2014, 16:16
  #2431 (permalink)  
 
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"How low do you think the main tank goes without the tx pumps"
I have done this test several times and each time with the main tank contents starting in and around 150kg, and the XFER pumps deselected the main tank contents decrease by approx. 20-30kg before the supply tanks start to decrease, but it never goes lower than 100kg in the main...
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Old 25th Feb 2014, 17:37
  #2432 (permalink)  
 
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Might the difference between ground test and air be accounted for by the lower deck angle in flight?
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Old 25th Feb 2014, 17:41
  #2433 (permalink)  

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Here's a couple of pics for you taken the night before last.

We were returning to base after a few tasks with 30 kgs in the main. During the pre landers I mentioned to the qualified police observers / TFO's that we should expect to see the fwd fuel pump caption come on as we slowed down and changed attitude. As it happened it didn't come on, maybe because it was a bit windy and the rearward attitude wasn't enough to make the pump run dry as would be expected.

Anyway, on the ground we settled with 25kgs in the main and no captions, which I found to be a bit strange as I would have thought we might have seen one or the other of the cautions by now.

As always, suspicion got the better of me and I decided to wait and see when the cautions came on and when the supply tanks started to be used.

1. The fwd caution came on at 19 kgs, and the fwd pump was switched off. As you can see from this pic, the aft caution accompanied it when the fuel in the main was 18 kgs and the aft pump was then also switched off.




2. As you can see in this pic, 9 minutes later at flight idle mpog, the main is empty and as would be expected the right supply tank qty has only then started to decrease.



Probably discussed in depth earlier, but hopefully these pics bring something else to the discussion. Clearly at least 20 kgs gets transferred between the main and supply tanks when the transfer pumps are turned off and this happens at levels in the main from zero to 100+ kgs.

skadi;
Just remember your groundrun after the ASB ( supplytank fuel sensor check )
http://www.airbushelicopters.com/sit...18-Rev0-EN.pdf

I do, but as the title suggests, it doesn't test when the transfer pump lights come on though does it?
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Old 25th Feb 2014, 18:26
  #2434 (permalink)  
 
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Anyway, on the ground we settled with 25kgs in the main and no captions, which I found to be a bit strange as I would have thought we might have seen one or the other of the cautions by now.
It could take 2 to 4 min for the caution to come after the pump started to run dry..

As for the decrease of maintank after selecting the XFER pumps off, there was a plausible explanation in the EC135 thread by "yellowbird135". To prove that, someone should leave the XFER pumps off after engine start and have a look whether the supply tank is decreasing adhoc or still the maintank at first ....

skadi
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Old 25th Feb 2014, 19:01
  #2435 (permalink)  
 
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I have thought for some time is it possible the TX pumps were never switched on in the first place. The reason is, it makes a little more sense never having turned them on than turning them on at start up and then turning them off for some reason somewhere before 76kg in the main tanks and not switching them back on again.

Why would the TX pumps ever be turned off before pump cautions which happen a lot later than 76kg in the main tank? (At 19kg and 18kg from Sid's post.)
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Old 25th Feb 2014, 19:46
  #2436 (permalink)  
 
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Hi Catch, Sids test was on the ground where the tank is probably level so both pumps are equally sat in fuel, in flight the fuel will move forwards or aft depending on aircraft attitude.

This whole business of the main tank fuel still transferring after the Xfer pumps are switched off is mind blowing, can't wait to find out the official reason for this, also why two aircraft that Were tested would drain the main to completely different levels with pumps off, stinks of a qty indication system fault.

I'm still thinking the Xfer pumps were manipulated as required during the second mission, then whilst in cruise back towards Glasgow the Aft pump (which was used during hovering) was switched off and the fwd not turned on. This could be the case for three reasons a) CAD failure, b) maybe the main was showing zero or c) pilot error (doesn't figure though as he would have cautions showing unless CAD fail)

CAD fail could also account for the Primes being switched on as a reaction to the Red Fuel Low, if a CAD fail is not discovered by the AAIB then I don't believe the true answers will ever be found.

FS
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Old 25th Feb 2014, 20:04
  #2437 (permalink)  
 
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What you, and many others on this thread fail to appreciate is that in attempting to discredit the fuel contents and indicating system you are actually promoting a culture where indications are no longer relied upon are indeed acted upon.
DB - I think for you to simply blame the pilot based on the limited facts available to date is premature and unfair. By doing so you also infer the police observers ignored all emergency & CRM training they had over the years too and were negligent.

I know all of the other EC135 trained crew members I fly with would query any cautions appearing on the CAD, and certainly immediately query any red warning and gong, and expect the relevant drills to be carried out. If it was something that required the termination of a task, they would inform the control room without delay explaining why. Unexpected cautions and emergency drills are something we practice regularly, yet you presume they said or did nothing, and told no one?

It is possible there may have been a fault with, or total failure of the CAD at a critical point in the flight, and SilsoeSid had done an excellent job of explaining the EC135 systems in detail with photos & videos, and shown great patience in answering the never ending technical questions, maybe you should read his recent posts again?

With a CAD failure there are no fuel level indications, no cautions to tell you if the transfer pumps are off, or if the prime pumps are on. We do not yet know for certain if the warning unit functioned correctly in displaying the red low fuel warnings at the correct supply tank levels.

Ok, the above scenario may not explain everything that happened leading up to the accident but it is worth consideration as IMHO there was more going on than an experienced police pilot & crew carrying out routine tasks and ignoring cautions and warnings until the engines flamed out.
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Old 25th Feb 2014, 20:14
  #2438 (permalink)  
 
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Good point about the last tasks not being routine, if say the CAD failed during the cruise back towards Glasgow would they have accepted routine tasks?

Maybe the pilot had calculated endurance remaining from the last live data available before failure and believing the Xfer pumps were on accepted the tasks.

Reflecting on my last post if the qty system was faulty and showing zero I would have thought RTB was the only option

FS
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Old 25th Feb 2014, 20:57
  #2439 (permalink)  
 
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Having read the above discussion about the fuel tanks, are we looking at a possible design fault contributing to the accident?

How many outlets from each fuel tank? Is is just one (central)?

Wouldn't it be better to have an outlet forward and aft, so that whether the helicopter is nose down or nose up there is always a fuel supply?
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Old 25th Feb 2014, 21:42
  #2440 (permalink)  

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One thing that's come to mind thinking about my hangar switchology the other day;

If someone with a 135 handy can try something out ... With the transfer pumps running, when you turn them off, how long does it take for the cautions to come on?
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