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DB,
HC has quite properly corrected me, and I am sorry for having doubted you. I only saw an abridged version of the report and that key bit of information was missing. Nevertheless I remain mystified as to how an experienced crew, who must have been aware of the developing situation, failed to convey their concern to their control room. I guess that we will never discover what really happened that night. The Pilot and the Police Crew were all experienced yet.......... TF |
Tiger fish, just my opinion but I don’t believe the crew fully understood or were aware of their situation until the first engine failed. Knowledge, understanding, comprehension leading to appropriate behaviour. When the knowledge or understanding is deficient...................... |
Originally Posted by DOUBLE BOGEY
(Post 10446547)
Tiger fish, just my opinion but I don’t believe the crew fully understood or were aware of their situation until the first engine failed. Knowledge, understanding, comprehension leading to appropriate behaviour. When the knowledge or understanding is deficient...................... * btw "pilot *****d up" IS NOT neccessarily the pilot's fault. IF the Regulator or Designer makes it possible for a pilot of THIS caliber to F'UP then OBVIOUSLY it is NOT his fault - it's their's. Right? |
ANFI - Oh! the joy of your SEH/MEH debate. To be clear though, the EC135 has effectively 3 separate tanks. 2 transfers pumps (one effectively for redundancy) and no booster pumps. Its simple. Provided you understand how its supposed to work and be managed in flight. Almost identical to the BO105.
The helicopter I operate at the moment is about 40 years older by design, has 10 tanks, cross-feeds, interconnects, transfer pumps, booster pumps and a bunch of NRVs. The main reason for all this gubbins is the design of the airframe leaving only small spaces to house the fuel meaning lots of tanks. In the case of the EC135, fuel starvation. The difference between the two supply tanks offers the pilots 30-40 seconds to react to what could happen next. Its not a lot and it requires the pilot to know this. Its the second engine that offers this chance. Having said that, a pilot who understands the EC135 fuel system should NEVER end up with fuel starvation provided the contents and warning systems are working correctly!!! To put it another way, the opportunity for a pilot to remain in flight thinking "Ah, in a few moments the first engine will flame out and I will have 30-40 seconds to get the lever down before the second engine flames out" is/should be non-existent. What I mean by this, is if knowledge, understanding and comprehension is fully formed, a landing/ditching should have been carried out under power AND the pilot would NEVER try a relight knowing he has effectively run out of fuel. So in this case, where a relight seems to have been attempted, two possibilities exist. either the pilot did not understand his system, indications etc OR the system//indications were misleading him to believe that the first engine flame out was not due to fuel starvation. Bearing in mind approx. 80kgs of fuel were remaining in the "system" albeit in the wrong place. |
Switches
So in this case, where a relight seems to have been attempted, two possibilities exist. either the pilot did not understand his system, indications etc OR the system//indications were misleading him to believe that the first engine flame out was not due to fuel starvation. Bearing in mind approx. 80kgs of fuel were remaining in the "system" albeit in the wrong place.[/QUOTE]
just my twopeneth, I flew the various UK Police 135s and though I was pleased to see the evolution from T1 Cpds, through to P2+/I I thought the method of changing the illumination of the CDS etc left much to be desired, reaching across the cockpit in the dark trying to put a vibrating finger on the Dim/Brt keys and keeping said digit in contact for just the right amount of time to achieve the exactly desired result was an exercise in try and try again. During a long night flight into very dark countryside I'd be regularly adjusting the Dim to the point the screen could be very dim towards the end of the flight as night vision became better. Why on earth did the designers think a rotary knob was too old fashioned! It's apparently good enough for PFD and ND? A few times returning towards base and doing a last minute job over the nearby town I realised the screen was then too dim to see anything because of the brighter town lighting outside changing my night vision, and then having to faff with the Brt key. |
DB, for clarity in this case, a relight was not attempted.
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Not every fatal accident or sudden death in Scotland results in a FAI. However, the Act ensures that EVERY case of a death during the course of employment results in a FAI.
It is a unique form of inquisitorial procedure. It is not about blame or prosecution. It seeks the truth of a number of matters, defined in the Act as follows. 6.-(1) At the conclusion of the evidence and any submissions sheriff's thereon, or as soon as possible thereafter, the sheriff shall make determination a determination setting out the following circumstances of the etc. death so far as they have been established to his satisfaction- (a) where and when the death and any accident resulting in the death took place ; (b) the cause or causes of such death and any accident resulting in the death ; (c) the reasonable precautions, if any, whereby the death and any accident resulting in the death might have been avoided ; (d) the defects, if any, in any system of working which contributed to the death or any accident resulting in the death ; and (e) any other facts which are relevant to the circumstances of the death. |
Originally Posted by DOUBLE BOGEY
(Post 10446051)
Hi HC, how's it going? Trust you are keeping well.
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Originally Posted by DOUBLE BOGEY
(Post 10446547)
Tiger fish, just my opinion but I don’t believe the crew fully understood or were aware of their situation until the first engine failed. Knowledge, understanding, comprehension leading to appropriate behaviour. When the knowledge or understanding is deficient...................... I was involved in the Dutch accident enquiry into G-JSAR. One of the factors was an engine disturbance causing Ng fluctuations and intermittent illumination of DIFF PWR (or was it Diff Ng on the L2, can’t remember). Anyway all the various bits - anticipator, FCU, DECUs etc were sent off for analysis but no fault was found. But clearly something was wrong because there had been no previous cases of this sort of intermittent Diff Ng caption. The same applies to the reported control restrictions. No cause was ever found. Of course the accident investigators don’t have the expertise and knowledge to test the equipment themselves, they have to rely on sending it to the manufacturer for testing. The manufacturers seem to put the equipment through routine testing such as might happen after manufacture or overhaul. It is not in their interest to determine that their specific piece of equipment was responsible for the accident and so I got the impression that the testing was superficial and minimal and certianly, they were not striving to prove that it was their equipment at fault. No doubt they didn’t lie, but they also perhaps didn’t expend as much effort as someone looking to prove something is faulty. |
Helicomparator,
To quote the final AAIB report. “It was not possible to determine precise timings but it was calculated that, before the helicopter reached Bothwell, the pilot was presented with a low fuel 1 warning caption, with the associated aural attention-getter. This aural attention-getter was acknowledged by the pilot. The warning caption then extinguished, before re-appearing after an undetermined interval. This, too, was acknowledged by the pilot. The caption extinguished again. The low fuel 2 warning caption then illuminated, with the associated aural attention-getter, and was also acknowledged. The time, in addition to the low fuel 1 caption then re-appeared a third low fuel 2 caption. This was acknowledged, before extinguishing again, leaving the low fuel 2 warning. The low fuel 1 and low fuel 1 warning caption then re-illuminated once more and was, again, acknowledged. After this, the low fuel 2 warnings captions remained illuminated for the rest of the flight.” it would appear the warning system was working. The unexplained area is the continuing to fly and take tasks after they had illuminated. Were they used to flying with Low Fuel captions so desensitised? FNW |
Were they used to flying with Low Fuel captions so desensitised? To get to that point you would have already passed "FUEL PUMP AFT or FWD" WARNING as appropriate which is triggered by measuring the current going to the pump and a time delay in the CPDS. You would also have the CAUTION "FUEL" which is part of the quantity system indicating a total of the supply tanks being below a certain level. If "LOW FUEL" captions were ever the norm and someone was desensitised by it something went wrong somewhere in the chain of events leading up to this accident. |
Originally Posted by FloaterNorthWest
(Post 10448029)
Helicomparator,
To quote the final AAIB report. “It was not possible to determine precise timings but it was calculated that, before the helicopter reached Bothwell, the pilot was presented with a low fuel 1 warning caption, with the associated aural attention-getter. This aural attention-getter was acknowledged by the pilot. The warning caption then extinguished, before re-appearing after an undetermined interval. This, too, was acknowledged by the pilot. The caption extinguished again. The low fuel 2 warning caption then illuminated, with the associated aural attention-getter, and was also acknowledged. The time, in addition to the low fuel 1 caption then re-appeared a third low fuel 2 caption. This was acknowledged, before extinguishing again, leaving the low fuel 2 warning. The low fuel 1 and low fuel 1 warning caption then re-illuminated once more and was, again, acknowledged. After this, the low fuel 2 warnings captions remained illuminated for the rest of the flight.” it would appear the warning system was working. The unexplained area is the continuing to fly and take tasks after they had illuminated. Were they used to flying with Low Fuel captions so desensitised? FNW The system thinks a caption was illuminated but clearly that system isn’t actually measuring light output from a bulb, it is something much further up a chain that thinks a caption OUGHT to be illuminated without actually knowing that it is. The report isn’t explicit about how these events are detected and stored and so I remain a bit dubious as to whether they are concrete facts or just the most probable (in isolation) explanation. One thing I learnt from my days in HFDM is that it is very easy to imagine a match between flawed data and an expected scenario, when in fact no such match exists. Given the choice between a pilot and 2 crew ignoring persistent warnings both trivial (prime pumps) and serious (low fuel x 2), over a prolonged period, vs a fault in the warning system that meant that, whilst the “brains” of the system wanted captions to be illuminated, in fact they weren’t, Occam’s razor might suggest that the latter is the simpler, and hence the correct, explanation. |
If one is going to follow the Occam's Razor argument, then I would suggest that all the technical equipment was functioning perfectly. The helicopter was operating close to the limits of its' endurance and the pilot may well have expected fuel warning captions to start to operate. Confirmation bias led to the warnings being cancelled without fully taking in what they were indicating due to confirmation bias. The engines flaming out came as a complete shock to all concerned. Human error, late in the evening, after a longish deployment. The only thing anyone is thinking about is finishing the tasking and getting back on the ground for a welcome cuppa and a trip to the loo. Been there, done that, albeit at ground level. |
Originally Posted by HeliComparator
(Post 10448428)
Given the choice between a pilot and 2 crew ignoring persistent warnings both trivial (prime pumps) and serious (low fuel x 2), over a prolonged period, vs a fault in the warning system that meant that, whilst the “brains” of the system wanted captions to be illuminated, in fact they weren’t, Occam’s razor might suggest that the latter is the simpler, and hence the correct, explanation.
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Devils advocate here. You have one cancel button for all warnings. If one caption is triggered but doesn’t illuminate and you then get a another less important caption that is cancelled..... you have cancelled both. Or many other reasons for pressing the button. The information used in the report was “best guess”, without a CVR. Is this robust enough to make a decision on all these lives and the reputation of a good pilot? i think it isn’t SOMETHING must have caused confusion in the cockpit that night. was it pilot error? Probably was he neglectful on purpose? No evidence at all does that matter? Hell yes! Why? So that it never happens again could there be a fuel system indicator fault? Don’t know dont know? Surely that needs addressing? ......... |
The secret lies in the shorted 24V tantalum capacitor on the warning panel that was reported in the original thread - I mentioned this ages ago and got shot down...via PM. But to me that's the smoking gun.
Kev. |
If you look at the long history of posts in the original thread there is a consistent theme running through it. That pilots at the time may not have had 100% confidence in the LOW FUEL warning/caution system.
In fact after the accident several machines under test displayed erroneous contents indications when the warnings and cautions illuminated. Water seemed to be the culprit. The clear and beautiful view from the "Hill-of-Hindsight" showed us that the FUEL LOW Red warnings were driven by Thermistors and generally applauded to be 100% accurate and a neat little backstop to the less reliable and pesky capacitance detectors driving both the contents indication system and the amber FUEL cautions (set for values ever so slightly above the RED FUEL LOW warnings). My God didn't we all Know this already???? (I am being cynical)! So maybe, low confidence in the system WARNINGS, CAUTIONS and indications, "fuelled" (no pun intended) by the Pilots failure to appreciate the Hill of Hindsight we now all occupy (thanks to several 1000 hours of testing and conjecture), coupled with erroneous indications that the 79 kgs of fuel that remained (or at least some of it) was indicating in the supply tanks and the stage is set. Chuck in several previous exposures to same. Add the cultural disposition to "accept it for what it is" (how many of us do that), and the fickle finger of fate is poised and waiting to deliver the fatal blow. In my considered opinion, there is much of all of us in this simple accident. There are many holes in the cheese that needed to line up. Some of them are already there, now, in our own working environments. Finding the holes and plugging them is the mission. Before, like this poor crew, it becomes too late. The single most important legacy of this accident is us knowing how Fuel Thermistors work and thus believing their pesky Warnings when they appear. |
The lovely blue pixel indications of fuel as displayed on the screen does give you the impression of a nice reliable system. I have seen with my own eyes indications of supply tanks full when in fact they were empty. The thermistors are the more reliable measure, and the capcitance fuel probes, once the tiny droplet of water which causes the error is dried out - they indicate perfectly well afterwards on a bench.
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Question. One imagines that this kind of flying isnt easily pre-planned but which is closer to the usual SOPs? Fly around until the low fuel alarm and RTB or have some broad understanding of your fuel endurance prior to stepping to the aircraft? If it is the later then failing tech (beyond your personal Casio) is unlikely to snag you very much.
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The remaining fuel endurance of the helicopter was similar to what one would have expected from a mental calculation, it was unfortunately in the wrong tank.
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