Why 1000ft?
 

Thomas, I'd assumed the 1000ft from the report's paragraph:

I interpreted this as "a series of returns from 1000 feet towards the accident site, and then one final single return from 400 feet on the descent". That may be a misinterpretation, as this paragraph includes details from the whole flight. I think it does mean that there is an unambiguous radar track, even if I have it wrong from the AAIB text.

Why miss the red warnings? If there was a display problem, maybe the red central console warning lights just weren't there to see, and the two non-flight crew wouldn't have known where to look for their backup replacements. As to why the pilot didn't - well, that's the key question.

TC, I am very much in agreement with you. Although I do agree with others that the 400' radar return came during the final descent.

I also see [TC, JEacott agree] no reason to conclude that he did not enter auto. On the contrary, intermittent low Nr warnings followed by later steady low Nr would indicate to me that he did.

My take:

A simple mistake during a XFER PUMP changeover and they are both off. Difficult to see panel (night, perhaps NVG) and no immediate visual indication that a pump was left off.

During the actions following RED indications, the PRIME's are turned on vice XFER's. (it is my understanding from all the reading I have done, that there is no caption for XFER PUMP in an off pos'n).

As for the landing: unless autorotations to touchdown are practiced regularly at night, it is very difficult to get it right. The normal reaction is flare too high. NVG's provide better visuals but in my day on them the depth perception was poor.

A very similar incident happened to a 212 in the Maldives. With no rad alt the flare was high, and the high G impact that followed was not survivable. Even high inertia blades stop quickly in an overpitch.

2 things that are often overlooked when considering how fast Nr will decay in such a scenario:
1. The engines are NOT at idle contributing residual thrust. This is significant in distorting the true Nr behaviour in a turbine a/c performing Autos.
2. Adding pitch to a rotor on the ground to slow it more quickly following a shut down (bad practice) is not the same as low Nr in flight. AoA is hugely different.

Finally, is it really considered plausible that an airframe could fall 1000' perfectly level, or that a tumbling a/c would land upright by chance?

Occam's razor.

I've discussed this report over the last couple of nights at the crew brief. The one word that cropped up from the TFO's on both nights was "disappointment".
Nothing to do with the AAIB's quality of reporting just disappointment that so many captions, warnings and clues over at least a 10 minute period which have gone either un-noticed by the TFO's or un-actioned by the pilot.
Following the appearance of any caption, if I have not acknowledged to the crew that I have seen it and explained why it's appeared and what I've done about it, they speak up. We cannot understand why at least 4 amber captions, (2 of which should not be on in flight under normal circumstances), 2 Red captions with audio and lowering supply tank levels have resulted in continuing flight rather than a precautionary landing.

Thomas, I think your perspective is in the ball park but I would add in the possibility that after moving away from the hover the prime pumps were selected on rather than the Tx pumps - reach up without looking, find 2 switches in roughly the right place that move in the expected direction -Cognitive failure - but still doesn't explain why the consequent captions were ignored or discounted.

Like yourself and MG, I have always done the same with regard to the switching of the transfer pumps.

P&A,

The time to slow the rotors is I think clear in the absence of changes to the controls - the rotational kinetic energy in the rotor, divided by the power required to maintain steady flight. That's a small number of seconds.

I think there's a good chance that a falling helicopter with low rotor speed would land skids down, as a shuttlecock or dandelion seed, due to drag from the blades.

As to whether it would "tumble", that's also possible, in the absence of angular momentum from the rotors, but the reports of "tumbling" come from inexperienced eyewitnesses. A shuttlecock effect would probably at some point cut in to stop any tumbling, and with 10-20s for descent from 1000ft that might be enough time to end up skids down even if it was "tumbling" at the start of the descent.

TC, that is the most plausible hypothesis I have seen so far.
The pilot was not worried about fuel, and accepted additional non urgent tasking. His gauges told him (erroneously) he had sufficient fuel, and when the red warnings appeared, they still showed sufficient, and there had been no amber warnings. He concludes that there is a fault, rather than a fuel shortage, and as he is enroute to base anyway, puts it on auto as you suggest and begins to troubleshoot.
When fuel starvation affects the first engine, still convinced by his gauges which are showing (erroneously) sufficient fuel in the supply tanks, he switches on the prime pumps as part of his response to what he percieves is a problem in getting fuel from supply tanks with plenty fuel, to the engines. Convinced the problem is not fuel quantity, a view supported by his contents gauges, he continues to head for the ever closer home base, which represents by far the best option for landing, and where the problem can be readily investigated and resolved without becoming front page news as a result of a precautionary powered landing within spitting distance of base. Alas we know the rest.
Assumes that the fuel probe problem was present , but if it was, it could explain why the red warnings, and even the first flameout were not properly diagnosed by such an experienced pilot.

Thomas coupling:
I have no particular reason to disagree with you. The Chinny in the right hands is an immensely capable machine, provided the mechanicals keep the blue side up! As I said earlier, we did used to train EOLs all the way to the ground, but I accept in the intervening years, that may have changed. That will be down to the system of course rather than any unprofessionalism on the part of the pilots? I do however know of an RAF chinook that survived an EOL in an operational theatre, so let's not get the suggestion out of perspective?

Fortyodd2

Your comments regarding the 'disappointment' of TFOs is well made. Of course we will never know what conversations were occurring in that aircraft. Somebody, somewhere actively took the decision to deny us the means to learn from those moments.

However...

People talk about 'authority gradients' in multi crew aircraft. When a TFO is commenting on a flying issue, his words may well carry much less weight than another professional pilot occupying the other seat?

We had a thread regarding twin pilot for police ops a while ago. Whilst we don't yet know what happened here, if the implied suggestions are correct, is it possible a second trained pilot may have helped prevent this tragedy?

Might it be a reasonable subsequent recommendation from investigators? Or would we simply have to accept that even the very best pilots working alone, will occasionally mess up perhaps more than two working together?

Sorry I'm not really a rotary wing pilot, question for me is how does a low inertia helicopter react when starting an autorotation into wind (as usual and best practise I suppose) but then being forced to fly a U-turn into downwind. I presume there could be some loss of energy/rpm? Wind was 300/7, but just a huge complex building in that direction (Ennoch centre) from the area were the real trouble started; landable ground all downwind..(car park, Glasgow Green). Could such a 180 turn mess up an ar at very early stages despite a successful entry? thanks for any answers.

Falcon900

Your last post would really fit with a pilot suddenly presented with a conflicting fuel display and warnings, the actions then taken by the pilot are of course a matter of speculation, but we know how it ended. I do think you have summed up what might well have happened.

I've tried to confine myself to describing the aircraft and the operational procedures.

I'm now really looking to the AAIB to identify a fault in the aircraft display or sensing systems before I start to think like others on here about the pilots actions.

The fact we know is that the transfer pumps and prime pumps were in the wrong positions, thus denying the only actual fuel present reaching the engines. What we hope to know is wether the displays and warnings were being accurately presented to the pilot. If they were it's probably all going to come down to wrong switch selection/position and not dealing with what happened afterwards.....

If the AAIB provide evidence that the fuel system or displays/warnings were not presented in the expected manner, we move on to a series of unknown responses by the pilot to unfamiliar and perhaps conflicting information. Of course there is no escaping the fact that with both engines out the ultimate task to perform a full EOL to the ground was unsuccessful if attempted, I think we shall never know many of these things.

Just had a thought that whilst not obvious, the police role equipment should contain some useful information, the camera/skyforce nav systems will have times of power on and off. Camera heading/attitude/altitude measured against against aircraft position etc The power off should have happened when the first engine ran down and took the generator off line, this might provide the time frame between first engine flame out and time of impact as I understand the engine FADEC only records the engine run time rather than actual start and stop times (might be wrong on that).

A long shot but I'm sure the AAIB are having it all checked. I also wonder wether there was any call from the TFOs to control, for 2 minutes to land, or informing of any fault that might preclude further tasking that night due to faults on the aircraft. certainly something that would be fairly standard for my crew to do if a fault occurred in flight. It just all smacks of things happening really so quickly as to overpower normal procedure and responses.

Good points Cabby, though there's obviously some differences in local unit procedures. Certainly the units I've flown with have standardised challenge and response pre-landing and emergency drills. I would expect the front seat TFO to challenge me with every appearance of a caution or warning, particularly if I seemed to be doing nothing about it. I'd also expect the rear seat to let control know of any interruption to the task for an aircraft problem, this is why I think things happened so very quickly.

Cabby

Why do you think it would be good if EC135 control systems could be modified to allow flight without hydraulics? Apart from no doubt the impossibility of this being viable, if, as TC says, the hydraulics lose effectiveness at 63% NR yet minimum recoverable autorotation NR is 83%, it's a bit academic isn't it?

@pilot and apprentice
You get two amber cautions when pumps are switched OFF! Look at post #2140!

skadi

Is there any warning that should appear under misc to request the pilot to check if the transfer pumps are on if the fuel level in the supply tanks goes below a set level but when there IS fuel remaining in the main tank?

skadi
2140 !!!!! how about post 435 :ugh:

tl:dr

They have a patent for an improved fenestron without hydraulic assist, but this is more a weight issue. Dunno about the rotor, sounds real challenging.

Is there a reason why the transfer pump switches don't have a third option in addition to "on" and "off" i.e. "automatic"?

Hydraulics, only if you have to.
 

The EC135 has a very small chord would it not perform well without hydraulics? The H500 does very well and has 5 blades of not much less chord?

It's just another 'system' which if it can be left out improves simplicity and reliability.

The amber “fuel caution” signal (lights and audio alarm) is linked to the sensors in the supply tanks, but failed to work. As the supply tanks drained of fuel there was still no indication that this amber sensor worked. So did this sensor " fail"?
If so would there be a display warning to indicate that the sensor had failed, and would a fuel sensor failure trigger resetting the supply tank fuel gauge to display zero?

My apologies. I had understood that a yellow caution indicated run dry, and did not note that turning the pump off lit another.

AOF, many thanks for your 2083 and clarification.

Thomas Coupling:

I do think it is now worth revisiting the witness statements in light of the latest AAIB update, while keeping an open mind.

http://www.pprune.org/8192615-post721.html

Could the pilot be positioning for an emergency landing and attempting a restart I note that Bargeddie is only a couple of miles east of the CTR perimeter so the ATC call timed at 2218 for clearance would likely have been around then. Working backwards from 2222, would I be right in surmising that the reds should have come on around 2212 and the ambers 2209 (subject to fault free operation).

Of course we can only be sure of the position of prime and transfer pumps at point of impact. The prime pump switches could have been on for the whole sortie, or equally possible, just for a few seconds prior. It is impossible to know the configuration at any time prior to the position in which they were found..

Imagine for a second that, hypothetically, the pilot had switched the transfer pumps on just a few seconds before impact but too late to have any effect. We would all be sitting here wondering how the xfer pumps could be on, everything functioning correctly but with empty supply tanks and fuel in the main tank.

PS I think there is a small error in the AAIB report where they refer to Uddington, I believe they mean Uddingston. Uddington is I believe much further south.