Police helicopter crashes onto Glasgow pub: final AAIB report
Purveyor of Egg Liqueur to Lucifer
P.96
Hmmm;
Rad Alt over a built up area.
Would one be able to rely on that height information for judging the height during an auto over the city. Could the preset ht warning (600' +), before the verbal ht warning be a further distraction?
Where to steer the light.
A steerable landing light would be steerable, but steered to where? Perhaps to a position at which the non steerable light, on the Ess bar, is already at? Or maybe straight ahead, but how high, for the flare or for the level?
Where is that steerable light pointing when you switch it on?
efish,
A good point about the dark spaces in built up areas; parks, roofs, car park, woods, cemetery, allotment or waste ground … feeling lucky!
As you goggle and I don't, how close are the goggles to the roof when in the stowed position? (fixed your seats up & down yet?
)
If you were to take them off, to relieve the neck muscles, where do you place them? (Surely not on the floor, loose articles and all that)
I once, while landing, had a set knocked off by the GOA in Kuwait that ended up between my feet. Now that was an interesting couple of minutes in the dark hole of a desert
Contributary Factors
2. The RADALT and steerable landing light were unpowered after the
second engine flamed out, leading to a loss of height information and
reduced visual cues.
2. The RADALT and steerable landing light were unpowered after the
second engine flamed out, leading to a loss of height information and
reduced visual cues.
Hmmm;
Rad Alt over a built up area.
Would one be able to rely on that height information for judging the height during an auto over the city. Could the preset ht warning (600' +), before the verbal ht warning be a further distraction?
Where to steer the light.
A steerable landing light would be steerable, but steered to where? Perhaps to a position at which the non steerable light, on the Ess bar, is already at? Or maybe straight ahead, but how high, for the flare or for the level?
Where is that steerable light pointing when you switch it on?
efish,
A good point about the dark spaces in built up areas; parks, roofs, car park, woods, cemetery, allotment or waste ground … feeling lucky!
As you goggle and I don't, how close are the goggles to the roof when in the stowed position? (fixed your seats up & down yet?
)If you were to take them off, to relieve the neck muscles, where do you place them? (Surely not on the floor, loose articles and all that)
I once, while landing, had a set knocked off by the GOA in Kuwait that ended up between my feet. Now that was an interesting couple of minutes in the dark hole of a desert
Avoid imitations
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Not having flown one, I've been quite surprised to read about the intricacies of the 135's fuel system. Having to push fuel around like this at low fuel states on a small helicopter seems to me to be a design "gotcha", if ever there was one.
I'm glad to know that the airframe fuel system of the small twin I "fly" is far less complex, being almost completely gravity fed. A transverse main tank drains naturally into a pair of 100kg supply tanks. A booster pump for each engine picks up fuel from a sump at the bottom of each of the supply tanks. Fuel naturally gets to those sumps by gravity. Unless you go horsing the aircraft around at very low fuel states (and the FM warns you not to), all but 5kgs of fuel gets to the engines. Nose up attitudes aren't a problem because the sumps are near the rear of the supply tanks. If a booster pump fails, the engine driven pump is entirely capable of sucking up its own fuel. This is verified by the after start checks.
If a helicopter gets to a really low fuel state, the pilot will generally be thinking about slowing down, making an approach, then landing. All of those things require a nose up attitude....... Yet on a 135, this is precisely when there is a potential fuel supply problem. Flawed design, imho.
I'm glad to know that the airframe fuel system of the small twin I "fly" is far less complex, being almost completely gravity fed. A transverse main tank drains naturally into a pair of 100kg supply tanks. A booster pump for each engine picks up fuel from a sump at the bottom of each of the supply tanks. Fuel naturally gets to those sumps by gravity. Unless you go horsing the aircraft around at very low fuel states (and the FM warns you not to), all but 5kgs of fuel gets to the engines. Nose up attitudes aren't a problem because the sumps are near the rear of the supply tanks. If a booster pump fails, the engine driven pump is entirely capable of sucking up its own fuel. This is verified by the after start checks.
If a helicopter gets to a really low fuel state, the pilot will generally be thinking about slowing down, making an approach, then landing. All of those things require a nose up attitude....... Yet on a 135, this is precisely when there is a potential fuel supply problem. Flawed design, imho.
Any 412 pilot would be well advised to understand the implications of failure to have the transfer pumps on as well, depending upon the initial the fuel load prior to flight. It's normal to have them on at all times it must be said.
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No no no no no no no
There are so many people making incorrect assumptions here about the fuel system.
I have 3000 hours on type, the majority being night police. I cycled the switches on hundreds of occasions, it's NOT complicated or dangerous. There SHOULD be plenty of clues well before things get dangerous. There are two pumps to allow for different attitudes and flaring on landing has zero effect because the fuel is in the supplies.
Really, it's not that complicated or terrible as long as the gauges are not stuck on full of course
There are so many people making incorrect assumptions here about the fuel system.
I have 3000 hours on type, the majority being night police. I cycled the switches on hundreds of occasions, it's NOT complicated or dangerous. There SHOULD be plenty of clues well before things get dangerous. There are two pumps to allow for different attitudes and flaring on landing has zero effect because the fuel is in the supplies.
Really, it's not that complicated or terrible as long as the gauges are not stuck on full of course
Do you guys make this sh1t up as you go along?
In order to recover the transfer pumps in the main tanks with fuel (which will after a while cancel the F pump caption even with the transfer pump switched off), TC said they used a nod -ie nose down - which moves fuel from the supply tanks (the ones which feed the engines) to the main tanks through the overflow pipes.
Without the transfer pumps running, it would need enough nose up for the fuel to flow back from the main tanks, through the overflow pipes to the supply tanks in order to keep the level in the supply tanks high enough.
It is possible - as the report shows, for more fuel to be shunted forward than expected and for the 4 kg difference between 1 and 2 supply tanks (to prevent both engines flaming out together) to be eroded if the aircraft is manouevered at low speed out of balance.
Crab,
"In order to recover the transfer pumps in the main tanks with fuel (which will after a while cancel the F pump caption even with the transfer pump switched off)" No it won't - Transfer pump OFF = Caption ON.
"which moves fuel from the supply tanks (the ones which feed the engines) to the main tanks through the overflow pipes."
No, it doesn't. It allows the fuel settled at the rear of the MAIN tank to slosh forward over the front transfer pump - which will clear the caption.
We are talking about a gentle nod - nothing aerobatic.
"In order to recover the transfer pumps in the main tanks with fuel (which will after a while cancel the F pump caption even with the transfer pump switched off)" No it won't - Transfer pump OFF = Caption ON.
"which moves fuel from the supply tanks (the ones which feed the engines) to the main tanks through the overflow pipes."
No, it doesn't. It allows the fuel settled at the rear of the MAIN tank to slosh forward over the front transfer pump - which will clear the caption.
We are talking about a gentle nod - nothing aerobatic.
Fortyodd - apologies, you are quite correct, I misread the report about the transfer pumps.
However, the nose down will, even just 5 degrees, according to the report allow fuel from the supply tanks to move to the main tank - doesn't it?
I gather it was widely known that the 'nod' would deplete the supply tanks by a few Kg, but not by as much as the tests showed.
However, the nose down will, even just 5 degrees, according to the report allow fuel from the supply tanks to move to the main tank - doesn't it?
I gather it was widely known that the 'nod' would deplete the supply tanks by a few Kg, but not by as much as the tests showed.
Crab,
Yes it will - if the level in the supply tanks is high enough to let it do so - where, if the transfer pumps are switched on, they will pump it back again. See the appendix B at the end of the report where it give a good set of illustrations.
Yes it will - if the level in the supply tanks is high enough to let it do so - where, if the transfer pumps are switched on, they will pump it back again. See the appendix B at the end of the report where it give a good set of illustrations.
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Goggles in a woolly hat in door pocket works. I'm 5'10" and have my seat fully up and the goggs don't touch the roof in the stowed position. But taller pilots have problems with clearance, our aircraft has marks on the perspex to prove it.
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Jayteeto
Well said 
No no no no no no no
There are so many people making incorrect assumptions here about the fuel system.
I have 3000 hours on type, the majority being night police. I cycled the switches on hundreds of occasions, it's NOT complicated or dangerous. There SHOULD be plenty of clues well before things get dangerous. There are two pumps to allow for different attitudes and flaring on landing has zero effect because the fuel is in the supplies.
Really, it's not that complicated or terrible as long as the gauges are not stuck on full of course
There are so many people making incorrect assumptions here about the fuel system.
I have 3000 hours on type, the majority being night police. I cycled the switches on hundreds of occasions, it's NOT complicated or dangerous. There SHOULD be plenty of clues well before things get dangerous. There are two pumps to allow for different attitudes and flaring on landing has zero effect because the fuel is in the supplies.
Really, it's not that complicated or terrible as long as the gauges are not stuck on full of course
jayteeto
I have 3000 hours on type, the majority being night police. I cycled the switches on hundreds of occasions, it's NOT complicated or dangerous.
I have 3000 hours on type, the majority being night police. I cycled the switches on hundreds of occasions, it's NOT complicated or dangerous.
you'd never switch them both off, right?
Is there ANY airborne situation at all, where you'd switch off fwd AND aft transfer pump?
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Is there ANY airborne situation at all, where you'd switch off fwd AND aft transfer pump?
Purveyor of Egg Liqueur to Lucifer
Reely340;
Is there ANY airborne situation at all, where you'd switch off fwd AND aft transfer pump?
Is there ANY airborne situation at all, where you'd switch off fwd AND aft transfer pump?
chopjock
I can answer that, YES. When flying with full tanks!
I can answer that, YES. When flying with full tanks!
1. Pump failure.
2. Pump running dry.
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Reely said: "
I have now read the report front to back three times and I have come to the conclusion that this is the most likely scenario. (I also went back and re-read the 170 odd pages of the first thread which was, errr, interesting).
I found 1.16.2, the G-NWEM incident, (just two weeks after this incident!), shocking. Not only were the supply tanks stuck on full during the ground test but the indicated level of the main tank was depleting with xfer pumps off! It would be easy for none of the crew to question that - (confirmatory bias). It would not prompt a check of the xfer pumps. I note with trepidation that neither would the fuel caution caption come on, and xfer pump captions do not come on if a pump that was switched off after running dry would not come on again if re-immersed. It only comes on after 3 mins of the pumps running dry or after 3 minutes of being switched off while immersed.
Falcon900 said
This is a really good point, we are all influenced by our past experience. It is easy to sit in an armchair and say it is inconceivable that 3 people ignored obvious warnings. Firstly, two of those people might have been comforted by a digital blue display more than a red lamp and audible tone (that the pilot had already acknowledged and cancelled several times).
Supposing I said to you the the oil pressure reading for your main rotor gearbox fluctuated wildly then suddenly went to zero, and that you knew that if it was correct you had 8 minutes max before you dropped like a stone out of the sky. Would you stake your life on that reading being wrong? I bet not a single person here would say that they would fly on and try to make base.
But that is exactly what happened here:
Investigation: Faulty filter cover, pilot error caused fatal Marine helicopter crash
The pilots were influenced by recent MRGB pressure sensor and transducer maintenance work and they were prepared to stake their life on a false indication.
The finding of the position of the prime and xfer pump switches are largely irrelevant, and in fact proven to be unreliable, although the photographic evidence favours at least one prime switch being OFF. I do not believe the pilot has confused the prime and xfer pump switches, for one thing, the caution captions for the prime pumps would have gone on if he has reached up for the xfer pumps in response to a xfer pump caution light coming on.
It has been said that the cause of the accident was the xfer pumps being off. Not strictly true, the cause of the accident was the pilot failing to put them on, their OFF position is the symptom not the cause.
I believe he had conflicting information and unfortunately, possibly due to past experience (someone on the previous thread mentioned running the tanks down to zero on a ground test and the Warning Unit red LOW FUEL 1 and 2 never coming on) chose to ignore procedure and rely on one of two information sources.
My vision of possible occurrences after reading the final report:
- both supply tanks did falsely indicated full on the CAD
(a 0.5ml (!) water globule at the capacitance based fuel sensors can do the trick, see p. 54, G-NWEM)
- "Low Fuel" Warnings (driven by correctly functioning thermistors), were considered as acting up "shi**y EC".
The were acknowledged as being irrelevant, because of (incorrect) triple "plenty fuel" indication on the CAD.
That is the reason why he flew that final task, although he just had acknowledged the Low Fuel warnings, multiple times!"
- both supply tanks did falsely indicated full on the CAD
(a 0.5ml (!) water globule at the capacitance based fuel sensors can do the trick, see p. 54, G-NWEM)
- "Low Fuel" Warnings (driven by correctly functioning thermistors), were considered as acting up "shi**y EC".
The were acknowledged as being irrelevant, because of (incorrect) triple "plenty fuel" indication on the CAD.
That is the reason why he flew that final task, although he just had acknowledged the Low Fuel warnings, multiple times!"
I found 1.16.2, the G-NWEM incident, (just two weeks after this incident!), shocking. Not only were the supply tanks stuck on full during the ground test but the indicated level of the main tank was depleting with xfer pumps off! It would be easy for none of the crew to question that - (confirmatory bias). It would not prompt a check of the xfer pumps. I note with trepidation that neither would the fuel caution caption come on, and xfer pump captions do not come on if a pump that was switched off after running dry would not come on again if re-immersed. It only comes on after 3 mins of the pumps running dry or after 3 minutes of being switched off while immersed.
Falcon900 said
"The AAIB report makes reference to issues with the fuel probes on G-SPAO earlier in the year, and explains that these were resolved. It does not explain whether the faults became apparent while the aircraft was in flight, and who was flying it at the time. I am wondering whether the accident pilot had some history with spurious fuel warnings on this aircraft."
Supposing I said to you the the oil pressure reading for your main rotor gearbox fluctuated wildly then suddenly went to zero, and that you knew that if it was correct you had 8 minutes max before you dropped like a stone out of the sky. Would you stake your life on that reading being wrong? I bet not a single person here would say that they would fly on and try to make base.
But that is exactly what happened here:
Investigation: Faulty filter cover, pilot error caused fatal Marine helicopter crash
The pilots were influenced by recent MRGB pressure sensor and transducer maintenance work and they were prepared to stake their life on a false indication.
The finding of the position of the prime and xfer pump switches are largely irrelevant, and in fact proven to be unreliable, although the photographic evidence favours at least one prime switch being OFF. I do not believe the pilot has confused the prime and xfer pump switches, for one thing, the caution captions for the prime pumps would have gone on if he has reached up for the xfer pumps in response to a xfer pump caution light coming on.
It has been said that the cause of the accident was the xfer pumps being off. Not strictly true, the cause of the accident was the pilot failing to put them on, their OFF position is the symptom not the cause.
I believe he had conflicting information and unfortunately, possibly due to past experience (someone on the previous thread mentioned running the tanks down to zero on a ground test and the Warning Unit red LOW FUEL 1 and 2 never coming on) chose to ignore procedure and rely on one of two information sources.
I can answer that, YES. When flying with plenty / full tanks!
Is there ANY airborne situation at all, where you'd switch off fwd AND aft transfer pump?
That would of course leave you with the contents of the SUPPLY tanks remaining.
Depending on your operation IFR, VFR or Ops Manual or NAA reserve requirements that may never or rarely happen if remaining within those constraints.
What do you think drove the design with respect to the SUPPLY tank size?
Interestingly should you fit the "FUEL FLOW" option kit - Time to END is predicated only on the contents of the MAIN tank.
Last edited by RVDT; 27th Oct 2015 at 18:02.
Avoid imitations
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Really, it's not that complicated or terrible as long as the gauges are not stuck on full of course
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Page 5 &6
22:06 - Arrived on task with approx 122 kgs of fuel………... Completed task then went on another task.
[76 kgs in main tank, 46 kgs (25/21) in the supply tanks]
22:09 - Arrived on task with approx 113 kgs of fuel………... Completed task then went to another task.
[76 kgs in main tank, 37 kgs (20/17) in supply tanks]
22:14 - Arrived on task with approx 100 kgs of fuel……...... Completed task and prepared to rtb.
[76 kgs in main tank, 24 kg (14/10) in supply tanks]
22:19 - Prepare to rtb with approx 86 kgs of fuel………...…... Informed ATC of intent rtb, no concerns.
[76 kgs in main tank, 10 kgs (7/3) in supply tanks]
I realise the AAIB can only report the findings, but something was not quite right and it's not, imho, simply the switch positions !
[76 kgs in main tank, 46 kgs (25/21) in the supply tanks]
22:09 - Arrived on task with approx 113 kgs of fuel………... Completed task then went to another task.
[76 kgs in main tank, 37 kgs (20/17) in supply tanks]
22:14 - Arrived on task with approx 100 kgs of fuel……...... Completed task and prepared to rtb.
[76 kgs in main tank, 24 kg (14/10) in supply tanks]
22:19 - Prepare to rtb with approx 86 kgs of fuel………...…... Informed ATC of intent rtb, no concerns.
[76 kgs in main tank, 10 kgs (7/3) in supply tanks]
I realise the AAIB can only report the findings, but something was not quite right and it's not, imho, simply the switch positions !
Last edited by SilsoeSid; 27th Oct 2015 at 22:01. Reason: Typo, thanks Pozidrive :)
Also interesting that apparently there probably was no F PUMP FWD or AFT CAUTION to prompt selecting the pumps off if the numbers are correct in the reconstruction and flight testing. What prompted the action to turn them OFF? There should have been a CAUTION after they were selected OFF though.
This is also backed up by the amount of fuel found in the aircraft.
Also it is apparent that if you fly a ball width to the right out of balance that you can reduce the differential in the SUPPLY tanks to "not much at all" ~ 32 seconds.
In "balance" the 135 flies left wing down - take a look at the STBY AI installation or the primary AI on level ground. So the differential if flown in balance might actually be greater than 4 kg.
This is also backed up by the amount of fuel found in the aircraft.
Also it is apparent that if you fly a ball width to the right out of balance that you can reduce the differential in the SUPPLY tanks to "not much at all" ~ 32 seconds.
In "balance" the 135 flies left wing down - take a look at the STBY AI installation or the primary AI on level ground. So the differential if flown in balance might actually be greater than 4 kg.