Police helicopter crashes onto Glasgow pub
I just can't see why they plumb the two pumps into one supply instead of each pump having a teed supply to each tank.
Join Date: Jan 2008
Location: UK
Age: 69
Posts: 292
Likes: 0
Received 0 Likes
on
0 Posts
AnFI 
'Simplicity' is all relative. The first aircraft I owned had the fuel tank in front of the cockpit and the gauge consisted of a cork on a welding rod poked through the filler cap. It never failed and there was no need to dip or sight-check the tank as you could feel the splash of the cork. The main fuel pump was an engine driven diaphragm with a car-type electric diaphragm as backup. The aircraft is still flying after nearly forty-five years service, with no reportable incidents, which makes it one of the most 'reliable' aircraft flying. Or does it?
As for fixed vs rotary wing, as a kid I used to make free-flight glow-plug model fixed wing planes (designed to be highly stable in all axes). They came down in a corkscrew after the engine stopped, of course, which puzzled me as a kiddie. I've never heard of a free-flight helicopter with no R/C or some kind of stabilising device (mechanical or electronic gyro,....). Even the simplest helicopter has far more moving engineered parts than a fixed-wing.
Helicopters fundamentally do not have to have 'FUEL SYSTEMS' with 5 fuel tanks with 6 fuel pumps 3 guages 4 non-return valves, 5 warning lights etc etc
Please stop refering to a helicopter as a complex machine and an aeroplane as simple.
Please stop refering to a helicopter as a complex machine and an aeroplane as simple.
As for fixed vs rotary wing, as a kid I used to make free-flight glow-plug model fixed wing planes (designed to be highly stable in all axes). They came down in a corkscrew after the engine stopped, of course, which puzzled me as a kiddie. I've never heard of a free-flight helicopter with no R/C or some kind of stabilising device (mechanical or electronic gyro,....). Even the simplest helicopter has far more moving engineered parts than a fixed-wing.
Join Date: Dec 2013
Location: Canada
Posts: 13
Likes: 0
Received 0 Likes
on
0 Posts
Manny spinner
Sorry the math has been done around the world that's why Helos fly offshore. If it was cheaper another way the oil companies would do it.
Helos save a lot of lives, yes there are accidents but far less than in most other areas - medical being one. I don't mean air ambulance the mistakes in hospital are exponential above aviation never mind helicopters. First world....
Helos save a lot of lives, yes there are accidents but far less than in most other areas - medical being one. I don't mean air ambulance the mistakes in hospital are exponential above aviation never mind helicopters. First world....
Join Date: Dec 2008
Location: N/A
Posts: 845
Likes: 0
Received 0 Likes
on
0 Posts
FMEA and CA
Henry - thank you for that educational point.
I'd be fascinated to see the maths and figures used for a real life FMEA. It would be interesting to see how the various factors are determined and whether wider implications are taken into account.
For example when mitigating engine failure risk (by using two engines) are the consequent additional risks factored in? (like: pilot closing the wrong throttle(happens), critical components having less margin, worse autorotation performance, more complex gearbox (malfuntions), reduced payload/utility, fuel system complications (eg the A109 in Wales)). Reliability of FMEA work? - is that factored in?
What severity is assosciated with ditching (very servere or low risk?) - when a twin flys over a 'safe assured landing' surface are the additional risks consequent to twins factored? Is the ratio of time exposed to time with 'safe landing assured' factored?
I presume the answers to most of those questions is yes - but it would still be fascinating to analyse a real example.
Helicopters are inherently Simplex with many neccessarily Single Point Failure Critical Components - I like the fact that those Simplex components appear impirically to be very reliable, whereas many of the Duplex components do not seem to be (I suppose the logic is that they don't need to be, theoretically?).
But you cannot disagree complexity provides many more opportunities to fail to spot the obscure consequences - the "Unknown Unkowns"
I agree FMEA should provide a framework for answering the complex addition of systems - IF the INPUT DATA and ASSUMPTIONS are correct. ("garbage in garbage out" - right?)
Seems, for the North Sea, the maths is dubious (on first inspection) wrt Ditching. If the risk of ditching is severe enough to justify 2 engines, and this risk is mitigated by 2 engines then why waste payload on floats? If floats are neccesary to mitigate the (frequent) need to ditch and they are effective (which they appear to pretty good) then going to extreme capacity reducing measures (2 engines) to avoid ditching can't be worth it?
Maybe, making 'all-weather water landing' risk-free, could help straighten out the maths?
I'd be fascinated to see the maths and figures used for a real life FMEA. It would be interesting to see how the various factors are determined and whether wider implications are taken into account.
For example when mitigating engine failure risk (by using two engines) are the consequent additional risks factored in? (like: pilot closing the wrong throttle(happens), critical components having less margin, worse autorotation performance, more complex gearbox (malfuntions), reduced payload/utility, fuel system complications (eg the A109 in Wales)). Reliability of FMEA work? - is that factored in?
What severity is assosciated with ditching (very servere or low risk?) - when a twin flys over a 'safe assured landing' surface are the additional risks consequent to twins factored? Is the ratio of time exposed to time with 'safe landing assured' factored?
I presume the answers to most of those questions is yes - but it would still be fascinating to analyse a real example.
Helicopters are inherently Simplex with many neccessarily Single Point Failure Critical Components - I like the fact that those Simplex components appear impirically to be very reliable, whereas many of the Duplex components do not seem to be (I suppose the logic is that they don't need to be, theoretically?).
But you cannot disagree complexity provides many more opportunities to fail to spot the obscure consequences - the "Unknown Unkowns"
I agree FMEA should provide a framework for answering the complex addition of systems - IF the INPUT DATA and ASSUMPTIONS are correct. ("garbage in garbage out" - right?)
Seems, for the North Sea, the maths is dubious (on first inspection) wrt Ditching. If the risk of ditching is severe enough to justify 2 engines, and this risk is mitigated by 2 engines then why waste payload on floats? If floats are neccesary to mitigate the (frequent) need to ditch and they are effective (which they appear to pretty good) then going to extreme capacity reducing measures (2 engines) to avoid ditching can't be worth it?
Maybe, making 'all-weather water landing' risk-free, could help straighten out the maths?
Last edited by AnFI; 26th Dec 2013 at 02:04. Reason: eliminating unintended rudeness - hopefully before seen! ;)
Join Date: Dec 2001
Location: Philadelphia PA
Age: 73
Posts: 1,835
Likes: 0
Received 2 Likes
on
2 Posts
It's worth remembering that any helicopter certified for Category A operations has as many redundancies and complications as a 737 or A320 in a much smaller package with many more variables in it's operation.
Join Date: Dec 2008
Location: N/A
Posts: 845
Likes: 0
Received 0 Likes
on
0 Posts
http://en.wikipedia.org/wiki/Failure_mode_and_effects_analysis
Failure Mode and Effects Analysis (FMEA)
The principle is used all over the place in assessing risk - I'd love to see a real analysis though. It may be flawed.
Failure Mode and Effects Analysis (FMEA)
The principle is used all over the place in assessing risk - I'd love to see a real analysis though. It may be flawed.
Join Date: Dec 2013
Location: Canada
Posts: 13
Likes: 0
Received 0 Likes
on
0 Posts
Anfi
Interesting discussion but I will have to leave the math to Shawn!
Curious when you refer to several issues that are not risk related ie payload capacity - yes has an effect on risk in number of trips and exposure but no impact on an individual flight. More of a commercial concern.
Why would a dual engine helicopter have assumed worse auto performance design than a single of the same weight? Because designers are anticipating an engine failure?
For offshore flying floats aren't required for an engine failure, they are required for any event that can put you on the water. And I agree it is far too frequent at this point in time.
But my biggest question would be a definition of a "safe and assured landing area". Sounds simplistic - What is that? What weather do you require to assure that? Day? Night? How big an area? Will losing one engine require an immediate landing? Can you continue to a runway? What about a tail rotor problem? These all can be handled very effectively with an appropriate landing area but it isn't a farmers field for a large helicopter, nor is a farmers field required. A landing at an airport would be more appropriate for all these issues.
Curious when you refer to several issues that are not risk related ie payload capacity - yes has an effect on risk in number of trips and exposure but no impact on an individual flight. More of a commercial concern.
Why would a dual engine helicopter have assumed worse auto performance design than a single of the same weight? Because designers are anticipating an engine failure?
For offshore flying floats aren't required for an engine failure, they are required for any event that can put you on the water. And I agree it is far too frequent at this point in time.
But my biggest question would be a definition of a "safe and assured landing area". Sounds simplistic - What is that? What weather do you require to assure that? Day? Night? How big an area? Will losing one engine require an immediate landing? Can you continue to a runway? What about a tail rotor problem? These all can be handled very effectively with an appropriate landing area but it isn't a farmers field for a large helicopter, nor is a farmers field required. A landing at an airport would be more appropriate for all these issues.
Join Date: Dec 2008
Location: N/A
Posts: 845
Likes: 0
Received 0 Likes
on
0 Posts
Thank you - very interesting.
"not risk related ie payload capacity - yes has an effect on risk in number of trips and exposure but no impact on an individual flight. More of a commercial concern."
Yes I was thinking more trips/exposure per payload delivered - a Lynx might take Food or Ammunition a Single Lynx might take both (as might a Gazelle more cost effectively/reliably). So; for example 100Engine.miles against 400Engine.miles (plus all the other doubly exposed failure points)
"assumed worse auto performance design than a single of the same weight?"
I don't think the Single version would be the same weight.... ? Yes - Auto performance generally much better in singles - more rotor energy stored per MAUW?
The floats circular discussion just leads one to conclude that ditching needs to be safer - detachable allweather survival cabins!? *&%£@! perhaps
The other topics make it too big a discussion - but the general theme is the weight justification of where in an airframe design you chose to spend weight on safety - if you spend it on Engines, Gearboxes and Fuel (to supply 2 engines) then for a given weight you have less to spend on critical components (tail rotors, pitch links, tail booms etc)(where the engine may not be one) - Airbags might provide a better yeild? - 2 Pilots might provide a better yeild? etc
OR you just have everything you can think of and make carrying 1 Kilo require 5Kilos of helicopter ?? Not practical?
"not risk related ie payload capacity - yes has an effect on risk in number of trips and exposure but no impact on an individual flight. More of a commercial concern."
Yes I was thinking more trips/exposure per payload delivered - a Lynx might take Food or Ammunition a Single Lynx might take both (as might a Gazelle more cost effectively/reliably). So; for example 100Engine.miles against 400Engine.miles (plus all the other doubly exposed failure points)
"assumed worse auto performance design than a single of the same weight?"
I don't think the Single version would be the same weight.... ? Yes - Auto performance generally much better in singles - more rotor energy stored per MAUW?
The floats circular discussion just leads one to conclude that ditching needs to be safer - detachable allweather survival cabins!? *&%£@! perhaps
The other topics make it too big a discussion - but the general theme is the weight justification of where in an airframe design you chose to spend weight on safety - if you spend it on Engines, Gearboxes and Fuel (to supply 2 engines) then for a given weight you have less to spend on critical components (tail rotors, pitch links, tail booms etc)(where the engine may not be one) - Airbags might provide a better yeild? - 2 Pilots might provide a better yeild? etc
OR you just have everything you can think of and make carrying 1 Kilo require 5Kilos of helicopter ?? Not practical?
Join Date: Dec 2013
Location: Canada
Posts: 13
Likes: 0
Received 0 Likes
on
0 Posts
ANFI
It's an interesting discussion of where to invest. My subjective experience is two engines are better than one and yes it made a difference on more than one occasion - including an airliner as I recall over the ocean...
Where money gets invested is very complex but I disagree with your premise that you can't have it all because at the end of the day that's the goal - you have it all - anything less these days is not acceptable. Especially when your flying 400 km over the Arctic Ocean with limited options. Outside of aviation there seems to be no tolerance for risk exposure, you have to have it all.
Where money gets invested is very complex but I disagree with your premise that you can't have it all because at the end of the day that's the goal - you have it all - anything less these days is not acceptable. Especially when your flying 400 km over the Arctic Ocean with limited options. Outside of aviation there seems to be no tolerance for risk exposure, you have to have it all.
Join Date: Dec 2008
Location: N/A
Posts: 845
Likes: 0
Received 0 Likes
on
0 Posts
interesting indeed - i wonder if that is really true?
Do all helicopters have to be S92s ? Isn't reliability worth anything?
AS350 in the Arctic does pretty well - Bo105's not so well?
Do all helicopters have to be S92s ? Isn't reliability worth anything?
AS350 in the Arctic does pretty well - Bo105's not so well?
ANFI
Reduced payload with two engines? Less margin on critical components?
What tosh you write.
For example when mitigating engine failure risk (by using two engines) are the consequent additional risks factored in? (like: pilot closing the wrong throttle(happens), critical components having less margin, worse autorotation performance, more complex gearbox (malfuntions), reduced payload/utility, fuel system complications (eg the A109 in Wales)). Reliability of FMEA work? - is that factored in?
What tosh you write.
I think this thread has run its course.
What tosh you write.
An Ffing Idiot
A sensible discussion of what might have gone wrong is fair, but your wanton expositions are offensive. They are also not new. Exactly these themes have been covered before, by you, and responded to genuinely from people who know a thing or two. But the time they took to share their experience and the reasoning behind design and operational philosophy made little impression on you. No theme too great or small for your musings eh? And why listen (read) when you can talk (write).
Request: Start a personal thread and then people can join you there and discuss stuff til the cows come home. You may even get a bit of a fan following.
Join Date: Jul 2013
Location: Uk
Age: 67
Posts: 59
Likes: 0
Received 0 Likes
on
0 Posts
MightyGem
[QUOTE]The two pumps supply both tanks, not just one.
Which is why I said. Each pump should have a teed supply to both tanks, ie each pump should be capable of supplying both supply tanks individually and not through a shared pipe using one way valves. it's the valves that are the weak point.
[QUOTE]The two pumps supply both tanks, not just one.
Which is why I said. Each pump should have a teed supply to both tanks, ie each pump should be capable of supplying both supply tanks individually and not through a shared pipe using one way valves. it's the valves that are the weak point.
Join Date: Dec 2007
Location: uk
Posts: 419
Likes: 0
Received 0 Likes
on
0 Posts
Pie,
Can you say why you think the failure of the nrv in the transfer system would lead to the loss of all the fuel from both supply tanks (back into the main tank) and lead to both engines flaming out before the crew could react to the various supply tank contents warnings?
Can you say why you think the failure of the nrv in the transfer system would lead to the loss of all the fuel from both supply tanks (back into the main tank) and lead to both engines flaming out before the crew could react to the various supply tank contents warnings?
Join Date: Dec 2008
Location: N/A
Posts: 845
Likes: 0
Received 0 Likes
on
0 Posts
"An Ffing Idiot"
NOW STEADY ON - that is rude and offensive - against the rules here and doesn't help balanced discussion. Withdraw it and apologise please.
So far on this threat NO-ONE has pointed out that the complexity of the design may be (probably is) a contributor to the accident.
Yes 'MY' theme is the maths behind twins is flawed - this balancing view needs to be heard.
Heard something you don't like?
Thread must have run it's course then ... revert to insults.
Anyway I don't want to piss on the twin bonfire too much I just want to sneek a little balance in here...
If you can't win a debate on merit you probably can't!
Just go with the insults and debase the discussion - why not?
The public beleive helicopters fall out of the sky when the engine(s) stop and so they demand 2 engines.
There is not only upside from 2 engines as pointed out by JimL there are negatives which need to be out weighed - a balanced understanding of that is in everybodies interest.
it certainly does not merit your disgusting insults! REF!!
NOW STEADY ON - that is rude and offensive - against the rules here and doesn't help balanced discussion. Withdraw it and apologise please.
So far on this threat NO-ONE has pointed out that the complexity of the design may be (probably is) a contributor to the accident.
Yes 'MY' theme is the maths behind twins is flawed - this balancing view needs to be heard.
Heard something you don't like?
Thread must have run it's course then ... revert to insults.
Anyway I don't want to piss on the twin bonfire too much I just want to sneek a little balance in here...
If you can't win a debate on merit you probably can't!
Just go with the insults and debase the discussion - why not?
The public beleive helicopters fall out of the sky when the engine(s) stop and so they demand 2 engines.
There is not only upside from 2 engines as pointed out by JimL there are negatives which need to be out weighed - a balanced understanding of that is in everybodies interest.
it certainly does not merit your disgusting insults! REF!!
When your arguments are substantiated by engineering design based fact regarding reduced critical component margin or worse autorotation performance caused by having 2 engines, confused pilots, complicated fuel systems or reduced payloads, I may listen.
It is you who fails to provide any merit for your "statements", they are not arguments because they lack any cogency.
Heard something I don't like? Not at all, I can hardly wait for the next installment.
It is you who fails to provide any merit for your "statements", they are not arguments because they lack any cogency.
Heard something I don't like? Not at all, I can hardly wait for the next installment.