GOM - yet another ditching
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....except the 'papers' forgot we have been running the NP route for decades, I was a very young SLF in 1977 flying from CPH to ANC with SAS and the NP was one of the waypoints. What they meant to say was South (same, same, but different as they say here) Pole. 330 minutes on one engine at MCT, I'm glad it's the cripple seven which was approved and not the scare bus.
TOD
(I'm too old to get into the helicopter with one or two engine argument - I just know which I prefer!)
TOD
(I'm too old to get into the helicopter with one or two engine argument - I just know which I prefer!)
js0798,
...and that is because the probability of one failure followed by a second from an unconnected cause ('a' followed by 'b') is 1 x 10**-10.
The issue, conveniently forgotten by AnFI, is not the probability of an engine failure – which remains constant at about 1 x 10**-5/hour - but the consequence of a failure if it occurs over a hostile environment (a hostile environment is where safe-forced-landing cannot be carried out – i.e. resulting in a catastrophic event).
What in fact is being advocated by js0798 is not flying a twin over the NP, but a single.
The statistics have not changed;they are just conveniently ignored whenever it suits for the purpose of recycling the argument.
... mathematically speaking!
Jim
...and that is because the probability of one failure followed by a second from an unconnected cause ('a' followed by 'b') is 1 x 10**-10.
The issue, conveniently forgotten by AnFI, is not the probability of an engine failure – which remains constant at about 1 x 10**-5/hour - but the consequence of a failure if it occurs over a hostile environment (a hostile environment is where safe-forced-landing cannot be carried out – i.e. resulting in a catastrophic event).
What in fact is being advocated by js0798 is not flying a twin over the NP, but a single.
The statistics have not changed;they are just conveniently ignored whenever it suits for the purpose of recycling the argument.
... mathematically speaking!
Jim
Last edited by JimL; 27th Dec 2011 at 07:02. Reason: Emphasis of the conditions of failure.
Now to refresh and old story about the FAA, Three Engined 727's, over-water flight, and life rafts/life jackets and statistics.
The FAA nodded to Eastern's solicitation to do away with overwater flight required flotation gear for flights between NYC and MIA as the over water portion was a short time and not all that far offshore. With permission granted....Eastern removed all the extra weight of the floation gear.
Less than two weeks later....a FE managed to starve all three engines of fuel...caused all three engines to fail nearly simultaneously...smack dab in the middle of the overwater portion of the flight.
The Crew was able to sort out the situation...restarted the engines...and only got a close look at the Oggin.
The over water gear went back into the aircraft....and I would suppose the FE got the ass kicking of his life shortly after landing!
Statistics are just that statistics....the probability of a second engine failure immediately following the failure of the other engine is only a guess and not a guarantee. They are independent events. There is no guarantee an engine will last more than 30 seconds after installation or that it will go to TBO. Five hours is a very long time to be hanging on one Donk in something like an Air Bus or Boeing with hundreds of folks wondering about how they have lived their lives and wondering about the final tally!
When the first Donk dies.....you are now rolling the dice big time....each second that goes by is another roll of the dice. I like to hedge my bets so I don't lose everything.
There is no such thing as too much power...too many engines....too much fuel.
The FAA nodded to Eastern's solicitation to do away with overwater flight required flotation gear for flights between NYC and MIA as the over water portion was a short time and not all that far offshore. With permission granted....Eastern removed all the extra weight of the floation gear.
Less than two weeks later....a FE managed to starve all three engines of fuel...caused all three engines to fail nearly simultaneously...smack dab in the middle of the overwater portion of the flight.
The Crew was able to sort out the situation...restarted the engines...and only got a close look at the Oggin.
The over water gear went back into the aircraft....and I would suppose the FE got the ass kicking of his life shortly after landing!
Statistics are just that statistics....the probability of a second engine failure immediately following the failure of the other engine is only a guess and not a guarantee. They are independent events. There is no guarantee an engine will last more than 30 seconds after installation or that it will go to TBO. Five hours is a very long time to be hanging on one Donk in something like an Air Bus or Boeing with hundreds of folks wondering about how they have lived their lives and wondering about the final tally!
When the first Donk dies.....you are now rolling the dice big time....each second that goes by is another roll of the dice. I like to hedge my bets so I don't lose everything.
There is no such thing as too much power...too many engines....too much fuel.
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And then there was the Canadian Airbus that ran out of fuel and did a dead stick landing in the Azores.
Actually, while we are on the subject of safety and statistics, I would like to mention survival gear and the GOM. I'm aware that in the North Sea and Canada, amoung other northern enviroments, survuval suits are required for passengers and crew. In the GOM you may have only a handful of days where the temperatures are below freezing, so there you are - statistically speaking - its not worth the cost or effort to equip everyone with a survival suit.
Back in the 70's flying 206's and looking at the white caps and the cold temperatures, I remembered an article I read in an offshore publication about a hypotheria study done by the University of Vancouver. As a result of that study, they developed a cold water jacket for just such occasions. After some effort, I bought a Thermal Float Jacket from Mustang Sportswear and either wore it or carried it with me for years when it was cold- until I, sort of, outgrew it.
Like SAS says statistics are a crap shoot.
Actually, while we are on the subject of safety and statistics, I would like to mention survival gear and the GOM. I'm aware that in the North Sea and Canada, amoung other northern enviroments, survuval suits are required for passengers and crew. In the GOM you may have only a handful of days where the temperatures are below freezing, so there you are - statistically speaking - its not worth the cost or effort to equip everyone with a survival suit.
Back in the 70's flying 206's and looking at the white caps and the cold temperatures, I remembered an article I read in an offshore publication about a hypotheria study done by the University of Vancouver. As a result of that study, they developed a cold water jacket for just such occasions. After some effort, I bought a Thermal Float Jacket from Mustang Sportswear and either wore it or carried it with me for years when it was cold- until I, sort of, outgrew it.
Like SAS says statistics are a crap shoot.
JS,
It is not so much the air temperature but the water temp that creates the real hazard...as water is a much better remover of body heat than air.
Add in the wind to arrive at a chill factor and air temp can be an issue as well.
Now that the rigs are much further out in the GOM...and flying shuts down just a half hour before dark for single engined helicopters....one might be a very long way from help and thus be confronted with a survival situation that includes darkness, a bit of sea state, cold air and cold water....and if not in a raft...it could be a very cold night.
I will bet there are far more periods of time an exposure suit is needed than currently thought, if an honest review of the situation was done.
But then I love the comment...."statistically it is not worth equipping Pilots/Pax with suits!"
It is not so much the air temperature but the water temp that creates the real hazard...as water is a much better remover of body heat than air.
Add in the wind to arrive at a chill factor and air temp can be an issue as well.
Now that the rigs are much further out in the GOM...and flying shuts down just a half hour before dark for single engined helicopters....one might be a very long way from help and thus be confronted with a survival situation that includes darkness, a bit of sea state, cold air and cold water....and if not in a raft...it could be a very cold night.
I will bet there are far more periods of time an exposure suit is needed than currently thought, if an honest review of the situation was done.
But then I love the comment...."statistically it is not worth equipping Pilots/Pax with suits!"
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Survival Suits - Yes or No
There are some very simple answers to that question:-
If 'Time-to-Rescue' is longer than worst case 'Survival-Time' = Yes
(just ask those that maintain that the reverse is the case to prove it with a realistic exercise or two).
If the hazards associated with heat-stress (for the pilots) are greater than the risk of a ditching scenario = No.
The remedy that seems appropriate is that in normal summer conditions during daylight hours (flight completed in daylight) then a survival suit may not be worn. During winter and/or stormy conditions or when any portion of he flight is at night then a suit is to be recommended.
In Europe where the concept of 'Duty of Care' exists the employer would have to demonstrate that to supply additional safety equipment would involve the employer in 'unreasonable additional costs'. It is difficult for any multi-million dollar company to cry 'foul' at a $1000 investment per employee.
G.
If 'Time-to-Rescue' is longer than worst case 'Survival-Time' = Yes
(just ask those that maintain that the reverse is the case to prove it with a realistic exercise or two).
If the hazards associated with heat-stress (for the pilots) are greater than the risk of a ditching scenario = No.
The remedy that seems appropriate is that in normal summer conditions during daylight hours (flight completed in daylight) then a survival suit may not be worn. During winter and/or stormy conditions or when any portion of he flight is at night then a suit is to be recommended.
In Europe where the concept of 'Duty of Care' exists the employer would have to demonstrate that to supply additional safety equipment would involve the employer in 'unreasonable additional costs'. It is difficult for any multi-million dollar company to cry 'foul' at a $1000 investment per employee.
G.
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Four incidents of interest
Azores Deadstick Landing Report REleased - Air Transat
Gimli Glider - Wikipedia, the free encyclopedia
British Airways Flight 9 - Wikipedia, the free encyclopedia
Air France 447 Flight-Data Recorder Transcript - What Really Happened Aboard Air France 447 - Popular Mechanics
The article from popular mechanics is disturbing but very accurate
Cheers
Gimli Glider - Wikipedia, the free encyclopedia
British Airways Flight 9 - Wikipedia, the free encyclopedia
Air France 447 Flight-Data Recorder Transcript - What Really Happened Aboard Air France 447 - Popular Mechanics
The article from popular mechanics is disturbing but very accurate
Cheers
Of course there are some causes which would cause a multiple engine out condition, poor fuel, volcanic ash etc.
However, statistically any engine is likely to suffer a malfunction induced failure before a multi engine out condition is caused by an environmental factor or an incident like the one that happened to Air Transat.
The fact remains that a single engine failure leading to an autorotation and water landing in the GOM is not actually that uncommon. Add some wind, no survival suits, winter, close to the end of daylight etc and you have several "escalation" factors, all of which could be mitigated by the use of twin engined helicopters.
However, statistically any engine is likely to suffer a malfunction induced failure before a multi engine out condition is caused by an environmental factor or an incident like the one that happened to Air Transat.
The fact remains that a single engine failure leading to an autorotation and water landing in the GOM is not actually that uncommon. Add some wind, no survival suits, winter, close to the end of daylight etc and you have several "escalation" factors, all of which could be mitigated by the use of twin engined helicopters.
In my earlier post I had pointed out (now emphasized) that the discussion was about engine failures due to unconnected causes – all the cases that have been referenced since were failures due to connected causes.
As Geoff has pointed out, hostility exists when the rescue time exceeds the survival time under the prevailing conditions. Here is a case in point:
There was a ‘reasonably probable’ expectation (R=1 x 10xx-5 per flight hour) that this engine would fail.
Jim
As Geoff has pointed out, hostility exists when the rescue time exceeds the survival time under the prevailing conditions. Here is a case in point:
On February 16, 2003, approximately 1225 central standard time, a Bell 407 single-engine helicopter, landed offshore (FAA speak for ditched) in the Gulf of Mexico following a loss of engine power.
The helicopter was owned and operated under Title 14 Code of Federal Regulations Part 135, by Houston Helicopters, Inc., at Pearland, Texas. The pilot and one passenger received fatal injuries, and three passengers received serious injuries. The helicopter has not been recovered and is presumed destroyed.
Note: these injuries were, in fact, the onset of hypothermia due to exposure.
Visual meteorological conditions prevailed for the flight, and a company visual flight rules (VFR) flight plan was filed for the on-demand air taxi flight.
Approximately 1210, the helicopter departed Harbor Island (Tesoro Heliport) at Ingleside, Texas, for the 26.1 nautical mile flight to the Ensco Rig 84 (Matagorda 700 block offshore).
The operator and the dispatcher reported that the pilot transmitted a Mayday call, engine failure, and that he was going to land the helicopter on the water. The Coast Guard at Aransas Pass, Texas, and Corpus Christi, Texas, were notified. Search and rescue was initiated by the operator, Coast Guard, water vessels, and other helicopter operators.
Two of the passengers reported that the helicopter rolled inverted within a few seconds after the landing. The pilot and passengers exited the helicopter, inflated their life vest, and awaited their rescue. Approximately 1425, the pilot and passengers were recovered by the Coast Guard.
The operator, the dispatcher, Coast Guard helicopter pilots, pilots of other search helicopters, and two of the passengers reported the winds were from the north at 25-40 mph with 5 to 9-foot seas (Sea State 5).
Where transient hostile conditions obtain, the operator (or oil company) has a duty of care to ensure that the Risk is Managed using ‘adverse weather policy’ - all the precursors were there.The helicopter was owned and operated under Title 14 Code of Federal Regulations Part 135, by Houston Helicopters, Inc., at Pearland, Texas. The pilot and one passenger received fatal injuries, and three passengers received serious injuries. The helicopter has not been recovered and is presumed destroyed.
Note: these injuries were, in fact, the onset of hypothermia due to exposure.
Visual meteorological conditions prevailed for the flight, and a company visual flight rules (VFR) flight plan was filed for the on-demand air taxi flight.
Approximately 1210, the helicopter departed Harbor Island (Tesoro Heliport) at Ingleside, Texas, for the 26.1 nautical mile flight to the Ensco Rig 84 (Matagorda 700 block offshore).
The operator and the dispatcher reported that the pilot transmitted a Mayday call, engine failure, and that he was going to land the helicopter on the water. The Coast Guard at Aransas Pass, Texas, and Corpus Christi, Texas, were notified. Search and rescue was initiated by the operator, Coast Guard, water vessels, and other helicopter operators.
Two of the passengers reported that the helicopter rolled inverted within a few seconds after the landing. The pilot and passengers exited the helicopter, inflated their life vest, and awaited their rescue. Approximately 1425, the pilot and passengers were recovered by the Coast Guard.
The operator, the dispatcher, Coast Guard helicopter pilots, pilots of other search helicopters, and two of the passengers reported the winds were from the north at 25-40 mph with 5 to 9-foot seas (Sea State 5).
There was a ‘reasonably probable’ expectation (R=1 x 10xx-5 per flight hour) that this engine would fail.
Jim
you have several "escalation" factors, all of which could be mitigated by the use of twin engined helicopters.
The BO-105's of an Operator sometimes did not meet that commonsense idea....and at least one of their aircraft DITCHED following an engine failure in the cruise portion of the flight returning ashore.
Remember this is the helicopter industry segment that at one time went ten years without granting a "Cost of Living" pay raise to its Pilots.
Cheap is a God down there.....and is worshipped religiously!
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Better and cheaper than using a twin would be just not making the flight. There are boats available, and it's not that long a trip, but most of the passengers I've ever carried would prefer the helicopter over the boat, regardless of the risks.
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The BO-105's of an Operator sometimes did not meet that commonsense idea....and at least one of their aircraft DITCHED following an engine failure in the cruise portion of the flight returning ashore.
After that a series of Brits were seconded into Shell Oil to get a grip.
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After that a series of Brits were seconded into Shell Oil to get a grip.
Sure SAS, the weight and balance issue goes without saying. But I refer really to the newer generation of twins that actually do have some OEI capability. I would not call a BO 105 or a 355F a twin for example because neither really have any credible twin performance.
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... some thoughts
The issue, conveniently forgotten by AnFI
Because
... mathematically speaking!
the probability of one failure followed by a second from an unconnected cause ('a' followed by 'b') is 1 x 10**-10.
Jim - what figure would you put on 'a' following 'b'?
is it in the order of 1in10?
rather than 1 in 100,000?
Would you also agree with me that it's not the risk of forced landing through the 'engine failure' cause but any cause which needs to be factored in?
So:
The other risks from having 2 engines should also be factored in. ie:
the risk of running a complex gearbox (Rgb)
the risk from running all the critical components to a higher load than would be
the risk of major destructive Eng failure etc.
The accidents we see, demonstrate that 1x10^-10 is not relevant.
Also the 'fatalness' of the hostile environment needs attention. You are using the consequence of failure in a hostile area as P=1 , all I was pointing out is that
the consequences need to be much worse than this to justify the unreliability of two engines.... mathematically speaking
it is mathematically speaking much easier to do something about that sized number than a number already this small - 0.0000001
People are generally not good at estimating risk.
Do you carry a knife when you carry a dingy in the cockpit?
Anfi, Jim quite clearly stated that the risk of an unconnected second engine failure (he even underlined it himself) used the square rule, whereas in the Meadows case the second death could not be considered unconnected as both babies were genetically and environmentally linked. One could say that this is analagous to a twin engine installation, however the whole purpose of the Cat A certification standards is to try and remove that 'environmental link' so far as is possible though isolation and protection features.
Most twin engined helicopters today have EFIS, Autopilots, EGPWS, TCAS and FADECs, are certified for IFR and are operated two crew. Within that list, there is plenty to reduce the risk of an accident from causes more common than engine failure, and most of those items are not present in a single!
One must also remember that there are other reasons to end up on one engine in a twin, beside a straight forward failure - such as chip lights, fire warnings etc - and in fact you may have one engine at idle rather than shutdown. Better to carry out a precautionary shutdown (or retard a throttle) and head home, rather than ditch - surely!
Would you also agree with me that it's not the risk of forced landing through the 'engine failure' cause but any cause which needs to be factored in?
One must also remember that there are other reasons to end up on one engine in a twin, beside a straight forward failure - such as chip lights, fire warnings etc - and in fact you may have one engine at idle rather than shutdown. Better to carry out a precautionary shutdown (or retard a throttle) and head home, rather than ditch - surely!
AnFI,
Let's deal with the engine failure first: it has been established (empirically) that the failure rate of helicopter (turbine) engines is about 1:100,000/flight hour. When two engines are fitted, and certificated, the rules require that each engine is protected (to the extent possible) from failure of the other.
If we exclude failure from (common) external factors such as salt water ingestion, ash ingestions, fuel starvation, FOD ingestion etc., we can assume the failure of each engine is an independent event. The probability of an engine failure is 1:100,000 (or 1 x 10^-5) therefore the failure of one engine followed by the failure of the other is 1 x 10^-5 and (times) 1 x 10^-5 or 1 x 10^-10.
Hence the probability of failure of 'a' followed by 'b' is 1 x 10^-10.
The result of an engine failure for a single is a forced landing; the result of an engine failure for a CAT A twin operating in Performance Class 1 is continued flight on the other engine.
However, the important issue is the consequence of the failure; if we assume superior skill in the pilot performing an auto-rotation and landing, what remains is the characteristic of the (forced) landing site. If the landing can be performed without harm to the occupants of the helicopter it is said to be a safe-forced-landing. Where the landing cannot be performed without harm to the occupants of the helicopter, it is said to be hostile.
Hostility is ICAO is defined as:
Where hostility of the environment is transient - i.e. at sea - but occurs frequently or can happen very quickly, some States take the precaution of defining it as hostile.
Where hostility of the environment is transient but occurs infrequently and with warning, the operator is left with the Risk Assessment and provision of appropriate 'adverse weather' policy/procedures.
As you have said, there are other reliability issues that have to be addressed; these are dealt with in certification and build standards, and component lifing; or, with redundancy. Some States also take the additional precaution of permitting flight over a hostile environment only in Performance Class 1 (certification in Category A being a more quantitative process).
All of this has been considered in detail for a number of decades; States and operators (and oil companies) have used the above tools to Risk Assess their operations and make appropriate provisions in their regulations/procedures.
It all comes down to the old adage, horses for courses.
This is not a single v twin but a risk assessment discussion. Mathematics /statistics /probability just provides us with the tools with which to make the best (and informed) decisions.
Jim
Let's deal with the engine failure first: it has been established (empirically) that the failure rate of helicopter (turbine) engines is about 1:100,000/flight hour. When two engines are fitted, and certificated, the rules require that each engine is protected (to the extent possible) from failure of the other.
If we exclude failure from (common) external factors such as salt water ingestion, ash ingestions, fuel starvation, FOD ingestion etc., we can assume the failure of each engine is an independent event. The probability of an engine failure is 1:100,000 (or 1 x 10^-5) therefore the failure of one engine followed by the failure of the other is 1 x 10^-5 and (times) 1 x 10^-5 or 1 x 10^-10.
Hence the probability of failure of 'a' followed by 'b' is 1 x 10^-10.
The result of an engine failure for a single is a forced landing; the result of an engine failure for a CAT A twin operating in Performance Class 1 is continued flight on the other engine.
However, the important issue is the consequence of the failure; if we assume superior skill in the pilot performing an auto-rotation and landing, what remains is the characteristic of the (forced) landing site. If the landing can be performed without harm to the occupants of the helicopter it is said to be a safe-forced-landing. Where the landing cannot be performed without harm to the occupants of the helicopter, it is said to be hostile.
Hostility is ICAO is defined as:
Hostile environment. An environment in which:
a) a safe forced landing cannot be accomplished because the surface and surrounding environment are inadequate; or
b) the helicopter occupants cannot be adequately protected from the elements; or
c) search and rescue response/capability is not provided consistent with anticipated exposure; or
d) there is an unacceptable risk of endangering persons or property on the ground.
Clearly: b) above can be mitigated with the use of life-vests (with splash hoods), life-rafts and survival suits; c) is dependent upon b) and the efficacy of search and rescue.a) a safe forced landing cannot be accomplished because the surface and surrounding environment are inadequate; or
b) the helicopter occupants cannot be adequately protected from the elements; or
c) search and rescue response/capability is not provided consistent with anticipated exposure; or
d) there is an unacceptable risk of endangering persons or property on the ground.
Where hostility of the environment is transient - i.e. at sea - but occurs frequently or can happen very quickly, some States take the precaution of defining it as hostile.
Where hostility of the environment is transient but occurs infrequently and with warning, the operator is left with the Risk Assessment and provision of appropriate 'adverse weather' policy/procedures.
As you have said, there are other reliability issues that have to be addressed; these are dealt with in certification and build standards, and component lifing; or, with redundancy. Some States also take the additional precaution of permitting flight over a hostile environment only in Performance Class 1 (certification in Category A being a more quantitative process).
All of this has been considered in detail for a number of decades; States and operators (and oil companies) have used the above tools to Risk Assess their operations and make appropriate provisions in their regulations/procedures.
It all comes down to the old adage, horses for courses.
This is not a single v twin but a risk assessment discussion. Mathematics /statistics /probability just provides us with the tools with which to make the best (and informed) decisions.
Jim
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Horses for courses...
Sure its a risk/consequence calculation where correct use of statistics are a tool - but you know what they say about statistics !
You say
- That is TRUE - BUT we can't - we can pretend/reduce/try/hope etc but we cannot render POWER delivery independent - Especially if they share a common drive chain - where the risk of combiner gearbox etc etc must be factored in.
We expect the engine to deliver a POWER LEVEL (OEI30secs or OEI 2:30) which it has not regularly been tested to - it is being expected to do that because one engine has failed. An engine that it has probably shared a history with (same manufacturing batch, same unaccounted for running on rocket fuel in Bongo-Bongoland? etc..)
Pilot's close down the wrong engine - extinguish the good one etc - many factors which come in at significantly greater than a compounded 1x10^-5,
If it really were 1x10^-10 then we would never see the examples we do - so we can see it is not correct 'by inspection'.
We might want to but we cannot fairly just compound 1x10^-5 and use that figure - other than very hypothetically.
Also the INCREASED risks you refer to:
Well it's really not fair to hide them out of the equation - they are the price paid for the (hypothetical) 1x10^-10
And many of those standards (dual hydraulics) - chickens in tail rotors(?) etc are equally applicable to singles....
The negating of Hostility by mitigation looks like it has merit especially wrt ditching survivability - any controlled arrival into any water state should/could be rendered survivable - surely? (is that true?)
If the probability of arriving in the water were truly only 1x10^-10 (which it is not) then that is SO small that carriage of floatation equipment would not be required/safer, the risk could possibly be higher....
It is surely flawed to make risk from one specific cause (engine) better without including the increased risk from other causes - (like the tail boom falling off etc etc ...)
Nick Lappos has/had a really excellent arguement about 'over-engined twins' wasting payload on an almost irrelevant slice of 'exposure' during the Take-Off/Landing Phase - he wrote an excellent article on it - (somewhere?)
I am not against TWINs - and agree with Jim that it:
So it's perfectly fair and reasonable that manufacturers should be free to supply the free market with whatever hair brained scheme their engineering ingenuity comes up with to deliver the safety outcome the market demands - even if it means fitting two engines - or floating saftey cell cabins - to make the safest product ... dubious maths should not be enshrined in law to dictate particular engineering solutions.
Although I suppose it helps push the manufactures along....
Customers / oil companies / police forces should be free to demonstrate their commitment to safety by procuring helicopters which their consultants believe are safer...
it's a very strong driver.
Do you really want to be up an Alp in an EC145 in preference to a B3(e?) ?
Power / capability / reliability / margin or accountability .... ?
One saves pilots/people the other saves ..... accountable managers.
Patrick Goudou (EASA) doesn't have time to consider this topic:
Opinion04-2011
Jim has done a great job of forcing some rational considerations up the flag pole and into law - but isn't it time we 'upped the game' and lent a bit of support in the same way to other solutions... are there any aircraft designers out there who can clarify the mathematics?
You say
If we exclude failure from (common) external factors
We expect the engine to deliver a POWER LEVEL (OEI30secs or OEI 2:30) which it has not regularly been tested to - it is being expected to do that because one engine has failed. An engine that it has probably shared a history with (same manufacturing batch, same unaccounted for running on rocket fuel in Bongo-Bongoland? etc..)
Pilot's close down the wrong engine - extinguish the good one etc - many factors which come in at significantly greater than a compounded 1x10^-5,
If it really were 1x10^-10 then we would never see the examples we do - so we can see it is not correct 'by inspection'.
We might want to but we cannot fairly just compound 1x10^-5 and use that figure - other than very hypothetically.
Also the INCREASED risks you refer to:
As you have said, there are other reliability issues that have to be addressed; these are dealt with in certification and build standards, and component lifing; or, with redundancy
And many of those standards (dual hydraulics) - chickens in tail rotors(?) etc are equally applicable to singles....
The negating of Hostility by mitigation looks like it has merit especially wrt ditching survivability - any controlled arrival into any water state should/could be rendered survivable - surely? (is that true?)
If the probability of arriving in the water were truly only 1x10^-10 (which it is not) then that is SO small that carriage of floatation equipment would not be required/safer, the risk could possibly be higher....
It is surely flawed to make risk from one specific cause (engine) better without including the increased risk from other causes - (like the tail boom falling off etc etc ...)
Nick Lappos has/had a really excellent arguement about 'over-engined twins' wasting payload on an almost irrelevant slice of 'exposure' during the Take-Off/Landing Phase - he wrote an excellent article on it - (somewhere?)
I am not against TWINs - and agree with Jim that it:
It all comes down to the old adage, horses for courses.
Although I suppose it helps push the manufactures along....
Customers / oil companies / police forces should be free to demonstrate their commitment to safety by procuring helicopters which their consultants believe are safer...
it's a very strong driver.
Do you really want to be up an Alp in an EC145 in preference to a B3(e?) ?
Power / capability / reliability / margin or accountability .... ?
One saves pilots/people the other saves ..... accountable managers.
Patrick Goudou (EASA) doesn't have time to consider this topic:
"However, within the timeframe available, stakeholders and the Agency were not able to gather the appropriate data and establish a safety case that would show the need to reconsider the basic underlying principle of JAR-OPS 3, which was to transition fleets to multi-engined helicopters, given subsequent technological advances and increased reliability of single-engined helicopters."
Jim has done a great job of forcing some rational considerations up the flag pole and into law - but isn't it time we 'upped the game' and lent a bit of support in the same way to other solutions... are there any aircraft designers out there who can clarify the mathematics?
JimL, 212man,
your efforts to have a rational and well-thought-out discussion with AnFI are mispremised sadly: Following the onerous and quite pointless "loss of visual references diatribe", it seems he has a new stick to beat and will go on talking rot as long as someone is prepared to engage with him.
An FI. You are offshore and have one engine and experience a failure. What will happen next? Get a grip man.
your efforts to have a rational and well-thought-out discussion with AnFI are mispremised sadly: Following the onerous and quite pointless "loss of visual references diatribe", it seems he has a new stick to beat and will go on talking rot as long as someone is prepared to engage with him.
An FI. You are offshore and have one engine and experience a failure. What will happen next? Get a grip man.
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TT: Trick question, right?
You are offshore and have one engine and experience a failure. What will happen next?
TT: You're onshore, CatA PC1, could auto easily if required, your tail boom falls off. What will happen next?
it is just not 1x10^-10 - is it?