Category A Takeoff: Background

[AnFI]

DB, Shy, megan, JE and BR

There are some really good points there, thank you.
They do throw out a few elements out that might help the religious extremists understand the infidels, and maybe vice versa.

DB: 2 engines as an insurance policy. Very good point on so many levels. If you had no accidents in many years then you would expect the premium to be low. ie STILL WORTH PAYING. If the premium is ridiculously expensive then it fails
Cost Benefit Analysis.
So its all about CBA !
Fully comp, 3rd Party?? $10k per year to insure the hull of a $10k automobile, not worth it. So 3rd party only.
INSURANCE (premium) IS A MEASURE of the RISK.
3rd Party Insurance for a helicopter to insure the risk of people on the ground IS THE free market PRICING of this risk.
Look at the ground payout risk to insurance companies for Twin Engine helicopters in urban areas. Cultha is expensive.
North Sea helicopters over cities... could be very expensive.
Carrying a spare engine as an insurance policy is very expensive:
What cost 500kg being carried for 100,000hrs??? $100,000,000?? Very expensive just to insure against a 'fender bender'. Unrealistic.
It does not indicate it's worth it, and because it doesn't make sense the state(? or who ?) imposes it. T'aint right.
People are generally upset with being pushed around without justification. We expect more from our 'experts'.
["applies to SEHs but no one has ever exploited it." (I think an operator out of London Heliport does)]


Hi Shy, my engineering degree friend, some questions for you:
1 'Mandraulics' (great term) sure, agree - no good for autopilots.
As for Tail Rotors: IF Hyd TR is not necessary AND HydTR can kill you, THEN do you chose HydTR? (AW139 drivers?)
2 "One engine = one power source for electrical equipment." Sounds like a thoroughly lousy reason to carry a spare engine.
Spare electricity can be provided in so many more ways. Maybe like HYD, a GENi on the XMsn(?), if you were really worried about that then 30kg of extra batteries would do it ... OR 500kg of spare engine complication ((that can kill you)).
Which source of spare electricity would you chose?
3 'Stats against Twins look bad, because the singles aren't flying there'. You said it. YES THEY DO LOOK BAD... they are bad. The singles ARE THERE (eg only restricted in LONDON by R160) and the rest of history and the rest of the world leaves a data set that blows that argument away, and that argument flips the other way too: look at the MAJOR twin accidents that have not killed people on the ground because they were over barren sea/land, and NOT over urban areas !! Had they been over urban areas we'd have a total disaster for helicopters in general. (maybe over the NS but over London? A risk worth taking??)
4 Engineering wise: isn't simplicity the goal? Leonardo DaVinci, Simplicity is the ultimate sophistication. Occam, Newton, Einstein, KISS (Kelly Johnson). Not a fan of simplicity ?

megan "the regulator decides what can and can't be done", yes and has a duty to do so judiciously (for better reasons than just the retirement plans of some ex-employees). They have a LEGAL DUTY to decide in a judicious way.
They have not laid out their reasoning, and they should. Is it ok to avoid the daylight and push this through on the QT? What is their ALoSP? What is the likely fatality rate in 3rd Party Deaths per 100,000 hours of urban overflight? How does it compare to singles? Estimates anyone?
"Remember the early days of a certain twin, we became expert at single engine landings" I think the common theme often here is the "early days", and it makes the position understandable. Sure in the very 'early days' there were 2 engines because they didn't have single engines powerful enough. Engines were very unreliable, and there's no doubt that there's a reliability number at which it is worth carrying a spare. There's also a number at which it is not worth it. THAT number is the question. For instance at 1 per million hours, the price of carrying a spare is almost certainly not worth the Cost of carriage, Complexity (pilot and systems) and Increased failures of other systems compared to the very very rare usefulness of it, will not be 'worth it'.

JE
You are right, there's no analysis from me there, it's just a fact but it's not an inacurate one (as you alledge). There are all kinds of factors to apply to see it 'in context'.(ie make excuses for it). It's not good though is it? There'd have to be a lot of flying going on in twins to reverse that bad news for twins. 8 times more to make twins just twice as good. If twins, with all their other mitigators, only managed twice as good would it be worth it? Twins are flown by more experienced pilots, required to have more training, often are Multi Pilot (the biggest yeilding factor), more likely to have better other equipment.
According to EASA Safety Review 2018
25% of Offshore fatal accidents were from engine failure (twin)
5% of Other Comercial Air Transport was engine failure (also twin, no singles), most other causes were wires and weather and LOC.
However we want to spin the stats (and they are spinable, of course), there is just not a clear case, especially if you want to be rational or proportionate, or to actually cost the idea. I note your criticism of police authorities wrt road fatalities.

BR "Now, I am no expert in aircraft economics but it does occur to me that what determines if a type is profitable or cost-effective to run, requires a few more variables than just the number of engines, and the associated capital and direct operational costs." Well I think that is a really good point. The scale IS important. When the aircraft is LARGE, and carries many people there is a good case for carriage of a spare engine. It becomes a very small proportion of payload and expense. So the CBA may well show a favourable result for larger helicopters.
"many hard lessons learned over decades." yes, mostly decades ago !! Out of date now.
I understand a lot of 'old timers' are emotionally attached to spare engines. Don't want to re-evaluate their religion.
"to be cost-effective, how much and how fast you can transport something is of more importance to the cost equation."
Good point, so there's a size element to the estimation, I agree.
"the liability should something go wrong, and what another engine costs becomes unimportant." This is imagined fear, and the cost is not unimportant, it needs to be proportionate, It does cost more than money, some big accidents too... GREDL over LONDON!?!? Cultha? They need to be factored in also.
Smaller helicopters make smaller holes in the ground and don't economically/justifiably carry a spare engine so well.
"Boeing and Airbus aren't investing their money in single-engined airliners?" It really is different for Airliners. Airliners carry many more people, land with much greater destructive energy (more than just a fender-bender), do have 'independant engines', don't have a common output mechanism, don't have so many other critical components that could use the performance expenditure better, aren't so critical on pure capabilities. From the 'Airline world' Pilatus really proves the point that smaller scale singles do outperform twins. Commanche anyone? If a single makes sense in an aeroplane it makes more sense in a helicopter.
"ridiculously over-simplified points" well it's either too complex or too simple, no pleasing some people. KISS !! ?


(and THEN you have to ask: If you put the same amount of effort it making a simplex system not fail, as the resource you put in to 'preserve its unreliability' through redundancy then what result would you get?
You'd get a helicopter that didn't need redundancy, along with all it's downside costs.)
Come on America, you want to have to use twins?