Category A Takeoff: Background

[Savoia]

Is anyone aware of the history behind the development of the Category A Takeoff. Where it was first developed, who were the development pilots or any information about its origins?

https://lh5.googleusercontent.com/-H4R_IWSZLmw/Uph8N1tfyWI/AAAAAAAAPkA/OxWpDJ_AFL4/w854-h473-no/cat+a+takeoff+fig+1.png

From an operational point-of-view, has anyone encountered any 'challenges' while performing this manoeuvre?

Is there, for example, any collision risk while conducting CAT A departures (especially off-airport) as a result of the restricted rearward field of view?

[jayteeto]

Is that a comedy profile? Spot the deliberate mistake..............

[Savoia]

Not intentionally, no. T'was the only illustration I could put my finger on.

[ShyTorque]

TDP = Takeoff decision point.

LDP = Landing decision point.

Is there, for example, any collision risk while conducting CAT A departures (especially off-airport) as a result of the restricted rearward field of view?

If you are a bit slow taking off from EGLW, someone might put up another crane right behind you.....

[paco]

I know that the screen height of 35 feet was based on a double decker bus (at Croydon)

Phil

[RVDT]

Sav,

One would assume that you would have taken a look at the departure/takeoff path beforehand?

FM Supplement -

NOTE The helipad maneuvering area and takeoff flight path shall be clear of obstacles.

And all reference to LDP in your pic should be TDP?

[SASless]

Was there Life before Cat A?

[Jack Carson]

SASless, Yes, it was called taking off and going flying. Many moons ago (30years) during my initial S-76A training, Cat A was explained as a selling point since the S-76A was certified for Cat A operations. The RFM included all of the appropriate charts. A close look at the charts revealed that, to meet Cat A requirements at gross weight, one would need an unobstructed helipad about 1500 ft in diameter. That is just what we had at Stratford.

[Savoia]

RV: Agreed.

However, in addition to fixed obstacles I was wondering too about the hypothetical risk in making a rearward vertical takeoff and the potential for climbing into overflying traffic; for example in a rural location on the periphery of a control zone etc.

My main interest however is in learning (if possible) 'when and who' were involved in developing this procedure.

[ShyTorque]

I'd be interested to see some stats showing how many lives have been saved by Cat A in helicopters. I know of only one actual engine failure during a takeoff and that wasn't being flown under Cat A because the S76 was not capable in the conditions required by the operation. The aircraft was safely landed.

[RVDT]

one would need an unobstructed helipad about 1500 ft in diameter

Then you would have used a DHC6 Twin Otter because it could lift more out of the same space!

[SASless]

Then you would have used a DHC6 Twin Otter because it could lift more out of the same space!

Far cheaper too!

When Shell Oil (Nigeria) went from Bell 212's to the EC-155....the Heliports became runways....that should tell you something about the effects of using Cat A profiles and performance.

I have practiced the "Reverse" Takeoff Profile....never ever did one for real in daily operations.

Also did some very convoluted gyrations in other aircraft that were supposed to provide for Cat A performance (with a very limited weight allowed) as well....but in the end would have been far happier just flying the machine like a helicopter it was.

I was never on a Civliian operation where an engine failure on Takeoff ever occurred....not that they do not.....just they never did anywhere I was based.

[John Eacott]

The helipad Cat A was around in the mid/late 70s and became part of British Airways procedures offshore on the Brent platforms with their large unobstructed decks (Brent B in particular). The diagram in the OP is not very representative as most profiles are far more vertical than is shown: the criteria is to keep the helipad visual through the chin window, not out of the front screen! We dabbled with the idea in BEAS 212s, but with rig shuttles and 5 minute turnarounds it wasn't deemed practical plus many of our into wind profiles didn't allow a back up.

The BA S61 drivers (when introduced to the procedure about 1977 or 78) actually started using it off the runway at Sumburgh, which seemed a strange thing to do with thousands of feet of reject area ahead on departure.

I've found the biggest challenge to be getting pilots to understand the overall concept along with judging the TDP properly. Once that hurdle is overcome then there is no real issue in carrying out the procedure.

[TeeS]

Hi Savoia

I believe that the rearward take off profile was produced to allow the mirror newspaper group to fly the printing plates from the rooftop helipad at their London office to the printing presses in Manchester. It's quite possible that I am talking bolloxs though!

Cheers

TeeS

[John Eacott]

It's quite possible that I am talking bolloxs though

Tees, more than possible ;)

The FAA produced a paper in 1991, Helicopter Rejected Airspace Takeoff Airspace Requirements (http://www.google.com.au/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&ved=0CDEQFjAB&url=http%3A%2F%2Fwww.dtic.mil%2Fcgi-bin%2FGetTRDoc%3FAD%3DADA243738&ei=K_2YUuvVEoiAiQfFxYCQCA&usg=AFQjCNHCxl-3Q8DUkP1c4LmeB43UUxrM6A&bvm=bv.57155469,d.aGc) which seems to be addressing the problems of too-steep departure paths and a more flexible airspace system to allow for this. Prior to this report, the helicopter manufacturers were following the fixed wing criteria laid down by the FAA (IIRC).

[Savoia]

Hi Savoia

I believe that the rearward take off profile was produced to allow the mirror newspaper group to fly the printing plates from the rooftop helipad at their London office to the printing presses in Manchester. It's quite possible that I am talking bolloxs though!



This is precisely what I remember (well done TeeS :D) but .. I didn't trust myself to bet that this was in fact the genesis of what would become the 'CAT A' departure profile.

Does anyone recall who Maxwell's driver was at the time, we are talking mid-to-late 80's?

https://lh5.googleusercontent.com/-mb63xvwvvB8/UQvenN71QPI/AAAAAAAALwk/oOeIxKSSbzA/s680/AS355F1+G-RMGN+Maxwell+Communications+8+Max+Hse+New+Fetter+Lane+1987+% 28Gary+Lakin%29.jpg
AS355F1 G-RMGN atop 'Maxwell House' in 1987 (Photo: Gary Lakin)

Here G-RMGN seen atop the former 'Mirror Group Newpapers' office aka 'Maxwell House' at no. 8 New Fetter Lane.

[TeeS]

Thanks Savoia

Hopefully I'm not entirely senile yet then. It may have been Flight International that had an article about the development of the profile and I would guess that was, as you say, around the mid-late 80's

TeeS

[John Eacott]

We pre-dated the London rooftop departures by 10 years or so with Cat A in the NS.

My copy of the 212 manual with Cat A profiles (including Vertical Takeoff Profile) has the revision dated in September 1976, with the original having been published in August 1972.

Forget the idea of the Mirror being at the forefront of this :=

[Savoia]

Forget the idea of the Mirror being at the forefront of this :=

Fair enough. Had my doubts.

Do you suppose it began with one of the manufacturers?

[TeeS]

Hi John

Thanks to the wonders of the digital World, I have found the article that led me to believe the procedure was developed for the Mirror Group operation. It makes quite interesting reading, if only for the dream of masses of rooftop helipads in central London. I now realise that the article doesn't claim this was the first use of helipad profiles (Worldwide) but you might see where my confusion started. Hopefully this link will work:

1985 | 2964 | Flight Archive (http://www.flightglobal.com/pdfarchive/view/1985/1985%20-%202964.html)

Cheers

TeeS

[CharlieOneSix]

I first landed on the IPC roof in London in January 1975 in a Bo105D - can't remember any formal Cat A being in force for that type at that time. In fact in wasn't until four years later in June 1979 that I flew some rooftop take off single engine failure assessment flights on a 105DB with George Locke (ex-CO D Squadron at Boscombe Down) who was MD of Helicopter Marketing, the MBB sales agents in the UK at that time.

[Savoia]

Well done Tees! :ok:


Mike Barrett, McAlpine Helicopter's chief pilot, sees the UK Civil Aviation Authority attitude to helicopter operations as enlightened, compared with the restrictive regulations in other European countries.

After an initial period of reservation, the CAA has been practical and co-operative in establishing criteria for the newspaper operation. McAlpine is confident that city rooftop pads have significant advantages over ground-level pads for safety, environmental, and utility reasons. The elevated platform allows improved clearance of surrounding obstructions, particularly in the event of engine failure during approach or departure. It ensures low noise disturbance (amazingly, this operation has received almost no noise complaints from local residents in more than three years).

Rooftop platforms may come in handy for rapid fire and medical evacuation. Few buildings in London's crowded skyline are stressed to take the weight of helicopter. Many roofs are cluttered with air-conditioning vents, railings, and other impedimenta which would make even an emergency landing a hazardous undertaking.

Perhaps designers of city tower blocks should give thought to the beneficial role that the helicopter can play as a public service vehicle. This is one of the fastest growing areas of helicopter usage in the USA today.

CAA regulations stipulate that the diameter of an elevated pad should be at least 2 times that of the helicopter's rotor—some 88ft in the case of the Twin Squirrel. In addition, the pilot must be able to lift-off from the pad to a Critical Decision Point (CDP) 90ft above the pad elevation, lose one engine, and either land safely clear of the building or continue with a single-engined departure without sinking to less than 35ft above pad elevation.

The square International Press Centre roof measures 46ft x 46ft, and the Twin Squirrel, with its 35ft rotor diameter, can meet neither requirement with a normal lift-off technique. McAlpine Helicopters has developed special procedures to meet the CAA criteria. These have been demonstrated to, and approved by, the CAA, and involve a lift-off to 15ft above the pad, followed by a climb in backward flight, keeping the pad in sight through the pilot's lower right-hand windshield. This reverse climb is continued to the 90ft CDP.

Single-engine safety is vital

In the event of an engine failure below this point, the pilot uses the departure pad as his emergency landing area. Should failure occur after CDP, a transition into descending forward flight is made, maintaining the minimum 35ft margin above roof elevation while accelerating to the take-off safety speed (Vtoss) of 40kt. Under IFR conditions the pilot must fly level, accelerating further to his best singleengined climb speed of 55kt (Vy), before starting his en-route climb. Under VFR, 40kt will be maintained in the climb until 550ft above departure elevation, before acceleration to 55kt.

Similar criteria apply for approach and landing, with a Landing Decision Point (LDP) 90ft above pad elevation. Engine failure above LDP entails a missed approach procedure, similar to the departure profile. Below LDP power loss entails landing on to the roof.

https://lh6.googleusercontent.com/-DKondPWih5c/UpkcbG2BG9I/AAAAAAAAPks/J4kVxiLXPYI/w808-h480-no/Roof+departure+profile.png

Before landing on the IPC, pilots take an engine condition reading to ensure full engine performance before starting an approach, wind 8mb off the London QNH (equal to the 240ft height of the helipad building), and then make an approach into wind (using local chimney smoke, or the flags on the Houses of Parliament two miles away) to land on the nearest into wind diagonal line across the roof.

This ensures the maximum landing dispersion distance, which allows leeway for the pilot's fore/aft touchdown error.

To the passenger the landing appears dramatic and, indeed, there is little room for error. Despite this, McAlpine research and development pilot Geoffrey Holder makes the technique look easy. He has played a major part in developing the rooftop techniques to the standards required by the CAA. Up to three passengers can be carried from the roof, together with the plates. In fact, there needs to be at least one passenger, in the copilot's seat, to prevent an aft e.g. position allowing the tail boom to strike the edge of the building.

Flight International, 2nd November, 1985

[ShyTorque]

The rearwards departure from a helipad is normal for a number of other helicopters (I do at least one almost every working day).

[John Eacott]

Is anyone aware of the history behind the development of the Category A Takeoff. Where it was first developed, who were the development pilots or any information about its origins?

I was under the impression that this was about Cat A T/O, not CAA acceptance of the same? (Disregarding the change to PC1/2 etc that has superseded Cat A)

The FAA had approved Cat A for the Bell 212 in 1972, so any development would have been well in place before that. The attached scans indicate both the approval date of the Cat A Supplement (18th August 1972) and the profile:

http://www.eacott.com.au/gallery/d/5989-2/Bell+212+Cat+A+title.jpeg

http://www.eacott.com.au/gallery/d/5992-2/Bell+212+Cat+A+profile.jpeg

I think it somewhat cheeky for the Flight article to infer that McAlpine had developed this technique some 13 years after this Bell 212 example, even allowing for journalistic license. I'm sure that there would be other examples prior to the 212, certainly the S61.

[SASless]

John Boy.....the FAA lead the CAA in something as sophisticated as this.....really?:E

We all know that the Yanks could not possibly understand the finer points of helicopter flying!:ugh:

[John Eacott]

We all know that the Yanks could not possibly understand the finer points of helicopter flying!:ugh:

You little scamp SAS. I thought the Belgrano invented flying? Next you'll be telling me that they allow civilian ambos to fly at night. Or use NVDs. Or winch. :p




I know that the screen height of 35 feet was based on a double decker bus (at Croydon)

Phil

Phil, sadly there aren't many double decker buses to hand at Ft Worth :hmm:

[SASless]

Belgrano House....sounds like a deep water Reef!

Sadly....the Brits were quite late to the party....and have had great success imitating more progressive nations re rotary wing flight.

Seems the Russians and Germans led the way.

A History of Helicopter Flight (http://terpconnect.umd.edu/~leishman/Aero/history.html)

[paco]

John - the bus was used for fixed wing, and we know the helicopter stuff was pinched from there :)

Phil

[Adroight]

They might have led the way in writing about it Sasless but actually applying it is another matter.

[ShyTorque]

A fairly simple question but ... as so often happens here, it quickly becomes another tree against which the old dogs rush to cock their legs. :rolleyes:

[AnFI]

seems like dubious maths to expose the aircaft (and it's other sytems) to such a prolonged vunerable state for the theoretical upside of being able to crash gently back on the pad if it's the engine that fails in this time frame.

[Savoia]

John: Thanks for the info on the 212. Would be interesting to read a more detailed instruction of the recommended procedure.

Perhaps then it was one of the Bell test pilots who developed the original CAT A takeoff?

seems like dubious maths to expose the aircaft (and it's other sytems) to such a prolonged vunerable state for the theoretical upside of being able to crash gently back on the pad if it's the engine that fails in this time frame.

AnFI: I believe the rationale was that even if it takes longer .. the craft follows a profile in which there is always an 'option'. In the case of McAlpines and the UK CAA (above) and given the TwinEcureuil's power (or rather lack thereof) combined with the departure area being over central London; it seems as if this was the only means of mitigating the risk of recovery from a loss of power immediately following takeoff. But .. I appreciate your point.

I believe 'low level, gain speed, then climb' departures are still used from airports (see below):

p2rCqdanWP4

But CAT A (reversing style) are carried-out from helipads (from 02:05):

jV2AM3GGPpg#t=02m05s

[NickLappos]

Just browsed by this thread and wanted to pass on my thoughts:

The first category a helicopter was the S61, which was certified in the early 1960s. It was a CAM 7 certified helicopter, the predecessor to FAR Part 29, and so it was certified to airline transport requirements. This meant that the FAA had to synthesize requirements that were similar to the Part 25 airplane airline transport requirements. Part 25 requirements had engine failure on takeoff, rotation speeds, accelerate stop distances, and takeoff distances. All were specified using careful flight test procedures.

The Category A procedures used for the S61 family included a runway procedure and elevated heliport procedures. The elevated heliport procedures were used for the very first transport operations between the Pan Am building in downtown New York and the New York world's fair Pavilion in Flushing Meadows, New York. The test pilots who performed these procedures told tales of flying over 1000 takeoffs and landings as part of the certification effort. I met Jim Plackis the other day, he was the FAA test pilot on these operations.

The S61 was the precursor to all these Category A operations that are now standard for part 29 helicopters.
http://blog.modernmechanix.com/mags/PopularScience/1-1964/heliport.jpg

[Savoia]

Nick thank you.

Just to confirm then, for the record as it were, that what is now the Helicopter Category A departure (rooftop/helipad style) finds its origins in the work of Sikorsky's test pilots (including Jim Plackis) in the 1960's flying the S61?

[NickLappos]

Savoia, To my knowledge, the S61 was the first Airline Transport helo, and had the first Cat A procedural approval, in either 1961 or 62. It was quickly (within a few months!) followed by a vertol machine, I believe the civil Vertol 107.

Here is a link to the historic archived TCDS, dated 11/1/1961, and including Cat A procedures: Type Certificate Data Sheet 1H15 (http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgMakeModel.nsf/0/8c63aca47626850a86257aee00772b61/$FILE/1H15_Rev_17.pdf)

The Bell 212 Cat A was dated 6/30/1971: Type Certificate Data Sheet H4SW (http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgMakeModel.nsf/0/e9be86048fa0cce18625792c0060c312/$FILE/H4SW%20Rev%2028.pdf)

The V-107 1/26/1962:Type Certificate Data Sheet 1H16 (http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgMakeModel.nsf/0/7aa84111df5b01b786257bb7005c3b3f/$FILE/1H16_Rev_14.pdf)

[AnFI]

Savoia - yes you are right that is the 'rationale'

There must have been some successful outcomes of an engine failing at the higher end of the back-up phase, say 50ft of say 90ft.
Are there any examples known here by ppruners? How did they fare?

I heard of an engine failure on climb out in a single in 1974, the outcome was successful.

I love the history - you can feel the optimism!
Roof top restaurant heliport - marvelous!

Of course back then engines weren't so reliable and they were running singles almost flatout to takeoff, making it even more attractive to have 2 engines.

[JohnDixson]

Nick, you are amazing.

Since I went to high school in Brooklyn, I can legally say, " You da man "!

[SASless]

John,

Nick did not win the Barnes Wallis Award because of his mere good looks and charm...(sounds of coughing heard)!:ok:

[John Eacott]

Nick,

Nice to see you posting again: but the photo of the NY World Fair reminded me that I visited it (the World Fair) in 1965, and I wasn't aware of the helipad until your post :cool:

How time flies when you're having fun ;)

[AnFI]

there must be some known cases of this proceedure working? Shirley?

[ShyTorque]

Nick did not win the Barnes Wallis Award because of his mere good looks and charm...(sounds of coughing heard)!

Please, let's have no comparisons to the bouncing bomb...

there must be some known cases of this proceedure working? Shirley?

AnFI, it certainly works every time I do my check ride, when the examiner fails one of the engines....

[SASless]

Do you do your Air Tests at 95% of MAUW per the charts.....or do you do the Check in a nearly empty aircraft?

[John Eacott]

A few Rotorheads have been in touch asking for a copy of the old 212 Cat A Supplement. I've scanned it in three parts to keep the file size down, you can download them from here:

Part One (http://www.eacott.com.au/gallery/d/6051-1/Bell+212+Category+A+Operations+Supplement+Part+1_001.pdf)

Part Two (http://www.eacott.com.au/gallery/d/6054-1/Bell+212+Category+A+Operations+Supplement+Part+2.pdf)

Part Three (http://www.eacott.com.au/gallery/d/6057-1/Bell+212+Category+A+Operations+Supplement+Part+3.pdf)

Please note, this is a scan of an old supplement which may have been superseded and may even be discontinued.

Not for operational use!

Each file is about 6mb, and there is a blue 'Download document' above the file reference.

[Savoia]

John: This is interesting, thanks for scanning and posting! :ok:

[albatross]

To the best of my recollection the 212 was never re certified using the 3b engines. Does anyone know if it ever was. Performance would be much better I think.
I no longer fly the 212. Just curious.

[AnFI]

Are there really no known cases working or occuring in anger? (Helipad TDP*0.5 or greater)

[TiPwEiGhT]

If you fly the S-92 then it was put in the last RFM update earlier this year. Unfortunately I am unable to send you it.

TiP

[chopjock]

Well I think these Cat A type departures are not as safe as they could be. There is too much reliance on the tail rotor. They have two engines and only one tail rotor, so should base the technique on risking the engines more than the tail rotor by climbing forwards and into translation lift sooner, instead of loading the tail rotor more and for longer than necessary by climbing backwards...

[FloaterNorthWest]

Chopjock,

If you climb forward you enter the avoid curve so if you lose one of the two engines you will crash. So it’s Catch 22.

FNW

[chopjock]

If you climb forward you enter the avoid curve so if you lose one of the two engines you will crash. So it’s Catch 22.

But you would have less exposure time and engines are very reliable... Cat A are supposed to fly on one anyway?

[FloaterNorthWest]

CAT A procedures are designed to keep you out of the avoid curve. If you are in it then you can’t guarantee a safe landing.

Tail rotors are statistically reliable too!

[John Eacott]

Well I think these Cat A type departures are not as safe as they could be. There is too much reliance on the tail rotor. They have two engines and only one tail rotor, so should base the technique on risking the engines more than the tail rotor by climbing forwards and into translation lift sooner, instead of loading the tail rotor more and for longer than necessary by climbing backwards...

You have an never failing ability to misunderstand procedures: and make absurd comments. Under your 'risk' analysis you have seemingly ignored one main rotor system in most helicopters let alone one MGB, one cyclic, etc etc. The Performance departure profiles are well developed and long standing, but nothing in aviation will allow for all and every possible failure: it's a best risk/failure outcome.

That sort of post is what gets traction with media researching this thread for shock/horror headlines without either understanding nor follow up research.

[nigelh]

Floater .... I don’t understand how slowly reversing can be less in the avoid curve than pulling vertically and transitioning to SE climb away ASAP ? Surely every knot of forwards speed you get takes you closer to getting out of the avoid ?? ( and in the same logic reversing would make the normal avoid larger , ie higher than a normal hover as it will take valuable seconds and feet to arrest the backwards speed before initiating a nose down attitude to pick up speed ??) I am not saying you are wrong, but to my mind I would feel happier getting to the speed I could at least maintain altitude as soon as possible . I also think that logically the time it would take to drop the nose and pick up some speed would double if you were going backwards with nose up rather than a flat hover ?
I think I must be misunderstanding something ....maybe the powers that be consider the downside of reversing ( which there really must be ) are worth taking for the upside (??) of being able to see your take off spot during the climb .... ??

Old Fat One ..I think some people on here think that for you to post a theory of what you think may have happened...you should have at the very least a proper understanding and almost certainly be an experienced, probably professional, pilot . I tend to agree . My comments are a genuine question regarding the effectiveness of Cat A type take offs and are probably therefore thread drift . Apologies .

[helicrazi]

Floater .... I don’t understand how slowly reversing can be less in the avoid curve than pulling vertically and transitioning to SE climb away ASAP ? Surely every knot of forwards speed you get takes you closer to getting out of the avoid ?? ( and in the same logic reversing would make the normal avoid larger , ie higher than a normal hover as it will take valuable seconds and feet to arrest the backwards speed before initiating a nose down attitude to pick up speed ??) I am not saying you are wrong, but to my mind I would feel happier getting to the speed I could at least maintain altitude as soon as possible . I also think that logically the time it would take to drop the nose and pick up some speed would double if you were going backwards with nose up rather than a flat hover ?
I think I must be misunderstanding something ....maybe the powers that be consider the downside of reversing ( which there really must be ) are worth taking for the upside (??) of being able to see your take off spot during the climb .... ??


so in this scenario in a stadium, how do you prpose to depart whilst maintaining a safe landing area? if you elected to transition forward without the reverse, before tdp you need a reject oei, that might take you into the seating area. After tdp oei you won't have the climb performance to clear the roof.

the profile flown gives you a safe landing area before oei before tdp, you drift down to where you started, oei after tdp you have sifficient height to transition and clear the roof

[212man]

Floater .... I don’t understand how slowly reversing can be less in the avoid curve than pulling vertically and transitioning to SE climb away ASAP ? Surely every knot of forwards speed you get takes you closer to getting out of the avoid ?? ( and in the same logic reversing would make the normal avoid larger , ie higher than a normal hover as it will take valuable seconds and feet to arrest the backwards speed before initiating a nose down attitude to pick up speed ??) I am not saying you are wrong, but to my mind I would feel happier getting to the speed I could at least maintain altitude as soon as possible . I also think that logically the time it would take to drop the nose and pick up some speed would double if you were going backwards with nose up rather than a flat hover ?
I think I must be misunderstanding something ....maybe the powers that be consider the downside of reversing ( which there really must be ) are worth taking for the upside (??) of being able to see your take off spot during the climb .... ??

Old Fat One ..I think some people on here think that for you to post a theory of what you think may have happened...you should have at the very least a proper understanding and almost certainly be an experienced, probably professional, pilot . I tend to agree . My comments are a genuine question regarding the effectiveness of Cat A type take offs and are probably therefore thread drift . Apologies .


Oh great - let’s have another HV curve thread. I guess we’ve only had about 10 or so in the last decade. A Cat A take off profile does not put you in the HV curve. It may appear to but the WAT graphs and profile/technique obviate it. The HV curve is a very blunt certification instrument that does not recognise Cat A profiles and is based on extremes of mass, C of G and density altitude. Kick it out of this conversation!

[nigelh]

So if you have gained , as in this case , a maximum of 20-30m by reversing ... you are at say 30-40m height . How much airspeed will you have available to settle back to the same spot ? Enough to be in transition ? I wouid say no . Enough to eliminate possible vortex again no . So what really are you gaining ? You could eliminate all the risks we have discussed in exchange for having to come down admittedly more vertically?
maybe not a point but in the 109 I would rather do vertical because when near transition speed she shakes and rattles like hell !

212 .. just seen your message . Fair enough !!

[Slowclimb]

Isn't the idea that, if you lose an engine, you fly down the path you just went up to that nice safe landing spot you were sitting on a few seconds ago?

[212man]

Isn't the idea that, if you lose an engine, you fly down the path you just went up to that nice safe landing spot you were sitting on a few seconds ago?

Yes - if you lose an engine. Do you think this is what happened? If not, what’s the relevance of your question?

[chopjock]

helicrazi

the profile flown gives you a safe landing area before oei before tdp, you drift down to where you started, oei after tdp you have sifficient height to transition and clear the roof

And this takes more than twice as long, exposing the aircraft to a kind of "tail rotor avoid curve". I cringe every time I see this type of departure thinking "I hope that tail rotor doesn't let go, why is it taking so long"...

[HeliComparator]

So if you have gained , as in this case , a maximum of 20-30m by reversing ... you are at say 30-40m height . How much airspeed will you have available to settle back to the same spot ? Enough to be in transition ? I wouid say no . Enough to eliminate possible vortex again no . So what really are you gaining ? You could eliminate all the risks we have discussed in exchange for having to come down admittedly more vertically?
maybe not a point but in the 109 I would rather do vertical because when near transition speed she shakes and rattles like hell !

212 .. just seen your message . Fair enough !!

it really doesn’t matter what you think about the profile, nor what anyone else on here thinks about it. The important point is that it is the flight manual procedure, certified following extensive testing by company test pilots.

I flew the AS33L2. It had a backing-up Cat A helipad procedure. I also flew the EC225, it had a vertical Cat A helipad procedure. Both procedures were entirely valid. The backing-up one gives better view of the reject area but you are backing up into unseen territory and overdoing the backing up results in too much rearwards speed. The vertical one is easier provided you can keep the landing area in view. As a TRE/TRI I did more OEI rejects from just before TDP than I care to remember. What a surprise - none of them had any hint of vortex ring!

[nigelh]

Ok .. I still see more negatives from backing up than positives so don’t ever do them myself. I get the point that if it’s in the manual you do it ..... just wonder how they came to that conclusion!!!

[JimL]

With respect to performance, the main point of a Category A procedure is to provide engine-failure accountability.

With an engine-failure anywhere in the profile, the pilot should be able to return to the take-off point or continue the flight safely (avoiding all obstacles) to a place where a landing can be carried out - all without damage to the helicopter.

For a helipad departure:



at any point up to the TDP and following an engine-failure, the pilot must be able to return to the take-off point and land the helicopter safely. That means that the pilot has to have sufficient visual cues to be able to conduct the landing, and the helicopter sufficient power to allow a controlled descent and landing.


from the TDP and following an engine-failure, the pilot must be able to clear all obstacles by a safe margin, climb and continue to the flight to a point where a safe OEI landing can be carried out.


Category A is a certification standard which provides assurance of continued flight in the event of a failure by employing design assessment, to reduce the probability of failure. Engine isolation ensures that one engine failure is unlikely to lead to a second, and fire in an engine compartment can be detected, contained and/or extinguished. These provisions give a level of confidence that the helicopter can be operated for continuous periods over a hostile environment.

Category A requires performance data so that One Engine Inoperative (OEI) obstacle clearance from take-off, through climb, cruise and landing can be calculated. This data should include: mass related take-off and landing procedures; heliport/helideck size limitations; distances and climb gradients (or rates of climb); and one-engine inoperative climb performance graphs. From these procedures and graphs an operator/pilot can establish an OEI flight trajectory.

The failure rates for engines and tail-rotors (should) differ by four orders of magnitude. When reliability of any system does not reach the desired level it is mitigated by the provision of redundancy (in this case two engines).

JimL

[212man]

Ok .. I still see more negatives from backing up than positives so don’t ever do them myself. I get the point that if it’s in the manual you do it ..... just wonder how they came to that conclusion!!!

both procedures have positives and negatives:

The vertical procedure is more easily reproducible - vertical climb to a radalt height using a given vertical speed ensures consistency and works well for elevated pads where going backwards will invalidate a radalt reading. However, there are greater performance constraints due to zero airspeed and it is easier to lose sight of the reject area (also leading to a lower usable TDP).

The Back-up technique allows a higher TDP and brings performance benefits due to being able to acquire airspeed from the higher reject heights. However, there will be greater variability in how it is flown as it relies on a sight picture, and the rate of climb and rearwards speed need judgement rather than fixed parameters. It also introduces the risk of backing into an obstacle if not properly assessed.

I've flown and trained both, and variations on them, including a hideous home-concocted company version for the B212 which was easily mishandled and was not a bunch of fun having to sit along during base checks/OPCs (actually caused more spread skids during training than actual engine failure events!)

[Sir Niall Dementia]

TDP = Takeoff decision point.

LDP = Landing decision point.



If you are a bit slow taking off from EGLW, someone might put up another crane right behind you.....

Shy;

:D:D Perfect! Sums it up in one!

SND

[chopjock]

JimL

The failure rates for engines and tail-rotors (should) differ by four orders of magnitude.

Now double the exposure time to the tail rotor in a reverse climb and what does that do to the orders of magnitude...?

[Sir Niall Dementia]

JimL

Now double the exposure time to the tail rotor in a reverse climb and what does that do to the orders of magnitude...?

Hovering down wind? It's the same thing really.

Like ShyT I do at least one Class 1 back up each working day. It is the safest way to operate. There is always power in hand, the profile is written that way, the reject in the event of a power failure simple and easily controlled. You're putting the whole back up out of proportion. And as FNW says "it keeps you out of the avoid curve." and he should know, he's been teaching this stuff for long enough, and in his current job deals with these profiles several times a day.

Don't try to re-write the laws of physics, they were written long before you and I came along, and they work just fine. I'd always prefer a class 1 back up from most sites to batting along with the collective under my armpit. The only one I had any real doubts about was the S76 vertical, which is quite an aggressive, full power manouvre.

SND

[JimL]

There is no Exposure Time in Category A operations.

'The reliability programme of aircraft in operation and maintenance is a combination of statistic monitoring and recording of the events associated with the airworthiness of an aircraft. The results obtained by monitoring reliability in operation may serve as a basis for supplementing or modifying the aircraft maintenance programme; such changes would indicate the malfunction of components or systems manifesting lacks and the need for early control, or replacement during utilization.'

https://www.maintworld.com/R-D/Aircraft-Reliability-Programme

Any failure of a tail-rotor in a larger aircraft results in a challenge to the pilot - as you have seen from experiences shared on other threads.

Helicopters are certificated on an understanding that they will meet the projected reliability rates. If they do not, it is for the Airworthiness Authority to establish a route to rectification. This can result in amendment to maintenance procedures but cannot mitigate the event that causes the review.

JimL

[chopjock]

SND
the profile is written that way, the reject in the event of a power failure

My point exactly, catering for event of power failure on very reliable engines (and you have two of them) and not catering for event of tail rotor failure and in so doing increasing exposure time too.

they were written long before you and I came along, and they work just fine.

Except not in this case...

[212man]

Now double the exposure time to the tail rotor in a reverse climb and what does that do to the orders of magnitude

As you appear to have a lack of knowledge about what 'order of magnitude' actually means, it's probably a pointless discussion to continue, although you don't give any evidence as to why the time is doubled? A back up procedure to a TDP of 200 ft isn't going to take double the time to reach 200 ft in a vertical climb - why would it?

[Sir Niall Dementia]

212man;

Please feel free to borrow my wall to bang your head against! You're arguing with the man who believed that taking off overweight was fine so long as you didn't overtorque or over temp. That took nearly 6 pages sto get some common sense going.

Chop; pay heed to JimL, he was my Senior Pilot once, knows his way round an aircraft and was the policy man at CAA and JAR where all this stuff was decided.

SND

[212man]

My feeling is that a rapid throttle chop and attempted AUTO from 120-200 feet and zero IAS may not be the obvious answer.

i agree - Nr decay and RoD will be serious issues

[212man]

212man;

Please feel free to borrow my wall to bang your head against! You're arguing with the man who believed that taking off overweight was fine so long as you didn't overtorque or over temp. That took nearly 6 pages sto get some common sense going.

SND

No, I've taken to sticking needles in my eyes - it's much more enjoyable!

[jellycopter]

My only comment and observation with respect to tail rotor drive failures and reaction time is; they don't happen without an associated thud, clunk, clatter, grinding noise or preceding high frequency vibration. As handling pilot, you should be in no doubt when the excessive yaw rate that you're experiencing, with the power pedal fully forward, is a tail rotor drive failure.

Several hundred horse power going through the tail rotor drive system doesn't fail 'quietly'. In many of the simulator sessions that I've experienced, these essential clues were often missing.

JJ

[chopjock]

A back up procedure to a TDP of 200 ft isn't going to take double the time to reach 200 ft in a vertical climb - why would it?

Let's say max take off power into wind in a vertical climb gives 600 ft/min ROC. so 20 secs to TDP then.

Now using same criteria going backwards, having less (if no) head wind, using more pedal (and therefore more power) and having a longer distance to go (The hypotenuse) with same power available will obviously reduce ROC, then you have to rotate even more at the top (from nose up attitude to nose down).Then allow time to accelerate forwards to zero GS. So taking twice as long is a guess on my part, but every one I have seen appears to take twice as long as a simple up, rotate and away.

[Loose rivets]

My only comment and observation with respect to tail rotor drive failures and reaction time is; they don't happen without an associated thud, clunk, clatter, grinding noise or preceding high frequency vibration.

Which pretty well describes the noises reported in the early posts, most notably by the 'Pundits' who, if nothing else, should be reasonably alive to a newsworthy occurrence since it's their livelihood.

[FloaterNorthWest]

Chopjock,

Not all aircraft prescribe climbing at MTOP during a VTOL procedure so your rate of climb calculation is flawed. Most outline a rate of climb to maintain so 200ft vertically or 200ft backwards will be reached at the same time.

FNW

[Thomas coupling]

Choppy - you are a cad arent you.
You're stubborn, I'll give you that.
we've established you have learning difficulties over the years so lets make it simple......again:
When a component is found to fail less often than another, checks and measures are reduced appropriately.
in the case of engines Vs tail rotors, its in the region of 4:1.
Our "authorities" bless them all, have experience and access to experts and stats.
With these tools, they risk manage the issue and produce best practice. If it doesn't work, they review.
No-one has come up with a better solution yet but i am sure they would love to hear from you.
Commercial ops departures have been revised and reviewed several times over the years as the odd engine failure pops up.
But sorry to burst your bubble choppie but tail rotor failures during departure (even when they are under extra strain) don't feature much in the stats.
Now i know we are a nanny state in the UK but we haven't quite reached the stage where every problem requires evasive manouevres - yet. If we did we'd either engineer tail rotors out of existence or stop flying altogether.......there....is that easier to understand?
Remember choppie....we're not talking about those radio controlled helos you fly.........
SEE POST NUMBER 79

[SASless]

I've flown and trained both, and variations on them, including a hideous home-concocted company version for the B212

Probably devised by the same fella that wrote the S-58T Profiles at the UK Centre of Excellence back in the 1970's.

I always felt like a proper dolt performing that take off as I looked down a nice long runway in front of me with thousands of feet of concrete well in excess of anything I would need to use during a rejected takeoff.....but what ho Skippy....it is the way we do things here.

At another Operator in the USA that is very well known for using EMS Airbus Singles for spontaneous bonfires....It was their policy during OEI landings in the 412 to make a shallow approach at 60 knots until 50-75 feet from the surface and then "dive" to get within a few feet of the surface so as to "be in ground effect" while making the run on landing well above translational airspeed.

When asked what would happen if the remaining engine failed while the "diving" to the surface (think nose down, descending, and very close to the ground while you consider that statement.....they opined no problem....just do as we say.

Had I not feared dying in the crash.....I thought about rolling off the throttle during one of those approaches on a Check Ride but always chickened out before doing so.

What I did do.....is follow the policy while doing the check ride then do what every operator of Twins advocated in doing OEI Landings.....omitting the diving part.

Somehow I always reach a conclusion that these kinds of things get over thought by the authorities because of factors not related to the actual safe operation of the aircraft.

[JimL]

Engines should meet a reliability figure of 1 x 10**-5; in ICAO parlance, this qualifies them as very reliable (the reason for the low standard is that a failure, at worst, should only result in an outcome of 'Major' - i.e. 'physical distress including injuries).

Tail-rotors should meet a reliability figure of 1 x 10**-9 because a failure could result in an outcome of 'Hazardous' or 'Catastrophic' - i.e. a fatality or multiple fatalities.

Reliability targets for tail-rotors are therefore 4 orders of magnitude better than engines - i.e. 10,000.

(A probability does not mean that a failure will occur after the reliability number has been reached, it can occur at any time but it should only occur once in the period.)

A helicopter certificated in Category A can depart or arrive utilising Category A procedures where failure of an engine should not result in damage.

A single-engine helicopter can depart or arrive using a Category B procedure where failure of the engine should not result in damage. It does this by accelerating below the HV avoid curve until it achieves a climb speed clear of the 'knee' of the HV curve.

Any departure other than that published in the Flight Manual - for either a Category A or Category B helicopter - could, following an engine-failure, result in a 'Hazardous' or 'Catastrophic' outcome (with a probability for a single of 1 x 10**-5, or for a twin or 2 x 10**-5).

An engine-failure in the cruise for a twin will be a non-event. An engine-failure in the cruise for a single might result in an outcome of 'Major' (as above) unless it is being flown over a hostile environment in which case the outcome might be 'Hazardous' or 'Catastrophic'.

In the recent accident, the profile flown was the AW169 Category A procedure. Whatever caused the accident was not the result of having flown this procedure. It was within the defined and certified operational envelope.

JimL

[MightyGem]

make a shallow approach at 60 knots until 50-75 feet from the surface and then "dive" to get within a few feet of the surface so as to "be in ground effect"
Something like this, SAS? Don't know if they were doing a single engine approach though.

https://www.youtube.com/watch?v=Iuzb81g_8BM

[chopjock]

JimL
Engines should meet a reliability figure of 1 x 10**-5; in ICAO parlance, this qualifies them as very reliable (the reason for the low standard is that a failure, at worst, should only result in an outcome of 'Major' - i.e. 'physical distress including injuries).

Tail-rotors should meet a reliability figure of 1 x 10**-9 because a failure could result in an outcome of 'Hazardous' or 'Catastrophic' - i.e. a fatality or multiple fatalities.

Reliability targets for tail-rotors are therefore 4 orders of magnitude better than engines - i.e. 10,000.

The logical question to ask is, are engines actually more reliable these days than this "low standard" when the CAT A profile was thought up many moons ago?
If so the CAT A PC1 procedure could be due an update...

[JimL]

The data that has been collected over the time since 'Exposure' was first introduced to regulations (circa 1999), indicate that that reliability has improved slightly - but not by an order of magnitude. When the data was first analysed for the regulatory risk assessment, it was believed that a number of engine/helicopter combinations would not be able to achieve 1 x 10**-5. In the event, most have. That could have been as a result of control and monitoring systems such as FADEC or UMS.

It would not be appropriate to lose sight of the objective of Category A certification stated in the definition:

Category A: With respect to helicopters, means a multi-engined helicopter designed with engine and system isolation features specified in Annex 8, Part IVB, and capable of operations using take-off and landing data scheduled under a critical engine failure concept which assures adequate designated surface area and adequate performance capability for continued safe flight or safe rejected take-off.

Category A departure and arrival procedures are deterministic - i.e. if there is a failure, safe flight can be continued. If engines ever reach a reliability figure approaching 1 x 10**-9, a rethink might be appropriate. (Under the current regulations, if OEI, HOGE is achievable, no additional procedures are required.)

There is already a great deal of flexibility in the system even with the current reliability status of engines. If a State wishes to have a 'Code of Performance' where failure resulting in a 'Hazardous' or 'Catastrophic' outcome has been risk assessed (to a defined safety target) and found to be 'tolerable' to its population, and those taking part in the CAT activity, that can be done (and is ICAO compliant). However, for those who are not taking part in the activity - i.e. third parties (including property), or for a higher number of passengers (greater than 19) - the current standards of Category A are usually applicable.

The whole regulation of aviation certification and operations is based upon risk assessment (the targets are set down in regulations and guidance). Controls are only in place where failure results in an unacceptable consequence to some defined degree. Yes there should be flexibility and adjustment of the system when societal mores change or when necessity dictates - but that is already the case.

JimL

[SASless]

JimL,

When the analysis was being done re Engine Reliability.....was it a generic determination applied to the total universe of Helicopter Engines or was consideration given to particular makes and models.

Some engines have a better Failure Rate than others and if some consideration to that would seem to penalize the better engines by lumping them into the pot with the lesser reliable engines.

[JimL]

All helicopter engines were analysed but the data-set was skinny; up to that time there was no requirement to collect usage data, and report failure - except when a reportable incident or accident occurred. (The reliability figure was for each engine/helicopter combination.)

No engine/helicopter combination was excluded from assessment. The system of reporting (both of usage and failure) was defined and signed-up-to by the Manufacturers (and they have been reporting reliability rates, for every engine/helicopter combination, ever since).

The safety targets for acceptance into the 'Exposure' regime were realistically set - the first for helidecks (where a problem existed) and then for elevated heliports. The safety target established for these operations was 5 x 10**-8; which permited 'Exposure' of 9 second for a twin and 18 seconds for a single . That target followed an analysis based upon profiles and data supplied by the Manufacturers.

Having set a pragmatic safety target, there were no immediate assessment failures (although the S61 came close to it later in its life, as did the S92 in its early traumas). A notable failure in the system did occur fairly recently with the S76 (the fatal accident in Myanmar) when a known bearing failure was not flagged for an AD because the regulators, unknowingly, left them out of the population for early rectification. In their view, they 'always flew in accordance with the Category A requirements' - i.e. with engine-failure accountability.

JimL

[SASless]

No doubt the hardest part of the process is to develop reliable Data by which to assess the Engines/Aircraft combinations....and probably some thought as to the actual operators and locations where they fly and what kind of work they do.

[JimL]

SASless,

The old adage that if you can't count it you can't manage it holds true.

With respect to the first part of your post: yes, but as soon as it was flagged that usage and failure data had to be collected, the system became more and more effective.

Category A and the Performance Classes (and controlled exposure) are applicable only to Passenger Carriage - although reliability figures are dependent upon the collection of data over the whole spectrum of operations. However, the manufacturer has some discretion over the inclusion of failures where failure results from "unsuitable or non-representative use (operation or maintenance)".

JimL

[Sir Niall Dementia]

SAS;

As part of current congested area operations where Class 1 can't be assured we as operators are required to provide the data as part of our risk assessments. For the 135 we can guarantee Class 1 all the time, the S76 has a problem with Battersea as the FATO is too small for S76 Class 1. Sikorsky collate the information continually and provide it to us on request, the data is based around the helicopter/engine combination and is very detailed. Certainly it means we can mitigate the risk right down to an insignificant level.

SND

[AnFI]

Engines should meet a reliability figure of 1 x 10**-5; in ICAO parlance, this qualifies them as very reliable (the reason for the low standard is that a failure, at worst, should only result in an outcome of 'Major' - i.e. 'physical distress including injuries).

Tail-rotors should meet a reliability figure of 1 x 10**-9 because a failure could result in an outcome of 'Hazardous' or 'Catastrophic' - i.e. a fatality or multiple fatalities.

Reliability targets for tail-rotors are therefore 4 orders of magnitude better than engines - i.e. 10,000.

(A probability does not mean that a failure will occur after the reliability number has been reached, it can occur at any time but it should only occur once in the period.)

....

JimL

The actual figures for tail rotors according to the UK CAA make your representation of the maths WRONG by a factor of about 50,000. And that's just the tailrotors!
Does that change your other maths? (why not?)
How many people died while using in upwards and backwards and PC type takeoffs?
There's the Norway 135 backing up into the real world wires maybe 4 or 5 other major accidents? (S76, 2x135, 139, 169, 902 others?)
10^-9 targets? really?
Catestrophic is having your rotorhead fall off, major is having to glide to a street/park/tennis court/carpark/sea/hillside etc

[AnFI]

SASless,
The old adage that if you can't count it you can't manage it holds true.
JimL

There's "can't count" and there's if you "can't count" by a factor of 50000 then you definately shouldn't manage it !

[Torquetalk]

There's "can't count" and there's if you "can't count" by a factor of 50000 then you definately shouldn't manage it !

“Going around“

[Nubian]

There's the Norway 135 backing up into the real world wires maybe 4 or 5 other major accidents? (S76, 2x135, 139, 169, 902 others?)


Now, which one is that again?? Do you mean the air ambulance that flew into wires while landing? Or are you making up stuff?

What are the other major accidents then??

[Apate]

Or are you making up stuff?


Surely not. AnFI is a bastion of truth and well balanced debate. :ugh:

[Hughes500]

Do we actually know why the engines fail ? Might sound silly but if it is something like running out of fuel. is that classed as an engine failure or pilot error ?

[JimL]

Are you trolling me AnFI?

The fact that tail rotors were not meeting their expected reliability led to CAA action resulting in a CAP with recommendations to address the issue. It does not change the mathematics but when reliability does not reach expected levels, it triggers a review process.

Hughes500: Perhaps that question should be addressed to AnFI, he might have relevant experience in that field.

Jim

[OvertHawk]

Do we actually know why the engines fail ? Might sound silly but if it is something like running out of fuel. is that classed as an engine failure or pilot error ?

Are you trolling me AnFI?

Hughes500: Perhaps that question should be addressed to AnFI, he might have relevant experience in that field.

Jim

:E :ok::D

Best response ever Jim!

[Hughes500]

Jim

It was a serious question ! Thank you

[AnFI]

Are you trolling me AnFI?

The fact that tail rotors were not meeting their expected reliability led to CAA action resulting in a CAP with recommendations to address the issue. It does not change the mathematics but when reliability does not reach expected levels, it triggers a review process.

Hughes500: Perhaps that question should be addressed to AnFI, he might have relevant experience in that field.

Jim

Hi JimL

No I am definately not trolling you. I only want a valid discussion. A "well balanced debate".
Has the CAA study you refer to actually led to an improvement in tail rotor reliability of a factor of 50000 !?
How have they acheived that? Seems a little unrealistic. Especially in light of Leicester. A tail rotor is an assembly of parts each made with the target 10^-9 in mind, how many critical components are there in a TR assembly?
You can't make a TR with a reliability rate of 10^-9, these are not realistic numbers. A simple TR is a more inherently reliable assembly.

You say it does not change the maths, but if you fix the cause of 1% of fatal accidents by increasing complexity and that results in other accidents more often and of a more catestrophic nature, then the maths are changed. You can't take the upside without accounting for the downside.

You have an odd idea of catestrophic.

This is catestrophic:
https://www.youtube.com/watch?v=hp0XnOHUKCU&t=4s

so is this
https://www.youtube.com/watch?v=oieiZxP7w5E

and this
https://www.youtube.com/watch?v=MUcWwQRpXh0

and this !
https://www.youtube.com/watch?v=eZ6m3D-1HCc

and this !
https://www.youtube.com/watch?v=sS--OX-LPNU


These on the other hand are MAJOR/inconvenient ? :
https://www.youtube.com/watch?v=bjUueBU6t8c

https://www.youtube.com/watch?v=LAjcN-npaPU

https://www.youtube.com/watch?v=iXF7deiAp5g

https://www.youtube.com/watch?v=mJ7WM4nTiPw

https://www.youtube.com/watch?v=kMrIyBNZBng

That's not to say 3rd party fatal consequences are impossible from engine failure in urban areas, there's a recent exception
in Tampa (and Sao Paulo), very unusual and unlucky, even in a gentle landing like this it can go wrong, hitting wires / poles can do that.
Any landing poorly executed can go wrong.
Wait for the report but it looks like it'll be an answer to Hughes500 question, reports suggest it was known in advance that the engine was sick.
BUT nothing like as bad as this would be in an urban area:
https://www.youtube.com/watch?v=MiDYqqfWxLs
https://www.youtube.com/watch?v=izpPJdFtcpU

Is it really justified to make the world perform to the engine-centric North Sea 'special case' - can you justify the safety yeild?
How much safer does 2 engines make it? Some/none/less ? Sometimes in specific scenarios?
What are the numbers?
99% of fatal accidents are from causes other than engines.
Even the slightest increase in the frequency of the 99% completely negates any benefit.
I don't expect serious answers because I don't think there are any serious answers to that.
If there are it would be great to hear them.

[[email protected]]

Would you be happier if we just made all the manufacturers put two tail rotors on every helicopter?

[MightyGem]

On a lighter note; love the way the KC Police helo just nonchalantly slides into view.

[[email protected]]

On a lighter note; love the way the KC Police helo just nonchalantly slides into view. if it had just stopped outside a donut shop it would have been perfect:)

[AnFI]

MG & Crab - yeeup, stylish arrival, and the girl dun good too (300hrs)
As for 2 tail rotors, yup there are some pretty silly ideas around, same with gearboxes, 2 of those too???
Control runs, duplicate? Even sillier what about 2 types of fuel incase one is contaminated?
Dual rotor head? KMax, either rotorhead can get to to the scene of the arrival??

What next? Two pilots? Ah yes that is good idea since 80% pilot error.
As for 2 engines, 600+? kg extra, for comfort (?) , why not, that seems sensible to some people?

[OvertHawk]

MG & Crab - yeeup, stylish arrival, and the girl dun good too (300hrs)
As for 2 tail rotors, yup there are some pretty silly ideas around, same with gearboxes, 2 of those too???
Control runs, duplicate? Even sillier what about 2 types of fuel incase one is contaminated?
Dual rotor head? KMax, either rotorhead can get to to the scene of the arrival??

What next? Two pilots? Ah yes that is good idea since 80% pilot error.
As for 2 engines, 600+? kg extra, for comfort (?) , why not, that seems sensible to some people?


Well I found it quite comfortable having two when one of them went bang over a congested area allowing me to fly to my base rather than ditch in a river. Pretty sure my pax did too.

[AnFI]

OvertHawk
You are of course spot on.
That’s the point, more comfortable.

Sometimes carrying a spare engine WILL be helpful. Like your case.
Quite right you feel more comfortable.
Much nicer to fly home than to swim to shore.

You must take that upside and weigh it against the downsides.
Against the ONE HUNDRED TIMES MORE PROBABLE likely causes of your death.

Your comfort from the spare engine needs to outweigh the downsides.
If it does 'you’re good'.
It needs to outweigh the chance that a freewheel unit will let go and tear off your gearbox and rotor head. That the overcomplicated gearbox doesn’t break and leave you without counter gravitational support. (poor sods). Your hydraulically assisted tail rotor (why does it need to be hydraulically assisted?) doesn’t force full travel and leave you like my friend in Leicester.

When those things happen you don’t get to swim to the bank, but you’d wish (briefly, as you remember this post) you could be given the chance instead to simply autorotate.

make sense?

[megan]

In 20K hours the only emergencies I ever had were two hand grenade engine failures, fortunately both in twins. The first one would have resulted in the likely death of all eleven had it been a single. Blessed are those who fly twins.

[chopjock]

In 20K hours the only emergencies I ever had were two hand grenade engine failures, fortunately both in twins. The first one would have resulted in the likely death of all eleven had it been a single. Blessed are those who fly twins.

So had it been a single, which one of those two engines would it have had? The one that blew up or the one that didn't...

[Flying Bull]

So had it been a single, which one of those two engines would it have had? The one that blew up or the one that didn't...

well, doesn’t really matter, cause he returned safely.
I recal al sputtering turbine on a Bell206, everytime I increased power.
Nursed it home and they found, that parts from the compressorhousing, the area where the blades spin, went through the engine....
What a tense feeling looking for spots to autorotate to in case of....
What a different, nice feeling in a modern twin, knowing that an engine failure wouldn’t impair take off or landing path.
Or hovering over a build up area, possible to relax cause the remaining engine would keep me there for 30 sec or with a little fuel burned, 2 ½ minutes, without any need of immediate action (sure I would react - but I wouldn’t be cought out looking outside i.e.)

[[email protected]]

Your hydraulically assisted tail rotor (why does it need to be hydraulically assisted?) I thought you were a helicopter pilot and instructor AnFI................

Surely you have flown something like AS350 and done hyd- out landings? Which was the most difficult control? Yaw by any chance? Now double the AUM and the size of the helicopter and try flying it without hydraulics...............

[[email protected]]

Of course AnFi - I was forgetting that your main interest is in trying to get singles access to fly over congested areas and also obfuscating when questions are asked about fuel planning on long overwater trips..........I suppose if you run out of fuel, the whole single vs twin argument becomes irrelevant...........

[timprice]

Personally I think with more reliable engines now this whole thing on CAT A take off's should change, recently looking at accident reports that has proved to be the case.
They are not fit more the modern helicopter the profile should change according to site landing/take off requirements to make the best of what you got.
How? that's a tuff cookie to crack, but surely were looking for the safest way in and out, should something unforeseen happen and a CAT A take off isn't it!!:O

[[email protected]]

Until you can guarantee 100% reliability of engines you are very unlikely to get things changed, especially without a viable alternative. I know that doesn't address any of the other particular component failures but finding a one-size-fits all procedure is the stuff of fantasy.

[212man]

I assume all the anti Cat A protagonists take the same view when it comes to their loved ones flying on commercial airlines? No need for any of that engine failure accountability nonsense - it will all be fine!

[albatross]

Good one 212man!
All I have to say is that when I had an engine resign (very loudly!) in a 206L I sure wished I had another one.
I had 3 engines quit on me all in single engine airframes. I was very, very lucky never to roll one up in a ball.
Strangely enough never had a failure in a twin.
I think my total time is about 50/50 between singles and twins.

[[email protected]]

I'm doing a lot of single time at the moment and. while the engine has a very good history of reliability, I am much more conscious of what I overfly and at what height!

[AnFI]

Hey Crab , i see you revert to your old practice of attacking the man, nothing constructive to say? Could we agree to keep it on the technical points?
(i feel a circular discussion coming on unless you can keep to the points)

(the point about hydraulics was to make you think. why are hydraulics necessary on a helicopter tail rotor? (it's a rhetorical question). Bad design maybe? Especially if it involves introducing an unecessary system to a system that can kill you, once per 50,000hrs. As for your point about forces on an AS350 with the hydraulics turned off, I am sure you can see the flaw with your question, moving hydraulic fluid around is hard work. If the centre of pressure is too far behind the pitch change axis then there also a lot of unecessary work to do, (bad design; that could be offloaded by spring). The main rotor of an H369 is about the same size as the Tail Rotor of a Mil26, 5 blades too. The H369 does not have hydraulics, and moving it's collective lever forces, with your feet would not be at all difficult. So why do you need hydraulics on a helicopter TR (?) , answer is you don't.)

Crab wrote: "I suppose if you run out of fuel, the whole single vs twin argument becomes irrelevant........... "
Yes spot on, and very topical wrt the Glasgow thread. Pretty pointless having 2 engines there and killing all those people.
Better over a Hostile Congested Area in a single with fuel, than in a twin with no fuel.
Given the choice 'spare fuel' or 'spare engine' which one delivers real world benefits??
Fuel is a real world necessity. (anyone flying over long stretches of the worlds most inhospitable water has probably worked out their fuel. If their engine were to stop, for some strange reason, then their chance of survival (according to JimL) should be 10^-9. If they did survive then its not 100% fatal right? It's just inconvenient. Inconvenient requires 10^-3 reliability ? )
Complexity kills too, you have fuel but you can't figure out how to get it to the engines, this is NOT PILOT ERROR, this is inherent in complexity.
Complexity is dangerous, 2 pilots partially mitigates that.


Singles do fly over congested areas. They do so almost completely safely, relatively (with 2 very rare recent exceptions).
Please ge back and look at thread #97 to see what heavy twins do in congested areas.
If 'North Sea twins' flew over cities, then the Catastrophic outcome would be obviously unacceptable. IMAGINE G-REDL in central London, ouch, it would look like Glasgow but much worse. 'Leicester' catastrophe, in the city centre, no good). If the Tail Rotor failure that happened to the police AS355 helicopter in Wales had been an AW139 then imagine the impact damage to the house. Mass kills.
The only previously airbourne helicopters that have killed anyone on the ground in the UK are twins.

There is no justification for mandating multi engine for helicopters over congested areas, it will lead to more deaths not less.

The focus on engines is totally distorting the approach to the actual cause of deaths. It's 99% NOT engines.
If you want to set an Acceptable Level of Safety Performance then looking at engines isn't going to get anything achieved at all.
What is the ALoSP for a State?
1 death per person on the ground per million hours ? 10 million hours?
Where is that number? Currently for twins is it running at about 1 fatality per 100,000hrs, worse ? Who knows? WHO is in charge of this?
The ONE THING that it is very insensitive to is engine reliability. It is the single least helpful indicator of anything to do with safety.

(serious if you can please Crab)

212 the engine argument for aeroplanes is totally different to the consideration for helicopters for many fundamental reasons.
Aeroplanes don't combine the drive to a common output. Airliners have more independent engines. Airliners land very much more energetically than helis in autorotation.
Gearboxes and freewheel units and tailrotors make the mix of what gives best safety yeild different. By far the most important component is the pilot. Aeroplanes just HAVE to keep moving. Helicopters can land non fatally almost anywhere. In a helicopter use of 2 engines introduces additional mechanical risk factors. Sometimes you are better off in a helicopter having a bigger window than another engine, more chance to see the wires. Helicopters operate in environments where the biggest practical benefit is real performance margins and reliability. Reliability is not acheived by redundancy. Redundancy gives increased unreliability in exchange for (a degree of) fault tollerance.

Albatross, unlucky/lucky you. You must have had a few more hairy moments too i bet.
Crab, singles, good for you, PM me if I can help, don't lose too much sleep about what you fly over, it's the OTHER 99% ways to die you want to watch out for.

[megan]

Why don't you get a job with the regulator and have the system/design changed. According to you the people doing the job don't have a clue.

Accidents by activity- Commercial air travel & aerial work - Training 7.62%, Positioning/Ferry 5.1%, Air travel 14.6%, Agriculture 7%, Passenger/Cargo aerial work 38.2%, External load 3.2%, Aerial observation 1.3%, Air tour/sightseeing .65%, Emergency medical 5.1%, Utilities patrol 12.7%, SAR 1.3%, Other 3.2%.

Accidents by immediate cause - System failure 22%, Errors 38%, Violations 33%, Other 7%.

Accidents caused by system failures - Engines 75.9%, Main gear box fire, Tail rotor blade breakage, Directional control failure, Pitch control failure, Tail boom breakage, Tail rotor pylon breakage, Trimming failure, each contributed 3.4%

Accidents by error - Misassessment of weather 18.2%, Misjudgement of landing 8%, Not going around 4%, Flight below MSA 21%, Overload 2.8%, Not considering wind 2.8%, Inadequate pilot judgement 34.7%, Poor circumspection 8.5%.

Accidents by violation - Violation of MSA 55%, Violation of weather minima 30%, Other 15%.

The figures are according to the International Helicopter Safety Team, but what would they know. PM me if I can helpCrab, my advice is, DON'T.

[JimL]

AnFI, if you intend to quote someone, perhaps you should provide a reference or justify your statement:

If their engine were to stop, for some strange reason, then their chance of survival (according to JimL) should be 10^-9.

You need to explain why redundancy with pilots, does not add unacceptable complexity!

Redundancy is only required when a component (or system) doesn't meet a specified reliability target and the consequences of failure is not acceptable - to some criterion.

Protection of third parties is the highest priority with aviation Authorities; the next is CAT passengers.

To my knowledge, there is no regulation that prevents a pilot, of other than a CAT flight, from flying over a sea area where a failure of the engine or another system would result in a hazardous or catastrophic outcome. Rules of Air kick in only when third parties are exposed.

Jim

[[email protected]]

(the point about hydraulics was to make you think. why are hydraulics necessary on a helicopter tail rotor? (it's a rhetorical question). Bad design maybe? Especially if it involves introducing an unecessary system to a system that can kill you, once per 50,000hrs. As for your point about forces on an AS350 with the hydraulics turned off, I am sure you can see the flaw with your question, moving hydraulic fluid around is hard work. If the centre of pressure is too far behind the pitch change axis then there also a lot of unecessary work to do, (bad design; that could be offloaded by spring). The main rotor of an H369 is about the same size as the Tail Rotor of a Mil26, 5 blades too. The H369 does not have hydraulics, and moving it's collective lever forces, with your feet would not be at all difficult. So why do you needhydraulics on a helicopter TR (?) , answer is you don't.)
Perhaps with your aviation time spent solely on light singles, you fail to understand the concept of disc loading - the harder you make the rotor work, the bigger the feedback forces and the more power required to combat those.

Have you never wondered why pretty much every helicopter over a ton and a bit has hydraulic assistance for main and TR?

Perhaps your ego asserts that you are man enough to manage such forces hour after hour but for us mere humans the hydraulics are essential.
You could of course just double the size of the main and TRs to reduce the power they consume but that's not very practical, is it?

As to playing the man, well you want to have your cake and eat it AnFI, you like to use your 'secret, Clark Kent' identity on PPrune to harangue and badger aviation professionals with your special agenda and use your 'Superman' persona to try to force your will on regulators.

Crab, my advice is, DON'T. Megan - don't worry, I have played that game before and he just gets abusive

[AnFI]

JimL, thanks for the sincere answer, great respect to you for that, I hope these are useful points.


AnFI, if you intend to quote someone, perhaps you should provide a reference or justify your statement:
Jim
Hi JimL; it's a paraphrse rather than a quote. it's a mathematically tongue-in-cheek implication of what you say about probability of catestropic events, you say should be 10^-9 (10^-6 would already be pretty darn good), this 'catastrophy' is a conflation of your product of probability of risk factor and probability of fatal outcome (catestrophic consequence). If you hold that the consequence IS 100% fatal (which you do) and If the risk x consequence is < 10^-9 (you use), 'given' that the risk becomes a certainty then if the consequence is actually survival (for an event), then it must have been very very very lucky to survive, something like 10^-9. Of course the truth is these consequences are being wrongly identified as 100% fatal. If you had a 99:1 chance of survival, and the acceptability of the event were 'reasonable' ie 1 per million hours, then the aircraft would only need 10^-4 probability of forced landing.



You need to explain why redundancy with pilots, does not add unacceptable complexity!
Jim
Good point. In a complex aircraft, the reality is that a single pilot can easily be swamped by work load and confusion, his 'flight secretary' can reduce the work load to a manageable degree. The pilot error rate for a complex single pilot machines opperated by the most basically qualified pilot would be ludicrously high. It's an error rate that can justify the extra weight of another pilot.
It's a weight / utility / complexity calculation:
A spare engine is only doing BAD STUFF for you, ALL THE TIME, it's introducing extra freewheel, extra explosion risk, extra gear box complication and payload consumed etc etc
It has to make up for it by being useful. The only time it gets to do that is ONCE per million hours. Really obviously not worth it.
A Spare Pilot is useful more than once per 100,000 hours when the other guy has a heart attack.
He is COMPLEMENTARY, that is he actually improves the overall performance of the piloting. This is the highest yeilding safety return.

So to summarise:
a spare engine is only bad until it's useful
and
a spare pilot is only useful until he's bad

(and then the spare pilot concept kicks in)
The Glasgow incident would probably be averted by a spare pilot, but was enhanced by a spare engine.



Redundancy is only required when a component (or system) doesn't meet a specified reliability target and the consequences of failure is not acceptable - to some criterion.
Jim
ALoSP: You need an expected death rate for people on the ground per 100,000hrs to determine whether it is an 'acceptable rate'.
The principle that you can't have any death at any cost is not realistic. If that were the case everything would have to be banned.
The HSE provide clear guidance about the value of economic activities incurring mortal costs and is clear that one can expect a degree of cost.
They suggest figures like 10^-3 per year. What is the probability of a given person on the ground being exposed to death from over flight of a single engined helicopter vs a multi engined helicopter? Something like 1 per 1000 billion hours?
What differentiation in that rate occurs by engine type? Anything measurable? How much is it? How unacceptable is it?
"you have to measure it to regulate it" - QUOTE?
Is someone actually computing the ALoSP - rather than some random application of an inappropriate criterion for component reliability.
10^-9 was set for critical components. A Tail Rotor, a Gearbox, a RotorHead, Control Runs are made from an assembly of many components where 10^-9 is applied in manufacture to those component parts. These are the component reliabilities that deliver between approx 0.1 and 2 fatalities per 100,000hrs.




Protection of third parties is the highest priority with aviation Authorities; the next is CAT passengers.
Jim
What outcome risk level is the criterion? There does not appear to be a 'target'. There is no case made for there being a greater or lesser risk by mandating engine redundancy.


Protection of third parties is the highest priority with aviation Authorities; the next is CAT passengers.

To my knowledge, there is no regulation that prevents a pilot, of other than a CAT flight, from flying over a sea area where a failure of the engine or another system would result in a hazardous or catastrophic outcome. Rules of Air kick in only when third parties are exposed.
Jim
Not only is it debatable that engine redundancy delivers reduced risk to these 3rd parties.
ALSO
as you say the priority is to 3rd parties. For people on the ground that would entail you restricting (banning) PRIVATE HELICOPTERS from overflight of hosile congested areas. (and under your definitions hostile congested areas include playing fields, parks, rivers, car parks etc etc)
Is it justified? By what criteria in deaths per hour, say?

Did you look at post #97, how do you account for that, most death is not engines.

Crab, v personal again, some heli TR have hydraulics not does not equal MUST have hydraulics. The 'why' i answered.

[JimL]

That is the most extreme example of the introduction of complexity seen for a while.

Will you please refrain from scattering your posts with false accusations and inaccuracies. For example:

it's a mathematically tongue-in-cheek implication of what you say about probability of catestropic events

For people on the ground that would entail you restricting (banning) PRIVATE HELICOPTERS from overflight of hosile congested areas. (and under your definitions hostile congested areas include playing fields, parks, rivers, car parks etc etc)

However tongue-in-cheek that might be!

[Nubian]

What outcome risk level is the criterion? There does not appear to be a 'target'. There is no case made for there being a greater or lesser risk by mandating engine redundancy.
Not only is it debatable that engine redundancy delivers reduced risk to these 3rd parties.
ALSO as you say the priority is to 3rd parties. For people on the ground that would entail you restricting (banning) PRIVATE HELICOPTERS from overflight of hosile congested areas. (and under your definitions hostile congested areas include playing fields, parks, rivers, car parks etc etc)
Is it justified? By what criteria in deaths per hour, say?

Did you look at post #97, how do you account for that, most death is not engines.

Crab, v personal again, some heli TR have hydraulics not does not equal MUST have hydraulics. The 'why' i answered.

Hey AnFI,

Here is links to 2 very recent accidents (and far from the only ones) with your favourite machine.... Both R-44's involved innocent dead 3rd partys on ground....

Brazil:

https://www.pprune.org/rotorheads/616930-sao-paulo-r44-crash.html

Florida:

https://www.pprune.org/rotorheads/620180-r44-down-killing-passenger-passing-vehicle.html

Now, I really look forward to see your explanation of these.....



When it comes to twin engine helicopters and the requirement for this. It has been produced twins long before it was seen as a requirement. (and HYD assisted flight controls as well)
I think helicopter designers around the world would know this better than a mere FI from England....

When you're on about the overcomplexity.... Why did your favourite brand introduce HYD for the R44?? It worked fine with the electrical trim..... (at least when it was working, but why did it need the trim in the first place??) Why did they had that big chunk of tungsten on the cyclic before the HYD was added? Feedback perhaps? On such a light machine?! Should be completely unnecessary!!!

[chopjock]

Nubian
When you're on about the overcomplexity.... Why did your favourite brand introduce HYD for the R44?? It worked fine with the electrical trim..... (at least when it was working, but why did it need the trim in the first place??) Why did they had that big chunk of tungsten on the cyclic before the HYD was added? Feedback perhaps? On such a light machine?! Should be completely unnecessary!!!

I believe Anfi has said twice he was referring to the tail rotor... And the electric trim was 5hite on the R44.

[[email protected]]

I believe Anfi has said twice he was referring to the tail rotor... And the electric trim was 5hite on the R44 no, he argued that since a 369 main rotor was the same size as a Mi 26 tail rotor and the former didn't need hydraulic assistance, it followed in his logic that the latter, or any other TR for that matter, didn't need hydraulics which is clearly cobblers.
Perhaps he forgets that the 369 had electric trim actuators to reduce the control loads as well - you never know with AnFI, he flip-flops from one part of the argument to another without pausing for breath.

Perhaps he would like to show how a 6 tonne helicopter can have a TR without hydraulic assistance?
I am sure his answer will be that it just isn't designed properly since his ego puts him so far above the legion of designers, engineers and manufacturers who have been making helicopters for many years.

AnFi, have you ever operated a multi-crew helicopter on anything other than a sightseeing jaunt? perhaps you might better understand that having a second pilot is for far more reasons than just giving redundancy for medical emergencies affecting the PF.

[[email protected]]

A spare engine is only doing BAD STUFF for you, ALL THE TIME, it's introducing extra freewheel, extra explosion risk, extra gear box complication and payload consumed etc etc
It has to make up for it by being useful. The only time it gets to do that is ONCE per million hours. Really obviously not worth it.
A Spare Pilot is useful more than once per 100,000 hours when the other guy has a heart attack.
He is COMPLEMENTARY, that is he actually improves the overall performance of the piloting. This is the highest yeilding safety return.

The spare pilot is useful all the time when used correctly - he is there to monitor the PF when conducting critical manoeuvres, especially IMC - not just to act as the in-flight secretary...

The spare engine is useful ALL of the time since it is not a spare but permits greater capability from the aircraft ( AUM, payload, speed etc) than a single engine helicopter. How many 6 to 8 tonne single engined, helicopters are there btw?

[chopjock]

crab
The spare engine is useful ALL of the time since it is not a spare but permits greater capability from the aircraft ( AUM, payload, speed etc) than a single engine helicopter.How many 6 to 8 tonne single engined, helicopters are there btw?

I'm not sure you are right there.
Have you considered the Bell 214 v Bell 212 for example?
Or the AS350 v AS 355?

The reason there are not many heavier twin types made is most likely due to the regulations requiring twins...
Ever thought why the K-MAX only has one engine?

[AnFI]

JimL
The points are serious and answer your questions. Not that complex. (compared to fuel systems of A109, EC135, (S61? 10 fuel tanks?! (how often do you get a fueltank failure? About 10 times as often as if you had 1 I suppose?))) Perhaps you could give a thought to some of my questions there?
and you can see I suffer from being selectively mis-quoted also... (which bit is inaccurate?)

Is it safer for urban overflight in Twins or Singles?
Given the nature of the catastrophic events that occur so often with heavy twins? see post #97

How do you calculate it? OR are you just taking the upside of less engine failure forced landings without the consequential (potentially greater) downsides?
Maybe try answering some of the points, are there answers? Do you have them?
Do you think it takes highly trained / experienced / checked / SoP'd multi crew to stand a chance of seeing the sliveringly thin theoretical upside of engine redundancy? Or can all pilots and operations benefit?
Do you think the 'North Sea model' is really likely to work 'onshore', world wide?
Lots of reasons why it probably won't.
One of which is the disproportionate cost, which prices out most potential helicopter users in order to return an unspecified theoretical gain. Removing the utility of helicopters for a vast number of ordinary people.
Oil / State / EMS are exceptionally highly funded areas, not typical or proportionate to the depth of pockets of the typical civil helicopter user.
What is the COST / BENEFIT ANALYSIS ? Is there one?

Crab, (still v personal := my ego has nothing to do with it.)
369 has trim actuators for cyclic loads. Tail rotors don't have a cyclic control, just a 'collective control', called yaw pedals. The 369 does not have trim motors to assist the collective, only the cyclic. It is 'well designed'. The main rotor collective control for a 369 is very light but able to control large thrust. The size of the 369 TR is about the same as the TR of a Mil26, which is a very large helicopter. The pedal forces are a function of the Centre of Pressure being a significant distance from the Pitch Change Axis of the TR blades, this is a function of design and is not necessary, therefore hyd assisted TR pedals are not necessary if the TR were designed to not require such large forces, which is evidently possible. If you can design it without an unecessary system that can kill you then you probably should try and do that. TR loads on HYD assisted AS350 have been known to cause accidents = not better off.

Crab I think you must have mis-read what I say about 2 pilots, you seem to be aggreeing, is that what you intend?:

Crab: "a second pilot is for far more reasons than just giving redundancy for medical emergencies affecting the PF"
Yes that's right, that's what this says:

Me: "A Spare Pilot is useful more than once per 100,000 hours when the other guy has a heart attack.
He is COMPLEMENTARY, that is he actually improves the overall performance of the piloting. This is the highest yeilding safety return.

So to summarise:
a spare engine is only bad until it's useful
and
a spare pilot is only useful until he's bad

(and then the spare pilot concept kicks in)
The Glasgow incident would probably be averted by a spare pilot, but was enhanced by a spare engine."
(and it answers JimL's point, although surprising he didn't know that/had to ask me to explain the difference. If you really wanted safety yield you'd mandate 2 pilots before 2 engines) (Crab: the second engine is a liability (in risk (fire, explosion, freewheel unit failure), weight and complexity, carried for the day it may be necessary/useful, that day has to come often enough to justify the downsides. Does it? (How often must you have an engine failure to negate these downsides?)). The 1950's concept of having 2 engines because one wasn't powerful enough has long gone. The performance/utility of a SE Lynx variant would probably be staggeringly good, weighing 500kg(?) less, doubling(?) it's utility. They still crashed them because of 1 engine failing and there was twice the chance.)

Nubian
Yes you are quite right. I mention that in #97:
"That's not to say 3rd party fatal consequences are impossible from engine failure in urban areas, there's a recent exception in Tampa (and Sao Paulo), very unusual and unlucky, even in a gentle landing like this it can go wrong, hitting wires / poles can do that."

They are extremely rare to end (that) badly, and until those 2 very recent examples, there were almost no cases, but in any case many fewer than caused by 2 engined helicopters in urban areas. Everything is possible and will occur with some frequency, it's really just a case of what that frequency is, how grave are the consequences and whether it's acceptable.
Nobody has defined what is the ACCEPTABLE Level of Safety Performance.


In the UK in the last 10 years the 'scores' for fatalities by engine philosophy are:
TWINS: 49 dead (people on the ground 8)
SINGLES: 13 dead (people on the ground NIL)

The reputational damage to helicopters has largely come from the 2 engine helicopter. (Societal Risk, ask Airbus)
(bigger splash !)

The case is NOT clear.
One hopes that there are serious 'experts' considering these points. (JimL, you? what's the logic?)
Rather than just being blindly wedded to the intuitive 'feeling of comfort' that the 2 engine religion gives.
Given the effectiveness of placebo effect, you can't deny that the 'comfort' plays a part. (especially for SLF)
If it makes you feel better .... you should be free to chose it, but no one should be forced into this dubious religion.

[AnFI]

In the UK in the last 10 years the 'scores' for fatalities by engine philosophy are:TWINS: 49 dead (people on the ground 8)
SINGLES: 13 dead (people on the ground NIL)

[[email protected]]

So now you have narrowed your 'excellent' statistical analysis just to UK because worldwide statistics don't suit your argument - that is both barrels in both feet AnFI

[AnFI]

:rolleyes:
xxxxxxx

[[email protected]]

Nobody has defined what is the ACCEPTABLE Level of Safety Performance. You certainly haven't.

They are extremely rare to end (that) badly, and until those 2 very recent examples, there were almost no cases, but in any case many fewer than caused by 2 engined helicopters in urban areas. Everything is possible and will occur with some frequency, it's really just a case of what that frequency is, how grave are the consequences and whether it's acceptable. Isn't that how statistics work? Sometimes nothing bad happens for ages and then it does? The 2 cases Nubian mentions happened, despite your logic and single engined helicopters with engine problems killed people on the ground - dress it up however you like but a single engine helicopter with an engine failure over a congested area is FAR more likely to have a catastrophic outcome than a twin engine helicopter having a single engine failure........

The pedal forces are a function of the Centre of Pressure being a significant distance from the Pitch Change Axis of the TR blades, this is a function of design and is not necessary, therefore hyd assisted TR pedals are not necessary if the TR were designed to not require such large forces, which is evidently possible. Do you mean center of pressure or do you mean aerodynamic centre? Do please explain how you will design a tail rotor system where the CP is consistently aligned with the pitch change axis - you understand that the pitching moments change with AoA????

One hopes that there are serious 'experts' considering these points. a bit like serious politicians considering UKIPs fantasies perhaps:E

[Lonewolf_50]

In the UK in the last 10 years the 'scores' for fatalities by engine philosophy are:TWINS: 49 dead (people on the ground 8)
SINGLES: 13 dead (people on the ground NIL)

Go back to school, and learn again the difference between correlation and causation.
AnFI: All Noise, Feckall Insight.

One would have thought that for as long as you've been involved in rotary wing aviation, you'd have run across a clue.
Nope.

[AnFI]

Crab ; yes you are right - I have not, (I have suggested some figures) ... but neither have those purporting to:
ref post #118 re ALoSP - why not ??
"Isn't that how statistics work?" yes it is. "dress it up" no need to, that's how stats work, I AGREE

"a single engine helicopter with an engine failure over a congested area is FAR more likely to have a catastrophic outcome than a twin engine helicopter having a single engine failure........" yes true, but that's not the point, that downside has to not be out weighed by the increased fatalities from other consequent fatal accidents, caused by excessively focusing on engine redundancy. (Like those in post #97). It is not clear that happens. It's just a 'nice idea'.

"Do please explain how you will design a tail rotor system where the CP is consistently aligned with the pitch change axis - you understand that the pitching moments change with AoA????"
I do, and I understand when they don't too. You'll have to look that up yourself, it's really obvious, class is closed for today.

Let's get to the bottom of this. I take it you aggree with much of what I say, eg 2 pilots/1950s/some downsides/some upsides
You agree that the upsides should be measured against the downsides and not just upsides in isolation?
It should be measured in terms of ALoSP (agree?), the people considering this issue are not producing this figure.
Why not? because it doesn't work?

[AnFI]

Lonewolf 50 "Go back to school, and learn again the difference between correlation and causation." I didn't make any comment regarding cause or correlation, it's just a factoid. What should I be learning about those ideas at school, and why should I learn it again? Always happy to learn, feel free to point out what clues you think I've missed.
"... for as long as you've been involved in rotary wing aviation" - I don't claim any experience, just looking for a logical analysis.

It would be great if JimL could answer some of the substantive points, it would be interesting, he is regarded as an SME. What's the ALoSP?
Should we balance upside against downsides? Is it worth it? How worth it?
What's the CBA? Is there one? Aren't you interested to know? or you already do?

[megan]

The reputational damage to helicopters has largely come from the 2 engine helicopter. (Societal Risk, ask Airbus)Here's me thinking that reputation was brought about by the Robbie. You do know the Puma accidents had nothing to with engines, or numbers there of? Perhaps not.

[Flying Bull]

I have to think about this quote
Never wrestle with a pig. You'll both get dirty, and the pig likes it.
Especially comparing a 369 mainrotor with a tailrotor - just from the size ...
Even a smaler BK117 tailrotor takes more horsepower, than a 369 has in total...
But I better stick to the quote ��

[DOUBLE BOGEY]

ANFI the rules, generally, mandate a “spare” engine to be carried when the helicopter is over terrain or taking off and landing in areas where loss of your engine (failure) would be catastrophic for you or persons and property below you. END OF ARGUMENT.

Loss of the single engine, in a SEH, over or into a congested area, wooded confined area, oil rig, water, scree scattered mountain slope, people, power line etc generally ends very badly. END OF ARGUMENT.

A catastrophic TR or MRGB failure in either a SEH or MEH will end the same way for both machines.

Now I am wrestling with the a pig and more than a little worried that I might be the pig!

[[email protected]]

I do, and I understand when they don't too. You'll have to look that up yourself, it's really obvious, class is closed for today. hahaha - that one is just hilarious...........

AnFI, why don't you just admit your agenda is doing battle with the regulators to allow (or not restrict) SEH over congested areas and stop beating around the bush with made-up statistics and circular arguments.

DB has summarised the argument succinctly but you keep banging on about engine redundancy like you have just invented the cure for the common cold.

DB - no, we all know who the pig is but it is fun to prod him now and again:ok:

[[email protected]]

Chopjock I'm not sure you are right there.
Have you considered the Bell 214 v Bell 212 for example? look at why the 214 was upgraded to the ST - performance, with safety as an added benefit.


The Bell 214ST was originally developed as a military project from the Bell 214B BigLifter, specifically for production in Iran (https://en.wikipedia.org/wiki/Iran) and the development by Bell was funded by the Iranian government.[2] (https://en.wikipedia.org/wiki/Bell_214ST#cite_note-Apostolo-2) The fundamental difference was the replacement of the Model 214's single Lycoming LTC-4 (https://en.wikipedia.org/wiki/Lycoming_T55) turboshaft (https://en.wikipedia.org/wiki/Turboshaft) engine with two 1,625 shp (1,212 kW) General Electric T700 (https://en.wikipedia.org/wiki/General_Electric_T700) engines, to improve the helicopter's hot and high performance and improve safety.

As for the Kmax - it has a single purpose which doesn't include CAT.

[albatross]

Funny story:
Years ago the Pope came to visit Canada.
The Vatican "Aviation Expert" wanted to have the Pope transported in a CH-47 or similar because it had two xmsn gearboxes and that "in the event that one failed they could continue on one to a safe landing on the other".
There was total silence in the room! (Well there may have been some muffled laughter).
We ended up flying the Pope in a 205A-1 with blue bed sheets roughly stitched over the bush seats. LOL

[Nubian]

Nubian


I believe Anfi has said twice he was referring to the tail rotor... And the electric trim was 5hite on the R44.

Hehe, Chop Chop!

I know very ''well'' how the trim worked, thanks...

Now, I wonder if you 2 geniuses can't just contact MIL and ask them why they don't develop a single engine MI26?? You guys are brilliant! For sure, it would be saving the weight of the ''other'' extra deadweight, combining gearbox, and all those extra bull**** systems not needed. Leave out the HYD systems, as that just complicate stuff...and a real Chop/AnFI designed machine would need only 1 pilot (with fairly strong arms) to fly it. When you're at it, maybe you should ask Sikorsky as well, why the hell they have been making the S64/CH54 all these years with 2 engines...Completely waste of time and efforts! Those were sure as hell not made with regards to overfly congested areas and CAT operations according to EASA regs.

Yeah, the Kamax is a real great example no?! What a success story....

As for the 214's, originally planned exclusively for Iran and military use. Khomeini changed that plan...

[Nubian]

In the UK in the last 10 years the 'scores' for fatalities by engine philosophy are:TWINS: 49 dead (people on the ground 8)
SINGLES: 13 dead (people on the ground NIL)

AnFI,

Without more info on the numbers, you don't have a case.
Can you from your numbers above, perhaps tell us the number of flight hours generated for twins and for singles, so we can divide the dead per hour? You can keep it for the UK for now, and we get the numbers world wide later.

Maybe you can give us a list of controlled in flight engine shut-downs (twin), due to some sort of problems, where the result was return to base, land and do some extra paperwork vs. Single engine failure, forced landing/crash and even more paperwork done by someone else?! Also per flight hours? The UK would do for now.
Preferably, split into private/corporate non AOC work vs. commercial operation.

[Bell_ringer]

AnFI,

Without more info on the numbers, you don't have a case.
Can you from your numbers above, perhaps tell us the number of flight hours generated for twins and for singles, so we can divide the dead per hour? You can keep it for the UK for now, and we get the numbers world wide later.

Maybe you can give us a list of controlled in flight engine shut-downs (twin), due to some sort of problems, where the result was return to base, land and do some extra paperwork vs. Single engine failure, forced landing/crash and even more paperwork done by someone else?! Also per flight hours? The UK would do for now.
Preferably, split into private/corporate non AOC work vs. commercial operation.

Numbers are easy to manipulate to support any agenda, even a poorly thought out one.
Without background data such as the amount of missions or hours flown, or even the number of accidents avoided, numbers on their own are meaningless.
The heavier category aircraft have all had a larger crew count, thus more fatalities, which has been used to imply the aircraft are less safe, which is creative mathematics in action.
Including Clutha in the calculation is just plain old fashioned scumminess.
With the backwards logic demonstrated, you would have to conclude that airline travel is incredibly unsafe - just look at the fatalities each year.
In Anfi's world that probably makes sense since those poor buggars are stuck with up to 4 engines, that's more than double the danger of any twin.

[[email protected]]

It should be measured in terms of ALoSP (agree?), the people considering this issue are not producing this figure.
Why not? because it doesn't work?
AnFI - as I am sure you know, creating ALoSP requires a State Safety Plan including Safety Performance indicators to accurately produce data. This data needs to be based on a mandatory reporting system that highlights the required SPIs and therefore relies on operators being truthful about causes of incidents so that accurate data is recovered.

Imagine if someone, say, ran out of fuel and lost an aircraft (fortunately without loss of life) and then was untruthful about the cause of the fuel shortage (piss poor planning perhaps) - surely that person would be guilty of undermining the whole ASoLP process - just a hypothetical scenario but worthy of consideration.

[AnFI]

DB

COST BENEFIT ANALYSIS: CBA

Yes - what you say is the B part, I agree!!! Not in dispute (mostly)

To make a valid decision you need to look at the C part: The COST
You cant just claim the B without the C. Can you? Do you not accept that there IS a cost?
Many are 'uninteded consequences', that cannot justly be ignored.

The Costs are many, some:
Economic activity stifled, jobs lost, utility hampered, ordinary people (taxpayers) priced out of utility of helicopters, super wealthy 'elites' only? Tried hiring/buying your own helicopter?
Fuel pressure: to be tight on fuel because you carry engine redundancy may not be safest.
Complexity of airframe, applies to systems and pilots, causes accidents that would not otherwise occur:
Leicester: as crab says a helicopter of AW139 size (due to engine redundancy) HAS to have a hydraulic Tail Rotor. It killed them.
Cultha: SIX (?) working fuel pumps and an experienced pilot can't get the 20+mins fuel remaining to the engines, because the system is complex and the pilot is confused, perhaps, because it is a twin prompting feeder tanks. 'Captain Murphy' will always come through.
AS332/H225: Gearbox's madly complex, breaks killing several helicopters full of people - FORTUNATELY not over urban areas, otherwise that COST would be very ovious.
Bigger energy impacts - imagine 15tons of helicopter in the Albert Hall on Proms night.
You cannot shut down the wrong engine in a single.
Critical components work harder: Any twin would have better margins for the same payload for many critical systems, (eg TR authority, etc etc etc).
Complexity has consequences !!!

If you don't asses the COST part of CBA, then you are clearly distorting the arguement.


I'd love to hear from JimL on this. ANY rationale? CBA? What's your 'A' part?
To exactly quote JimL:
"The argument that simplicity is safer than complexity is a given, only the consequence is in question"
I agree, DB - you don't?

What is the quantification of risk to 3rd parties on the ground ? ALoSP??? What is it?
We need to know because we must weigh the C against the B that you correctly identify.
We have to DO the 'A'. ABC : CBA !!

(ref 4 engines, yes ETOPS calculations include reduced risk of negative consequences of more engines (that can explode, and CAUSE the problem), this is similar to the exposure to more freewheel units, for example, EH101, Thruxton AS355)

[Crab - no argument with the Authorities, the Authorities have no view on this topic.
There are former employees, 'consulting', with a view to impose this on the rest of the world through ICAO.
They'll have consulting jobs for life, trying to explain to developing counties why they must take off upwards and backwards.
They are trying to move the goal posts: Hostile Areas WILL lead to Catastropic outcomes - really???
The current ICAO "land without undue hazard to persons and property on the ground" is being changed completely to become a Catastrophy requiring 10^-9. T'aint right, wake up world these rules are coming your way soon !!
They have not given their rationale.
They will undermine the credibility of the ICAO base line (and others), that has done so much good for the world.]
Bell, yes the stats are open to abuse, but one should try, feel free, go ahead, try and find neutral truth. Maybe twins do 4 times as many pax.hours, I don't know, i doubt it, but even then it doesn't seem like a good result does it? Worth the COSTs?

[DOUBLE BOGEY]

ANFI, assuming you drive a car on a public road Iassume you have it insured. You pay this every year. Everyone does and yet very very few have accidents that involve claiming on the Insurance.
‘The second engine provides the same insurance against an unlikely event. You don’t then say because I have not had an engine failure I can do without it forever.

Having said that, and this you may not know, in certain operations we exploit the reliability of both engines, to operate AEO where an OEI event could be catastrophic. We call it PC2 With Exposure. To do it we have to prove reliability, monitor the engines with HUMs and crucially, operate the helicopter in accordance with procedures to minimise the exposure time.

Such operations are restricted to those that exist in the public interest like HEMS or HOFO.

The same rule applies to SEHs but no one has ever exploited it. You can but wonder why.

DB

[ShyTorque]

A fully "Mandraulic" helicopter i.e. one without powered flight controls cannot, by definition, have an autopilot. Any helicopter flown in IMC requires an autopilot. Having trained to fly unstabilised, single engined helicopters in IMC from an early stage in my career and having had to fly an unstabilised twin in a later public transport role (it used to be allowed some twenty years ago), I would not want to do it ever again.

One engine = one power source for electrical equipment. If it stops, you are going downhill and possibly without some of the normal electrical systems, making your life even more difficult.

Accident statistics involving twin engined helicopters operating over congested areas might seem relatively high compared to singles, but a single cannot have an accident over a congested area if it is not allowed to be flown there.

[megan]

class is closed for todayYou opening classes is a waste of time. Find another profession, I'm a slow learner, but I've failed to learn anything from any of your posts. Just a troll IMHO.

All things aside, the regulator decides what can and can't be done with a single or twin, flight over water being a biggy.

Remember the early days of a certain twin, we became expert at single engine landings (not that it takes any great skill) because of precautionary shutdowns. Engines were eventually sorted. Not unlike the MAX having recent engine failure troubles, down to carbon build up on the combustor disrupting airflow pattern. Glad it had another to get back, else there would be a third MAX in the dirt, parked in the suburbs of Orlando.

[John Eacott]

In the UK in the last 10 years the 'scores' for fatalities by engine philosophy are:TWINS: 49 dead (people on the ground 8)
SINGLES: 13 dead (people on the ground NIL)




AnFI, I've tried to stay out of the circular arguments that ensue from your assertions, but I'd suggest that statistical analysis is one area that you need to brush up. Flat base stats without background are meaningless, since the exposure of single/multi engine types to the operational areas is a main feature which is ignored by you yet would significantly change the data that you are (so far) presenting.

Something like the year-to-date road fatalities so loved by many roads and policing authorities which completely ignore VKT, annual growth numbers, age groupings, 5 year trends, 12 month comparisons etc. You really are making a bit of a clot of yourself by creating inaccurate data references which mean absolutely nothing :ugh:

[Bell_ringer]

Bell, yes the stats are open to abuse, but one should try, feel free, go ahead, try and find neutral truth. Maybe twins do 4 times as many pax.hours, I don't know, i doubt it, but even then it doesn't seem like a good result does it? Worth the COSTs?

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.
You can choose to ignore that regulators determine the minimum required for operations and that this has been done as a result of many hard lessons learned over decades.
There is only so much you can move with a single, to be cost-effective, how much and how fast you can transport something is of more importance to the cost equation.
Add to that the liability should something go wrong, and what another engine costs becomes unimportant.
Why do you think Boeing and Airbus aren't investing their money in single-engined airliners?
You continue to choose ridiculously over-simplified points to support an argument that is entirely non-sensical.

If you really want to save everyone some money, then perhaps you can also discuss how pointless certification and testing is. This really does cost people money, so let's get rid of that also, it's just unnecessary regulation if you ask me.
While you're at it, all this training that has to be done. What a waste of time and money, let's get rid of that as well.
We need more visionaries like you :}

[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?

[megan]

Breaking News - The AnFI Aviation Safety Authority has discovered that all accidents were preceded by the crew eating food. The recommendation is that henceforth all crews be not permitted to eat food.

[AnFI]

and most are too low at the time of the accident ...:8

[[email protected]]

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. Probably one of your most fatuous arguments AnFI - it's like arguing that if we had adjoining tectonic plates and volcanoes in UK we would be much more likely to die in an earthquake or eruption.
'Look, over there, that's really bad - imagine if it was over here!' So very Daily Mail and no basis for anything other than scaremongering.

IF Hyd TR is not necessary AND HydTR can kill you, THEN do you chose HydTR? (AW139 drivers?) I thought we had established that on larger helicopters ie most twins, a hyd TR is necessary because of the power required to operate that TR with the high disc loadings involved.
Even light singles trying to get by on a non-hyd TR can run out of authority because the designer is trying to keep the disc loading low.

And btw the crash you keep harping back to was a 169 not a 139 - another erroneous 'fact' from you.

Any TR can fail and kill you, especially in a 400' hover at high power - your argument, as usual, lacks logical progression - just because it was a hyd TR doesn't mean all other TRs are inherently safe.

Do you seriously want free access to London for singles? What is wrong with the existing helilanes? They allow sufficient access whilst minimising risk to those below - what is wrong with that.

Twins can be allowed more freedom but are still most likely to be routed along the helilanes so what is your beef - do you want all singles to have the same freedoms as the air ambulance, police and SAR? That wouldn't make doing their job more difficult would it????

[ShyTorque]

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 ?

1) The A139 accident appears to have been caused by a tail rotor control failure, not by a hydraulic failure. As you obviously don't hold an engineering degree, perhaps you haven't grasped the reality that control feedback forces increase markedly with an increase in aircraft size. Perhaps you drive a car with servo assisted brakes or power steering? If so, have you complained to the manufacturer that both systems add unnecessary weight, complication and expense? I doubt it. Perhaps you would prefer to fly in an airliner without powered controls? I doubt it.

2) The main thrust (!) of your campaign is to make the main rotor gearbox simpler by only having one engine. Yet now you advocate making them more complicated to generate electrical power.... I fail to see any contiguous logic in that.

3) I take it that you operate singles in other congested areas. I hope that you make a point of obtaining the necessary CAA Permissions. I always do, for twin engined helicopters.

4) Engineering always requires compromises and there is seldom a simple answer. There could never be an autopilot or stability systems, a point I already stated and with which you agreed. Pilot fatigue would become a more important factor. If you wanted to build a large helicopter with no hydraulics, there would be considerable design compromises. These would include heavier control runs, which in turn would require structural reinforcement, adding weight and reducing payload. A much larger, single engine, rather than two smaller ones, would require a far stronger and heavier gearbox that you might at first imagine. Again, it would require a far heavier structure to support it. A doubling of size doesn't necessarily result in a doubling of material strength. - it might require a "square" increase. Again, see my answer 2).

A further point. I noticed that you posted your last two replies at 01:07 and 03:54. As flattered as I am that you consider me a friend and that a prompt reply to my post obviously so important for you to stay up so late, I suggest you get more sleep, it helps engender rational thought. Obviously, as an instructor, you already will know that. I'm not flying today, but still got a good night's sleep. I hope you aren't in the air until well rested. ;)

[212man]

The main thrust (!) of your campaign is to make the main rotor gearbox simpler by only driving one engine

Shy - looks like you needed a bit more sleep :E

[[email protected]]

Cost - of allowing SEH unrestricted access over congested/hostile areas = negligible, just a paperwork exercise

Benefit - to those few exercising such privileges = increased freedom - to those millions living underneath the privileged few = decreased through noise and additional risk as any failure is likely to lead to loss of life on the ground.

Analysis - pretty much a waste of time since - to quote Mr Spock - the needs of the many outweigh the needs (or desires in this case) of the few

[ShyTorque]

Shy - looks like you needed a bit more sleep :E

Yes, looks like it! I've edited the word "driving" to "having".

[Bell_ringer]

I take it that you operate singles in other congested areas. I hope that you make a point of obtaining the necessary CAA Permissions. I always do, for twin engined helicopters.

Ah, the simple joys of being in places where special permissions aren't required and singles can operate over congested areas.
Incredibly, they do seem to get this right without flattening people below.
Catastrophic failures do seem to be few and far between.

[megan]

Statistics for the US FY 2018 – first % is fleet size, second % is accidents. To make it easy those in blue have zero accidents

S350 7% 5%
BK117 2% 3%
EC120 1%
EC130 2% 3%
EC135 2%
SA330J < 1% 1%
206Bs 8% 6%
206Ls 5% 1%
212 1%
407 6% 3%
412 1%
429 1%
R-22 7% 15%
R-44 13% 21%
R-66 2% 1%
S-76 2% 3%
S-92 1%
Brantly B-2 1% 1%
Enstrom 280 1% 1%
480 1%
F28 1%
Cabri G2 < 1% 1%
Hiller UH-12/H-23 2%
Leonardo A109 1% 1%
(formerly Agusta Westland) A119 1%
AW139 1%
MDHI369 6% 15%
600N < 1% 1%
Restricted Category (all TCs) HH-1/TH-1/UH-1 5% 5%
OH-58 3% 4%
Schweizer Rotorcraft Services Group 269/300/TH-55 4% 8%
Scott's Bell 47 5% 1%

[[email protected]]

Megan - don't tell AnFI but it almost looks like single engine helicopters have the highest accident rate......................surely that can't be true or AnFI would have told the truth in the first place:E

[Nubian]

Woah, who would have thought....

[Bell_ringer]

Statistics for the US FY 2018 – first % is fleet size, second % is accidents. To make it easy those in blue have zero accidents


There is still no correlation to hours/missions flown nor does it distinguish between accidents resulting from engine failure and other causes.
Like the stats ANFI used to push his cause, these are interesting but mostly meaningless.
It is obvious that singles make up the majority of the fleet so should represent the majority of accidents.
More data is required before any credible deduction can be made, until then stats can be used to justify any point of view.

[megan]

There is still no correlation to hours/missions flown nor does it distinguish between accidents resulting from engine failure and other causesCorrelation to hours or missions flown is rather pointless, it depends on the use to which the aircraft is being put. An R-22 doing an hour of endless autos with a student is far higher up the risk scale than a 206 used for commuting, or indeed a R-22 used for commuting. Figures I quoted in an earlier post cite engine failure being responsible for 16.7% of ALL accidents.

[Bell_ringer]

Figures I quoted in an earlier post cite engine failure being responsible for 16.7% of ALL accidents.

That does sound high, are they including loss (ie running out) of power in that statistic?
Robbies in particular seem to have many power loss accidents with fully operational engines.

[EESDL]

There was mention of the use of PC2DLE in Hems and O&G. Excused under the banner of Public service/use.
Can we just be very clear on one thing.
PC2DLE is used because the machine is simply not viable in whatever role it flies if flown PC1 - or can’t fly PC1. It is a marketing tactic, based on logic and data sets.
PC2DLE is a method to extract as much use as possible out of an ageing design.
It is a commercial consideration - not a safety-based one.
There is an air Ambulance Service in the North of England which is authorised to fly PC2 to rooftop hospital helipads - within congested areas (As365n2)
This is despite there finally being PC1-capable machines available for use.
We have seen the O&G sector slowly catching-up with reality and public opinion with the implementation of genuine PC1 machines.
Manufacturers clung onto grandfather rights and old designs for far too long as they had a ready market under the Public Service/use banner.
So who ‘carries the can’ where there is a readily-available PC1 option but the operator continues PC2 operations?
The Accountable Manager is covered by the National Aviation Authority and insurance policy?
The NAA is covered by lack of civil service accountability and bureaucracy?
So, when the Safety Plan is based on ALARP, and the CBA is based on a possible increase of insurance premium rather than genuinely mitigating the risk, you know that safety is rarely an operators’ first priority.
So have as many, or as few engines as you like - it is not the issue.
The ‘foot selfie’ 350 into NY waters would not have happened if same trip flown in a twin - simply because the fuel cocks are in the ceiling in the 355.
It would not have happened if the 350 was designed for such a role - ie, true protection of critical areas from ‘Joe Public’.
We all know that Helicopters are a compromise but can I suggest that it can not afford to be regarded as such. ‘Multi-role’ designs have no place in today’s market as we have discovered that ‘multi -role’ really does mean not truly fit for anything specific.
I am not a Kamax salesman ;-)
I further suggest that if the OEMs had designed and built a true O&G Helicopter all those decades ago then the world for a helicopter passenger would be a safer place today.
The ‘helicopter transport’ budget for O&G companies is minuscule in comparison to the rest of their spreadsheet and yet continuous ‘CBA’ pressure has helped to stifle technical and safety progress - and tolerated by NAAs.
Where there is a will, there is a way.
There has been little ‘will’ and therefore a lack of ‘way’.
This situation is markedly different to the airline industry.

[megan]

That does sound high, are they including loss (ie running out) of power in that statistic No, it would be filed under one of the "Error" categories, which make up 38% of all accidents ie Accidents by error - Misassessment of weather 18.2%, Misjudgement of landing 8%, Not going around 4%, Flight below MSA 21%, Overload 2.8%, Not considering wind 2.8%, Inadequate pilot judgement 34.7%, Poor circumspection 8.5%

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That does sound high, are they including loss (ie running out) of power in that statistic?
Robbies in particular seem to have many power loss accidents with fully operational engines. Is that because pilots think if they can get under the line on the HOGE graph, they can do anything they like? Any OGE operations should have a power margin available to allow for pilot errors, wind, turbulence, imperfectly clean blades etc etc

Standard UK mil ops require a minimum of a 5% thrust margin - it is easy to calculate, you just reduce your AUM by 5% of the maximum HOGE graph value at your intended operating DA.