Flyaway manoeuvre

[[email protected]]

Any suggestions from the knowledgeable out there as to the differences in suggested flyaway (engine fail in the hover - transition to achieve safe single engine speed) manoeuvres between aircraft?

The Lynx procedure is to select 15 degrees nose down, the 139 is to adjust the attitude 20 degrees from the hover (giving 10-15 degrees nose down) and the S92 is 20 degrees nose down.

Meanwhile the venerable Sea King is generally no more than 5 degrees nose down.

Now it maybe because we (on the SK) are concerned with minimum height loss whereas the industry standard wants the quickest time from failure to SSE accepting the large height loss involved with such large nose-down selections.

Disc loading on the 3 above mentioned helos is much higher than the SK and they also all have cambered blades, unlike the SK which is a symmetrical aerofoil. I don't know if either of these are relevant factors.

Would an S92 or 139 pilot really select 20 degrees nose-down from a night, overwater hover or would the flyaway be modified for winching scenarios?

Answers, suggestions (and if necessary some crab banter) gratefully accepted.

[Aser]

The big difference for me it's the hover height.

I tried once the -20 in the 139 from a 200' hover over the sea... I didn't like it! :\

If I'm at hover with less than 90% PI and below 150' I'd put 0º and pull until 90% rrpm hoping for the best.

With more PI and less height, I'll accept the ditching.

just my two cents.

Regards
Aser

[bb in ca]

Sikorsky S-61 RFM
Page 3-3

Acceleration to forward flight after an engine failure at the CDP can be accomplished by immediately rotating the helicopter to approximately 20 degrees nose down.

Gross weight, wind, density altitude, height of water or land, hostile environment etc. would be some of the factors affecting a pilot's decision.

[drugsdontwork]

I think a 20 deg nose down in the SK is likely to convert a potentially viable flyaway to a ditching. Similarly getting the attitude even slightly wrong converts a post ditching SE take off with limited power into a second ditching.

That's what happened on Waterbird course anyway. Can't speak for other types.

[Geoffersincornwall]

I feel a little uncomfortable arguing the toss about a situation that would probably take you somewhat by surprise. The 'seriously nose-down' advocates may find that the level of rotor decay and height loss frustrates the 'fly-away' and the prospect of 'tent-pegging' into the oggin is not a happy one. Arm-chair theorists need to exercise a little caution as the intervention time may be more than you think.

The key as far as I can tell in the sim, (and no I cannot vouch for its fidelity in this respect and we can only look at weights up to 6400kg), is windspeed. If you have 20 knots through the disc you can just about get away with anything by just flying away and keeping the Nr above 92%.

Obviously the more shp you have the better position you are in and the latest generation of twins certainly aim to deliver in that department. It seems however that increasing the shp to make the OEI situation any better will keep pushing the cruise Ng/ITT into the lower/less efficient part of a turbine's operating range and increasing the fuel consumption as a result. Can we make turbines any more efficient in the mid-range? After years of focussing on the top end it may be time to look at this aspect of turbine design.

If a helicopter's primary task is in the HOGE environment then we owe it to the crews to address the issues an OEI situation raises. Exposure can be acceptable for take-off and landing but not - I suggest - during a rescue, during a low-speed search, during anti-submarine operations and any other task we dream up that leaves us languishing in the most hazardous part of the flight envelope.

G.

[diginagain]

The Lynx procedure is to select 15 degrees nose down,

Sounds about right. For Wallop. If you found yourself sitting in a downwind hover on a warm German summer's day, one bloke with his head in the sight, the other working like a one-armed paper-hanger (which we did, from time to time) it seemed a little academic.

[[email protected]]

The wind across the disc in the hover is certainly a major factor when determining the viability of the flyaway - downwind it can result in several times the into-wind height loss to gain airspeed.

As we all know the key to SSE flight is speed or having the height to trade for speed - the question is, is the amount of nose down specified in the RFMs the result of actual test points during certification and, as I alluded to earlier, all about the quickest way to gain that speed instead of minimising height loss?

I would have thought that for any OGE hovering ops, minimum height loss would be the overriding requirement but I wonder if the RFM techniques are purely aimed at low speed configurations on departure or approach.

[JimL]

Before arriving at the correct manoeuvre, you need to be aware of the conditions under which the engine is lost. As Geoff has said, the intervention time will vary with the conditions of the failure.

For a manoeuvre with an expected failure and where the indication are clearly annunciated - i.e. at TDP and with a good audio warning (a voice for example); intervention time can be as low as 0.5 seconds (which is permitted in CAT A design). For a failure that occurs in an extended hover, the intervention time is likely to be more than this.

For an aircraft performing hoisting under HEC Class D; there is almost no penalty for an engine failure and the aircraft will not loose more than 10% of the line length or 4ft whichever is the least. For a heavily loaded aircraft performing hoisting under rescue (or aerial work) conditions the drop down is likely to be conditional upon the engine control system (a FADEC system is always preferable to a hydro-mechanical system), the mass and the environmental conditions (including wind).

When the HAPS manoeuvres were being modelled, simulating an engine failure at RP (TDP) with a 1 second intervention time showed that a rotation 'through' 20 degrees provided the least drop down when the wind was below 5 knots. With the wind at or above 20 kts, a 20 degree rotation would add about 50ft to the drop down.

Modelling the optimum rotation showed that a linear reduction from 20 degrees (for a five kt wind) to about 5 degrees (for a 20 kt wind) would optimise the drop down (and have little effect on deck-edge clearance).

Any procedure that is put into the Flight Manual has to be clear and simple; for that reason, you are unlikely to see a graduated rotation with any published procedure. (The CAT a procedures also have be tested under low wind conditions (the most demanding) which leads to a single (published) rotation figure.)

With a take-off procedure that can lead to a drop down below deck height, the first part of the procedure is optimised for deck-edge clearance and little or no benefit is (can be) taken for wind effect. Wind accountability is usually only provided once the initial part of the manoeuvre is completed.

More if you wish later.

Jim

[Flying Bull]

Hi,
the problem with numbers is, that you tend to stick to them and loose the varity of options you have.
In the military and with some operators you have to give rules to adhere to, otherwise the young pilots do all the things they shouldn´t do ;-)
Still, it all depends on the wheather and the height / temperature / weight etc.
With about 30 to 40 knots most twins are happy to fly on one engine - and you don´t have to put the nose down 20° to get there.
Big attitude changes means also big workload - and that, while you have the problems of an engine failure anyway.
With just a little nose down - and collective adjusted from transient power to emergency power (or just keeping the Nr within allowed limits), in most cases you will have good chances to get away safely without a massive height loss.
Once you have the 30 to 40 KIAS ´isch, you can then go for Vy and safe altitude and deal with the emergency.
You can try it yourself with both engines operating (most helicopters beeing TQ limited) and go in an OGEH and then reduce the collective to 1/2 emergency-power from one engine (say 140% OEI allowed - go twin 70%) and look what happens, if you stuff the nose down 20° or just about an itch.
Try the same with less power - and get a feel for the behaviour of you bird and widen the varity of options you can choose from for the case of the real emergency.

Greetings Flying Bull#

P.S. Except over the sea - where you tend to make the decision "Fly away" or "ditch" when you know your power margin, you still have the option to land over land - and there 30 to 40 KIAS is better than rushing down with 70´isch and then have to do a giant flare.
So starting gentle keeps the options open :O

[Tourist]

Is it something to do with how much airspeed through the disk you need to get translational lift perhaps?

Seaking "burble" comes pretty quick, therefore not so much nose down and subsequent height loss required.

Perhaps other aircraft require more vigourous acceleration to get the benefits of translational lift due to relative rotor size?

That being said, we used to practise single engine failures next to Rinsey Cliff (approx 200ft) in the SK 5 by lowering the lever rapidly to single engine power, and you needed a lot more than 5 nose down to get going.

[Horror box]

Some very good points here from Geoffers and Jim. I would be very interested to hear more Jim, especially with reference to modeling of different types and specific data. I have long tried to reinforce the need for a better understanding, instead of just flying numbers, and whilst it makes perfect sense and is logical that the amount of pitch down would decrease with wind speed, one has to be careful instructing and advising without good test data and or training to support. For most of us the RFM is the only thing we have. I personally feel very uncomfortable using 20 degrees nose down in an S92 in anything other than calm conditions, especially at night or in poor weather. I believe that some of the RFM information serves to confuse rather than clarify in some areas, and where the RFM procedure states simply "rotate to a maximum of 20 degrees nose down" this leaves some discussion as to whether this is referenced from a hover datum - which in an S92 is often around 8-10 degrees up - or referenced from the AI.
If referenced from the AI we are talking about a rotation of nearly 30 degrees, which I believe to be a potentially dangerous route to over controlling and could lead to a dangerous further decay in Nr in many cases, with a greatly increased initial rate of descent. I believe Jim hit the nail not he head with the wording rotation through 20 degrees, not to 20 degrees.

[212man]

I believe that some of the RFM information serves to confuse rather than clarify in some areas, and where the RFM procedure states simply "rotate to a maximum of 20 degrees nose down" this leaves some discussion as to whether this is referenced from a hover datum - which in an S92 is often around 8-10 degrees up - or referenced from the AI.
If referenced from the AI we are talking about a rotation of nearly 30 degrees,

I thought that had been resolved some time ago - for OEI it's an absolute value of 20 degrees nose down. The AEO case is a delta.

[Horror box]

212man - Yes I remember it being discussed, and I have sought clarification, but as yet have had no concrete answer, so thanks. Do you have a reference for that? I don't believe the RFM was ever ammended, although I could be wrong, but I have not seen an amendment here in our company.

[JimL]

When this was being modelled (in a medium, medium/heavy and heavy) we decided on a through rotation to ensure consistency of results. As Horror Box has said, the actual pitch angle will vary with loading and conditions (of wind). Under design conditions the wind conditions (usually light to calm) and C of G has to provide a deterministic set of conditions for flight test. (I doubt if any manufacturer has tested a take-off procedure under all of the conditions found offshore.)

However, this is slightly off thread because Crab was asking a question about 'flyaway'; the only reason I introduced the results of the modelling was because it was from experience and reasonably hard numbers could be quoted.

It is well to remember that, for a take-off, we usually are describing a 'dynamic' manoeuvre where there is already energy in the manoeuvre before the failure. For a flyaway manoeuvre the start point is static with respect to vertical energy (although there might be some wind effect).

If the flyaway is being conducted from somewhere near OEI Vstayup the loss of height will only be the result from the remaining engine ramping up to max power (a hydro-mechanical will involve lag because the rotor slowing will provide the cue).

As someone else has mentioned, beneficial effect of rotation will only apply when the mass is low enough to enable a recovery; under all circumstances, an aircraft will ditch if the mass is too high for recovery. Under condition where ditching is the inevitable result of the engine failure, rotation is not required to effect a OEI recovery but to minimise the rate of descent.

To rotate to 20 degrees when ditching is inevitable, might place the aircraft in a high rate of descent and accelerating condition.

It may be a dumb thing to say but the best condition to be in is knowing: what will be the result of an engine failure; and, if flyaway is possible, what the Vstayup and Vtoss is and (as asked by Crab) what the optimum rotation will be for recovery.

As previously described, a small rotation with light wind conditions will only work if the mass equates to HEC D mass; conversely, a large rotation with a higher wind will (unnecessarily) sacrifice drop down.

Lastly, it is not just the rotation that has to be considered, it is also the time that the pitch angle is held. With some manufacturers, it is recommended to ease back on the cyclic as soon as the angle has been achieved; with others there is a Vt (target speed - before Vtoss) so as not to overshoot the Vtoss.

Jim

[Geoffersincornwall]

I am just sitting here thinking that all this 'science' is for nought if you are TIBMIN sitting in the hover at 40-50 feet when the donkey stops you are not going to be able to do much if mass is much greater than OEI hover.

Sea states unsuitable for ditching are more often than not associated with stronger winds thus the window for forced ditching is reduced - how much we can only guess but we may be arguing about a remote possibility. Put that alongside the possibility of an unsatisfactory ditching due to excessive nose down on contact (blade strike > rollover) and the waters are muddied.

What happens to the rad alt reading with an attitude change of up to 30 degrees?

Maybe adequate rehearsal in the sim is a smart move but no-one has yet tabled a request to me for such an exercise but the OEI at TDP on a helipad vertical has got to be close.

G.

[JimL]

Geoff,

The simulator only comes into play if the outcome is known to be positive; what can be done under those circumstances is to play with the rotation to see the effect. Eventually you will establish the safe envelope (and will show acceleration distances and drop down).

That is precisely what was done in the modelling; we ran a series of plots with increasing wind and varying pitch angles until we had a graph of the pattern. The results were as I indicated.

Nothing is better than modelling for such what if questions.

Jim

[[email protected]]

Jim, if that modelling is only using simulator data, surely it is only valid if those same test points that provide that data have been taken from the manoeuvres flown in the real, test-instrumented aircraft.

Obviously the condition I am most interested in is the OGE hover since that is what us SARboys do a lot of and, as seems to be the case, there is no specific data in the RFMs for that condition, just a generic manoeuvre (amount of nose-down, duration of attitude and target speed) which is more likely to be applicable to rig work or Cat A (or whatever the latest name for it is) performance.

Jim the HEC D you talk of is presumably a limit on AUM to ensure that effectively an aircraft is SSE in the hover if winching is being conducted - such limits do not apply to us nor, if I have got my information correct, would they apply to civSAR on a rescue since they only have to consider aircraft performance (in public transport terms) once the rescue is complete.

[[email protected]]

However, it seems clear that the concensus is that 20 degrees nose-down from a normal winching height hover, especially at night over the sea, is a non-starter due to potential disorientation, large likely height loss and the strong risk of compromising the ditching.

[Geoffersincornwall]

The AW 139 does indeed have some relevant data in the RFM Section 4.

A procedure is detailed and a graph provided that details the height loss under various conditions. For example:

sea level
20 deg C
6400 kg
Height loss = 55 feet

Procedure calls for :

FLYAWAY PROCEDURE
1. Collective/Cyclic control — Rotate nose down in 1 second to an attitude of -20°. Recover pitch attitude to 5° nose up in approximately 5 seconds. Maintain this attitude while using the collective to droop the NR to a minimum of 90% NR, if necessary, to
arrest the descent.
2. Acceleration — Maintain pitch attitude at 5° nose up and accelerate to
VTOSS (40 KIAS).
3. Climb — When the aircraft has achieved VTOSS (40 KIAS) and a positive rate of climb lower collec- tive to recover NR to 100%,

You can see why taking longer than the test pilots allow for reaction time may leave you smacking into the surface with the nose wheel instead of the main wheels.

If you guys saw what I see every day you probably wouldn't be quite so bullish about the performance of a significant minority of colleagues who in all probability could not match your expectations.

We used to have great fun doing 'OEI flyways' in the MBB 105. We had to start at 200 feet min for the HOGE because a minor misjudgement by the student would not give the instructor much time to recover the situation. Then again the MBB 105 was not famous for its OEI performance.

G :)

[Horror box]

However, it seems clear that the concensus is that 20 degrees nose-down from a normal winching height hover, especially at night over the sea, is a non-starter due to potential disorientation, large likely height loss and the strong risk of compromising the ditching.


I think I have to agree with you here. Hitting the water 20 degrees nose down has got to be less favourable than a more controlled ditching with less ROD, even at night. This then raises the question, that possibly Crab is alluding to, should we increase the perfromance margins when expecting to operate HOGE at night? How practical this is will be another question, especially for SAR, when loiter time is a key factor.

[JimL]

Don't try to 'up' the margins for SAR; just risk assess the activity by establishing the probabilities and see if they are acceptable.

Jim

[[email protected]]

I knew the 139 constantly reviewed the performance data and gave you a min height for hovering that would allow a flyaway - does the S-92 do the same thing?

The Sea King obviously doesn't have any 'drop-down' data in the ODM to calculate height loss whereas the Lynx does have graphs for predicted height loss in the hover (into wind). We do have the ability to hover higher to maintain a flyaway but the assessment of performance is still only based on hover torque even though the proximity to ETL makes a huge difference to the height loss during the flyaway.

Junior pilots will always want a simple 'one-stop shop' answer to flyaway or not flyaway but there are so many variables that it is impossible to shortcut experience. For example, tonight we were hovering at 125' alongside a large car carrying vessel - we were about 100 degrees out of wind and the boat was doing 15 kts - our airspeed across the disc was next to zero and when the HP tried a practice flyaway we had to throw it away so as to avoid the water. He flew a normal profile of 1 or 2 degrees nose down as he would into wind and it didn't work - when we tried it again with 7 or 8 degrees we made ETL and flew away with relative ease.

[SARREMF]

Hi Crabb

When I got to the 412 it had a similar issue with the flyaway technique. It too required a 20 degree change - note it used the phrase "up to". I tried the Sea King standard min height loss tech Kaye and it appeared to work well. I used the same technique described already for students by going to half power twin engine and trying both techniques to show the difference. It was simply stunning the difference in height loss and effect it could have on a crew. I had the chance to go to the Bell factory and discuss this with the TP's. They referred me back to the phrase "up to". that said they then produced a supplement to the RFm that we hadn't had as well! Long story and not a good one!

I have seen the same remarks with regard to the EC225 as well regarding fly away - it wAs demonstrated by the TP's in the Sim.

So, my gut feel says if the RFm says select an attitude then some clever people have checked it and you are probably not wise to mess about. If it says "up to" then perhaps ther is scope to gain experience before the worst happens and you need it for real.

[Shawn Coyle]

Wouldn't it be nice to have a good low airspeed indicator so that you could know (within 2-3 knots) what the actual airspeed through the disk was - that way you could know with a good deal more certainty how much nose down to use?
We have the technology, we just lack the political will....

[[email protected]]

SARREMF - yes, the only known engine fail at SARTU on the 412 would have been a ditching if the QHI had used 20 degrees nose-down. As it was he used the Sea King technique and flew away despite being theoretically committed.

Shawn - yes, that would solve a lot of issues - what technology exists that isn't being used or is it just better designed and positioned pitot tubes we need?

At least it seems that disc loading and blade design don't seem to be factors, it is simply the case that a 'one-size-fits-all' technique for dealing with a single engine fail in the hover doesn't exist and, whilst guidance in the RFM/ODM is one thing, there is no substitute for experience and practise.

[MightyGem]

Our EC135 FLM doesn't give any guidance on the amount of nosedown. It just says: Airspeed - increase if possible. It's quite a benign occurance for us, even 90 degs out of wind and at our typical weights. Pull to 30 second power and we can fly away without any height loss.

[FLI]

MG, that is very impressive OEI performance.
How much are you below gross weight to give 'a Hover, no loss of height fly-away' on OEI?
Does the EC135 also have a CAT A Helipad take off profile that allows take off at gross weight AND no drop-down with engine failure at TDP?
FLI

[MightyGem]

Only done the flyaways during OPCs when our weight is typically around 2600kgs(max 2910), so probably better performance that when at the max.

Yes, we have helipad capabilty at MAUM(+17 C at S/L). The TDP for Cat A(Perf 1) is 120ft, and, again at OPC weights, there is very little height loss. Even so we can flyaway without having to use the 30 second rating, so it's possible that using that at MAUM the performance could be similar. Then again, maybe not.

[RVDT]

I would have assumed that to carry out winching you would have OEI/HOGE performance. Then again it would depend on the classification of the operation.

EC 135 has OEI/HOGE published data of course. Simple rule of thumb is that most times 128% Q (depending on model - quoting P2+ here) is available at 30 sec OEI rating. Therefore if torque required to hover is less than 2 x 64% on the digital readout (Not FLI value) = no brainer. However at values above that the following is published as an "Operational Tip".


Section 10 Manufacturers data (NOT APPROVED)

10-3 Rev. 2

HEIGHT LOSS AFTER ENGINE FAILURE / HOVER PERFORMANCE

10.2.1 i.e. a safe forced landing cannot be accomplished, or for overwater operations. This information is NOT applicable for operation requiring OEI-HOGE performance.

10.2.3 Flight procedure after single engine failure in hover (HOGE)

Procedure

1. Attitude - Nosedown ~ -20°

Under wind conditions the following values are recommended:

Up to 20 kt -20°

~ 30 kt -10°

above 40 kt 0°

2. Collective lever - adjust to 30 sec. Power

3. Attitude - Adjust to near level attitude while accelerating to V TOSS = 40 KIAS and initiate climb.

Height loss chart would indicate via extrapolation the following for :

PA 0'

At least 12' in all cases but at the following weights and temp no more:

2500 kg 46 ℃

2600 kg 36 ℃

2700 kg 0 ℃

STD day at 2910 kg MAUM you would lose ~ 75'
10 knots of wind would reduce that by about 25' = 50'

NOTE: UNAPPROVED DATA

[ODEN]

In a night hoisting without beeing able to hover OEI we almost always breif a landing (ditching) in case of engine failure. This because it is the safest way.
To think that you would react quick enough and fly away according to all the theorethical values in the FM without hitting the water is abit overconfident.

Safety first...make a controled ditching...survive, get a new chopper.

[RVDT]

Safety first...make a controled ditching...survive, get a new chopper.

Progress next.........get a new chopper that CAN hover OEI. :rolleyes:

[[email protected]]

Oden, we make a call based on hover torque - either safe single engine, flyaway or committed but there will always be marginal cases and carrying out a 'controlled' ditching in a high sea state might not be that safe.

[JimL]

You make a good point crab; an uninformed decision either way will be wrong. Ditching when you have sufficient performance for a flyaway is a bad decision.

The only way to deal with this is to know: the performance in hand; the optimum rotation; and the likely drop down. It is only the marginal cases where a decision will be difficult.

Fortunately, high seas are normally associated with high winds - the aviators saviour.

Jim

[Geoffersincornwall]

Maybe the decider is the pilots awareness of his reaction time. If you are really on the ball when a donkey stops and the right answer is -20 and go then have a shot. If, on the other hand you were caught flat footed then an extreme nose down is probably not going to be a good investment.

Rehearsing in the sim can be a great way forward but we need more assurances about the fidelity of the sim in a regime not necessarily covered during certification.

G.

[Tourist]

The decision does not have to be final, either.

I know a couple of RN guys that had a single engine failure on take-off from a carrier.

Nr drooped well below 91% so they decided to land on the water. During the flare the Nr recovered enough to continue flying at very very low level in ground effect until speed/Nr recovered back to reasonable values.

[Test 1]

Teaching flyaways from 50ft in a Lynx several years ago, the conditions were such that if slightly more than 15deg nose down was selected, the rate of descent built up and we had to run on; any less and the aircraft failed to accelerate quickly enough and we ran out of height, again necessitating a run on.

Only by selecting and holding 15deg were we able to fly away. This demonstrated to me the importance of carrying out the recommended technique.

[Saint Evil]

The AS332L2 SAR Support allows for you to calculate your weight for the 30sec rating and then if required it is a normal transition into forward flight. If you're too heavy then you can use the 15deg nose down method. That is quite exciting.

[Sven Sixtoo]

Having been HP for a bent SK while practicing OEI flyaway - way back in about 1985 when the QHIs hadn't worked out properly how to simulate using manual throttles - I can confirm that 20 deg ND in a SK is likely to lead rapidly to the scene of the incident. Less ND, while not necessarily changing the chance of a flyout, would have given us better attitude / VV at impact and would probably have resulted in less damage.

Also, the SK procedures and numbers as used in the RAF are designed to cope with the IFR autohover case. There is, I believe, an inbuilt assumption that large attitude changes at low level are likely to lead to (Un) CFIT, and thus the numbers are designed to get you gently out of an inherently recoverable situation without losing control ie it's not just about power margins.

Sven

Gently eradicating 33 years experience with red wine

[Spacer]

I guess what we've agreed on is that different types, environments, etc need a different response. Some with a large nose down, others not. But then we probably knew that, as even on the same type you may need two different techniques on different days.


Fly safe!

[bast0n]

Crab

If you were in a Wessex 5 you probably would not notice the engine failure.................

Going for lunch now.......

D

[proudfishead]

For comparison, EH101 advocates a delta minus 15 pitch attitude change, whilst simultaneously cutting the sonar cable, pulling through to up to 136% Tq OEI and drooping Nr to the low 90s. NHP calling NR.

However, it was revealed after some discussion with AW, that the procedure has the following caveat: Day VMC, twin pilot assuming instantaneous pilot reaction . . . . hmmmm . . . . good luck night dipping then. There have been regular mumblings of a "modified" or "half" flyaway that is less severe in terms of attitude change. We shall see.

[ianp]

Interesting thread, seems to following two avenues at the moment;


what to do if you have a sudden power loss (flyaway technique) and

what happens if you have a sudden power loss (performance charts graphs, intervention times etc).

For my two penneth' worth

Flyaway is the technique developed for a specific ac to get you to the min power speed, often a compromise between acceleration and height loss. Normally a single defined manoeuvre mainly because it would be too difficult to teach multiple techniques for the infinite number of weight and environmental conditions. This technique will depend on many factors, control power, control response, ERG, etc.

What happens , lots of variables here, firstly the ideal situation is obviously one where you have enough power to transition normally. If not an ac manufacturer/test centre can conduct flyaway testing to establish height loss in the event of sudden power loss. This will normally be done using the defined flyaway technique (see above). Firstly you then need to work out intervention time (mentioned in earlier posts) this is actually the sum of two things, rotorcraft response time (time taken for the pilot to notice the engine has stopped) and pilot response time (time for the pilot to do something about it). Armed with this information testing can then take place to establish the flyaway height loss also described in earlier posts, normally Nr is used as control parameter for this and long story short, a load of flaways are flown and empirical derived data obtained for how much height is lost when you fly the standard procedure. Nowadays this data is used to prove a mathematical model which is used to publish ODM flyaway height loss charts.

So what does this actually all mean, basically the ht loss published will give you a pretty good idea of how much ht you will lose if you fly the published technique perfectly. We all know that engine failures rarely happen day VMC with a runway in front of you so the judgement call is on the pilot to consider all those variables, day/night/NVG/cliffs/mountains/tail or crosswinds etc. and add sensible margins if you can. Obviously if you fly something older with no flyaway data then best advice really is to try and establish the most efficient way to achieve min power speed, maybe asking the question of your operating authority as to why you doon't actually have this information?