Multi Engine Helicopters & the HV Curve

[tbc]

Section 5 (Performance Data) of a typical (lets use the EC 135) RFM gives data on the Critical Height-Velocity envelope. It allows calculation of an 'avoid' area which is critical for helicopter operation in the event of a single engine failure during take-off, landing or other operations near the ground.

The area is a combination of height (agl) and IAS as a function of gross mass, PA and OAT.

As an ex Single Engine QHI of some experience I can cope with this, as well as getting my 'bloggs' to grasp it too, in the knowledge that if the engine fails within the avoid curve the likelyhood is that I/he/she will crash due to a lack of height (time) or speed to do something with an autorotation.

Can someone advise the applicability of such an avoid curve in a ME Helicopter that is operating to CAT A - Class 1 performance standards?

Am I close is suggesting that this data is provided for either:

Non-Class A operations - such as the military where they load and lift so to speak where losing one engine in this regime could hurt, despite the other one doing the business as best it can, (not a convincing argument but you never know!!)

or

Is to advise a pilot who ends up OEI that he should avoid or at least minimise exposure time on landing (methinks) as he reverts back to the understandable use of the Avoid Curve for SE helicopters.


212man (from Flight Testing forum) confirms that this data has to be given in the RFM under regulatory requirements - but any thoughts/advise/guidance etc.??

[NickLappos]

tbc,

The avoid area is provided to guide you as to expected response. It is somewhat independant of Cat A procedures, which also separately test response, but use different entry conditions, weights and delay times, so they are not directly comparible. Some elaborations:

Cat A uses different weights, so response can be better than the avoid area's chose weight (almost always max gross).

Cat A has dyanmic conditions during acceleration especially. Avoid areas are set in steady flight.

Once OEI in a Cat A machine, the avoid curve isof no use at all, it will not predict how much trouble you will be in if the remaining engine quits.

Cat A uses lesser delay times, generally set to .3 seconds. Avoid area uses 1.3 second above the knee. .3 below.

I have been of the opinion for a long time that the avoid area HV curve is of very limited use for a twin turbine, in practical application, and with ever more reliable engines, is not of primary importance. I have now fastened my seat belt for the fairly typical pprune onslaught where engine failure is the Cause of All Evil, and with hard Cat A, six engined helos, our accident propensity will drop to nil! ;)

[212man]

Nick,
a more reasoned response might be: "why don't more manufacturers provide sets of graphs so that the HV curve can be derived for any given set of weight, altitude and temperature, such as that found in the Bell 212 FLM?"

The graphs most FLMs have are simply there for the regulations and not directly relatable to day to day conditions.

Interestingly, according to a conversation I once had with an ECF test pilot (now head of Flight Test), there was a move to try and miss out the testing altogether on large expensive multi engine types, as it invariably resulted in a 'crash' at some point in the proceeding with lots of bills and delays.

[NickLappos]

212man,

An even more reasoned approach might be to actually test and approve those elements that can eliminate crashes. Look up the stats and tell us the last time a twin had an engine failure where the HV curve (or full Cat A) would have made any difference. You will not find a useful HV curve, because HV OEI failures produce NIL accidents.

I sound like a broken record, but here goes! We think, practive, study and learn engine failure from our first piloting breath. It is so ingrained into us that we believe engine failure tolerance, procedures and performance are synonymous with safety. This pilot-cultural conditioning is like the lemmings who rush from some danger and end up drowning.

We have accidents in twins because we do not have the right warning kit (EGPWS, TCAS) because we do not have the right instrument equipment (SAS, GPS) because we do not have the right helicopter instrument routes let-downs (Heliport precision approaches) and becuase we try to fix what feels good (engine failure response) rather than what kills us.

We get a F in self improvement, and it gets worse every time we again debate engine failures, and not accident causes.

[212man]

Nick,
I don't dispute that statistcally engine failures are not a big proportion of accident causes (the NASA report into all rotorcraft accidents in the US from 1964 to 1997 puts it at about 10% for twins, I recall) and I applaud the introduction of devices such as EGPWS etc.

(I think the USCG may have a different take on that one though!)

It still doesn't make you feel any more comfortable landing or taking off from a swamp barge in the middle of a jungle clearing, knowing that if an engine does fail there is very little your training will do to prevent an accident, and a bad one at that.

Of course, the irony is that in 5-10 years time when we are all whizzing around in a/c with EGPWS, de-icing, TCAS2 and coupled approaches to the ground, the engine failure accidents will become a large proportion of the total! (assuming no change in failure rate, which is likely as people are saying they don't fail so why change anything?)

We can then re-debate the relative merits of Cat A then!

[NickLappos]

212man,
The 10% is inaccurate, to say the least. The data I have seen from OGP says that the accident rate for Cat A twins (cat A enroute) is absolute zero due to engine failure.

the 'Irony" that we would solve all the crew error and maintenance error accidents, then the other mechanical failures, and the mid air collisions, and then we would be behind in fixing the engine failures is really stretching! In the approximately 2 million hours logged by those in the OGP list, with about 1/2 million hours in twins, zero is a number that doesn't need fixing, let alone worrying about how we wasted our time driving down the 80% of all accidents when we built a full IFR precision approach network with routes, equipped all helos with TCAS and EGPWS, created full error-free maintenance systems and then said "Gosh! We screwed up, now the engines will start failing!"

I don't think we really know how much energy we spend trying to fix the unbroken, while the real accidents go on, labeled 'crew error" and thus no real problem.

[Katfish]

If I might submit a gentle input to this debate. My organisation has SPIFR EMS 412's (definitely non Cat A!), and has a strong Check & Training program during which we practice all forms of engine failure every 6 months. We also spend thousands of dollars (Oz) on sending our pilots to a 412 sim to practice even more OEI emergencies. We have been doing this for many years. I hear what you say regarding record of OEI in twins (I personally know of 5 in the last 10 years) however the other week a pilot had an engine chip in which the company procedure was to shut down the engine. No engine failure, but OEI non the less. He was very glad of all the OEI practice landings and approaches he had done over the years. I suggest there are many reasons why one might end up OEI other than outright engine failure.
We also carry out Cat A profile rearwards takeoffs when the power is available, as this is the safest flight profile from a restricted area or rooftop pad.
We use the Cat A HV as a guide. As we all know, HV's have been around a long long time. even the Sycamore had them. Their concept hasn't changed. Low IAS at some heights agl is not conducive to a safe landing follwing an engine failure, multi or single doesn't matter. The only difference is the multi HV area is much smaller due to some power being available to either fly away or to cushion the landing.
I look forward to the iminent generation of truly Cat A helicopters (AB139 at el) that can hover OEI at MAUW at 25 deg C. And like computers and NVG's, we will wonder how we ever flew without them.

[212man]

(Source: NASA report into civil US rotorcraft accidents)

7.4.1 Loss of Engine Power (39 Accidents)

As table 30 shows, introduction of twin-turbine helicopters to the civil fleet dramatically reduced the percent of loss of engine power accidents from 31% to 13%. However, table 32 suggests that a very disturbing trend began when larger helicopters capable of carrying more people were introduced: any serious accident affects more people and likely receives greater attention by the public. This trend exactly parallels the situation faced by the fixed-wing industry as they moved from the 1920s Ford Tri-motor to modern day, large jet airliners, such as the Boeing 747.

Sorry, I was wrong it wasn't 10%

As Katfish says, you don't have to have an engine failure to end up on one engine: engine chip, false fire warning, loss of oil pressure, are all events I've seen in the recent past.

[Jack Carson]

Don't confuse the HV diagram with Cat A certifications. Cat A means a multi engine rotorcraft designed with engine and system isolation features specified in Part 29 and utilizing scheduled takeoff and landing operations under a critical engine feature consept which assures adaquate designated surface area "land back" and adaquate performance capability for continued safe flight in the event of an engine failure.

HV assigns an area "shaded" where an average pilot with adaquate warning will be not able to make a safe touchdown once an engine fails.

[NickLappos]

212Man:

It is generally a good idea to read the report, since you then know how to support your arguments from its information. If you had read it, you would see that, indeed, you were simply wrong. Here is what the report actually says:

1) The report says that 13% of all twin engine helo accidents occur from "loss of power" but you failed to tell us that about 2/3 of these "power" losses involved both engines failing due to fuel starvation and the like. Exactly how does this support your argument for Cat A standards?

2) The actual losses where we can account for an engine failure in this data is 16 out of 302 accidents, for 5% of all accidents involve twins where an engine fails. In other words, you wish to solve the 5% problem. The report you quote states that the number of engine failure accidents is "relatively few" and "not statistically meaningful" in twins.

3) the recommendations from the 35 year study state the following areas of concern for twins (and no mention of engine failure improvements is made):

A) Solve loss of control problems, especially in bad weather.
B) Employ an alert system to warn pilots of approaching limits
C) Improve crew selection and training and insure that operational info is available to the pilot
D)Improve criteria for time change components, based on sound materials science
E) Require HUMS

Does this list look like the one I gave above, albeit with somewhat different wording?

Here is the report:
http://safecopter.arc.nasa.gov/Pages/Columns/Accidents/NASA%20TP%20209597.pdf

[Thomas coupling]

tbc:
If you fly i.a.w. CAT 1/Gp A in the EC135 atleast, then you will not enter the avoid curve (Fig 5-9 FLM) under any take off or landing circumstances. In fact it confirms this at: FLM: 9.1-1 - 37

That's one of the reasons why they invented this profile.
The 'Deadman's Curve' is of no relevance to normal Cat 1 ops. Even (as you state) under OEI.

But I would agree that for non CAT 1 ops then you would have to consider the curve.

[Jack Carson]

You are correct only if your takeoff distance including a land back area meet the requirements outlined in the operators manual.

[212man]

Nick,
I wasn't doubting the rest of the report: I was simply backing up my original quote of "about 10%" which you appeared to dispute.

Surely, though, the very fact that these figures are so low is a direct argument for twins in the first place? And it is the fact that engines have improved in their reliability and excess power that has improved things further. These figures are for accidents, by what factor can we multiply these figures to get the number of safe outcomes from failures? Quite a large number I suspect. However. It is no use having a twin and operating at a weight in excess of what the single engine can handle, as you just end up with longer before you hit the ground.

Ending up single engined is not as uncommon as you seem to imply, I think.

I flew Super Pumas for just over 4 years and in that time there were two engine seizures on the fleet (caused by tie bolt failure and subsequent ingestion of the bits that dropped off). One on the approach to a ship, the other in the cruise. Another lost its engine oil and had an inflight shutdown. Safe outcomes for the crews involved.

When I was doing my 212 conversion I had a P3 tube union fracture which meant loss of governor air and the engine ran down to idle. No problem as we were at a 'training' weight. Not much fun in the GoM having come off a rig at 11,200lb using the 100% Tq technique we have read about elsewhere, though!

More recently, I've escorted a 76 back to shore that had an engine failure on T/O from a rig. Actually, a loss of N2 signal to the overspeed protection box, so it shutdown as the N1 went up. Sensible weight, so no problem.

I can think of half a dozen 212s flying back single engine following chip warnings. No problem, all at Cat A weights.

Spurious fire warnings in two types in the cruise, safe landings single engine at sensible weights.

Numerous chip warnings in the 155 requiring the engine to be placed in idle, but never a problem as never at MGW.

Not one of these was an accident. In each case, had the aircraft been at the max Cat B weight the outcome would most likely have been different. Some would have ended up in the water or forced landing onshore. Others would have had engines with chips running at normal power, or remaining engines running above continuous OEI ratings ("hey Bill, we're going down at OEI continuous, what do you think; stick it in the jungle canopy, or pull 2 minute rating for another 15 minutes, or relight the engine we just shut down with a fire warning that we now know was false?")

So, I don't doubt the statistics that say accidents from engine failures are rare and not the largest cause. All I am saying is that based on personal experience (and a relatively short one at that compared to many) I can say that failures are not as rare as one might think, and there are plenty of other things that can go wrong which leave you single engined. The fact that they do not result in accidents is largely due to being at a weight appropriate to the conditions i.e. a PC1 or 2 weight.

I'd also like a TCAS and EGPWS too, by the way!

[NickLappos]

212man,

The base issue is where to place the next dollar spent on safety. If one starts with the premise that a Cat A enroute twin is the right baseline, then do we agree that the next safety dollar, and the next pprune wish list entry should not be about engines?

[212man]

Well, that depends! If you take the premise that existing a/c can be operated with commercially viable payloads whilst remaining within the PC1 or PC2 constraints, then by all means. If you take the view that the only way to operate is at max Cat B weight, and that (for an example) it's perfectly acceptable to take off from rigs by waffling around IGE at 100% Tq waiting for a breath of wind to allow you to 'throw yourself' off the deck, then I'd disagree.

As I said above, ignoring any risk of failure at rotation, there is a still every chance things may go 'pear shaped' very rapidly with a relatively minor problem en-route, and for what? So one extra 300 lb driller could take the trip rather than the next one? (believe me they come in all shapes and sizes, though that would not be your 95th percentile I admit!)

So, spend the dollars on engines if you don't like dropping payload at 20 C (because you want to operate PC1/2) and know you could add the 2S2/2C2 and keep your loads till 29 C (ball park figures as an example). But don't keep the same engines and say "well, I don't want to drop load I'll just stay at max gross anyway and end up PC3."

Then concentrate on the other goodies, matched with quality simulator training with scenarios designed to reflect the high risk areas like CFIT. Quite possibly we agree but are wording the points in slightly different ways. Possibly not!

[Head Turner]

The MD900 does show a Height Velocity Diagram in Section 5 - 9. and is pertinent at weights above 6000lbs Gross Weight. It prescribes an area which starts at 35 feet agl and extends upwards to 75 feet agl and the tip of the 'nose' is at 17 knots IAS.

Therefore MD has evaluated the flight profile and discovered that a safe landing would not be guaranteed in these situations. So no hovering or slow speed ops in this area.

Below this weight (6000 lbs) there is no height velocity diagram.

What happens if the helicopter is being flown backwards? Or sidewards?

[NickLappos]

Or at 5,000 feet; or with OAT at 25 degrees above standard; or with an engine 5% more powerful than specification; or when the avoid area is entered in a 500 foot per minute rate of descent; or when you are 20 knots faster than the curve but in a 1000 ft/min climb; or.... I guess I could go on, but I hope you get the point.

The HV curve is one of those charts that looks great, and tells only one story, when you come down to brass tacks.

[Rich Lee]

Or at 5,000 feet; or with OAT at 25 degrees above standard; or with an engine 5% more powerful than specification; or when the avoid area is entered in a 500 foot per minute rate of descent; or when you are 20 knots faster than the curve but in a 1000 ft/min climb; or.... I guess I could go on, but I hope you get the point.

Geez Nick. I find these arguments rather weak. There are many ways to diagram an HV curve but most I have seen are corrected to density altitude and MGW. Are you saying a more powerful than specification engine would result in poorer HV or single engine performance? Am I reading this the wrong way around? Generally entering autorotation from descent equates to reduced pitch which means less rate of rotor decay and/or a more rapid transition to the autorotative rotor state - usually not a negative following engine failure. The last example has so many variables it is hardly worth comment. Certainly the use of better examples would add more weight to your argument.

[Hullaballoo]

Don't confuse the HV diagram with Cat A certifications.

But the two can't be separated. Cat-A certification requires that the scheduled procedures have sufficient margin to avoid the H-V.

And for Part-29, the H-V is a limitation, while for Part-27 it is considered "only" performance information. So a Part-29 aircraft operating under Cat-A has no business being in the H-V, nor should the procedures take you there...

Once OEI in a Cat A machine, the avoid curve isof no use at all, it will not predict how much trouble you will be in if the remaining engine quits.

What??? I might agree if you said, "Once OEI while operating under PC1 in a Cat-A machine..." If you were operating at Cat-B weights within the H-V, a Cat-A design won't be sufficient to keep you from smacking the ground once OEI. With no Cat-A ops rules in the US, I fear that too many are confusing "Cat-A design" with "Cat-A operations" (like mixing the terms "IFR" and "IMC").

[Shawn Coyle]

Hullaballo:
Category A supplement will say that the HV curve is no longer valid (all that I know of say this).
HV curve is a limitation only with more than 9 passenger seats - very long story about this - see my book 'Cyclic and Collective' for more details.

[JimL]

Shawn,

Whilst your statement is true in the sense of basic certification (29.1), it would have to have been certificated with 9 or less seats. That would be rather unusual; for that reason, the overwhelming majority (in fact I cannot think of any to which it doesn't apply) of Part 29 helicopters have the HV diagram in their FM limitations section.

As Hullaballo has already pointed out, the majority of operations with Part 29 helicopters do not operate in PC1 using the CAT A procedures. In fact for offshore operations, none of them do. It is only because of the relief from the HV diagram provided by FAR 91.9(d) and Appendix 1 to JAR-OPS 3.005(c) that they are able to stay legal (and it is not clear how that plays out in States with other regulations).

For onshore operations, JARs have relief but not FARs!

Jim

[skiddriver]

It's comparing apples and oranges because of the differences in testing and delivery requirements, but if Nick goes to the Tech Pub library at his current employer and pulls the AH-1W NATOPS manual, he'll see a very useful chart (two charts actually) that provide the minimum hover height and airspeed for a safe OEI landing at a range of density altitudes and gross weights. We understood a "safe landing" as to be one which would result in no injury and minimal aircraft damage.

When I was working as a TP at Pax River on the H-1 program, we had a well defined test process (as did Bell) to develop and test these numbers. To be clear, we verified manufacturer numbers, Bell developed them.

The information was useful, though due to airspeed indicator unreliability below 40 knots, the minimum airspeed number was advisory at best. The ground speed indicator and maintaining an awareness of wind direction was of some help.

There is no reason other than liability concern that prevents manufacturers from providing this data to dual engine helicopter pilots.

[212man]

There is no reason other than liability concern that prevents manufacturers from providing this data to dual engine helicopter pilots.

Exactly, and the really progressive ones do this................(with credits to Aser)

http://i66.photobucket.com/albums/h263/aser_martinez/ECKYR/P6250458.jpg

[N116B]

Shawn Coyle in his book titled "Cyclic & Collective" on page 338 details an interesting fact about Civil helicopters over 6000Lbs, certified under Part 29, Transport Category with more than 9 passengers ie S76, AS365, B412 etc.

The HV curve is placed in the LIMITATIONS section of the flight manual.

Therefore, conducting a vertical climb for takeoff procedure eg from a confined area (as detailed in the CAT A Supplement) is violating a Flight Manual limitation unless the helicopter is operating at or below the CAT A performance weights.

Exemption
HEMS helicopters however can be exempt from this limitation as they carry less than 9 persons, however a Flight Manual Supplement must be approved by the FAA/CAA for their Air Ambulance Operation.

Does anyone have one of these FM Supplements in their flight manual and are able to email me a PDF copy?

[JimL]

...don't forget the alleviations from the HV curve contained in FAR 91.9(c) and Appendix 1 to JAR-OPS 3.005(c).

Attempting to regulate operations from inside Part 29 was always an unrealistic proposition. This has been recognised for some time but still results in a head-in-the-sand attitude by some regulators. (Explain to me how offshore operations can be conducted in the GOM without breaching this limitation - not just for the helicopters mentioned but also for the S92 and EC225.)

Fortunately there is a move by EASA to resolve this (at least for Europe); they have it on their work programme to be addressed before EASA OPS comes into effect.

The masses have changed in recent years - the break between Part 27 and 27 is now 7,000lbs not 6,000lbs.

Jim

[HeliTester]

...don't forget the alleviations from the HV curve contained in FAR 91.9(c) and Appendix 1 to JAR-OPS 3.005(c).



Fortunately there is a move by EASA to resolve this (at least for Europe); they have it on their work programme to be addressed before EASA OPS comes into effect.


How will EASA OPS address this issue? Seems like it has already been addressed (outside Part 29) by FAR 91.9(d) and Appendix 1 to JAR-OPS 3.005(c) for heliports constructed over water. Will EASA OPS specifically address HEMS in addition to heliports constructed over water?

[JimL]

HeliTester,

Yes, the issue needs to be addressed in a more general form than the two alleviations shown (which are under scrutiny because they both contradict the Flight Manual).

The move to introduce exposure into the regulations (and subsequently into the ICAO SARPs) brought this into focus some years ago. The alleviation was seen as sufficient to address the operational necessity to have the required flexibility. Even though the European alleviation was comprehensive, the FAA one wasn't (addressing only over-water departures).

The move to put the European Regulations onto a more legal footing has now resulted in a reluctance to continue with the current rule alleviation and a more permanent solution is being sought (hence the move to remove the HV diagram from the limitation section).

There is no problem for HEMS, or any other operation permitting exposure during the take-off and landing phases. AL 5 introduced ground level exposure, which provided the additional flexibility that was omitted (deliberately) from NP 8. Exposure is now permitted in all but a congested hostile environment; for the HEMS Operating Site this is also permitted. HEMS locations (hospitals) in a congested hostile environment (other than a HEMS Operating Base) are addressed by the Public Interest Site provisions. This is unlikely to change with EASA OPS.

The (apparent) provisions of FAR 29.1 and the inclusion of the HV diagram in the Limitations Section can confine a Part 29 helicopter to operations in Performance Class 1 (using a CAT A procedure). The fact that Europe has a slightly different slant on the interpretation of Part 29.1 is mainly because the definition of CAT A differs between the FAA and Europe (ICAO appears to favour the European position). In the European definition the performance data that is provided in compliance with Part 29 is seen as facilitating the use of PC1, not requiring it.

Jim

[212man]

It would also help if the HV data was more comprehensive to allow more precise determination of when it is actually extant. The Bell 212 had this over 30 years ago - it's a shame that most current RFMs have such a simplistic indication.

[HeliTester]

212man,

I am familiar with the more comprehensive H-V diagrams to which you refer. Figure AC 29.79-2 shows three different ways to present H-V data, the most simplistic of which is the one commonly used today where the H-V avoid area is fixed and accommodates all gross weight/density altitude conditions at up to the HOGE weight (for all altitudes and temperatures within the certification envelope).

I understand your desire for a more precise determination of the H-V avoid area. But H-V testing is a risky business, and one could argue that exposing the test aircraft and crew to the number of engine cuts necessary to develop a more comprehensive H-V diagram is not worth the risk. It is my observation that more parts are bent during H-V testing than during structural demonstration testing, including hard landing tests where the aircraft is flown into the ground at a pre-determined airspeed and ROD.

HT

[FlexShaft]

Gents,

I know this is a very old thread, but it seems that there's plenty of misinterpretations in my current field of operation - off-shore and seemingly in other fields too.

Cat A and Cat B are design and build certification requirements - correct. The manufacturers will tick the boxes as laid down to certify the Cat A and B requirements. This will be i the form of Profiles, Performance Charts and Emergency Procedures. Ultimately the aircraft is certified to use the Cat A and Cat B procedures as published. How the aircraft is "Operated" then becomes a matter of Performance Classes. This will be dictated by the area of operation and the level of risk that the client or operator is prepared to accept. The considerations would be take off/landing environment, surface as well as the relevant altitude and temperatures.

Some articles and threads I've read recently state that Cat A Profiles assure that the H/V Areas will be avoided. I thought that this was only the case for the Cat B profiles? Cat A assures the OEi capability, and Cat B assures the Cat B profile will keep you out of the H/V Curve.

Surely the H/V Diagrams are only concerned with Auto-rotational landings - hence engine failure in a single engine helicopter and double engine failure in a twin ?

Cat A Profiles and Emergency Procedures are only concerned with OEi accountability - correct? And thus there will be Cat A profiles that do put the helicopter squarely inside the H/V Curves in many cases

I'm listening for your inputs and insight

Respectfully

[switch_on_lofty]

Flexshaft, basically no.
The ME avoid curve is derived from the H/V combination where a safe landing is not assured after losing one engine. I.e going from AEO to OEI. Nothing to do with autorotations.
Due to various torque/engine/pilot limitations you are not necessarily "safe single engine" in all phases of twin-engine flight.
As an example the Lynx which I flew typically had a minimum single engine level flight speed (MSELFS) of 0-50kts, depending on the environmental conditions and AUM. Flying below this speed at an altitude which did not allow a descent to increase speed to recover is inside the twin HV curve.
Hope this helps.

[SASless]

As Katfish says, you don't have to have an engine failure to end up on one engine: engine chip, false fire warning, loss of oil pressure, are all events I've seen in the recent past.

My highlighting the words "engine chip".

How many Engine Chip lights preceded an actual engine failure?

If Brother Lappos thinks we worry about a mere 5%.....I would submit that worrying about an Engine Chip Light being any kind of warning that requires any sort of immediate action beyond re-setting the Master Caution Light then monitoring some instruments and listening for abnormalities..... is really over the top.

I guess some folks whistle as they walk by a cemetery at night too thinking that helps keep the Haints away.

[megan]

I would submit that worrying about an Engine Chip Light being any kind of warning that requires any sort of immediate action beyond re-setting the Master Caution Light then monitoring some instruments and listening for abnormalities..... is really over the topYou take me back to the early days of the 76 SAS, factory advice varied from shutdown immediately to reduce to idle. The shutdown immediately was not without reason, collapsed bearings were frequent, but that may be a reflection of the hard use we gave those Allisons in our particular operation. I think we averaged about 400 hours on an engine, and engines were actually blueprinted on overhaul to maximise performance. That was the days when we owned the engines and prior to the pay by the hour nonsense (Turbomeca) that introduced engines so miss matched at times it was unbelievable. Trimming engines where one was N1 limited and the other TQ.

Did a US Army accident course at Headshed Vietnam and they showed an interesting video of the establishment of the zero airspeed line of the OH6 HV curve. Started high and worked his way down in altitude, you could see things were getting progressively more exciting, the final rolling into a ball and coming to rest on its side. Driver climbed out unscathed, turned, looked at the wreck, removed helmet and threw it at the comatose Hughes.

[fadecdegraded]

Interesting Thread.
My old and wise instructor told me that the H/V curve in a CAT A certified machine was only associated with the clear area T/O and landing profiles.
It is not relevant to VTOL procedures for obvious reasons.
And applys to all CAT B operations. It applys to clear area PC 1 and PC2 as it’s only the TDP and LDP points that change.
I am sure I will get some feed back on these thoughts.

[JimL]

Flexshaft,

The requirement is established in 29.1517:

Sec. 29.1517

Limiting height-speed envelope.

[For Category A rotorcraft, if a range of heights exists at any speed, including zero, within which it is not possible to make a safe landing following power failure, the range of heights and its variation with forward speed must be established, together with any other pertinent information, such as the kind of landing surface.]

Amdt. 29-21, Eff. 3/2/83

The overall position is discussed in the following paragraph from a 'response' document sent to EASA:

All Category A and B procedures (provided in accordance with Subpart B ‘Flight’ of Part 29) ensure that the helicopter can tolerate an engine failure on take-off or landing: for Category A, by providing profiles that have demonstrated engine-failure accountability; and, for Category B, by providing profiles that remain clear of the H-V avoid curve.

All dual qualified helicopters have a ‘capability’ (as expressed in the EASA definition of Category A) of using the Category A or Category B procedures; helicopters cannot be ‘operated’ in Category A or Category B they have to be ‘operated’ in accordance with the Performance Classes (or with exposure) – i.e. it is the ‘Code of Performance’ that determines which Performance Class has to be employed. Certification in Category A does not, by itself, mandate the use of the Category A procedures.

The issue is complex but if you have the stomach for an interpretation of the issue, it can be found in the 'response' document here:

[SASless]

JimL.....the comedian....whoever would have guessed!:ok:


The issue is complex but if you have the stomach for an interpretation of the issue, it can be found in the 'response' document here: