HV Chart Part III

[Steve76]

Well I know we have thrashed this to death already but I found something interesting in the S76A manual the other day while I was reading it on the loo....

Turn with me brethren to Part 1, Sect 2 of the Normal Procedures Page 2-15 of the Book of Sikorsky and follow along while I read the gospel of Nick.

Cat B Approach and Landing:
1. Establish approach to arrive at 100ft/50kts.....etc
2. Decelerate to pass 50ft at 40kts.
3. Continue approach and decelerate to running touchdown or hover. Observe limitations shown on HEIGHT VELOCITY diagram (fig 1-4)
Thus sayeth the law.

SO! according to the FM for the 76 you must observe the HV curve for a period of the approach phase of flight. Previous discussions about this had resulted in my change of opinion to consider the HV curve irrelevant during approach due to the reduced collective (pitch) settings.

I think I have found a little loophole here to rebut this theory.
Whadda you reckon mates? :ok:

[IHL]

The HV chart says " Note: Avoid flight within the shaded area except to execute a safe landing after an engine suddenly becomes inoperative or after initiating flare for a normal landing.

Therefore:Height and rate of flare initiation are directly proportional to time spent in the shaded area when conducting a normal landing.

[NickLappos]

Steve76,

Sharp eyes!

Two comments:

1) The general is not proven by the specific. In this case, the use of the HV curve as additional information for the approach does not mean that every HV curve is important for every approach. This particular apporach has the aircaft get pretty slow, as I recall.

2) The HV curve is established in level flight, with a 1 second delay in pilot response built in above the knee. In actual descent the behavior of the aircraft is much better, and the delay might be less so the aircraft would probably be a lot better than the HV curve. In other words, the HV curve might be a limit, but it might not be very accurate (remember that a limit does not have to be real, it just has to be published!)

[IHL]

For Nick: 1)If the H/V chart is in the limitations section of the AFM , can you fly in side the shaded (restricted area) for purposes other than landing ?

> If not then every rig take-off with a 76 or 61 would be illegal , because ( assuming a 100 ft deck height) as soon as you rotate off the deck you're in the curve. Further logging/slinging (long line) operations would not be possible.

I find it some what confusing and ambiguous.:confused:

[Shawn Coyle]

Just to further confuse things, there is a let in the operations section of the US regulations, part 135 that allows you to ignore the HV curve if you are taking off over water and have floats. How this was ever done is beyond me. Would we permit this in fixed wing aircraft???

[NickLappos]

IHL,
This is why I dislike HV curves. Imagine that the town had a speed limit that demanded that you drive no faster than 45, and no slower than 55. that is the HV curve, when posted in the limits section. It should not be a limit, as it has little meaning as such. it is the plot of the performance of a rotorcraft under one strict set of possible events, and only that. It is almost useless as a predictor of behavior of the aircraft, except under one strict set of conditions, and it does not particularly add to the safety of your operations. (It does keep this web site going, however!) That is why you can ignore it in so many circumstances, because the examiners know that too. Thank heaven, or else we'd be walking to the rigs.

Many helicopter rules were developed during a period of relative ignorance (this does not mean the folks who did so were not very bright!) Now that we know more, we cant figure a way to change the rules, because they are rules!

You will not find out how to re-write the book by reading it in the book.

[Steve76]

Thanks IHL, Shawn and Nick. Great comments to further enlighten me. Safe flying.

[212man]

The concept of the HV curve not being so critical for descents is really only applicable for steady states. Most approaches I know of, terminate in a hover. So, at the very least you need to ensure that the final hover height is below the HV curve. The period of deceleration and power application to reach that point is also important and should certainly take into account the normal HV limits as a guide, even if not strictly applicable.

There will always be some safety margin because HV curves are for MTOW and high Density Altitudes, but how much of a margin there will be for any given circumstance is unknown.

Next time you do a Base Check/OPC/PPC ask the Training Captain if you can see the effect of an engine failure after LDP where the a/c has been slowed prematurely. If the a/c is at a reasonably high training weight, it should serve as a prompt to fly accurate approach profiles (I'm not saying you don't!).

[Shawn Coyle]

A further complicating factor for the HV curve that is very relevant to this thread is that a) the low hover point is based on no collective lowering following the engine failure and b) that all the points below the knee are done at takeoff power.
The FAA logic, and it's pretty good, is that in a hover you aren't expecting an engine failure, and it would presumptuous to presume the pilot is awake enough or well enough trained to remember to lower the collective to get the helicopter moving toward the ground before there is an almighty pull at the bottom. If you are smarter / quicker / luckier than that - great. If not, at least you were warned to stay away from that height.
So, if you are coming into the hover and the engine fails, unless you are pulling up on the collective at exactly the time the engine fails, you should be in a better situation than indicated by the curve, as the blade pitch is slightly less than the hover blade pitch (unless you are doing a really agressive quick stop).
(note to self- good stuff for next edition of book...)
Hope this doesn't muddify the confusion too much.

[Another KOS]

Is it possible to have a late input to this thread:

Shawn points out that Part 135 permits an alleviation from the HV curve when taking off over water and when wearing floats!

When JAR-OPS 3 was being produced the authors were looking for a similar device to that used in Part 135. Why? Because when taking off from a helideck or elevated heliport and using exposure, the HV curve was bound to be infringed. (By virtue of the dynamic procedure used on the North Sea and elsewhere.)The same could be true of the landing manoeuvre. It was the view at that time that the regulator and the operator should shoulder the burden of responsibility along with the pilot.

Hence Appendix 1 to JAR-OPS 3.005(c) permits a momentary flight through the HV envelope (curve) during the take-off and landing phases when using exposure (to a helideck or elevated helipad).

Indeed, all of us who have flown to helidecks during our careers will have exercised this privilege (knowingly or not) on a number of occasions when the wind was below (say) 20kts.

The limitation of the HV curve exists only in FAR/JAR 29 - it is information only in FAR/JAR 27.

Why do the FAA/JAA permit this Shawn? Because there is no technically feasible and economically justifiable alternative!

We might even postulate that with Nick's latest gem, it is likely that, when landing on some rigs, the HV curve will still be infringed.

What should we do about it:

Rumour has it that the operations folk have approached the airworthiness folk with a proposal to put the HV curve back in the information section from whence it came.

Disappointingly, there is a notion that a Transport Category helicopter (JAR-29) can always operate within a Category A procedure - thus mirroring the Transport Category aeroplanes.

We have not yet seen the Transport Category helicopter that can operate in Class 1 in all phases of flight under all circumstances. We are nearly there with the JAR 27 smart twins (as was indicated in another thread) - as their growth potential is constrained by the weight growth limit of FAR/JAR 27 (7,000 lbs) and any additional installed power and gearbox improvements can only add to their performance.

Within not too many years we will see the smart twins with HOGE OEI performance (reaonable temperature and altitude) at which time only the location could be a constraining factor. At this time we will also move away from the most constraining factor on Category A procedures - the size of the heliport.

[Steve76]

Personally, JAR-Ops sounds like a pain in the arse......hang on I correct myself....THEY are a pain in the arse. Why the hell doesn't the EU adopt the FAA's rules instead of re-inventing the wheel. :rolleyes:

[JimL]

Don't you just love the American sense of humour!

[sarboy w****r]

Why don't we ask PPruneFan#1 for his opinion?