CAT A / B versus Class 1 and 2 + LDP

[OffshoreNewbie]

Hi Guys,

As a newbie to all this twin engine performance stuff excuse me for being a little confused about the differences between performance Categories A and B and performance categories 1 and 2. From the many individuals I have asked I have been given as many answers in return. Is it perhaps true to say that its not just me that is confused??? Please guys I am interested in hearing your thoughts!

Also interested to hear definations of LDP on offshore approach Class 2 or Cat A- I THINK (76). Do most of you call it "A point at which you could no longer avoid the structure or do you define it as a combination Airspeed and Torque combination? Again varied answers have been supplied to me:\

Thanks In Advance!

[peter manktelow]

Hi OffshoreNewbie.....you raise a very interesting issue and one that , as you have found out , has many many different interpretations.

I have been playing with the whole issue since 1979 when I first went offshore. It is clear in my mind now , but I can well imagine the confusion for someone just starting. Unfortunately I am a bit strapped for time to go into the detail you require. Let me have another kick at it in a couple of weeks time when I am back at work. (Next stop the Bohai/China in its full winter glory !)

Start your research from the very basic premise that as offshore pilots our first and over riding priority is to "stay out of the water". The FAA website has a wealth of info on definitions of Cat A etc but it is all tangled and a bit of a mess.

good luck


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[Shawn Coyle]

LDP is normally defined as the point past which you are committed to land if you are single engine.
Engine failure inside LDP - no question of going around. If single engine you can go around prior to LDP and will miss the structure by at least 15'.
Hope that helps - it's a decision point for landing.
Normally defined as a combination of airspeed and height above the structure, which implies you need to know the barometric altimeter setting for the landing site, as radar altimeter may not be accurate due to waves, etc. Also the LDP will be defined based on a rate of descent.
All of this should be in the FM or Category A supplement for the helicopter.

[donut king]

Can an individual CHANGE the ldp as stated in the RFM? Maybe Shawn or Nick can answer?

My earlier thread went unanswered. If the RFM states X airspeed at X rate of descent at X height above obstructions, can an individual arbitrarily change what is stated/ tested as per the manual?

I emphatically say....hell no!!!

D.K

[LMCCOY]

The definitions of CAT A and LDP give you the basic idea of what the operations are about. The ability to return to a takeoff point or continue the takeoff and fly away following a engine failure is a reassuring thing while offshore. The FM for your particular aircraft should have a supplement covering CAT A operations for that airrcraft. Some of the procedures used will vary from aircraft to aircraft and operator to operator. An example is the use of a 'drop down' chart. When taking off CAT A from an elevated platform the height of deck from the water can be used in determining the allowable weight. Some aircraft and operators have these charts, others do not.
The CAT A operations I am familiar with call for a vertical assent, a decision being made to continue, and the aircraft leaving the deck. After the aircraft leaves the deck, it should be able to continue on a single engine.
LDP is a point at which the decision is made to continue the approach to landing. Offshore the point is not only based on the FM definition but the point at which you will either land on the deck or go around. Ideally both these points will occur at the same time.
I hope these points make sense to you. The FM of your aircraft will give you the numbers you need to get to the technique that will work for your aircraft.

[peter manktelow]

The problem with the RFM is that it does NOT set out CAT A procedures for offshore rigs !!!

Yes , the 76C+ now has performance and procedures for elevated helipads but that is a first. Certainly the 3 types I have (76 , 212 and 61) all had their Cat A developed from the runway environment , not offshore. (Correction , the 61 , in its long history , did have elevated helipad figures ....think they were for New York Airways ??? but extremely degraded payloads)

You could damn near write a book on this subject.

As for LDP....when I say "COMMITTED"...you better be sure that whatever happens , I aint going around. In my regulatory environment , the LDP at the rig is a judgement call based on many factors but to put it simply , it is the point when I judge it either impractical ,impossible or unsafe to attempt a single engine go round.

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[peter manktelow]

When I refer to the RFM , I am not including any CAA Supplements which can be very comprehensive and include seperate/different performance graphs/procedures. These supplements are not normally issued to other than Brit registrered aircraft. The rest of the world gets the FAA version.


- Cat A
- Cat B
- (New FAR changes to the definitions of the above)
- Group A
- Group B
- ICAO Class I , II , III
- JAR Class I , II , III
- Cat A Developmental Charter (old Aussie one)
- and various company variations where the particular Regulatory Authority does NOT mandate a MINIMUM PERFORMANCE STANDARD but expects to see one defined in a particular company's Operations Manual

.....and on and on it goes....

No wonder we are confused when all we want to know is how to .........

STAY OUT OF THE WATER !!!!!!!!

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[NickLappos]

OffshoreNewbie,
Don't let all the terms throw you, they are all describing the same basic thing, predictable performance in the event of engine failure. The exact details as to terms used to describe the procedures, powers used, climb rates or gradients available are details that differ with the JAR or FAR, but the concept is nearly identical.

Donut King,
No, an individual can't develop a new LDP or CDP, unless he has a good flight test background.

A capsule summary of the various procedures:


Cat A/JAR-OPS 3, Class 1:
A set of procedures which, when followed precisely, allow assurance that an engine failure anywhere in the flight will allow safe landing on a prescribed surface or safe continued flight. The idea is to establish a weight for the helo (using the Weight-Altitude-Temperature curve -WAT curve) where the performance matches that used in flight test. For shorter landing areas, which need more excess performance, the aircraft weight is reduced, thus allowing slower speeds at CDP or LDP, and correspondingly shorter heliport dimensions. The slowest speed might be a hover, with a vertical or back-up procedure. At these procedures, payload might be half what it is when not restricted in landing length.


JAR-OPS 3, Class 2:
same as Class I but some exposure time at takeoff and landing is permitted, based on engine reliability. No corresponding FAA Catagory exists.

Cat B/JAR-OPS 3, Class 3:
If an engine quits, a forced landing must be made.

Here is the JAR-Ops 3 rule book, see page 64 and 65 for engine failure procedure definitions:

http://www.jaa.nl/section1/jars/35/53/355318/355318.pdf

[peter manktelow]

Nick......you make it sound so simple. Where then , can I find the OFFSHORE rig platform departure/arrival profile and WAT charts for an S76A , A+ or A++. It sure as hell is not in the RFM. Where it is , is derived figures and profiles by individuals , usually senior check training pilots , using RFM info such as HOGE charts. The OFFSHORE LDP/CDP varies from company to company and in the final analysis , is a judgement call , albiet one that may have been derived by the above check training pilot and then ensconced as law in a company SOP or Ops manual. This applies not only to the 76. I have flown the 61 under CAA , Australian and Canadian registry and all three had different OFFSHORE rig take off and landing profiles/LDP/CDP & WAT.

It is the OFFSHORE environment that creates the real challenge , not the arrival/departure from a runway environment. It is the OFFSHORE area where we lack meaningful manufacturer's figures.

The BHAB pointed this out some years ago , when they were involved with establishing OFFSHORE rig take of and landing ccriteria using simulators and aircraft (Puma , 61 , 212)

Of course all this becomes academic when we finally get a twin helicopter that can take of and land at gross weight , OEI , at sea level and 30 degrees C. I dont think I am going to fly that machine before old age gets me although I am impressed with the 92 numbers I have seen.

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