TDP and CDP

[gnow]

I wonder if some of you more learned guys out there can throw some light on this subject. I know they mean almost the same thing but there is a difference. Is there any defination in the JAR Ops?

[helimutt]

Take off Decision Point and Critical Decision point. Point at which, if an engine failed, you either decide to continue or land. It's just a 'decision' point during the take off (or landing), and AFAIAA they mean the same thing. TDP is just a new way of saying it. CDP was the old way of saying it. Same as LDP/CDP
Is that about right or am I talking b******s?

[212man]

The change came in CFR 14 Part 29 amendment 39.

Part 29 is the Certification standard for large rotorcraft (and CS29 the EASA equivelant), and it includes the requirements for Cat A performance. Eralier amendment referred to CDP and from 39 onwards TDP. From Joe line pilot's perspective, no difference!

If you want to read more, look up Part 29 and also AC29-2C (just google, with FAA thrown in to narrow it down)

[Munk]

CDP/TDP etc etc = translational lift. Wonder how many times those graphs are used?

[cougar77]

In my opinion, i believe that there is a slight difference between TDP and CDP. CDP is derived from the charts where you use either speed or time for the CDP.

TDP, eg if you are taking off from a long runway. You could be passed your CDP but because there is still sufficient runway remaining for you to land safely in the event of OEI. So, my TDP will be a point where i will deem not able to land the aircraft due to insufficient runway length corresponding to the speed and height at that particular point (where this is mainly DR) for me.

I stand to be corrected

[212man]

Stand duly corrected! See post 3:ugh:

[verticalhold]

212man;

Cougar may be right. On the AS332 on take off from a runway, if I remember correctly we used to call TDP as the point the aircraft passed the single engine fly away speed and CDP was the point at which we couldn't reject the take off at all. One was speed based, and the other height and runway length remaining.

A Puma past VTOSS with 5000 feet of runway remaining could easily be flared and the TO rejected. I stand to be corrected as it is quite a while since I flew the Puma.

VH

[Brom]

Totally agree with flungdung, if you reject after TDP and something goes wrong, i.e. you run out of runway, whatever, it's going to be your fault and you better have some very good reasons for your actions. A gentleman/woman in a black gown and funny wig is going to be asking you some very pertinent questions to try and make sure that everything that hits the fan lands (and sticks) to you. That's blame culture for you, it's the society that we live in, like it or not.
Could well culminate in a visit to 'Aviation House' to deliver licence to CAA shredder.

[verticalhold]

Brom,

Don't forget that an RTO can be the result of many things going wrong, not just an engine failure. As I said in my original post CDP was treated as a runway length/height point on that particular operation. There always comes a point when there isn't enough tarmac left. The operations manual left a large amount to our discretion should we need to reject, but was very clear that runway length was the final factor. Slight drift, but the 748 pilot who had an uncontained engine burst at Stansted some years ago when already airborne rejected straight ahead onto the runway. He was pilloried by many who had no idea that it was an approved manouvre for the 748. Turned out he was very right due to a very weakened main spar which would not have survived a circuit.

I personally rejected a take off well after TDP due to a very sudden severe eyeball bouncing vibration. 4000' of runway left so no problem IIRC airspeed was about 100 kt when the desicion to re-land was made. MRB delamination was the problem. It could have been much worse had I taken it round the circuit.

VH

[Brom]

Verticalhold,
You're quite right and I totally agree with you, that's why I said '...you better have some very good reasons for your actions'.
Good decision by you to reject in that instance,:ok: this is where experience comes into it's own, the less experienced may have continued with disastrous results. Personally, I'd rather miss the runway completely and live to argue the case than have a MRB fall to pieces downwind, however, rejecting and running out of runway following an alternator failure or a drop in engine oil pressure may be a little more difficult to explain.

[verticalhold]

Brom;

One day the lawyers will all have been shot and we will be able to get on with our jobs without constantly looking over our shoulders.

Just think, only management to worry about:E

VH

[TeeS]

Hi Flungdung

Since I have my pedantic head on, and if memory serves correctly! TDP is defined as the point at which the take off can either be rejected or continued. A nanosecond before or after is a different matter though.

Cheers

TeeS

[Brom]

Verticalhold,
All except Flying Lawyer, he seems OK(ish):E

[NickLappos]

When the rules changed, the acronym changed. They actually mean the same thing TDP=CDP

The old rules used LDP and so do the new rules.

This illustrates rule three of The Governing Rules:

1) Acronyms shall be used to obscure reality.

2) The best acronym shall have the worst technical justification.

3) When you need to look as if you have done something profound, rehash an old thing to make a new acronym

[rotordude]

More info on the subject:

New 14 CFR 29.55 Takeoff Decision Point: Category A

Notice 90-1 proposed to add this new section to redefine the takeoff critical decision point (CDP) previously contained in Sec. 29.53; it further proposed to remove the requirement to identify the CDP by height and airspeed, since height alone or other factors may be more appropriate. A commenter suggests that the section title and other references to ``critical decision point'' be changed to ``takeoff decision point (TDP).'' The commenter notes that TDP is compatible with the term ``landing decision point (LDP)'' already in other regulatory parts. The FAA agrees; accordingly, ``critical decision point'' is changed to ``takeoff decision point.''

Additionally, a commenter to Sec. 29.59 states that engine failure and the TDP do not occur at the same time because of necessary pilot- recognition time. The FAA agrees that a time interval for pilot recognition of the engine failure must be included when establishing the TDP. Calculating a pilot-recognition time interval when determining the TDP is a natural part of the TDP-determining process. Current industry practice already adequately considers this pilot-recognition time interval in determining the TDP. Therefore, to explicitly state this requirement in the regulations imposes no additional economic burden on manufacturers. Also, to harmonize Title 14 and the Joint Aviation Requirements (JAR's), the certification requirements for the Joint Aviation Authorities (JAA) of Europe, an explicit adoption of the pilot-recognition time interval is necessary. Therefore, since a pilot- recognition time interval is currently being used by manufacturers, and the FAA and the manufacturers are interested in harmonizing Title 14 and the JAR's, a new paragraph (c) has been added to Sec. 29.55 to require that a pilot-recognition time interval be included in the TDP determination.

[Mr Toad]

For Cat "A" Elevated Heliport takeoffs, the S76C+ is lifted sharply and vertically out of the ground cushion to 50' Rad Alt; a tone then marks TDP and you immediately rotate smartly nose down to about 22 degrees. You are committed at the instant of cyclic input.
Yes Rotordude, a pilot recognition time interval is a necessary part of the process. But for this type of take-off you've got to go for it and you've got to nail the numbers; if you hesitate it will be messy.
No, the passengers don't like it much...

[gnow]

I was told during my AS 332L2 conversion at Helisim that TDP is a fixed point which is predetermined based on ambient conditions so we have a fixed airspeed and ht above which we are to continue. For CDP, a good example would be take off from the rig where the CDP is the point of rotation. This point is not fixed by the numbers but more by pilot's feel ..and maybe not the most accurate point as it can vary slightly between pilots. I wonder if most of other pilots agree to this.

[SASless]

"Fixed Points"....strongly disagree to that. Example...45 knots of wind across the deck...empty aircraft in the North Sea in February compared to same aircraft in the Arabian Gulf in the Summer while at max weight and no wind to the same deck.

We are talking apples and oranges in that comparison.

Does that explain the wide difference of approaches being used around the world?

It always comes back to a variable decision point made by the pilot when making a decision as to being able to land vice go-around as affected by the circumstances.

Helicopter flying cannot be done by the "numbers" alone....otherwise there would be no need for pilots as autopilots could do the same job without all the attendant whinging and moaning.

[soggyboxers]

SAS,
That's because what you're referring to regarding offshore decks, is mostly related to performance Class 2, though even for that RFM graphs give credit for wind and temperature. Very few helicopters are capable of operating Class 1 from an offshore deck with more than a few passengers. Many pilots will call committed at the point of rotation from an offshore deck, but that doesn't mean they can fly away, it just means that they're committed to continuing the take off in an attempt to gain sufficient airspeed to at least fly level, or even better start to climb before they enter the water. Under most jurisdictions, even Class 2 operations require that a twin engine aircraft must be capable of Class 1 performance at some point, often 1000 feet above the take off elevation.
TDP and CDP, as has been stated are basically the same thing. The DP is the essence; it's a decision point used for Class 1 operations. It's the only point at which in a multi-engine helicopter, the pilot may either decide to reject the take off, or continue it in the event of the failure of a critical power unit (after all the helicopter may have more than 2 engines and it may be able to climb on one or more engines after any one fails). If an engine fails before TDP/CDP the take off must be rejected and after it must be continued. In many companies this will be further modified inasmuch as there may be considerably more runway length available than that necessary for the relatively short accel/stop distance required by many helicopters (the distance required to accelerate to TDP speed and then safely recect and come to a stop on the prepared surface). If the Vtoss is low (CDP/TDP speed is usually related to Vtoss and a lower TDP speed means less space is required to safely reject the take off), the accel/stop distance will be correspondingly shorter. When there is a very long runway ahead the pilot may still be able to safely land back on even after TDP, though my experience with pilots under training shows that many less experienced pilots may find this difficult to achieve because we usually don't train much for this and it's a difficult thing to judge. You'd be surprised at the number of pilots who would have overrun the runway had I not restored an engine when under training. At least then pilots have an experience to relate to should it happen again for real. The TDP/CDP is really only critical when operating from a runway which is equal to the accel/stop distance for the weight of the aircraft in nil wind for a given temperature. This may well be the case when operating from small heliports, not fixed wing airfields.

Pauses for breath, has another cup oif strong coffee and goes off for a little sleep............ :}

[papa68]

Nick as always is spot on with regards to acronyms.;)

To take the whole acronym thing to another level, the Oz military (and presumably others) actually called them TLAs (Three Letter Abbreviations).

I always thought having a TLA for a TLA was kind of funny (but then I am easily amused).

Papa68:ok:

[212man]

TLAs are a misnomer: acronyms should be pronouncable as a word e.g RADAR, LASER, HUD...

TDP and CPD (and TLA) are abbreviations.

[JimL]

Gnow,

The answer to your question was pointed to by 212man and precisely answered by 'rotordude' - simplistically, the change from CDP to TDP in amendment 29-39 permitted the decision point to be defined by a single parameter - e.g. height - instead of by speed and height. This in recognition that height might be the only parameter that can be defined within certain procedures (vertical, sideways or backup).

It was also the amendment that introduced 'pilot recognition time' - thus separating the point at which the engine is assumed to have failed from the point at which the decision is made; thus continued take-off is assured from TDP even with an engine failure up to one second before TDP (with some manufacturers, the recognition time is reduced to 0.5 second because of the efficacy of the engine failure warning system).

Early helicopter procedures followed fixed wing in that they encompassed an accelerate/stop distance and even used V1 as the point at which a Go/No Go decision had to be made. These procedures provided a speed and height for the V1 that kept a level accelerating helicopter out of the HV diagram.

It was only with the introduction of more powerful engines that the flexibility of the helicopter to do other than a fixed wing type take-off started to be explored. The S61 with its 'ground cushion' and 'oblique' take off procedures showed that the rejected take-off distance could be minimised - by introducing a vertical section - while preserving a reasonable take-off mass (an optimisation of the 'oblique' is still in use at Penzance today). Sikorsky also introduced a back-up procedure for elevated heliports but at a greatly reduced mass; Bell certificated a sideways (three dimensional) procedure for helidecks with the B212/412 that has been further developed for the B427 (and presumably the B429) - this is a good procedure because it preserves an extensive Field Of View (FOV) by utilising a sight picture out of the side window (this procedure is still one of the best because the improved FOV permits a take-off and approach angle of almost 90 degrees whilst preserving a full picture of the touch town and aiming point)

Eurocopter Deutschland produced a back-up procedure for the Bo105 which has been further refined for the other models in the EC range. Initially this profile was established with a fixed TDP but was subsequently improved by permitting a variable TDP (this variable TDP permits the helicopter to tolerate obstacles in the take-off distance by avoiding them vertically; as the TDP is raised, the 'mindip' is raised accordingly - i.e. if the fixed TDP of 50ft gives a 'mindip' of 15ft above the take-off site a TDP of 100ft will provide a 'mindip' 65ft above the take-off site). I'm sure all will see the potential of a raised TDP (if it is permitted in the procedure).

No need to linger on the PC2 offshore procedures as that has been well described by 'soggyboxers'; 'helicomparitor' has also explained PC2e in the S92 thread.

Operating PC1 using a Category A procedure from a (long) fixed wing runway provides no safety benefit. Equivalent safety can be shown by using a PC2 procedure - always providing that obstacle clearance is shown in the 'take-off flight path'. Performance in the 'take-off flight path' is identical for PC1 and PC2 (at that point the helicopter is operating in PC1 regardless of the take off procedure).

As a matter of interest, when the ICAO Heliops Panel started to work with the Performance Classes, they were defined as PC1a, PC1b, PC2 and PC3; PC1a being a procedure where a helicopter could remain in the hover on one engine. This (exceptional) performance was also anticipated by the FAA when they were amending FAR 29 back in the 1980s - this was (probably) the reason that ICAO and FARs were directed at 'a PC1 helicopter' and not at 'operations in PC1'. The complex PC1 designation was dropped before the introduction of the first comprehensive Annex 6 Part III and we have continued to develop procedures for PC2 in accordance with Risk Assessment.

Jim

[Chopper Jog]

AS332L2 data:

1. TDP(Take off Decision point) Definition - Abort the take off if an engine fails before the TDP and continue the take off if the engine fails after the TDP.

2. TDP is defined by a speed and height and is indicated by V1 (speed) and h1 (height). For example V1=20kts and h1=20ft, V1=30kts and h1=30ft, etc.

3. TDP is calulated as follow: VTOSS (IAS)-10kts=V1 (IAS)

Note: Minimum VTOSS=35kts TAS

[Max_Chat]

Munk. TDP is not at the point when translational lift takes place, it is a point during take-off when the ability to fly away on a single engine is assured. This could be height and/or IAS related.

Just because you happen to be at or beyond TDP when an engine fails does not necessarily mean that you are obliged to "fly away" with a given Continued Take-off Distance available.

IMHO

[Perro Rojo]

From a Line Pilot's point of view this is how I see it.

TDP(CDP) are OEI decision points only, as calculated for the current conditions. They are not a commitment to continue a Take-off given some other problem. That would be a pilot judgement call given the prevaling terrain conditions. Even the OEI decision could be affected by the terrain at the time of occurrance. If one is operating from 10,000 feet of runway an RTO after TDP would be prudent if it can be performed safely.

With the 332 in our operation we brief the Class of performance we are capable of, the perfomance Class profile we are going to fly (Pilot Flying discretion) and if Class 1 from a runway or Class 2 from a helipad or deck this includes a "Committed" to fly point by the Pilot Flying in additon to the TDP.

[Munk]

Max Chat
Yup, your definition is correct. Ergo it is not mandatory to continue the t/o with oei when TDP is reached, providing a reject can be safely completed - notwithstanding soggyboxers’ comments re training and other comments about lawyers. I can imagine a lawyer dryly querying, “was a fly away with an engine fire really necessary with 10,000 feet of runway remaining………”
I merely point out that the point at which TDP is reached coincides with the onset of translational lift. Other decision points, eg: rig take-off’s are committal points, not oei fly away points. A vertical take-off, or a helideck take-off use nose down fly away techniques with oei during which, of course, t lift is reached.

[Brom]

Monk,
In your post you say I merely point out that the point at which TDP is reached coincides with the onset of translational lift.That may be correct for some Helicopters/Take off profiles, however, it isn't true for all. As an example the Puma L2 (when operated to Cat A) can have a TDP which varies dependant on a number of different factors - take off space available, aircraft weight, temperature etc. I'm not going to go into detail on the calculation, but the TDP can be between 25 and 70 Knots IAS, well in excess of the onset of translational lift.
Brom.

[212man]

I merely point out that the point at which TDP is reached coincides with the onset of translational lift

Nonsense! ETL is typically around 17 kts and most IAS based TDPs range from 25-70 KIAS (few, if any civil aircraft can register accurate IAS values below 25 kts anyway). Not to mention that TDP can be purely height based with zero airspeed!

[Shawn Coyle]

Munk:
There is absolutely no connection between ETL and TDP.

[soggyboxers]

Munk,
TDP has nothing to do with translational lift. In a normal forward twin-engine take off in older helicopters such as 412/S76/365 (to mention but a few) it's the point at which you have reached, or can accelerate to your Vtoss. This is the airspeed for a given weight and temperature at which the helicopter has reached a point on the Power required/TAS curve where it has enough excess of power available over power required to be capable of climbing on one engine at 100 feet per minute (with landing gear down, on wheeled helicopters) using 2 minute power (on aircraft having a 2 minute power rating). Then at a point, normally 200 feet, the helicopter can be accelerated to Vy (or Vbroc, depending on whether your RFM is American or European!) and climbed to MSA.
Perro Rojo,
As pointed out, the TDP is an absolute after which the aircraft must be flown away in the event of the failure of a critical power unit if you are operating from a heliport where the accel/stop distance for a given airspeed is critical. For example, you may be required to operate from a 1200 metre heliport and in order to operate Class 1 you have to restrict your take off weight for a given temperature because of this. If you were to have an engine failure after TDP and decide to reject, then have any of your passengers suffer injury, the lawyers would indeed be after you and have a good case. As you say, if you have a long runway ahead, then it's your call as to whether to reject, but as I say, I've seen a lot of pilots mess it up when the runway isn't quite so long, or they have commenced a take off from a point other than the threshold where they have no idea exactly what distance they now actually have available.
Remember also that TDP refers only to engine problems in multi-engined helicopters. It's entirely single engine performance thing after one has failed and has nothing to do with gearbox, tail rotor or other non-engine-related problems. The other point to bear in mind is that even if operating class 2, you are allowed to damage the aircraft when you land, but if you injure a third party outside, then the lawyers will also be after you :}

[JimL]

Munk,

Continuously repeating a statement will not make it any more correct – TDP is far more complex than you make it out to be; it has to conform to the text of AC 29.55 (a)(2):

(2) The definition of the TDP is based on a minimum required total energy concept. A specific minimum combination of kinetic energy (airspeed) and potential energy (height) should be attained at the TDP to ensure that a continued takeoff can be accomplished following the complete failure of one engine. In § 29.55(b), TDP is required to be defined by no more than two parameters. When using a single parameter such as time, height, or airspeed as a method of identifying the TDP, the identification must be combined with a precisely defined takeoff path and crew procedure to provide the required equivalent level of safety. In addition, it should be demonstrated that the pilot technique used during the takeoff sequence is easily repeatable and consistently produces the required energy (i.e., airspeed and height combination) when the TDP time, height, or airspeed is attained. This condition should be verified during the flight test program.
In the underlined text you will see that, in the absence of kinetic energy (speed) there must be sufficient potential energy (height) alone to assure the ‘continued take-off’. There are potential complications with vertical procedures because some helicopters which sustain a critical failure before or at the TDP enter into an accelerative descending flight mode – it is therefore important that the exact procedure is employed when carrying out a rejected take-off (with some helicopters, this requires that, during the descent to land, the collective is raised and held at the FADEC 30 second rating).

In fact the TDP satisfies two main requirements; with a power-unit-failure recognised at the TDP it is: (a) the last point from where a rejected take-off can be carried out (in horizontal and vertical extent); and (b) the first point from where a continued take-off can be achieved.

In the continued take-off to the take-off distance (TODRH), all obstacles (including the take-off surface) must be avoided by a specified margin. To comply with PC1, the take-off mass must also be such that, from the TODRH, a sufficient climb gradient is achieved to ensure that all obstacles are missed (or avoided) by a defined margin (greater for IFR than VFR) in the take-off flight path.

To be able to achieve the continued take-off, the location of the TDP must be established sufficiently accurately to ensure that all succeeding points on the take-off flight path can be established in three dimensions. Obviously, the critical failure will be one at one-second before the TDP (or whatever the intervention time is establish to be); I would suggest that the probability of a failure precisely at that point is Extremely Remote and so margins will almost always be better than those planned.

If it is not expected that the Category A take-off will be flown as written (as discussed in some of the posts above) alternative procedures such as PC2 should be considered. If flying a PC2 procedure, alternative terms for decision/committal points should be used to ensure that all members of the crew are in agreement with the procedure/consequences should an engine failure occur. Following JAR-OPS and for offshore, they could be Rotation Point (RP) and Committal Point (CP). These calls should be part of the briefing routine in accordance with SOPs.

Jim

[Brom]

Flungdung,
Whilst I do agree with you re the definitions, consider the following...
The scenario...
On an IFR departure with cloudbase between 50 and 100ft, vis 150 -200 metres and the nearest single engine diversion almost an hour away (all legal for North Sea Cat A ops).
The problem...
Just after TDP, but before going into cloud, with the runway ahead of you still visible, you have an engine fire warning, would you continue the take-off, or put it back on the ground?
I'm sure I know what I would do. If I could get it back on the ground that's where it would go regardless of any 'legal definitions'.
Brom.

[rotordude]

On an IFR departure with cloudbase between 50 and 100ft, vis 150 -200 metres and the nearest single engine diversion almost an hour away (all legal for North Sea Cat A ops).
The problem...
Just after TDP, but before going into cloud, with the runway ahead of you still visible, you have an engine fire warning, would you continue the take-off, or put it back on the ground?

Not trying to make an argument about what´s right or wrong here, but there is a couple of things one should be aware of during a low visibility TO:

1. Determining the runway available after TDP is really difficult under these circumstances. Be prepared for an overrun.
2. "Ballooning" the AC, while trying to decelerate, might leave you in a situation where you end up IMC with 10-20 deg. nose up. This time with no fly away capability.

[212man]

I concur with the last two posts, but would add that the scenario you describe should no longer be described as a rejected take off: it is now an emergency descent from a climb, a separate thing entirely. Understanding this is key. As has been pointed out, it is not a manouevre that is trained for, is familiar, or has any graphs associated with. It's not wrong per se, just don't consider it a rejected take off, and be prepared for surprises.

[Munk]

Appreciate the detailed briefings from all regarding definition of TDP/CDP – should have revised the facts rather than rely on isolated experience. Currently, on the type I fly, the CDP, which is time based, coincides with ETL.
Couple of questions though:
212man: I thought that TDP was time based precisely because of the lack of accurate IAS values at low airspeeds. What types have TDPs which are IAS based?
Brom and 212man: Have you, or anyone else used a TDP equating to 70kts, or 60kts, or even 50kts?
In these cases, a reject just prior to TDP would be interesting.
And, soggyboxers: You must have observed during your training/checking on short runways that quite a few pilots negate the parameters of their (calculated) TDP by, for example, reducing the effect of the flare during a reject by over leveling the aircraft, or flaring insufficiently etc etc. How do you ensure consistency in this area?
And, finally, flungdung: Your dictionary definition uses the noun. Common courtesy dictates that I should retract a statement when proved wrong. Doesn’t mean that I have to….

[212man]

212man: I thought that TDP was time based precisely because of the lack of accurate IAS values at low airspeeds. What types have TDPs which are IAS based?

Civil IAS gauges typically are invalid below 25 kts and on some older types are inaccurate below 40 kts. That's without introducing crosswinds, where the errors are compounded. So, yes, on some types where a low TDP airspeed is used, the method of determining that point is to count down. That relies on a given acceleration and an accurate time, so is inherently inaccurate in itself, but seems to be "close enough for government work!"

Types that have a TDP based on IAS? Well, I can personally vouch for the AS332, S-76, B212, EC-155, S-61 and S-92, and I know other types do too.

Brom and 212man: Have you, or anyone else used a TDP equating to 70kts, or 60kts, or even 50kts?

On the EC-155 the TDP range was from 30 KIAS to 70 KIAS, resulting in Vtoss values from 40-80 KIAS. 60 KIAS was the change over point from first segment to second segment limiting, i.e. there was no further payload benefit from higher 70 or 80 KIAS Vtoss, but it left your decision till later. Precisely for the reasons stated (going IMC etc.) On the S-92 the TDP range is 30 - 55 KIAS with Vtoss values of 45-70 KIAS.

In these cases, a reject just prior to TDP would be interesting.
And, soggyboxers: You must have observed during your training/checking on short runways that quite a few pilots negate the parameters of their (calculated) TDP by, for example, reducing the effect of the flare during a reject by over leveling the aircraft, or flaring insufficiently etc etc. How do you ensure consistency in this area?

I have always taught maximum performance reject technique (as described in the RFM) so that it is the instinctive first reaction if the failure occurs for real. If, you decide that with 2000m of runway left you'd like to back off the flare, or not droop the guts out of it, that fine, on the day. But, if you have always been taught the gentle, run it on with 30 kts type technique, then come the day you really are RTDRH limited (short runway, big trees at the end) then you don't want to be learning it as you go along (though the big trees will help the learning!) Same applies for landing.

(No, LDP is not the point of loss of ETL, either ;))

[tistisnot]

Gawd lavverdacks ..... no wonder the client complains of gobbledegook if we can't get this sorted amongst ourselves!!

I may be a stoopid line pilot, and you can call me ignorant of my professional duties, but there is somewhere when I call committed and before or after that I will carry out what was briefed - land/reject or continue/ go round.

[Mars]

OK Brom - I'm hooked; what would you do if you had the same emergency just as you entered cloud?

Have you ever discussed this in a CRM session?

Mars

[Max_Chat]

tistisnot, I agree with you that a committed (to land/fly away) is a great idea. Cat A Ops may say you must be assured of a given flight condition if OIE, but if all on board are aware of your intentions at a given point then all is clear.

As far as when TDP/LDP occurs, and what you do, differs with type so cut your cloth accordingly and the Lawyers will be no more well off than they are now. Win Win I think.

[Swamp76]

Flungdung,
Whilst I do agree with you re the definitions, consider the following...

The scenario...
On an IFR departure with cloudbase between 50 and 100ft, vis 150 -200 metres and the nearest single engine diversion almost an hour away (all legal for North Sea Cat A ops).
The problem...
Just after TDP, but before going into cloud, with the runway ahead of you still visible, you have an engine fire warning, would you continue the take-off, or put it back on the ground?
I'm sure I know what I would do. If I could get it back on the ground that's where it would go regardless of any 'legal definitions'.
Brom.
http://www.pprune.org/forums/images/statusicon/user_offline.gif


All this discussion only applies to OEI. All other issues, problems, emergencies are a seperate issue.

This what happens when we use airplane logic/regulations and apply it to helicopters.

[soggyboxers]

Munk,

Yes, on AS355, A109E, B212, B412, SA365 (all models), S76 (all models), S58T, S61 CDP is IAS based.

How can time possibly have any relationship to ETL? I think you're rather confused or not explaining yourself too well.

tistisnot,

Well said. As you say it all comes down to a proper briefing.

As has already been said all of this applies only to the engine failure case in a multi-engine helicopter. For any other emergency it's pretty much irrelevant.

[WIGYCIWYT]

Perhaps the finest exponents of the art of calculating and flying to a TDP is demonstrated on the S61 ops at Penzance.

Due to having to operate genuine Class 1 out of a 380 metre strip (2 pilots, 1 cabin attendent and typically 28-32 pax) a specific take-off technique was devised (in the 70's) which has a 'variable' TDP dependent on aircraft weight and wind velocity. It varies from 50ft/20 kts IAS to 170ft/20kts IAS (or positive groundspeed if w/v >20kts) - all heights are Bar Alt heights (no Rad Alt fitted when they were devised!). It is a complicated calculation involving accountable wind/temp/press etc.

As we always attempt to depart at max RTOW believe me when I say that TDP is DEFINITELY TDP in that there is simply no space left to reject after it ( as any available 'space' would be converted back into payload)!

I think much of the confusion above concerning TDP may come from operators not used to Class 1 operations?

[soggyboxers]

WIGYCIWYT,

I had meant to mention Penzance as one of the places which is genuine Class 1 as I believe it is a scheduled airline operation, the same as most public transport fixed wing operations. Nearly all TDPs, particularly for older generation helicopters, are variable dependent on weight, temperature (because they affect DA) and most depend on accel/stop distance and have an altitude component either to clear the tail during the flare when decelerating or to give adequate terrain clearance and/or the ability to accelerate to a higher airspeed when using a technique such as the 170/20 TDP you describe. A number of operations have gained specific clearances from the CAA once they have been demonstrated to work. A couple of others which come to mind were the clearance for the AS355 for the early Manchester Police operations and the rooftop clearance for a smaller-than-normal pad for G-RMGN for Robert Maxwell.

In the offshore oil industry many oil companies pay lip service to Class One operations, whilst actually utilising Class 2 procedures. I remember XOM in Cameroun initially specifying Class 1 operations for their trans-Cameroun pipeline helipad operations until they found out what payload that would give them :}. Many pilots also receive little or no ground training regarding Class 1 or 2 operations as too many companies (both operators and oil companies) will try to get away with the minimum training time they can :ugh:

[rumline]

To me....LDP (landing decision point) is (was) made 80nm offshore, at the moment I shoved cyclic foward coming off the rig!...:ok:
CDP is that point at which I am able (given weight/power/atmospheric conditions) to fly away....not that I have to, mind you (if there's still 3000' of runway ahead) but that I can. Within our ops...it's a call reserved for Class A operations. In Class 2 ops..we use a 'VTOSS' call.
To, again, keep it simple(er)..we use a 'fly away' call to declare the point at which I am not going to land straight ahead. (pilot's descretion) but either remain VMC and set up for a quick return or request immediate return for an approach...preferably radar vectors to an ILS.

[Shawn Coyle]

rumline:
What forms the basis for the decision for 'Fly away'?

[rumline]

Hello Shawn..Haven't had the pleasure of talking with you since...about '93!
Hope your well !
My decision on the fly away call is twofold. First and foremost is to inform the other crew member (PNF) that in the event of an engine failure/fire/rundown/ I will NOT return to the take-off environment...ie: runway, displaced threshold, reject area, or in the case of an offshore installation that I shall be attempting to maintain flight ie: ditching is the second option..
It also reinforces in my head what I am going to do...the decision has been made and should any of the above conditons occur...I shall continue.
It's a judgement call that in my opinion should never be fixed to a number... instead relying on experience and airmanship as well as assessment of how the aircraft is performing. (as we've all experienced times when no matter what the charts say....this thing ain't goin' nowhere!)
Anyways....look foward to hearing other approaches to this..

[Mars]

rumline:

I think you will find it extensively discussed here:

http://www.pprune.org/forums/showthread.php?t=169124

Mars

[Shawn Coyle]

rumline:
Nice description of something that ought to be done on every takeoff, by every pilot. You've already got a plan of what you're going to do should something happen.
Keep up the good work!