TDP and CDP
Joined: Sep 2001
Posts: 600
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From: In the Haven of Peace
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.
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.
Joined: May 2004
Posts: 20
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From: Cornwall
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?
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?
Joined: Sep 2001
Posts: 600
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From: In the Haven of Peace
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 
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
Joined: Sep 2000
Posts: 49
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From: On the Beach, On the Rock, On the Lake
CDP, LDP, TDP...3pgs and still ambiguity?
To me....LDP (landing decision point) is (was) made 80nm offshore, at the moment I shoved cyclic foward coming off the rig!...
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.
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.
Joined: Sep 2000
Posts: 49
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From: On the Beach, On the Rock, On the Lake
CDP, LDP et al
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..
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..
Joined: Jun 2003
Posts: 320
Likes: 0
From: Off the Planet
rumline:
I think you will find it extensively discussed here:
http://www.pprune.org/forums/showthread.php?t=169124
Mars
I think you will find it extensively discussed here:
http://www.pprune.org/forums/showthread.php?t=169124
Mars
Joined: Dec 2001
Posts: 1,835
Likes: 3
From: Philadelphia PA
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!
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!
