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