Originally Posted by
Cough
So, theorising what might have occurred (please understand - This is just one of many possibilities!). Say you have two obstacles to be cleared, one close in, one further away.
For the intersection departure, the thrust requirement is a large one to clear the close in obstacle. As you have a large amount of thrust on, the OE climb angle is steeper and acceleration segment is shorter and you climb away without the second obstacle having any effect.
But for the full length departure, the thrust requirement to clear the first obstacle isn't too great so the performance app reduces the thrust to just clear the first obstacle be the required margin. But because the subsequent climb out and acceleration are that much longer the second obstacle comes into play, requiring the performance app to raise the EOAA to avoid this...
But say you take off from the full length with intersection data - Because you'll have the higher thrust selected, you'll not only avoid the second obstacle by miles, you'll also avoid the first by a greater margin...
That may very well be a more correct description of what caused the change. Nevertheless, from strictly an operator perspective the important point is that there was a change to EOAA that needed to be accounted for. For this reason and a few others stated above, while the intersection data will in the vast majority of cases be reasonably close for a full length departure, it may (depending on a particular airline's policies) not be considered technically legal. The question the PIC really needs to ask is, "If something were to go amiss during takeoff, would my choice of using the original intersection data be considered proper?"