Beware the hidden obstacle!
I should have been a bit more specific with my comments about the possibility of a more distant (NOT distant) obstacle arising from the lowest published gradient, an example.......
There are two Distance / Gradients available, 1.6% and TODA 1.82%
Two separate obstacles may well have caused these two gradients, one fairly close in, and one
more distant (for the 1.6%). By geometry, we can establish one intersection of the 2 gradients, the "phoney" obstacle will be higher and more distant than the one causing the TODA 1.82% Gradient, but will be
LOWER and
CLOSER IN than the real obstacle causing the 1.6% Gradient.
If, on the other hand, you have 3 gradients available and all produce 2 intersections which are, for all practical purposes, at the same point, there's a 99% chance that we're dealing with only one obstacle.
The conservative way to go if you don't have "good" data close in (like Type A charts) is to assume the 1.6% obstacle at the Survey Limit. If you're dealing with 15,000M Survey Limits, that creates a 'worst case' obstacle of 787.4 Ft above Airport Elevation at 15,000 M. For a 2 engined aircraft, this will require a 1217 Ft 3rd segment, just nudging the type of 3rd segment heights which cause a problem if your engine has a 5 minute limit at Takeoff Thrust / Power.
Of course, there may still be numerous hard bits beyond the Survey limit which may affect both 2nd and 3rd segment performance, time to get out the Topo charts......
Regards,
Oldf Smokey