A case of getting whatever you can lay your hands on at times .. and then occasionally throwing a theodolite over the shoulder and doing a quick survey of critical problems.
There are various "normal" sources available, published either by the airport authority (typically Type A and, if you are lucky, Type C charts). The Australian authorities also collate simple inclino survey data (which may be the result of a simple survey or worked back from a detailed survey). Jeppesen has had a program for some years to collate the more readily available data which may end up being very useful.
In Australia some State government land authorities (Queensland is a good example) have set out to collate such commercial data as is made available to them.
One of the problems is that much of the existing data has come from privately sponsored surveys (eg mining companies) and the existence of such data is not generally known. Sometimes it comes back to networking ... there have been numerous times where I have made the usual round of phone calls trying to track down data for an out of the way place when one contact or another recalls that such and such a company did a survey in that area some time ago .... another contact .... more phone calls ... and sometimes the data which can be begged or bought is very pertinent and useful. Sometimes the data, especially the enhanced OPMs can be too good for convenient use .....
As I have said on a number of threads, doing the sums is the province of a trained monkey .... optimising the escape path and putting the sums over a good obstacle profile is the real skill of the engineer.
Last edited by john_tullamarine; 7th April 2002 at 00:28.