Hi Rich et al...
Since no terrain analysis is involved, I think one easy & safe answer could be:
1) Determine drift down distance from AFM + drift down distance including a turn of 180 deg.
2) Corret these ESADs to ground distance for the forecast w/v on particular day.
3) Find the first position (after clearing the terrain) on your route where you could legally maintain the net ceiling acievable for the planned actual mass at the critical point (if v. long driftdown from, say, F430, you might need to repeat the process a couple of times to get from an assumed mass to something a bit more precise). Now, work backwards with the "continue"-distance and find your OEI "top of driftdown - continue".
4) Find the last position (before crossing the terrain) where you could legally maintain the net cieling after a driftdown with a turn-back. Then work forwards with the "turn-back" distance and find your "top of driftdown - turn back"
5) If "top of dritfdown - turnback" is
further down the route than "top of driftdown - continue" - you are safe and need just worry about the "top of driftdown - continue". Should you loose a powerplant before this point, you know you'll be well above turn-back minima - should it occur after, you'll be well above the the minima to continue.
6) If "TOD - turnback" is situated prior to "TOD - continue" - you have several options:
a) Re-plan via new route
b) Reduce fuel load & plan a fuel-stop after crossing the high terrain
c) Reduce payload (doh!)
- not an option on a BJ, 'spose...
d) Use a drift-down alternate that you can safely reach anywhere between the 2 TODs
Hope this helps - best regards fm
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