Originally Posted by
FM_A320
how many miles do you add in order to decelerate? Normally I use 3xAltitude (even if some colleagues suggest 3xdistance as this gives a shallowe profile) plus 5 miles from 250. I see this rule works very good and is even conservative if I can descend all the way down at 250, level off and decel, configure.
Hi,
The more correct formula is "altitude/slope = distance". Altitude x3 puts you on a 3.33° slope (approx) so is indeed steeper.
A good rule of thumb is to add 5 miles for 320kt to 250, and another 5 miles for 250kt to under VFE2.
If you're about 500-700ft above profile you should be more than okay for a decelerated approach (at least on my FMS standard which wants to do an early stabilized..)
If you're (very) high, it's usually best to slow speed first, get flaps 2, full spoilers (sometimes gear down even) and then dive. This will give you almost 10 degrees..
To avoid unstabilzed approaches, I put the runway in prog page and don't turn to base then final unless my altitude is lower than distance x 3 + 1000ft (to account for the turn)
You can also compute your own FPA. Compute your nautical miles per minute first : 120kt is 2 nm/min, 180 is 3 and so on. Just use the nearest figure, closest to your ground speed. Then, there is 100fpm for each degree and each nm/min. For example at 240kt, if you want to go down by one degree, you need 400fpm.