A few days ago I had a T.E.M class and the FOQA guys gave us some nice numbers to remember (data collected using a huge number of monitored flights) and help managing the energy during approaches that are going south...
1) If you're 1000ft high on the VNAV profile you'll need (using speed brakes):
- 6nm at 280kts
- 10nm at 250kts
- 12nm at VREF40 + 70
2) For every mile on a 3deg glide path you will lose, roughly, 10kts (SPEED DECREASING WITH GEAR DOWN)
3) For every dot high on the glide slope (<10nm from threshold), you will need 1 extra mile to get back to the profile (SPEED DECREASING WITH GEAR DOWN).
4) You'll need 3nm for every 1000ft high on the VNAV profile (GEAR DOWN / DECREASING SPEED)
5) You'll need one extra mile to dissipate the energy generated by 20kts of tailwind on a 3deg glide path (GEAR DOWN).
So... For example: Let's say you aim for 150kt at the FAF (5nm from RWY) and you're with 190kts, 1 dot high with 20kts of tailwind. When should you ask for the gear down ?
19 - 15 = 4 + 1 (high on the glide) + 1 ( 20kts of tailwind) = 6nm from the OM. According to what they observed on all those flights (900+ daily ops), you should ask for the gear around 11nm from the runway in this case.
It was a pretty nice class... Some great recordings of messed approaches !
On the other hand, I still prefer using V/B & V/S indications on the DES page. Much more straight forward with far less thinking !
Hope it helps
