VNAV Path construction and Flap Speed
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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
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
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Wow. That's a lot to remember! It is interesting looking at the FOQA data in ground school for approaches that guys really botched; but I think it is good to keep in mind that it's easy to Monday-morning quarterback. And usually the FOQA guy, who is shaking his head in amazement at how badly it was botched, spends little time as the Man in the Arena, flying the line.
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B737SFP: That would have been mind-exploding for most of the cadets I've had through TR's in the past 15 years. Ask them questions like that and the first thing that is brought out is their Japanese brain. Simple mental arithmetic skills seem to have disappeared.
What I found missing on the line was the appreciation of quick 'gross error' checks. This could be load sheets, flight profile, sector fuel required, etc. Perhaps, one is they were never taught, and two is they require mental sums.
What I found missing on the line was the appreciation of quick 'gross error' checks. This could be load sheets, flight profile, sector fuel required, etc. Perhaps, one is they were never taught, and two is they require mental sums.
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My most fav VNAV observation that tells me instantly that it is not understood goes like this. "I'm starting down early to get a head of the path." Ok says I and nobby promptly selects DES NOW or mashes that there altitude selector. We now start a shallow descent and THR HOLD presents itself. We continue on that 1200 ish fpm descent until re intercepting our original flight idle descent path that was 40 miles in front of us when we started down on this oddisy. The TLs go to IDLE and "What did we just accomplish" says I to a blank stare.
But that's 4nm early for FL360, not 40mn!
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I find the NG tends to overspeed in the descent above FL350.
Do you mean if TOD is >FL350, or for the 1000's when above FL350? But given that you are still >100nm from touchdown does a little overspeed matter; and that depends on your CI anyway.
Do you mean if TOD is >FL350, or for the 1000's when above FL350? But given that you are still >100nm from touchdown does a little overspeed matter; and that depends on your CI anyway.
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I mean if the cruise is above FL350, as we initiate descent, the plane often pushes close to MMO. We use .78/280 in the descent usually. Even with automated descent winds, the plane will still get close to the clacker.
I'd prefer not to have to write up an overspeed 100nm, 50nm or 2500nm from touchdown.
I'd prefer not to have to write up an overspeed 100nm, 50nm or 2500nm from touchdown.
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I'll start down early if cruising above FL350 with 4nm/1000' before TOD. I find the NG tends to overspeed in the descent above FL350.
