You are on the right track.
3x tables at 250kts or below can be a little optimistic for the NG, because it is very slippery until Flaps 10 or Gear Down. Flaps 1 and 5 offer almost no extra drag, and the speedbrake is almost useless below 250kt. If you find yourself in trouble with too much altitude/energy below 5000’, you really need to request extra track miles or just put the gear down early. Going F5 at 249kts won’t help (and it is very bad practice). With experience will come finesse. But you need to be always thinking about your energy vs NM to run or your won’t gain the experience, because you’ll never know why it did or didn’t work!
Set a couple of “gates”. Obviously 3000’ at 10NM flaps 5 at 180-200 kts is a good one, but if you are moving from a tailwind to a headwind, even that might require early gear. Be aware of the wind. Flaps 25 can be your friend also, as it has a high placard speed compared to F30 and provides significant extra drag over F15.
The next gate would be 5000’. 20NM at 230kts and reducing. If you are doing 250kts at 5000’ then you probably want 22NM. I fly a lot in high temperature environments, these gates vary with conditions, so work out what works for your operation.
Judging track miles to run:
Where I fly, ATC advice of track miles to run as about as accurate as as a muzzle loader fired from the hip in a duel.
Calculate your own track miles to run. You have a beautiful map in front of you with range rings - use them, with the abovementioned gates, and your 3x tables (minus a bit). I’m old. I learned to fly jets before ND’s, so I used DME’s and VOR/ADF to estimate NM to run when being vectored for final. It was amazing how accurate one could be without a map. We used to challenge each other to get it right so accurately that if you had to touch the speedbrake or thrust levers before 1500’ you had failed. That was the old days. We don’t encourage that sort of dick-measuring these days. When ND’s with range rings were invented I couldn’t believe how easy it became, and I’ve probably lost the skills I used to have after 30 odd years of map displays.
Interpolate the gates. If you have 25NM to run, 250kts, what should your altitude be? I would be saying “well, my next gate is 5000’, 230kts at 20NM, so I need to lose 20kts, and descend, so lets knock off 2NM for the 20 kts of IAS, that leaves 3NM, that’s 900’, so I should be 5900 feet. That might sound like a lot of mental maths, but you’ll get good at it after practice. That is a bit conservative, but that’s not a bad idea on the NG, and depends a lot on weight, temperature (allow more NM for high temp), and wind changes.
Be a bit conservative when you are new on type. If your colleague next to you has more experience on type, ask them! (Regardless of which seat you are in - it’s quite common in my airline to have a new Capt with zero B737 hours who has transitioned from widebody F/O who might be sitting next to an F/O with 3000 hrs on type. But they are so keen to prove their new Capt status, they won’t dare ask for tips from the F/O!).
If you want to be a child of the magenta line, you can pre-plan a “base” waypoint in the FMC (if ATC generally vectors you on a similar path), and connect it to the IAP. When you get on a downwind vector, execute a “direct-to” base, and you will have an approximate VNAV profile. Don’t engage VNAV. Use the “above/below” profile as a guide, and use LVL CHG and V/S as necessary. Use V/S when you are trying to achieve speed gates, as LVL CHG won’t achieve what you want. When using V/S, don’t let the thrust come up unless you know you are low on profile. Don’t become a VNAV sucker, it doesn’t know about the wind changes and potential vectors. Use the Progress page for track miles to run, and go back to your gates and mental maths.
Finally, don’t let ATC screw you - if they cut you in and shorten your track miles unexpectedly, don’t accept it unless you know based on your experience that it’s achievable. Just. Say. No. Your safety is more important than their efficiency. If they didn’t give you any notice of reduced track miles, make it their problem not yours.
Last edited by Derfred; 9th Oct 2020 at 14:16.