737-800 energy management while receiving vectors.
 

What methods do you employ to plan your descent while receiving radar vectors to an approach?

What kind of a reduction can you expect to the ROD of descent with TAI selected ON?

You can expect maybe 100-150 fpm less than the actual vs with TAI on.
on downwind abeam the field, assuming 10nm final if you are 250CAS 6000' you can do a nice CDA. Look always at the "green banana" (the MCP alt prediction which is showed as a green arc on the nd).
try to update as much as you can your path.

anyway std metod: ALTx3 + HWC/TWC and DECEL to up SPD(1 nm each 10 kts above up spd)

Well...

After discovering how useful is the DES page, my life became much easier !

Just insert a point like the OM/CROSSING ALTITUDE there and watch the magic happens. No more constant position updates or mental math to discover how you're on the profile. The fmc will tell you continuosly what is the required ROD to the point you previously inserted.

Remember that in a clean config, without speedbrakes, the acft's rate of descent is something close to 1100ft/min.... 1400 using the speed shaker !

So, if you see anything more than 1000ft/min there mind that you either will use the speed brake to slow down during descent with that rate, or you can level off, slow down to the flaps 5 speed and descend with the new calculates rate for that config.

I don't know which - 800 do u fly, but in some variants the slats will go to the full extended position with flaps 10, and that, my friend, works like a charm.

By the way, it's very rare, at least where I fly, to see pilots using this helpful tool.

Fly safe and remember, never blind follow the atc vectors, if you're not confortable, say you're unable !

As you are in the UK chances are you'll be given miles till touchdown. If you're given 25nm, for example, multiply that by 3 would equal 75 (7500ft). A rule of thumb is the -800 will lose 10kts in 1nm of level flight. And 1nm x3 equals to 300ft. So at 220kts you'll need to lose 20kts for up speed. 2x3 = 600ft. So 25nm to go at 6900ft would be spot on.

But the important part is that you need to be descending at the right rate (half ground speed). 250kts ground speed you'd want to descend at ~12/1300ft/min. If you're not then you're high or will be high at some point. From then on just estimate how many miles you have left. Easy way to do that is look at the progress page to see your miles left on the as soon as ATC give you your miles and using the difference you can work out your miles left at any point. Obviously the magenta line as to be in the same general direction as your HDG for this to work. So be careful with this one.

Alternatively use the green banana, remember you'll still need to decelerate so it's a good idea to get the green banana to be level early.

Unfortunately it comes with experience on what to do. Flaps are your friend if you're high. If you're not sure how it's going you can always turn to the other guy and ask.

I'm sorry, but...

Wouldn't 25 miles to touchdowb give you something around 8000 feet to lose?

The acft descends 1000ft for every 3nm, right?

1k....3nm
Xk...25nm

X = 25 / 3 = aprox 8k.

As in your example the acft had to reduce 20kt to the flaps up speed, we would have something around 23nm to descend. Thus, 7500ft would be the right figure in my opinion!

But this is a slick bird, its always a good policy to have 1 or 2 extra miles in ur pocket in case you face some tailwinds.

737-800 energy management while receiving vectors.
 

It's never too early for the gear!😁