Maximum angle of descent
 

Hello all,

I was wondering the other day if there was a particular speed that one should fly for the best angle of descent. Vx and Vy are given, and best rate is Vmo plus spoilers. But say ATC gives you a big shortcut on a really long STAR, so now you find yourself pretty high. How do you determine your maximum angle of descent? Some will say start to configure early and watch the altimeter wind down, and others will say spoilers and FLCH /OP DES. I don't think both methods can be right.

Is there anywhere it's published,or any way to get a rough estimate of the speed required?

When I'm fast, prefer method 2.

If already slow, prefer method 1.

As slow as possible, as much drag as possible. Of course, ATC will not be too impressed if you have full flap and gear down but the angle will be unbeatable! Loss of angle in slowing up is more than compensated for by the resulting descent angle. Even better in a strong headwind.

If that 'slow' is not possible, do it as slowly as you can get away with and with as much drag as you can at that speed.:). Any EXCESS speed will make your overall angle worse as you lose the speed at the bottom - assuming you need to land!

If you're on a STAR, you don't have many options. My own favoured option is point the nose down into a Stuka dive- you lose energy gaining speed and descending rapidly, and bleeding it off again is better than a steady descent. Also we don't usually have solid 250kt/10,000' restrictions over here. But on a STAR, speedbrake and look where the green line goes, if still no good, dump the gear. If that will still not do it, you are not in a position to accept the clearance!

Thanks for the quick reply guys. I just had a thought- if we slow up and configure really early, we'd have lost the time we gained by going direct:ugh:

Yes, but you will get in! Alternative is extra track miles to get stable=time. It all depends on the parameters for the 'direct':=. You choose the solution as appropriate. That is what they pay you for. It is cats and skinning, but you asked the question and I answered it as phrased!

Not criticism BOAC, it's just something I thought of after reading the posts. I agree that (as always) it's situation depedent.

Copy. Don't forget to 'weave' as much as possible too. Turns increase descent rate and increase track miles and ATC normally will not decline a 'gentle meander' around the direct track (in the UK at least:)). 30/60/60.... is normally acceptable I have found.

'gentle meander' around the direct track

:)I'll make sure to use that term next time someone point out that I'm not tracking the localizer perfectly.

30/60/60

What does that mean?

.....er..... a weave?

Ummm... does this mean that, just for example you understand :} ... the steep approach to London City doesn't suit ATC? :eek:

Does this mean that the approach wasn't submitted to ATC for comment in the first place? :confused:

Roll and pull, roll and pull............. land :E

'gentle meander' around the direct track, weave, Roll and pull, roll and pull............. land, that's a good summary of descriptions of my normal approach technique, what do I do if I need to steepen the approach?

Regards,

Old Smokey

To work out rough estimate of height vs distance if short cuts are the norm,try PF CDU LEGS page,PM CDU PROGRESS PAGE and note current distance and estimated FMC heights,then join short cut but do not excecute,the PROGRESS PAGE will come up with distance gained then divide by 3 and put that height/speed reduction at the point where you think the short cut might occur,this will give you the vertical deviation and work form there.
And always have Smokey's '''gentle meander' around the direct track, weave, Roll and pull, roll and pull............. land, that's a good summary of descriptions of my normal approach technique, what do I do if I need to steepen the approach'' method ready.

Thanks for all the advice guys. I'm afraid I still haven't found a definitive answer though. Will I get a steeper angle by flying near the minimum speed or closer to the maximum speed. The data is easily obtained for getting up, but not down? Is there any rough formula I can use to determine speed for max angle?

Thanks

Once again, slow, fully dirtied and into a headwind gives best OVERALL angle. If you are in a T****t, reverse on number 2 (heavens - did I nearly mention T****t?:eek:)

Barber's Pole/speedbrake may give you a good angle too but getting the speed off at the bottom don't half screw that!

Everything depends on your situation and aircraft type.

As a rough rule of thumb:
300kts = 30 000'/min (over the ground obviously)
250kts = 25 000'/min
etc.

What is your aircraft's ROD's for these speeds with spoiler and/or gear/flap?

Disregarding the level bit at the bottom where you have to slow down from the high speed descent, then 3000'/min @ 300 kts will give you a 1/10 descent, where you only need 2500'/min @250 to get the same angle profile (or 2000'/min @ 200). Anything above these values for the speeds given will give you a better angle.

I have found to my disgust that slow and dirty beats fast and steep almost every time.

The other advantage of slow and dirty is that when you are getting near to MSA and you are limited to 3000fpm or thereabouts you will get that better height loss/mile you need. I'm with nugpot on the 'pain' of it but on the R35 VOR approach at PRN, 210/gear used to be the only way to get down in the distance near to the high MSA. Also if you are left high abeam doing a visual, you will get down without losing sight of the field:)

Thanks guys. It seems that slow and staedy wins the race (again).

Never! Quite simply, the faster you fly, the quicker you drop out of the sky. I know you are hamstrung over there with a hard 250kt/10,000' limitation, but throughout the descent, if I'm high, I wind the speed up. Try a 737 at 330kts instead of 280- it means often you don't even need speedbrake. you expend so much energy speeding up and in a high drag regime that even with slowing up again, you have gotten down far quicker than if you came down at 280 with speedbrake.

We were given jets to get there quicker! Slow up early, and you should be a turboprop pilot.