B737-800 approach speed/flap procedure?

[LandingLights]

Hello,

Please could someone advise me on the speed/flap procedure for the B737-800 at the London airports. I am calculating arrival procedure and looking at this aircrafts performance based on the NATS speed schedule: 220kts to 20nm, deceleration to 180kts, 180kts until 10nm, deceleration to 160kts, 160kts to 4nm, deceleration to 140kts.

Can some pilots perhaps comment on the below:

1) I am finding that at 220kts the aircraft struggles to descend at 3 degrees in a clean configuration. I guess the most important question is this... does this actually happen in practise?

For calculation I can get round this by shallowing the angle of descent slightly, but what would happen in practise/what would a pilot do? A small level segment perhaps?

2) I am also finding that deceleration from 220 to 180kts cannot be achieved within a reasonable distance using flap 1. For calculation the use of flap 15 appears reasonable. (beyond that point flap 15 is fine also for deceleration from 180 to 160)

If someone could describe how the approach is controlled operationally in terms of height/speed with flap I would be most grateful.


Regards
LandingLights

[omnidirectional737]

The London airports require a continuous descent approach so flying level is not ideal. You could either accept the ROD or if you are high use speedbrake to increase the ROD. Normally I would use V/S to maintain the profile.

The flap you need to fly 180/160 knots depends on how heavy you are. At light weights you can fly flap 5 at about 160 knot, but you might struggle to keep the speed back, so you could use flap 10 which gives the same speed but a bit more drag. You can then maintain this until 4 miles. If you are heavy then you will need to have gear down flap 15 to get flap speed back to 160 knots.

Cheers

[LandingLights]

Many thanks omnidirectional for your comments, they are very useful. To just come back and clarify some more... when flying a CDA at 220kts, if in a clean configuration the aircraft is not giving you a high enough ROD would you elect to first use speedbrake, or go to the next flap setting (flap 1), or a combination of both?

Lastly, having selected the next flap for a deceleration (either 220/180kts or 180/160) might speedbrake be used during the deceleration if the profile is not being maintained or would you just go another flap level?

For interest I am using the different flap drag coefficients in my calculations but I am finding that the aerodynamics of this aircraft (and some others) are quite slippery and as a consequence it is 'harder' for them to maintain the profile. In particular around the 220/180 decel and prior to this. When at high weight (close to MLW) to decelerate to 180 from 220 on a 3 degree slope I am having to use (model) flap 15 (otherwise I am way too high). However, I have not got any info on speed brake (the drag they provide) or how much they are used in speed control, hence my questions above. Have no problem calculation wise closer in than the 220/180 knot deceleration. Any insights would be much appreciated.

Wildweasel81 to answer your question I did not get the speed control from a document, somebody told me it, although I understand it is in the public domain... if you dig around for it.

[omnidirectional737]

Boeing say that you should not use flaps as speedbrakes, but I suppose it depends how much you need to lose. From the FCTM Vref 40+70 which is clean speed dependent on weight ROD 1100 fpm with speedbrake 1400fpm. But on a normal approach you would not use speedbrake because it is inefficient and can be uncomfortable for passengers.

Also a point worth noting is that in the London TMA approaches are radar vectored so typically you will be back at 180 knots before intercepting the glide any way.

But if you are really high use gear & speedbrake.