General Descent Procedure (flap usage/max speeds) (MEJ)

[mjtibbs]

Hi Guys.

I was hoping someone could kindly tell me the general decent procedure from cruising altitude to around 5000ft.

Mainly in flap usage and at what speeds they should be used.

When descent is about to commence, is the aircraft slowed to around 250kts first, then the descent starts and flaps start being deployed? or can the flaps start to be deployed before descent begins?

maybe a better way to ask the question is, at what speeds should you use each flap angle?

thanks in advance.

-tibbz

p.s this Q is in referance to general MEJ's like 737/757/767 etc.

[LAX]

Hi

For 737 find a Flight crew training Manual as theres loads of stuff in it regarding decent, approaches and when to slow, deploy flaps and configure.

Basically lets forget VNAV, however this is what I do. To calculate your approx decent point from the airport Nav aid multiply your altitude by 3, divide it by 1000 and add 10 = Top of decent in nm eg (35000ft/1000)*3 +10 = 115nm top of decent. I would put a 115nm circle in the fix page from the Airport Nav aid to mark the point. You will need to allow for tail or headwinds. At approx FL260 your speed needs to be around 280-290kts.

At 25 to 30nm from the Airport aim to be at FL100 - 240-250kts. Put a 25nm circle in the fix page from the airport nav aid to mark the MSA and a 25nm point to go. Remember at some time you will need to decelerate from approx 280 to 250kts, this takes around 25 seconds in a 737 in level flt (half this time using the speed brakes). I would generally start to slow from 280 to 250kts at approx FL115

At approx 12nm to go you should aim to be at min clean speed 210-225kts and around 5000ft.

As soon as you are given a turn and heading (assuming normal radar vectors) to intercept the inbound radial or LOC for landing call for Flap 1 and then 5, slow to 180-190 kts. If you intercept much faster than this you will overshoot the VOR radial or Loc. Then configure the Aircraft depending on altitude, distance to go etc on the approach. If you are flying a full procedure be at Flap 5 speed 180kts outbound from the beacon.

Use the Green Banana on the EHSI, it will tell you if you are going to be high or low depending on your distance to go. If your too high or fast use the speedbrakes to get yourself back on the correct profile.

Hope this helps.

[scroggs]

Mr Tibbs is not a pilot, judging by his profile, so some of your reply may be too technical. I'll try and de-tech it!

Basically, the aircraft is descended at high speed until speed limit regulations are encountered (or ATC requires a slower speed). This will be at 10,000ft in many countries, and at specific distances from holding fixes in others. The speed will be reduced to 250kts, then holding speed if applicable. Flaps will not be deployed normally until the base leg part of the approach whilst slowing to 180kts-ish and gear will be lowered once established on the final approach.

Scroggs

[mjtibbs]

Thanks for the response guys.

Scroggs is right, im not officially a pilot/studying as of yet.... im merely a flight simmer and recently installed fs passengers but kept getting penalised for exceeding flap speed limit, hence this topic!


I managed to follow it but just have a couple Q's.


By "Top of decent" do this mean when you should initially start decent?

also does "flap 5" mean full flaps?

this is very helpful, many thanks.

also thanks to scroggs for simplifying.

[kenparry]

"Top of descent" means the point at which you leave cruise altitude.

Flap settings: there is a difference between Airbus and Boeing.

Airbus use small numbers to describe their settings, and have about 3 or 4 flap settings, described as Flap 1, 2, 3 (and 4 if it exists - I can't recall).

Boeing uses different numbers, which vary with model. 737-200adv had Flaps 1, 2, 5, 10, 15, 25, 30, 40. Settings 1 to about 15 could be used for take-off, with the lower settings on longer runways. Normal 2-engined landings would be Flap 30 for low noise & fuel burn; F40 was used many years ago, but is probably not now. A 1-engined landing would be with F15.

B757 & 767 have less settings: 1, 5, 15, 20, 25, 30. Again, lower settings are used for take-off (though my recollection is the 757 uses at least F15 to avoid tail scrapes) and F30 for normal landing, F20 in the 1-engine case.

The use of flap settings through the speed range needs some explanation. Taking the B757/767, the speeds are related to Vref30, an airspeed at which with Flap 30 you are at (I hope I remember correctly) 1.3 times the 1g stall speed. At a typical landing mass this will be around 130kts. Above Vref30 + 80kt you can fly with flaps up; at that speed you select Flap 1 and can fly down to Vref30 + 60 kt; then Flap 5 and down to + 40 kt. This is the usual configuration to acquire the ILS localiser. Then, approaching the glideslope, select gear down, Flap 20, speed back to Vref30 + 20, and finally at about 4 miles to touchdown select Flap 30 and slow to final approach speed - which is not Vref30 but something more which depends on the wind and any gusts, the increment being between 5 and 20 kt.

Hope this helps.

[Capt Claret]

B717:

Usual cruise speed M0.78, descend at that speed into 320ish KIAS, almost at flight idle power.

Usually slow to 250KIAS by 10,000' and hold this speed in the clean configuration till 3500' AAL. At 3500'AAL slow to 210KIAS, still clean, and take Slats approaching 210KIAS, slowing further to take Flap 18 approaching 190KIAS.

Approaching 170KIAS, gear down followed by Flap 40 and speed reducing to V-APP (V Approach) which is usually V-REF + 5KIAS.
If it's been well planned & flown, the thrust will be nominally at flight idle from TOPD (TOP of Descent) until V-Approach is achieved.

On the flap setting side of things, the 717 has

Flap 0, Slats retracted
Flap 0, Slats extended
Flap 13 (degrees)
Flap 18 (degrees)
Flap 25 (degrees)
Flap 40 (degrees)

Additionally there is a variable flap setting mechanism which allows any angle of flap from 0 to 20 to be set for take-off. Having said this, the Flight Manual mandates a minumum flap setting for take-off of 5 degrees. In the list above, all flap settings greater than 0, require the slats to be extended, and as the one lever controls both slats and flaps, it is impossible to have flap extended without the slats being extended, unless the slats have failed in the retracted position. Flap 25 & 40 are the normal landing flap settings, and in our operation it is normal to land with flap 40 unless OEI (One Engine Inoperative), in which case flap 25 would be the norm.

[mjtibbs]

thanks once again for the input fellas.

its answered my question and more!

I never realised that you don't need full flaps on take off.

also, on takeoff, do you increment the flaps while commencing roll, or do you pre-set them before starting roll? (last Q by the way lol)

thanks :)

[kenparry]

Always you select the flap before starting the take-off: it's one of the items in the before take-off checklist in every type I have flown. You retract flaps when you have reached a pre-designated speed and height, and there may be more than one stage to the flap retraction, depending on how much flap was selected initially.

[LAX]

Hi

Quite simple. Before leaving the gate the Aircrafts take off and climb performance is calculated based on a given flap setting.

As Taxi clearance is recieved from the stand the Captain starts to taxi the aircraft to the runway in use and calls for Flap XX. The First Officer then sets the flaps to the take off position (normally on a 737 this is flap 5).

During the Taxi checklist or Before take off checklist the pilots verify that the flaps are in the correct take off position and that they have all deployed correctly.

[mjtibbs]

thanks again. :ok: