KLM-MD11
Topic Author
Posts: 429
Joined: Thu Mar 28, 2002 8:09 am

### Ascent And Descent Speed Planning

I have a question about speeds during ascent and descent. (i.e.B-737)

During ascent, having reached 10000 ft; what speed is usually selected until reaching cruising altitude? Let’s say on an average weight, flying economically (trying to save the boss money on fuel cost)

on descent, when leaving cruising altitude (let's say 37000 ft) at 320 knots IAS do you reduce speed at the point where descent starts or continue same speed during descent?

If one continues same speed during descent, at what point WILL speed be reduced?

I know that the max. speed at and below 10000 feet is 250 knots, so is speed being reduced just before reaching 10000 ft. at once or gradually? And if gradually, how?

One last question… from which point on is the rate of descent 500 ft. per minute ?(which I believe is common just before touch-down) as the rate of descent from cruising altitude is around 2000 ft. per minute if I'm not mistaken.

I'm sure these topics have been brought up before, but I couldn’t find it.

Thanks very much for your replies!

Regards,

KLM-MD11

GELUK IS GELUL MET EEN K

donder10
Posts: 6945
Joined: Sun Oct 21, 2001 5:29 am

### RE: Ascent And Descent Speed Planning

Most(very close to all)flights out of LHR are told 'no ATC speed restriction'when on climbout so they can speed up quickly.Not sure on other major fields though

Guest

### RE: Ascent And Descent Speed Planning

Dear Klm md11 -
xxx
For all airplanes the climb speed (and often descent speed) is function of weight - with considerations for fuel economy... all airplanes have different speeds - here are some for the 747 Classic -
xxx
Intial climb speed below 10,000 feet is V2+100 kts = generally 280-290 knots, even though the legal speed limit maybe 250, we advise ATC we need higher speed because of flaps up speeds...
xxx
Enroute climb is depending on weight - 747 varies between 335 KIAS when heavy, or 275 kts when very light... until we intercept Mach .82-83, time at which we continue to climb at that Mach number...
xxx
Descending, we can select hi speed i.e. Mach .86 until indicating 340 KIAS, then we continue at 340 until 10,000 feet, time at which we will reduce to 250 KIAS... If you wish you can also make a descent at 280 KIAS, it is supposed to "save on fuel", but I noticed only minimal savings...
xxx
Enroute descent we indicate about 2,500 FPM rate of descent... according to ATC procedures, the last "1,000 feet" is done at the rate of 500 FPM... To reduce hi speed descent (340) to 250 below 10,000, we start reducing speed at approximately 12,000 feet...
xxx
I only flew 707, 727 and DC8s as other airplanes in my airline career, so cannot give you speeds for "modern aircraft i.e. 767... be aware that with these old airplanes, we climbed at 320 and Mach .82 generally...
xxx
Tot ziens, vriend -
(s) Skipper

KLM-MD11
Topic Author
Posts: 429
Joined: Thu Mar 28, 2002 8:09 am

### RE: Ascent And Descent Speed Planning

Thanks very much Skipper!

very helpfull info indeed!!

regards,

klm-md11
GELUK IS GELUL MET EEN K

cedarjet
Posts: 8202
Joined: Mon May 24, 1999 1:12 am

### RE: Ascent And Descent Speed Planning

Skipper, fascinating stuff. What if ATC couldn't let you speed up during a climb when you were heavy? How much of this kind of thing was handflown?
fly Saha Air 707s daily from Tehran's downtown Mehrabad to Mashhad, Kish Island and Ahwaz

Guest

### RE: Ascent And Descent Speed Planning

Dear Cedarjet -
xxx
I cannot recall any instances of ATC preventing acceleration to required climb speed V2+100 - I assume "they know" we need such speed and clear us to such and such level and vector us accordingly...
xxx
In the situation that they would deny the speed, we would have to keep some flaps - for us would be "flaps 1", which would permit us to climb at V2+60 - most cases is around 240 knots or less...
xxx
Again, ATC knows about the 747, and I am certain we are not the only type of aircraft having that speed problem...
xxx
Happy contrails -
(s) Skipper

Guest

### RE: Ascent And Descent Speed Planning

The 747 isn't the only airplane with similar speed issues. The Galaxy that our company owned for a couple of years had a "clean wing" speed of up to just under 240 KIAS depending upon weight. We would need to climb out at 290 KIAS. It was a real issue when we operated out of airports underlying Class B airspace, where the speed limit is 200 KIAS. We always got what we needed from ATC, all we had to do was advise them.

Climb speed, as Skipper says, is dependent upon many factors. All things being equal, you can climb at V2 or you can climb at the Barber Pole, or any speed in between those two extremes - safety isn't the issue. What is at issue is getting the most "bang for the buck"; in other words, what speed will give us the most distance down range for the amount of fuel consumed. Many companies look at the speeds which yield the best "specific range" - the distance traveled per unit of fuel consumption.

The general rule of thumb when it comes to turbojet flight planning is that it's always best to climb as high as you can, as fast as you can, remain at altitude as long as you can, then descent as quickly as you can. Does ATC always allow us to operate accordingly? No, but it's something the we usually try to shoot for. For example, in the aircraft that I fly, the general rule of thumb for selecting an appropriate cruise altitude is 2 X Distance = The Cruise Flight Level. On a short 100 mile leg, we would usually file for FL200 west bound and FL190 east bound. Any leg longer than say 200 miles would justify a climb to FL390/FL410. Does ATC accommodate us? Out in the West and Midwest they usually do. On the East coast it doesn't usually happen - they tend to hold you down on climb out and start you down way too early. Oh well, we just carry a bit of extra "ATC Fuel" to compensate.

As far as descent planning goes, nowdays we simply program the FMS and it flys the descent for us. In the old days, we used a simple formula to give us the descent point and descent rate: 3 X Desired Altitude Loss = Descent Point and 5 X Ground Speed = Descent Rate. This resulted in an approximate 3 degree descent path. As far as speeds held in the descent - it depends upon what and where you're flying. In the stuff I fly, in domestic U.S. and Canadian operations we simply allow the airspeed to increase to (conditions permitting) a speed approximately Mmo/Vmo -5 KIAS. At around 13,500' we simply go to flight idle and the airspeed will slowly bleed off to allow us to meet the 250 KIAS / 10,000' speed restriction without too much fuss.

AAR90
Posts: 3140
Joined: Fri Jan 21, 2000 11:51 am

### RE: Ascent And Descent Speed Planning

>I have a question about speeds during ascent and descent. (i.e.B-737)
>
>During ascent, having reached 10000 ft; what speed is usually selected until reaching cruising altitude?
>Let’s say on an average weight, flying economically (trying to save the boss money on fuel cost)

FMS ECON CLIMB. Normally ~295-305 kias (weight dependent assuming standard cost index).

>on descent, when leaving cruising altitude (let's say 37000 ft) at 320 knots IAS do you reduce
>speed at the point where descent starts or continue same speed during descent?

Descent is normally performed at cruise mach until reaching desired indicated airspeed. Normally .78-.80m / 290-310kias.

>If one continues same speed during descent, at what point WILL speed be reduced?

Not sure I understand the question. Max speed is .82m/340kias. Speed reduction can be done at any time. Normal descent is performed at cruise mach until reaching desired indicated airspeed, then maintaining that indicated speed until further reduction is required/instructed by ATC/FAR/approach situation.

>I know that the max. speed at and below 10000 feet is 250 knots, so is speed being
>reduced just before reaching 10000 ft. at once or gradually?

Pilot technique and very much dependent upon what (if any) ATC instructions have been issued.

>And if gradually, how?

With no ATC limitations, my personal preference is to maintain speed and make gradual reduction in both speed and rate of descent so as to be level at 10,000' at 250 knots at the point in space where further descent below 10,000' will begin. If done properly, passengers should not notice attitude or speed changes unless they're specifically looking for them.

>One last question… from which point on is the rate of descent 500 ft. per minute ?
>(which I believe is common just before touch-down) as the rate of descent from cruising altitude
>is around 2000 ft. per minute if I'm not mistaken.

Normally you would not see 500fpm descent rates except during transitions (flare & level-offs). Normal descent rates are 1000fpm-3000fpm. Normal approach descent rates are 700fpm-800fpm.
*NO CARRIER* -- A Naval Aviator's worst nightmare!

411A
Posts: 1788
Joined: Mon Nov 12, 2001 10:34 am

### RE: Ascent And Descent Speed Planning

Regarding descent...
If ATC is unable to approve descent from cruise altitude when desired (for example at 100-110 nm approximately) it is often useful to reduce cruise mach number, so that when descent is approved, the nose can be lowered to accelerate while at the same time closing throttles. This results in a descent rate of 6000+ ft/min initially (while accelerating to M.86/350KIAS) to get rid of the excess height.
This works very well in the Lockheed TriStar, (lower speeds for other types).
One must be careful however if the destination airport is near sea level, as the cabin altitude descent rate will normally not exceed 300-400ft/min during descent for pax comfort...and this takes time.
Older types (B707 for example) required that the throttles NOT be completely closed during initial descent, as the turbocompressors needed sufficent bleed air to be able to pressurise/descend the cabin.

XXXX10
Posts: 706
Joined: Mon Jan 03, 2000 7:10 am

### Ascent And Descent Speed Planning

Descent is normally performed at cruise mach until reaching desired indicated airspeed. Normally .78-.80m / 290-310kias.

Does this mean that if you descent at a constant Mach No the IAS will increase, then, when you reach your max IAS you maintain that figure until you have to reduce for ATC ?

AAR90
Posts: 3140
Joined: Fri Jan 21, 2000 11:51 am

### RE: Ascent And Descent Speed Planning

>Does this mean that if you descent at a constant Mach No the IAS will increase,

Yes.

>...then, when you reach your max IAS you maintain that figure

Not necessarily the max KIAS, but rather your desired KIAS. 737NG max speed is 340kias, but there is an AD that limits speedbrake use to 300kias or less (improved horiz.stab being installed to fix this problem). So my desired speed is normally somewhere close to 300kias to allow SB use or increased speed to adjust descent/level-off point to make any arrival restrictions.

>...until you have to reduce for ATC ?

When you have to slow down, you have to slow down.   OTOH, most of my flights have been red-eye transcons with little/no early morning air traffic. I attempt to reach a point 30 miles prior to the runway at exactly 10,000' above the runway at exactly 250kias all without moving the throttle position from where I place them at the top of descent. With very smooth (and slow) transitions the first time the F/A's wake up the pax they'll be 10-15 minutes from landing and are normally quite grateful for the extra few minutes of sleep.
*NO CARRIER* -- A Naval Aviator's worst nightmare!

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