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Data from this question's answer states 2300 kg of fuel is used for takeoff/climb and 2500 kg of fuel per hour is used at cruise altitude. Half hour idle descent burns 600 kg per hour (2% of total fuel use).

Using simple modeling of fuel consumption at glide, cruise, and climb (as a mirror image of glide) the "rule of thumb" fuel consumption for climb would be around 2x cruise based on a half hour descent at idle matching a half hour climb and a similar IAS and flap settings.

From all this, it is reasoned that airliners climb to cruise at around 1000 feet per minute. How close are these numbers to actual climb rates of passenger airliners?

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At low altitudes, like below 10,000', the climb is much steeper than the descent, like a climb at 2,000 to 5,000 fpm & 250 knots, vs a descent at 1,500 fpm & 250 knots, or 1,200 fpm & 200 knots, or 800 fpm and approach speed (with some power being carried).

At high altitude, like optimum cruise, generally in the high 30's or FL 400/410, the reverse is true, with climb rate down to 1,000 fpm or less, but descent rate from altitude is easily 2,000 fpm or more depending on weight & descent speed.

On balance, the descent typically takes more time. Part of this is due to a greater prevalence of level segments on an arrival procedure than are found on departure procedures, but even in a case of uninterrupted climbs & descents, that generalization would still hold.

You're bound to have some descent segments that are level or close to it since you slow from ~280 knots to 250 at 10,000', and then from 250 back to approach speed later on (not necessarily all at once). Those segments trade about 10 knots per nm spent level & idle (until gear & flaps start coming out below ~200 knots); at climb power, acceleration happens much more rapidly than that.

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A two-engined airliner will outclimb any WW II fighter aircraft at low level. Since the requirement to stay airborne with only one engine running means that the second one can fully be used for adding climb speed, a modern twin will climb at about 22 to 25 m/s at sea level. Typical sea level climb speeds in WW II rarely exceeded 20 m/s.

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  • $\begingroup$ Yes, they have excess power, and might be most fuel efficient to nose up and climb at full thrust (for a shorter amount of time). For a massive jet, one can see how that, without very carefully checking airspeed, can lead to stall issues. I'm interested in bigger slats to help out. $\endgroup$ Aug 8, 2021 at 15:08
  • $\begingroup$ @RobertDiGiovanni You want to keep L/D high, and slats won't help with that. In fact, the higher airspeed with clean configuration and best L/D produces the best climb speed for pure turbojets. $\endgroup$ Aug 8, 2021 at 17:48
  • $\begingroup$ It will, but notice their angle of climb is all over the place because of variable mass. I'm thinking hook the slats to the stickshaker. The stabilator is in a world of downwash and turbulence at high AOA. $\endgroup$ Aug 8, 2021 at 20:45
  • $\begingroup$ @RobertDiGiovanni Sounds like Auto Slats: see page 22 in this document: 737ng.co.uk/B_NG-Flight_Controls.pdf $\endgroup$
    – Ralph J
    Aug 9, 2021 at 0:04
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Here's some figures used for "unreliable airspeed" situations for one of the largest current airliners - the pitch attitude and thrust settings result in the given IAS and V/S at different weights and altitudes. (disregard data within grey shaded cells):

Climb Descent Go-around

During normal flight, the use of reduced/derated thrust would give correspondingly lower V/S values during climb and go-around. [with thanks to Boeing]

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