High Speed Climb

[Elevation]

It is common knowledge that modern fan-jet engine is at its most fuel efficient self when operating at high altitute.

By performing a high speed climb out (i.e. eliminating the 250 KIAS below 10,000ft ATC restriction), the aircraft would have to spend more time at lower altitute accelerating as compared to above 10,000ft.

How is it then possible to "save" fuel when a high speed climb out is performed ?

[quid]

Accelerating as soon as possible to the best "rate" of climb speed will get you to your optimum altitude sooner than any other. Depending on your aircraft, it's usually much faster that 250 kts.

[411A]

But OTOH...it does not make all that much difference.
IF you should EVER hit a large bird at high speed, the results are not pretty.

Case in point:
727 approaching Khartoum, high speed at low level, hit a vulture and the bird went..
through the radome, forward pressure bulkhead,
broke the First Officers left leg,
through the flight deck door,
and ended up in the F/C lounge.

Personally viewed the damage.

NOT nice...at all.

[18-Wheeler]

Agree with 411A.
If given the choice, I prefer to climb at best rate (Approx V2 + 100kts in the 747, so that will vary from about 235kts up to about 275kts) for the birdstrike reason and I also think that by getting the plane above 10,000' as quickly as possible helps reduce the fuel burn, as you're buring a LOT of fuel down low.
(Can't back this up with real figures, I'm just guessing based on when I used to fly a Citatio 2. We used to use a little bit less fuel by doing it that way and it didn't hurt the sector times that much)

[SuperRanger]

i usually request for high speed climb whenever possible. the Best Rate of Climb is usually higher than 250kts for most acft which is different from Best Angle of Climb which is usually a lower speed. from the computer, you saved close to 100kg for climbling at high speed (b777). dont know how accurate this is in real life but i am sure of the savings, just not the quantum.

as for bird strike, it's a consideration but i personally feels it's a very slim chance we have to take (as in the safest airline is one whose planes dont takeoff). there is no guarantee there's no bird above 10,000.

SR

[druckmefunk]

18 Wheeler
I dont mean to be nitpicking, but why would you apply citation theories to flying a 747. I'm fairly sure Boeing do a fair bit of their own research before they advise you that high speed climbs are more fuel efficient in big jets. I could well be wrong, but i am fairly sure that this point is beyond argument.
It is not just a matter of altitude, it is the combination of altitude and distance. i.e Normal (high speed) climbs are a compromise between altitude gain and distance covered, therefore reducing cruise distance as well. It may well be possible to use less fuel to TOC using a different profile than high speed, but what really matters is how much fuel you have at destination, not TOC. Although you may initially gain altitude quicker at 250kts, you eventually have to accelerate sometime, and this is done more efficiently at lower levels where more excess thrust is available.

Bird strikes are a different consideration, as 411a pointed out.

[Young Paul]

There are other reasons for going for angle of climb rather than rate. For example, getting above inbound traffic might give you an earlier climb to high level. If you are worried about birds for whatever reason, or know things about the local traffic situation, or are in US airspace and don't have a choice, then there are reasons for sticking with 250kts/FL100.

However, my understanding is that all else being equal, from an aircraft performance point of view, the best strategy is to go for best climb speed.

A vague hunch that your aircraft might be different from all the others doesn't constitute a valid reason for not doing it.

[18-Wheeler]

Quite fair, Drunk.
It's probably six-of-one, etc, but it worked well in the smaller jet.
But I always try to do the max rate climb thing when pointed away from the direction I ultimately want to go, as I figure when I eventually turn around to head that way I'll be higher up and so have a longer cruise segment.
... or so the theory goes .... ;)

[Young Paul]

Yes, that's something that also occurred to me yesterday as a "local" reason why you might not want to go to climb speed. There is no point in accelerating the wrong way, and then having a turn that covers four or five more miles and takes a minute longer as well. In fact, even if you have to level off and have no speed restriction, it may be worth keeping the speed back to make manoeuvring tidier.

[jtr]

Sometimes you need high speed to get clean. Max wt A340 or -400 in the order of 280kts min clean speed, and that is just to get you to best angle speed, i.e. still below best rate.

[GearUp CheerUp]

Also if you're climbing into a strong increasing headwind if you speed up earlir then you are exposed to the headwind for less time.

[BN2A]

Increase Airspeed, hence ground speed, sooner....
Get to destination sooner....
Get to stopover hotel bar sooner....:D

[Dan Kelly]

BN2A

The word quicker doesn't apply to a BN2! :p

[Chosun]

The Boeing B744 Data manual quotes an average saving of 1800 lbs of fuel from brake release to TOC by accelerating to Econ Climb asap after cleanup, as opposed to 250 to 10,0000. At high weight Econ Climb (Cost index 100) may be 350 knots. I have compared fuel to flight plan at TOC, and this prediction is accurate. Climbing at best ROC (approx 310 at high weight) doesn't make any improvement.:)