Increasing thrust for climb?

[shroom]

Has anyone ever done this? This is a standard procedure at my current employer (depending on the initial T/O power setting, of course) in the 747-400 and 747 classic. I've never done this at any other place where I flew these planes. It always seemed, for instance, that if the initial T/O power setting was going to be a reduced thrust setting, it was never reduced below what the climb thrust setting would be. However, there are plenty of occasions here where we take off at a particular thrust setting, and push the power UP at climb, either on an NADP 1 or 2 departure. This seems counter-intuitive, both for noise reduction and for engine life. I've tried to look for anything Boeing published about this procedure but have come up empty, short of calling Boeing and talking to one of the engineers.

Does anyone have any insight into this? Have you done such a thing or do you do so now? Any help is apprieciated. Thanks!

[Intruder]

Yes, it happens when you use a deeply reduced thrust setting (TO2 or 50+ deg assumed temp), and select full CLB thrust. It does illustrate the idiocy of the deeply reduced TO thrust settings, since there is NO additional "engine savings" gotten from the deep reductions, and performance & safety margins are reduced proportionately.

Along those lines, our check airmen got a briefing from a GE engine guy earlier this year that confirmed that there is no "engine savings" to be had from CLB1 or CLB2 settings, and they also increase overall fuel consumption. So our new policy is to use full CLB thrust regardless of TO thrust setting.

Supposedly the upcoming (Sep or Oct) AeroData performance software revision for the 747-8 will restrict the maximum thrust reduction in Assumed Temp calculations such that TO thrust will never be below full CLB thrust...

[shroom]

Thanks for the fast replies. Our SOP is always to use non-derated climb thrust, so with the explanation of using TO 1 or 2 or assumed temperature (all of which we do often enough, based on what OPS says) it stands to reason that the takeoff thrust setting would be so low as to require an increase in thrust for climb. Thanks again.

[misd-agin]

Not uncommon with 2/3 load's flying trans Atlantic (7-8 hrs) to take off at cruise thrust in the 777.

[Natstrackalpha]

Do you hold this througout crz clb to crz?

I`ve often wondered about something similar and once got interested in the idea of the speeding up to crz spd early on in the clb but then again climbing 270kts at 2,000` will be pretty much faster at FL330. thread drift?

If you could nail 280 or indeed 320 at, say by 3,000`! Ok, make it 300 dependant on WAT

anyway, if you nailed a higher speed lower down you would have the power for clb, the spd in the bag, the dist used to get to alt (as in crz clb)

less fuel used than blasting from sfc to accel alt?

but then a lesser clb rate versus more fuel used having got up to spd at a lower alt. . . or not?

There is a thing here, by doing it this way (obviously not always possible due to traffic, invariably) but you would also gain on the level out from the clb to crz - as you would already be at crz spd (thereby demanding a reduction in pwr setting to maintain that crz spd)


as opposed to hanging around in the crz (at an accel pwr setting FMS or not) waiting for the spd to increase, at a greater gff - just a thought.

Summary: Could you select 300 after T/O subject to traffic all the way to the crz FL?

GFF would be +/- 6T/hr in the climb. anyway.
So you could prolong the climb but use maybe 5T (as you`re at reduced climb rate you would gain on dist anyway, without the `wait` at crz alt for the spd to dribble up?

[galaxy flyer]

Misd-agin

Not exactly true, while the engine indications (N1, ITT) might be the same, the thrust produced at T/O and at FLs will be significantly different, with cruise thrust being lower.

GF

[Denti]

Not flying the 747, but on our 737s it is common to increase thrust at reduction altitude. Since there is no additional saving to be had by using the automatically selected reduced climb settings we use full climb thrust wherever an unrestricted climb is expected. Our engines stay usually quite long on the wing, the longest was well over 30.000 hours. Full reduction at take off to save on maintenance and full climb thrust to save on fuel.

[JPJP]

Here's the reasoning at our operator - We lease the engines on a 'Power by the hour' agreement from the manufacturer. Prior to 1000' AGL the manufacturer gives credit for de-rated or assumed temperature takeoff power reduction. That equals less cost to the airline.

Above 1000' AGL these 'credits' end. At this point it saves fuel to climb to the optimum cruise altitude as fast as possible using maximum climb thrust. Again, equalling less cost to the airline.

This is true for a CFM-56-7 power plant under a power by the hour agreement on our 737NG.