757/767 Climb Derates?

[Localiser Green]

I wonder if any 757/767 drivers out there could help me with this?

What determines whether you use CLB/CLB1/CLB2 thrust derates. Is there just a "magic" weight below which you can do CLB1 and another (lower) weight below which you can take CLB2?

Also does the derated climb thrust stay in all the way to TOC? I heard that on the 767 at least it slowly "washes out" as the aircraft climbs. Does this also apply to the 757?

Any response would be appreciated. Thanks.

[expedite_climb]

Loc Green:

757 and 767 are the same.

Climb 2 will give you 88% of full climb thrust
Climb 1 will give you 94% of full climb thrust

Our SOP is to derate to Climb2. When the ROC decreses to 1500 fpm (notwithstanding acceleration), go to Climb1, and the same again for the change to full climb power.

If you have a particularly high take off derate you might not be able to set it without derating the climb. i.e. it stops you setting a take off derate that would work out as a lower take off thrust than the current climb thrust set.

Some people dont like using climb 2 if they've done a full power take off (for e.g. engineering request), as it is such a large power decrease 'it scares the pax' !!

[Localiser Green]

Thanks for that information. I can see how TO to CLB2 would be a pretty sharp reduction for the passengers!

If any other pilots use different procedures for this derate business please let me know.

[Jetdriver]

Expedite_climb has summed it up very succinctly. different airlines will have a recommended level of sustained rate of climb that they use for selection of climb 1 from climb 2 in our case it is around 800 fpm.

climb 2 is normally used on all departures at all weights. The use of preselected climb 1 ( or full climb power if necessary ) would depend on the anticipated need for higher power after takeoff. Terrain prolfiles or boundary level restrictions would be 2 examples where this might be the case. At low weights a use of climb 2 may be adequate to achieve any altitude restrictions whereas at higher weights the use of preselected climb 1 may be more prudent.

There is a temporary reduction of climb rate as the aircraft climbs through FL 290 to FL 300 as the speed schedule changes from TAS to Mach no. This is often the point you will see many pilots erroneously select climb 1 when it is not really necessary. After a short delay the aircraft would resume close to its previous rate of climb. Use of appropriate Speed intervention on the autopilot panel would also eliminate this temporary lag. In the same vein when getting close to cruising altuitude use of climb 1 can often be avoided by speed interjection.

The use of reduced climb thrust settings results in much higher engine life and although this is very difficult for pilots to quantify and monitor it is nevertheless a major cost consideration which usually outweighs the fact that there is normally an increase in noise footprint and fuel usage.

As already stated it is often recommended to use preselect climb 1 after a full thrust takeoff for the reason already stated, although climb 2 might be selected subsequently. The preselection is just a game plan as is the FMC route selection. It can and often is changed once airborne and its use is always at the Captains discretion.

[expedite_climb]

Interestingly though, the use of climb derates will actually increase the overall trip fuel burn, due to increased time to cruising level.

[McD]

Yes, it will, EC, but the trade-off is that the "extra fuel burn cost" is most likely far less than the "early engine replacement" or "engine damage" costs.

At my company, we normally use Climb 1 until we're cleaned-up and are accelerating (or have accelerated) to our initial climb speed of 250. Then we switch to Climb 2 and use it as appropriate, depending on rate of climb due to weight, etc.

As jetdriver stated, there are other conditions which might require the use of another initial climb power setting. If terrain is a significant factor, we will use "normal" (non-derated) Climb. On the flip-side, there's a location where we go from TO directly to Climb 2 due to a very strict noise abatement procedure. In this case, we usually pre-brief the passengers so that they're not frightened when the engine noise decreases noticeably.

One point worth emphasis is that we always have full climb thrust available if necessary. We use these reduced thrust climbs because they are helpful to the engine, but we aren't limited by them in the event that we need more thrust.

[Localiser Green]

Thanks very much for these very interesting explanations, they have cleared up my misconceptions.

[Silvershadow]

On the 757 the derate is available to TOC.
However on the 767 the derate starts to wash-out at 11000ft and by 12500ft you have full climb power.

[BN2A]

Errr... Jetdriver,

Doesn't the rate of climb INCREASE at the FL 290 IAS to Mach Number transition? The IAS decreases with constant Mach number and increasing altitude, so to reduce IAS the rate of climb increases... Usually to about 2000 fpm in the 757..

:)

[expedite_climb]

BN2A,

I had thought the same, but I think Jetdriver may have been aluding to the fact that people arent often aware of the change when selecting full climb or climb 1.

i.e. Shortly before the change ROC will have dropped off significantly. If you still have a climb derate you don't necessarily need to remove it because very shortly it will change to Mach and climb away again.

[Jetdriver]

BN2A

In VNAV mode there is a short lag as the schedule changes from CAS to Mach number. This results in a slight reduction in pitch and consequent reduction in ROC. As you point out the change to constant mach number will result in a increase in ROC although climbing through the 30's the gradual reduction in performance tends to mask the difference.

The point I was making was that if left alone or a temporary use of the speed mode is utilized the aircraft will either resume its previous ROC ( or close to it) or if speed mode is utilized the reduction in ROC can often be avoided. It is very common to see climb 1 selected due to the VNAV pitch/ ROC reduction at FL290/300 when it is not really necessary.