Climb Thrust

[burm 3]

I use PFPX and Topcat for flight planning. Topcat will advise on Assumed temp and derated takeoff power.

How do I decide to use Climb, Climb1 or Climb 2?

I think airlines use published tables for airport runways but we do not have these in the sim world.

Any ideas on doing this?

thanks

Paul Burley

[thibodba57 462]

The computer automatically assigns the value. Just use that.  By default my companies FCOM does not allow for use of CLB-2 in the 400 (we can with the -8, it is even preferred when the computer selects it).  I haven't looked at PMDG documentation in the pre-flight area as I use my companies but look into the Final Performance Data section of the preflight checklist.  That is where my FCOM states not to use CLB-2.

The only reason I can think of manually selecting CLB over CLB-1 is if your heavy and have Altitude constraints you really need to make.

[Fabo 213]

CLB constraint is selected automatically so that climb thrust is actually lower than takeoff thrust, not higher.

You can remove the derate at any time.

[skelsey 765]

Airline SOP plays a part as well.

SOP at one large operator to use full CLB until clean; then select CLB1 (or CLB2 if sufficiently light).

[77west 139]

Its the tradeoff of lower power but longer climb time vs higher power and shorter climb time, and airlines use a number of factors to determine which one costs less. As mentioned, altitude constraints are also a factor.

[berts 97]

Paul,

The majority of B744’s fitted with RR engines (and others) use the Assumed Temperature Method (ATM) and for most departures this will normally result in a takeoff thrust which is less than the rated takeoff thrust for the runway in use under the ambient conditions on that day. The primary reason for doing this is to lower the EGT and extend engine life.  CLB1 is the normal (EPR) thrust reduction for takeoff, so within FSX or P3D just accept what the FMC selects for you and don't worry too much about using CLB2.

Notional weights in excess of the maximum structural takeoff weight are provided in the B744 aircraft performance manual to enable the highest possible weights to be used when reduced thrust, contaminated runway, pressure altitude or acceptable MEL defects apply. Therefore, the takeoff thrust setting parameter is not normally considered to be a limitation - and there is nothing to stop you advancing the thrust levers manually to the maximum rated thrust if you need to; e.g. due to unexpected windshear, temperature inversion, engine failure etc(but watch your max EGT's and other engine parameters if you do!).. During the climb there is also nothing to stop you manually changing the CLB Derate between the various settings if you need to – for example if ATC asks you to expedite or slow the climb or whenever the ROC drops off below 500ft/ min as you approach the initial cruising altitude.

Reduced thrust is used by the majority of B744 operators whenever the aircraft’s TOW is less than the runway performance limit and the noise abatement procedures permit it. The desired thrust level for each takeoff is obtained by inputting the SEL (Assumed) TEMP value obtained from the individual runway performance chart or table into the THRUST LIM page of the FMC. The FMC will then calculate the thrust reduction (EPR) and takeoff speeds for you. Although the FMC will also generate the V1, VR and V2 speeds, for various reasons the actual V1 to use on the real aircraft is always extracted from the performance data and, whenever necessary, it is input manually into the FMC.

During the climb this EPR figure will gradually increase to full CLB thrust; usually somewhere between 15,000ft and 35,000ft but these heights can differ e.g. due to engine model or thrust rating, FMC software mods, airline requirements etc. Reduced thrust is not used whenever the runway is contaminated, braking action affected or when operating from hot and high airfields.

Incidentally, there are also two fixed Derates from full takeoff thrust that are available on the FMC Thrust Reference page i.e. TO1 (usually 10%) and TO2 (25%). These Derates are used whenever the performance manual or other operational procedures require it, such as on contaminated and VMCG limited runways, or at very light weights with a minimum fuel load . Although the % amount of Derate can also differ, theTO2 setting is generally used for three engine ferry operations and, as far as I am aware, there has never been any requirement to include these two Derate settings in any normal takeoff summaries.

I hope you find this info useful.

Bertie Goddard

 

[tcas_climb 45]

Something I have noticed with the "automatic selection of CLB rating" is it doesn't seem as "smart" as the 777. It seems to favor CLB 2 even at relatively high gross weights (740k lbs) and lowish Atm (eg 35) which causes the aircraft to not accelerate or level off for a quite a long time while it tries to accelerate. As I gain more experience I know now to choose a different rating as I monitor the aircraft performance, but aside from that do you find the real thing to be conservative in its automatic selection? 

[downscc 1,327]

5 hours ago, tcas_climb said:

which causes the aircraft to not accelerate or level off for a quite a long time while it tries to accelerate.

This concerned me when I first starting beta testing the Queen; however, it turns out that very much unlike the 777, the 744 will accelerate at about a 500 fpm climb during the acceleration transition.  You only have a problem if you cannot accelerate, then you should consider visiting the thrust page in the FMC and setting a higher climb limit.

[tcas_climb 45]

Thanks Dan, this is definitely one of those gotcha things, especially when terrain clearance/climb gradient is a concern.