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How do you cruise climb?

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    How do you cruise climb?

    Hi all,

    Just wondering what autopilot and auto throttle modes you use for cruise climbing. Is there a cruise climb function in the FMC? As of now I just disengage the auto throttle, set the altitude in the FMC that I want to cruise climb to, it will go into VNAV PTH, I'll set cruise RPM and it'll slowly mosey on up.

    Any tips on how to do this otherwise?

    Cheers.
    Daniel Glover

    #2
    Cruise Climb = step climb? In cruise I'm always in vnav/lnav so I just dial in the new altitude and press altitude intervene. Although first, of course I set the step climb altitude on the climb page and then climb at the right time.
    Last edited by AndreH; 27Dec2021, 10:59.
    André Hansson

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      #3
      Yeah not step climb. Cruise climb being the aircraft climbs due to it becoming lighter as it burns fuel, while a step climb is done at climb power I believe a cruise climb is done at cruise power and is much more gradual. A cruise climb is probably a lot less common in the world these days due to the busy airspace since you would probably need a block level to do a cruise climb.
      Daniel Glover

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        #4
        About the only time this was used was with Concorde and some Military Jets who were far above traditional FLs and had the upper sky to themselves. Concorde would fly a continuous climb at low FPM to keep her at her optimal performance altitude, as weight decreased. Sadly, she flies no more.

        For the more common steps, one could also use SPD/VS at 3-400 fpm so as not to tinkle the Martinis in First....

        HTH
        Last edited by cavaricooper; 27Dec2021, 12:02.
        Best- Carl Avari-Cooper

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          #5
          Originally posted by Dannnnn View Post
          Yeah not step climb. Cruise climb being the aircraft climbs due to it becoming lighter as it burns fuel, while a step climb is done at climb power I believe a cruise climb is done at cruise power and is much more gradual. A cruise climb is probably a lot less common in the world these days due to the busy airspace since you would probably need a block level to do a cruise climb.
          Cruise climb would first require a block of altitudes cleared by ATC and in most of the traveled air spaces this is a rarity. There's very little to be gained over the now common step climb where the FMC has already taken into account the fuel burn for the climb verses the savings and in some types the wind as well. Depending on your CI, the FMC may often recommend an altitude other than the optimum because optimum is not based on CI. We use the automation.
          Dan Downs KCRP
          i7-10700K 32GB 3600MHz 3080Ti

          Comment


            #6
            There is no AP mode for a cruise climb as it's basically not used anywhere in the world where the 737 (or any other of PMDGs simulated aircraft types) operates.
            The OPT altitude increases by a hundret feet about every 8 minutes'ish, so not even a 50fpm climb in V/S mode would give you a cruise climb. It's simply nothing the aircraft is meant to do.

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              #7
              All things being equal, carrying out a Cruise Climb is considered to be the most fuel efficient way of operating a long range jet aircraft in the cruise. As Carl has already said, it was a routine procedure for Concorde on its flights across the N. Atlantic and it was also very common in the early days of commercial jet operations when there was very little other traffic about.

              Provided there is no known turbulence about and the air traffic is light ATC may clear a long range aircraft on request, to Cruise Climb by blocking the airspace between two flight levels; usually with a restriction to be at the higher requested flight level by a certain position or time. For example, an aircraft such as the B744 would use the A/P and A/T and the MCP and FMS would be updated with the new flight level. The aircraft would then be slowly climbed - usually at the indicated FMC cruise speed and the current OPT altitude for its weight - using V/S mode. A small climb rate of +100'/min is used as required as the aircraft becomes lighter and it is important to keep the aircraft below the maximum altitude for its weight.

              In the B744 both the planned climb speed and the selected cruise speed will not be adversely affected by the speed envelope as there should still be sufficient manoeuvre margin and excess thrust available at the higher altitude. However, this procedure needs to be monitored very closely, especially in the last 300ft of the Cruise Climb. There is no speed protection if an early ALT Capture takes place and this could result in an undesirable loss in Mach No./airspeed before the aircraft levels off at the new flight level.
              Michael Codd

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                #8
                Earlier jet autopilots had a mode called Mach hold, which functioned in a manner similar to IAS hold except that it held the mach number. If a cruise climb was going to be done, this was how it was done, with the Mach hold mode of the autopilot, and typically with max continuous thrust set.
                Tony Vallillo

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                  #9
                  Thanks for the responses, interesting stuff.
                  Daniel Glover

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                    #10
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                    Last edited by PedroKRoss; 21Feb2022, 07:49.

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                      #11
                      Only aircraft I know have this kind of things are Concorde...
                      In RVSM airspace, you have to keep altitude very precise, and when changing altitude, you'll have to report ATC if you can't maintain above 500fpm or need more than 1500fpm
                      ZHU Hai
                      B737 Ground instructor

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