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I am trying to understand how high an aircraft can get to at its maximum takeoff weight (minus whatever fuel is consumed in getting to that altitude). Can it make it all the way to its service ceiling? Or is there a payload/altitude tradeoff beyond a certain level? If there is such a trade-off, at what altitude does it start to occur? Meaning what is the highest a plane can go at its maximum takeoff weight? Is it the cruising altitude? If not, what is it called and where would one find it for specific planes (thinking of KC-135R, A330 MRTT and Pegasus KC-46).

Apologies for throwing so many questions at once.

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  • $\begingroup$ Those are all fairly complex calculations depending on atmosphere conditions and will be very different from one aircraft to the next. You're going to have to narrow it down some. $\endgroup$
    – TomMcW
    Jan 9 at 3:41
  • $\begingroup$ @TomMcW Right. For instance, the KC-135R has an MTOW of 322,500lb and a service ceiling of 50,000 ft. I am trying to understand if it can make it to 50,000 ft at ~320,000 lbs (minus the fuel burned) or does one have to be traded-off for the other? If there indeed is a tradeoff between maximum weight and service ceiling, then could you help me understand how high can it get at its MTOW? Now I understand that this would depend on atmospheric conditions, so please feel free to assume a scenario if that helps. $\endgroup$ Jan 9 at 18:55
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    $\begingroup$ The problem is that this would differ between types. Some may have enough engine power to reach the ceiling at MTOW and others not. Someone would have to have access to the particular numbers for each type. Typical ariliners on long haul flights have to do a step climb as fuel is burned. But at what point they have to do that would require calculations specific to airframe and engine stats. Since the KC-135 is based on the 707 I doubt it could, but it might have different engines. You'd have to find someone with those numbers. There is not a generalized answer to your question. $\endgroup$
    – TomMcW
    Jan 9 at 19:05
  • $\begingroup$ Since generally air carrier type jets have to step-climb as fuel is burned (assuming the aircraft took off very heavy and the goal is to reach its max possible enroute altitude) it's not possible to provide a specific answer without consulting the AFM and using the aircraft's charts/graphs (or equivalent computer data) to make the determination you are requesting in you question. The specific aircraft's AFM could answer your question. $\endgroup$
    – 757toga
    Jan 9 at 20:04
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The absolute MTOW is a limit imposed by structural considerations, not altitude limitations. At every point on earth, a max allowable TO weight must be established by the pilots based on runway length, pressure altitude, climb performance etc.

The service ceiling can be reached at structural MTOW: it is defined as the altitude where the maximum rate of climb = 0.5 m/s (100 ft/min). At lower weight, the aeroplane simply needs less thrust to reach cruise speed. It will be cruising at an altitude below the service ceiling.

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    $\begingroup$ MTOW is established and fixed by the manufacturer (during the certification process) and does not vary with existing environmental conditions, existing runway available for takeoff etc. Perhaps when you use the word "restricted" MTOW you were referring to a "max allowable or permissible" takeoff weight (MTOW adjusted for operational or performance limitations such as temp, runway length, altitude etc.). Also, do you have a source validating that the aircraft's "service ceiling" can be reached at structural MTOW? Thanks $\endgroup$
    – 757toga
    Jan 9 at 17:45
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    $\begingroup$ @Koyovis What about the MTOW set by the manufacturers then? Also, is the maximum rate of climb independent of the weight of the aircraft then? Shouldn't the rate of climb go up (all else being equal) if a plane is lighter? $\endgroup$ Jan 9 at 20:10
  • $\begingroup$ @757toga Have amended the phrasing, thx. Reaching the service ceiling at MTOW will be very sub-optimal for fuel consumption and severely limit range, however add more thrust and the plane will climb. $\endgroup$
    – Koyovis
    Jan 10 at 4:51

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