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Big_Les

Step climb

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I've been trying to get step to work without any success, the FMC always says "unable" at step point. Heres what I do: 1. At cruse level FL340 I set MCP to FL3602. Look at optimum cruise level in FMC and check it's above FL 3603. FMC cruise page set step to FL3604. Execute change I'm expecting to see an auto calculated step point and then a step climb at the point, all I get is "unable" at the step point on the FMC. Any ideas? I think I'm doing this as per the manual, but if I'm honest, I haven't ingested the whole 2,000 pages of it yet......

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I've been trying to get step to work without any success, the FMC always says "unable" at step point. Heres what I do: 1. At cruse level FL340 I set MCP to FL3602. Look at optimum cruise level in FMC and check it's above FL 3603. FMC cruise page set step to FL3604. Execute change I'm expecting to see an auto calculated step point and then a step climb at the point, all I get is "unable" at the step point on the FMC. Any ideas? I think I'm doing this as per the manual, but if I'm honest, I haven't ingested the whole 2,000 pages of it yet......
Many reasons : Cruise setting on MCP, Performance (fuel weight, payload), pressurization.

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Well, i think that MAX FL is considring the performance and weight, isn't it?What do you mean by preaaurization? Should i set the new FL in the cabin alt in order to get the FMC to calc SC point?

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I've been trying to get step to work without any success, the FMC always says "unable" at step point. Heres what I do: 1. At cruse level FL340 I set MCP to FL3602. Look at optimum cruise level in FMC and check it's above FL 3603. FMC cruise page set step to FL3604. Execute change I'm expecting to see an auto calculated step point and then a step climb at the point, all I get is "unable" at the step point on the FMC. Any ideas? I think I'm doing this as per the manual, but if I'm honest, I haven't ingested the whole 2,000 pages of it yet......
I submitted a ticket regarding a bug in the FMC step climb behavior just yesterday, Ryan put it on the bugs tracking list (the internal one, not the one pinned in the forums). Robert

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"Unable" doesn't mean that the plane cannot climb, but that there is no fuel savings from performing the step climb. Consequently the FMC is "unable" to compute a point where you should step climb. If you look a bit further down on the CDU, you should see that there is either a savings of 0% or a penalty computed for the step climb.

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Or you should change the FL on the INIT PERF page to the higher altitude. (?)
If you want to change your cruise altitude, change it on the CRZ page, top left corner.

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Got it to work fine after setting up on the ground today, step and step point was calculated correctly and stepped after hitting altitude intervention on the mcp.

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So Big_Les,What was missing?
Not sure. The only differences were:No windSetup step on the ground not in the air
Many reasons : Cruise setting on MCP, Performance (fuel weight, payload), pressurization.
As I said in my original post.... MCP cruise is increased to FL360, performance is covered by the optimal flight level suggested in FMC and pressurization??? not sure what relevance that has unless you're trying to go above max flight level (which I'm not) so....none of the above.

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This is a simple process. 1) determine if you can attain the new cruise altiude by going to CRZ page and cecking the OPTIMUM crz level. Some companies have different criteria for this. In THIS example lets just say the OPTIMUM sys 360. 2) dial 360 on the mcp altitude window3) on cruise page enter 360 in top left LSK and EXECute it.4) plane should start climbing. THATS IT. 5) the pressurization panel is reset to 360. It has NOTHING to do with step climb other than adjusting the differential/ cabin altitude

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Jack,The climb itself is easy - like you explaind. The question is, foe example, I'm cruzing at FL340. The FMC advise OPT FL373 / MAX 378. When typing FL360 for the step climb, the STEP POINT is UNABLE.

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UNABLE usually means that the step point is within 200 (if I remember correctly could be 100) miles from the ToD or no SAVINGS but PENALTIES. FYI : It calculates a "parallel" flightplan with the step point. You can also downselect it and put in 1LSK. FYI : Continuing from above post... In CRZ phase you can also roll your MCP ALT to 360 (say) and press ALT INTV. PS. Warning when you ask for a STEP above the MAX ALT it will issue a warning like MAX ALT FLXXX but will calculate

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rgr - i'll try itOK now i get it... that kind of step save me 0.2% only... maybe the reason not to step att all :) thanks

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I think there is somewhere a bug or so. Like Sagi said it tells in CRZ page UNABLE and 0,0% savings when enter a higher altitude on the step climb entry, especially that the OPT crz level is higher than the altitude entered in step climb.If I enter the higher CRZ altitude @CRZ ALT it thinks it is ok and tells me for example 2.28 % savings. It looks like that it doesn't care if I enter a possible step climb altitude. edit: I always tried being in the air

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I get "UNABLE" much more often then not, thats on long flights with good % savings and a TOD hours away. I have been just doing the step climb anyway without issues.

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I think it is even more subtle then that. Say you are at FL340, optimum is FL370 and you enter FL360 as your desired target. The FMC says x% savings but that saving is what you would get if you were already flying at that alt. If sometime between where you are now and 200 miles short of T/D, the fuel used to climb to your target, and the fuel saved flying at your target is less then the fuel you will use flying at your current level, then it will tell you to initiate that climb and when to do it.

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I know what you mean. But i don't think this is the point on this issue. Today for example, I was around 1000nm away from my T/D.There should be enough savings to afford the climb.

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I know what you mean. But i don't think this is the point on this issue. Today for example, I was around 1000nm away from my T/D.There should be enough savings to afford the climb.
Not knowing your actual figures, I can only make some guesses. But if you were quite heavy, then the cost of climbing to a higher altitude now, or later in the cruise, might still exceed any savings from flying at a higher altitude.

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Tried this today while cruising at FL360, 975 nm from TOD with FL378 as OPT on the CRZ page. Entering a step climb to 380 gave me "UNABLE", however entering 380 at left LSK1 predicted a saving of 4.5%. After climbing at cruising at FL380, predicted fuel at my destination is 200Kg more than it was at FL360, so there does appear to be an issue with the step climb calculation.

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