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Vulcan

Strange ToD problem

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OK this is probably pilot error but would appreciate help to understand the problem.Today I took part in the Cross the Pond event on VATSIM.I filed for FL320 in the PMDG744.The FMC indicated a step climb to FL350 part way across the Pond but I stuck at FL320 and entered that in the legs page against the w'pt that was showing FL350.On my descent my first ALT constraint was 11,000ft but some 700nm from that w'pt the FMC was creating a ToD point!!:-hmmm Fortunately I was on vectors from ATC so they gave ALT constraints otherwise i would have just used level change and watched the green arc.Can anyone advise why that odd ToD was given and how to avoid it if I again decline the step climb?TIADave

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That is an odd one Dave.If during flight you elect not to step climb and would prefer to remain at the current altitude then there are 3 ways to acchieve this:1. Go to the PERF page and enter 0 as the step climb value.2. On the VNAV cruise page enter 0 as the step climb value.3. Enter your current cruise altitude in the Step to altitude box. This way the step climb info will disappear and the FMC will give correct fuel predictions downstream and also an accurate TOD point.If you wish to, later on, you can re-enter what ever values you wish.CheersSteve


Cheers

Steve Hall

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Vulcan,You do NOT enter manual step points this way into the FMC. In fact any waypoint restriction higher than cruise altitude is rejected (INVALID ENTRY). Any hard altitude restriction after the top of climb causes the FMC to think "descent".If you wish to enter "planned step points" (as they are called) this is the proper way :You should enter 35000S next to the waypoint. Note the S descriptor following the altitude entry. (a) This creates a "planned" step point and the FMC will provide you information (VNAV CRZ page) about when to start climb to cross the aforementioned waypoint at 35000 (in this example). If the FMC predicts that MAX ALT at this waypopint is less than the planned step altitude value, you will see AVAIL AT followed by time and distance info for this planned step alt to become possible (this will also freeze any step predictions since the FMC can not / will not comply with initial request).(:( Distance to step will not be greater than the leg associated with the "marked" waypoint. © There will be no S/C indicator on the ND in this case. (d) The FMC will CANCEL any automatic steps up to that waypoint. (e) You can enter any number of manual step points in the LEGS page (up or down). If the last manual step is UP the FMC will resume automatic step point predictions AFTER the last such marked waypoint until reaching 200 miles from top of descent. (f) Regardless of last step point, automatic steps will use as a reference altitude (odd/even rule for east/west flight levels) the cruise altitude selected when the aircraft took off and the active stepping scheme entry in 4L in VNAV CRZ page. This is referred to as "hemispheric altitude lock". You can "unlock" this if the active RTE is swapped or after a go around.Example : Initial cruise altitude was 32000 and step size is 2000. Last manual step point was 35000. Next available altitude is 36000 not 37000...Another more complicated example. Assume initial altitude was 34000. Last planned step point is 37000. You use an ICAO stepping scheme. The FMC will provide information for auto step to next available WEST flight level in ICAO airspace (since initial altitude was even) i.e. 39000. In other words additives to last step or even current cruise altitude assume that you maintain direction of flight as defined when the aircraft took off. Smart gadgets big Boeing FMC's, no ?Hope this helps,VangelisPS. By the way, why did you use an ICAO stepping scheme in RVSM airspace ? If you want to circumvent FL340 which is usually not available on westbound NAT TRACKS you can do a a different sort of trick : Enter 2000 as a step size (RVSM airspace as per normal) and then enter 35000 in LSK 1R in VNAV CRZ page. This is called a "manual step" input and tells the FMC to calculate a step point for FL350 (first) and then resume as normal for everything above (FL360, FL380 etc). Note that the font size for manual steps is larger than auto steps.===================================== E. M. Vaos Precision Manuals Development Group www.precisionmanuals.com=====================================


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E M V

Precision Manuals Development Group

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Thanks for your replies Steve & E M Vaos.When I get chance Steve I will try your method, I hadn't thought of 'killing' the step climb as you describe.On long hauls off line I just let the FMC work out the steps and accept them as they happen.Thanks for detailed explanation E M, I will save those details to file for further use.RgdsDave

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