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MCP VNAV/SPD buttons when A/T disengaged

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I turned the A/T off and wanted to finish my approach manually. I was in VNAV when I turned the A/T off, but VNAV remained lit and I could not engage SPD. However, if I turned the A/T on, I could engage SPD, and then when I turned A/T off, SPD remained lit as desired. Basically, I wanted to dial in my final approach speed of Vref+5, and I could not do it without the A/T engaged. That does not sound right.Lee Hetherington (KBED)

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Lee,Could you rephrase that ? I'm afraid I don't understand...To clear the speed dial blanker, just disengage VNAV or go to another pitch mode... ?anthonyAnthony MertonPrecision Manuals Developmenthttp://www.precisionmanuals.com

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Hi Lee,The way I have always understand the Boeing AFS philosophy is that "SPD" mode on the MCP is actually an autothrottle mode and not an autopilot F/D mode. All it basically does is adjust the Autothrottles to maintain the speed dialed in on the panel, it doesn't change the pitch to maintain speed like FL CH mode. I am certainly no the FMC expert but I though that the approach numbers on the NG came out of the FMC and would display on the ADI ? Anthony??RegardsPaul Gollnick :-coolTechnical Operations/Customer Operational SupportPrecision Manuals Development Groupwww.precisionmanuals.com

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Sorry. That was confusing. Once I turned off the A/T, I could not turn off VNAV. The VNAV light was stuck on when I turned A/T off. The only way I could disable VNAV was to first turn the A/T back on, select a different mode, and then A/T off.I wish I had taken better notes. Here is what I think I did. I was flying an RNAV approach, in VNAV PATH, when I decided to take manual control. CMD off and A/T off, and I was going to fly the FD. Once I turned the A/T off, I could not disengage VNAV to get an MCP speed window so I could set my final approach speed bug. What is the correct procedure in this case?Lee Hetherington (KBED)

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Ok got it.Off the top of my head, only when the following conditions are true is the VNAV button inoperative- AP in CWS mode (but this is not implemented yet) - but then selecting AP in CWS would disengage VNAV beforehand- APP is engaged (both GS and LOC) - but then the VNAV select would not be lit... ???Could you shoot a screening of the panel in the situation you describe, with PFD announciators ?But anyway, here's what I'd do in the situation you describe :- disengage all AP modes (CMD off, cycle FDs)- turn on FDs again(BTW those 2 steps are part of a non precision approach on some airlines. Making sure no mode stays engaged...)- switch off AT- arm APPanthonyAnthony MertonPrecision Manuals Developmenthttp://www.precisionmanuals.com

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In my best Homer Simpson: Doh! I should have just cycled the FDs.I'll try to recreate the situation.Lee Hetherington (KBED)

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