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Papsonline

VNAV held airspeed at 240 also above 10,000'

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Hello all, soon after reaching cruise altitude and in VNAV I found the FMC was holding my airspeed at 240 kts. A clue to the reason might be that early in the flight - maybe during the climb - an FMC message reminded me that I hadn't selected approach parameters. Also, I wasn't able to select the CLB and CRZ buttons. It seems the FMC thought I was descending and nearing approach. Any thoughts how this could have happened?Geoff


Geoffrey Kent

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Guest neerajpendse

What airplane were you flying? :-)In the CLB page, did you set a selected speed? Were you on a flight plan created by yourself on the FMC or imported from somewhere? Was there a speed restriction on the RTE or LEGS page for certain Nav fixes?On the PFD, did you see "FMC SPD" annunciated or "MCP SPD" annunciated? What was the speed selected on the MCP? Lots of questions :-)- Neeraj

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The flight was 1000 nm and I was cruising at FL330.I noticed the problem early in the cruise phase - should've picked it up earlier of course.This was a B738.No, I didn't set anything in the climb page.I imported the flight plan and there were no speed restrictions apart from the usual ones in the SID and STAR.And I knew I should've made a note of the annunciations but didn't.Having found that VNAV was holding my speed down I cancelled VNAV and wound the speed up manually to 0.79. When I then re-engaged VNAV, the speed fell again to 240.Guys, the clue here is the FMC message asking me very early in the flight to select approach parameters. What event causes the FMC to do this? It normally occurs towards the end of a flight. I think the FMC thought I was below 10,000'. I'll fly it again and see what happens.Geoff


Geoffrey Kent

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