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FMC message: OVR SPD DISCONNECT

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Hi All, I finally thought I was comfortable with the FMC on my B737 NG. Today I found an accurate STAR and APPROACH for Glasgow UK airport and specified it in the FMC at the end of my route. When the FMC was just turning to intercept the localizer it reported OVR SPD DISCONNECT and left me to finish up.Earlier it had reported an overspeed situation with something about DRAG REQUIRED and I activated the spoilers a couple of times. I was flying with both LNAV and VNAV activated. Each leg's speed/altitude parameter corresponded to my Glasgow charts. Everything looked to be set up correctly.So, my questions:* How did the situation arise without the FMC anticipating it?* How can I anticipate this happening?* How do I get the FMC back in control?Geoff"Welcome on board. This aircraft is fully automated.Nothing can go wro...ing can go wro...ing can go wro...ing can go wro..."

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Hi Geoff,The overspeed disconnect message is being generated because of an unrealistic or unattainable speed constraint that was written into the procedure. There are a couple of options:1. Manually control the speeds and altitude and place the MCP into APP mode once you're established or receive approach clearance from ATC. You can determine altitudes from the chart of the procedure in question.2. Put speed and altitude restrictions into the FMC that the aircraft can maintain. You cannot expect the aircraft to lose 6000' and 40 kts of speed in 2 miles.Jim Karnhttp://www.precisionmanuals.com/images/forum/pmdg_pf.jpg

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Thanks Jim,That's just it - the speed and altitude restrictions mirrored those specified in the STAR and APPROACH that I put into the FMC and they seemed to make sense.Certainly keeping manual control avoids surprises. I've recently seen a forum entry by someone whe reported that on a real flight he'd observed that VNAV was never used - speed and altitude was always controlled through the MCP.CheersGeoff

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Keep in mind that on a PATH descent that the FMC is concerned with keeping the path and not the speed. Restrictions at times need some help from the PIC to achieve. Remember that you should be very aware of your speed and need to keep one step ahead of it at all times. Reaching vmo/mmo or a few knots prior will revert you to LVL CH. This in reality should not happen if you follow the above suggestion. OTTO is a tool but is not a pilot so learn to make the best of it, use other modes like VNAV SPD, V/S or LVL CH. STARS do not take many factors into consideration but you certainly will................Randy J. Smith................A PROUD MEMBER OF THE PMDG BETA TEAM[h4]Evolution is a process that results in heritable changes in a population spread over many generations[/h4]

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