A Few More FMC Questions?

[cmpbellsjc 2,960]

I am finally getting comfortable with the 737NG and the FMC after the last two weeks. Thanks to the tutorials that Tim and Fred put together. However I have a few problems that I can't seem to figure out.1. When enroute and climbing I sometimes get a message on the FMC that says "CHECK MCP ALTITUDE". If for example the top of the climb and cruise is set for FL350 do I also have to put that altitude in the MCP Alt box?2. When I am cruising at say FL350 and getting within 100 or 150 miles the VNAV never seems to take over and begin a descent. I always have to do it manually. I thought the FCM would follow the forecast altitudes? Do I have to do something in the MCP Alt box to get this to work right?3. On the note of descents I often get a "VNAV DISCONNECT" message on the FMC. What I am doing wrong to get this?I appreciate any suggestions. Thanks for the help on my last questions.Sean Campbell

[Guest BrunoF]

Hi Sean,Very quickly (Because I have to go, sorry) I'm sure someone will jump in and provide you with a more extensive explanation.Anyway:" 1. When enroute and climbing I sometimes get a message on the FMC that says "CHECK MCP ALTITUDE". If for example the top of the climb and cruise is set for FL350 do I also have to put that altitude in the MCP Alt box? "Yes, you have to. Because if not you are restricting the Autopilot to only climb and maintain the ALT that is set on the MCP." 2. When I am cruising at say FL350 and getting within 100 or 150 miles the VNAV never seems to take over and begin a descent. I always have to do it manually. I thought the FCM would follow the forecast altitudes? Do I have to do something in the MCP Alt box to get this to work right? "Make sure you don't have your MCP Alt still at your Cruise level, but instead to the level you wish to descent. " 3. On the note of descents I often get a "VNAV DISCONNECT" message on the FMC. What I am doing wrong to get this? "This is because the FMC and VNAV don't have protection against overspeed limits so before your descent check the DES page and make sure your speed isn't very high.Bruno Francescoli. "On the run" ;)

[Guest sj3]

Sean: Hopefully just a few words can clean this up for you. Our wonderful aircraft, no matter what you have entered in the FMC, will not go lower than the altitude set in the MCP, under VNAV. Although over-simplified, this appears to be the cause of your consternation.If you go through one of our tutorials and see the way the steps take you from cruise to descent, this will become clear to you. And, yes, re: #1, you do need to enter your cruise altitude in to the FMC as the previous poster said. I also routinely set my cruise altitude in to the altitude window on the overhead panel during pre-flight. I'm not sure what the sim or the NG use this for though. Maybe someone more knowlegeable can let us know what this is used for. Good luck.

[Guest tmetzinger]

>Sean: Hopefully just a few words can clean this up for you. >Our wonderful aircraft, no matter what you have entered in the>FMC, will not go lower than the altitude set in the MCP, under>VNAV. Although over-simplified, this appears to be the cause>of your consternation.>>If you go through one of our tutorials and see the way the>steps take you from cruise to descent, this will become clear>to you. And, yes, re: #1, you do need to enter your cruise>altitude in to the FMC as the previous poster said. I also>routinely set my cruise altitude in to the altitude window on>the overhead panel during pre-flight. I'm not sure what the>sim or the NG use this for though. Maybe someone more>knowlegeable can let us know what this is used for. Good>luck.The overhead panel section where you set your altitude is for pressurization. It lets the pressure controller know what sort of altitude range it's working with. The pressure controller actually "climbs" and "descends" the cabin at different rates from the airplane itself, and knowing the cruise and landing altitude helps it to do it's job better.

[crvm 0]

" 2. When I am cruising at say FL350 and getting within 100 or 150 miles the VNAV never seems to take over and begin a descent. I always have to do it manually. I thought the FCM would follow the forecast altitudes? Do I have to do something in the MCP Alt box to get this to work right? "Make sure you don't have your MCP Alt still at your Cruise level, but instead to the level you wish to descent. I would just like to add that @ 5 miles from TOD, the FMC will display a caution message on the CDU's scratchpad reminding you to re-set the MCP's ALT window (if not re-set prior). Consider the MCP's ALT window as your *guide* for altitude desired either positive or negative. [h4]Best Wishes,Randy J. Smithhttp://www.precisionmanuals.com/images/forum/betaimg.jpg