HiThe top of decent sometime does not respond. I am flying at FL370, and I approach the T/D. The MCP ALT is set for lower and I fly over the T/D and the Decent does not engage. Is this because the Arrival runway has not been confirmed or is it something else I am missing?I set an altitude restriction on a leg and the MCP still does not respond. Now this is all intermittant. Sometimes it works, sometimes it does not. go figure... Any ideas or instructions would be welcomed.Thanks

Here is what is happening. And when I tell you, you are going to bang yourself on the head because you know this.Go to the FMC, push the INIT/REF button, and set your Approach Ref Flap/Speed. (on the APPROACH REF page click LSK R2 or LSK R3 and then click LSK R4)

Mike,sometimes I don't set the APP speed till after Descent has begun.I think this problem might be more to do with the selection of an arrival procedure - similar to getting the PERF INIT completed when you have not selected a dep runway.

HMMMMM.....It happened to me last night inbound to KLAS on the CLARR1. First time ever. I tried DES NOW, still no joy. About 5nm past the T/D, she started down ON HER OWN. Perhaps it has something to do with the STAR?Or maybe just maybe I'm flying a GHOST SHIP... from HELL!DS CVA3339 / UKD149System: Attlon 900 McW Hamster/Gerbilized Quantum Accessible 55Gig Iodized-Encrusted Four-poster with Mega-brill Farzenhuuven http://vatsim.pilotmedia.fi/statusindicato...tor=OD1&a=a.jpg

Does it have to do with STARs that have constraints like 3000A in it, but no hard constraints?I too flew a few nm past T/D last night on the SKEBR2 into KLAS. I was about to try DES NOW or take over by hand, but then it started the descent itself.Wierd it all happened to so many of us last night. I don't remember seeing it before.Lee Hetherington (KBED)

If I am not mistaken, the FMC needs it's green circles to descend ie= TOC TOD E/D etc...[h5]Best Wishes,Randy J. Smith[/h5][h6]The Next Great one? PMDG's 737NG is here![/h6][h3]" A little learning is a dangerous thing"[/h3] [h5]AMD XP 2200 |MUNCHKIN 512 DDR RAM |ECS[/b ][i] K7S5A MB[/i] |GF3 64 MEG @ 215/545|WIN XP PRO |MITSUBISHI DIAMOND PLUS 91 19"[/h5]

Mike,Is that information really needed ? I think that entry is just for reference in this version FMC.Tero

I flew right past the T/D green circle.Lee Hetherington (KBED)

I found this Iwrote a while back, I think it explains this question "To calculate the descent profile the FMC must know the end of descent point, the end of descent point is the lowest alttitude constraint, for an ILS approach it's near the final approach fix [FAF] but before the glide slope intercept point. The end of descent point is entered automaticly when you select an approach. To determine the descent path the FMC looks back from the end of descent point along the active route and calculates where the descent should begin. This is the top of descent point. The angle of the descent path is calculated to control speed for descent at idle thrust. Before reaching 10'000 feet the descent agle flattens to reduce airspeed to 240 knots. 240 knots is used as the command speed below 10'000 feet rather than 250 knots to provide a 10 knot buffer. Prior to the end of descent point the the descent path agian flattens so that airspeed at the final approach fix is at 170 knots. When you are within 200 NM from the top of descent point the time and distance to the T/D are displayed on the cruize page. On the real bird well before you reach the T/D you would enter forcast winds for the descent path which would adjust the descent agle for any head or tail winds. This Also applys to using engine thermal anti ice during the descent. If we could enter forcast winds etc for PIC the T/D would show a change. When the T/D point is reached and idle thrust econ speed descent automaticly begins and the descent page becomes active then the throttle hold mode engauges and the airplane pitch varies to follow the FMC descent path which has been calculated to matain econ speed. For most approaches the runway altittude constraint is shown in the upper left corner of the descent page. For ILS approaches the alt is set to the G/S intercept alt. One thing to remember, when approaching an airport where the a speed restriction is not in effect it may be removed by using the DEL key. Because the speed transition [240/10000] is automaticly included when the FMC calculates the descent path, it should be removed prior to the T/D point. This also goes for entering any speed issued restrictions, when possible enter them prior to the T/D point. At times we will need to descend prior to reaching the T/D point. After enitation the DES NOW, The autothrottle will command a target EPR and the pitch mode changes to VNAV SPD. A shallow descent is flown until the calculated descent path is reached. Normally 1000FPM. When the calculated descent path is captured the autothrottle sets idle thrust and the pitch mode returns to VNAV PATH mode and maintians the descent path. If you must level off before reaching the E/D point, set the desired alttiude on the MCP. When you reach the MCP alttiude, VNAV disingages and the airplane levels off and the IAS window unblanks showing the existing speed. If you do not resume your descent in a very short time it is useally not possible to recaptue the FMC calculated descent path. We can select another pitch mode such as FL CH to continue the desent. One last thing, if you encounter un forcast winds your airspeed will vari. If your airspeed loss is more than 15 knots when above 10'000 feet or 10 knots when below 10'000 feet, the autothrottle mode switches to SPD and thrust increases to FMC commanded speed. Likewise, if you encounter un forcast tail winds with an increase in airspeed 15 knots above 10'000 or 10 knots below 10'000 a DRAG REQUIRED meesage is displayed in the scratchpad.' [h5]Best Wishes,Randy J. Smith[/h5][h6]The Next Great one? PMDG's 737NG is here![/h6][h3]" A little learning is a dangerous thing"[/h3] [h5]AMD XP 2200 |MUNCHKIN 512 DDR RAM |ECS[/b ][i] K7S5A MB[/i] |GF3 64 MEG @ 215/545|WIN XP PRO |MITSUBISHI DIAMOND PLUS 91 19"[/h5]