Hi,I am flying 11000 and to make sure that the Autopilot can obtain the programmed altitude (8000) set by the FMC, I set the right altitude of 8000 in the MCP, way before reaching the ToD. When the airplane reach the ToD, it starts to descent and reach the 8000 altitude just before getting to the next waypoint. Up to now everything is OK. --- The Problem is, after reaching the 8000, the plane stays level and does not follow the descent pattern established by the FMC. Eventually, I get the message: (rw/app crs error ) and later on (Des Path Unchievable)Question: Why does the plane remain at the 8000 level ?P.S.: Take off and cruise are normal.I have updated the NG to the 737-800/900I make sure that there is a normal distance between fixes to achieve a normal descent.Thank you,JohnMontreal/Canada

After you reached 8000ft,did you reset the MCP altitude to the next constraint?John http://homepage.eircom.net/~eamonnmca/images/logo_ba.JPGwww.bavirtual.co.uk Senior Captain Simflight.com Staff Reviewer

Does mean that FMC will not automatically descend the aircraft? You have to reset the MCP at each waypoint?

Yes, as a safety measure. The altitude you set in MCP is the altitude the FMS will descend to. If you only set 8000 it will descend to 8000. Normally if I am cleared to descend all the way, I just set the MCP to the constraint before ILS capture (normally FL03-04). the FMS will capture that altitude at the last waypoint while still meeting other restrictions at any preceeding waypoints.

Thanks !!!

Thank you Mr. Senior Captain and Mr. PrestonIn response to Mr. Senior Captain, Yes I did reset the MCP to 5000Details: After reaching the 8000 level, I did enter the next 5000 level in the MCP. The plane flew straight level at 8000 to the airport. The FMC ignored the 5000 level input in the MCP.After reading all the replies, I did what Mr. Preston suggested. "Normally if I am cleared to descend all the way, I just set the MCP to the constraint before ILS capture (normally FL03-04). the FMS will capture that altitude at the last waypoint while still meeting other restrictions at any preceeding waypoints."And it worked.Thank You again.JeanMontreal/Canada

Was the VNAV light extingushed after leveling at 8000 feet?If it was did you try pushing the VNAV button again after setting 5000 feet in the MCP Altitude window?Floyd

Hi FloydThe VNAV light did not extinguish after leveling 8000.Later on, I did the same flight and intentionally turned the VNAV off and back on again, and the plane started its descent to 5000.Conclusion, I strongly believe that the DESCENT PROCEDURES should be REWRITTEN more clearly.Thank You,JeanMontreal, Canada

Yes, VNAV can be tricky.Floyd

Hi,I was having the same problem awhile back. I emailed PMDG, but they didn't have a solution. Since then, I have determined the following:Say you have Waypoint A set to cross at 8,000 and Waypoint B to cross at 5,000. If the plane doesn't cross Waypoint A at exactly 8,000 feet, maybe it crosses at 8,050, the airplane will not continue down to Waypoint B properly. VNAV will stay engaged, but the bug on the Vertical Speed indicator will show around -1,000fpm, but the plane doesn't descend. If the plane crossed Waypoint A at 8,000 feet, it will continue down to Waypoint B normally. To work around this problem, I have to quickly disengage and reengage VNAV after crossing Waypoint A so the plane keeps descending to meet the next restriction. This is also what Jean said he did, and it works.Hopefully, it will be fixed so we won't have to disengage and reengage to keep coming down.Happy flying,ChristianPrivate Pilot, Single/Multiengine Land, Instrument Airplane

Bonjour ChristianDescent procedures: I found out that the FMC/CDU can be used to achieve two major tasks: (1) Reaching the Localiser, (2) Landing on the runway.(1)Reaching the Localiser: let's say, you are flying at 15000 to KSFO runway 28L and you have already set the FMC with the arrival KSFO ILS 28L + Trans RAMND at 4100 plus the radio frequency and Course. Before reaching the ToD, set the Altitude at 4100 and the FMC will get you to RAMND, then switch to VORLOC, CMD B then APP.(2) Reaching the Runway: Same situation, you are flying to KSFO at 15000, before ToD, set the Altitude to 100 feet. The plane will reach the runway, but at a lower altitude compared to the ILS. At 100 feet, the FMC will disconnect and you will have to land the plane manually.Voila,Thank You,John,Montreal, Canada