Fellow PICers,Lately, I have noticed an inconsistency in MCP behaviour with some flights when I am nearing TOD. AP is engaged and in LNAV & VNAV mode with MCP alt, actual ALT and VNAV crz alt all matching up nicely. At 16nm from TOD, the FMC calls out to me (RESET MCP ALT!) and as I start to do just that, one of two things happens. Most often nothing happens, ie. VNAV and LNAV remains engaged and aircraft remains at cruise alt until the distance to TOD ticks down to zero, after which the aircraft starts descending on the VNAV profile. But sometimes, VNAV kicks off and SPD and ALT modes engage, as if I have overflown TOD, but there is still 15 odd nm distance remaining until TOD! In this latter case, I can not reengage VNAV until after I have reached TOD, and then the aircraft will commence descent in LNAV and VNAV mode as per normal.Any ideas?Gary

Perhaps I should have spiked this question with an FS2004 compatibility or PMDG 737NG comparison comment to elicit a response. ;-)Seriously though, has anyone experienced such MCP behaviour, or can at least give me a suggestion of something to check?Gary

bump

I have seen this happen ONLY if you are on a second flight and did NOT shut off your engines and re-set/re-programme your FMC on the ground before the second flight. In half-asses layman's terms, the FMC gets stuck in DES mode and gets confused when faced with a TOD again.Hope this helps.Rob.

This has happened to me on two occaisions.At first I thought it was alcohol related.Now I believe it to be some corrupted STARS - happened inbound KLAS and KPHX from the west.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

This has happened to me on a number of occasions. I have never made note of the situation when it does happen though - so I can not say for sure if it only happens when on the second leg of a flight. Often when flying multi-legs I'll shut down the engines at the gate while preparing for the next leg. I always recycle the Flight Director but rarely shut the APU down if I'm going to do another leg.Being wary of this behaviour - I often don't reset my MCP altitude right away when yelled at by the FMC - often I will wait until closer to TOD. In this case I won't clear the "byatch" (edited cause this forum doesn't like bad words) message, I'll leave it there to remind me to reset it. I have in the past been known to clear this message, not reset the MCP ALT, leave the cockpit to prepare a fresh beverage containing an overpriced vodka, only to come back wondering why I'm 15nm from my altitude restriction of 12,000 at CLARR while still thundering along at FL290 and .78.This usually causes me to gulp down the whole beverage - while randomly pressing all of the buttons on the MCP handling various modes until I can get it to descend automagically again. Since I gulped down the entire beverage, I can never remember what order of button pressing me produced the desired results - nor can I remember why I didn't descend in the first place. It's at this point I realize that my vodka glass is dry - and I need to head BACK to the galley to fix another mixture of vodka, lime, ice, and something "fizzy" to fool my wife into thinking I'm not drinking straight vodka (which at this point I am). By the time I get back, I'm usually off course and wondering where my CLARR chart is. Seeing how my Jeppesen's are 2 years old - I always pull out that old CRESO3 chart - only to have the ZLA controllers tell me that arrival is not good for a B767.At this point I take a short breath, sit down in my Captain's seat, put on the headset, take a quick shot of courage from the clear fizzing liquid in my glass, switch off the Autopilot and Autothrottle, grab the yoke with one hand (need the other for my drink), key up my mike and check in.Happy Friday everyone.

:-lolLee Hetherington (KBED)

:-xxrotflmao

If you're flying online, or with some sort of online weather, you're probably just unlucky enough to get a weather update with a large enough change in the altimeter setting between the old and new stations to make it look like your pressure altitude just jumped. I've observed this behavior several times, both in VNAV and not. If your MCP altitude and your current "cruise" altitude don't match when this happens, VNAV will kick off.cz

With FSUIPC settings, specifically smoothing pressure changes (technical tab I believe), you can pretty much eliminate this occurence.Lee Hetherington (KBED)

Lee,I see this even WITH the FSUIPC settings, unfortunately.cz

Thanks for the replies. Some interesting causes have been proposed, which I address as follows:Alcohol - a definite candidate, however alcohol induced aircraft misbehaviour is usually more broad in its application of issues during a flight eg. oops, forgot to put flaps to 5 / set trim on take off roll, heavy landings from misjudged flares, more obvious presence of the FS maintenance police, liquid spills on the flight deck, the list goes on.Corrupt STARs - a distinct possibility, although they result in a more catastrophic crash to desktop when selected. Next time it happens, I will try with and without STARs to see if it is the culprit.Coincident baro changes - I'm pretty sure this is not the culprit as my altimeter matches exactly with my VNAV cruise alt and I have weather transition smoothing through FSUIPC and Active Sky WxRE, but I'll check again to be sure.Gary

Ian,Do you follow a similar pattern whilst controlling? This would explain a lot ..... ;)ps. the wacky accent is pure bedfordshire UK not wagga wagga Oz ;)