'End of Flight' message on FMC seems to be wrong

[Guest Dianne_S]

Hello,Upon arriving at my destination with the PMDG 737, the FMS will frequently display 'end of flight' and blank out programmed waypoints while I am still airborne and before even turning on final approach heading. This recently happened when I was in a radar vectored downwind, abeam my landing runway centerpoint and about 10 miles laterally offset from the runway. The FMS erased 2 waypoints on my final approach ILS when this happened.Is this a known bug?Thank you.

[Guest bobsk8]

I haven't seen that but I have seen it report "end of flight" when you overfly the airport on the approach.

[Qavion 19]

Sounds like offpath waypoint sequencing, Dianne.... Don't know if this is applicable to the 737NG (Smiths) FMC, but some types of FMC erase (or "autosequence") waypoints even if you are not exactly following the FMC LNAV route.Haven't seen anything in writing on this, but I think if you are offtrack... but within a certain distance of your planned LNAV track, the waypoints will autosequence when you are level with (90 degrees to) the waypoint....or at least that is the trigger for it (It may not erase at that precise moment). I'm not sure if the inbound leg or the outbound leg is used as a reference (you don't want the waypoint to erase before you get abeam of the waypoint if there is a bend in the route at the waypoint).You mention 10nm, so this may be within the defined autosequencing path.I apologise if this information is incorrect for the NG FMC... but I'm sure PMDG's programmers will correct me on this if I am wrong ;-)Cheers.Ian.

[Guest Dianne_S]

Hi Ian,See, I never knew this stuff. In the real world I sit at the other end of the radar screen while airline pilots get to have all the fun and it's not fair. I will play around with some approaches and watch the behavior of the FMC to try to discern some of the autosequencing logic. Thank you so much for the information!

[Qavion 19]

>In the real world I sit at the>other end of the radar screen while airline pilots get to have>all the fun and it's not fair.You definitely have my sympathies, here, Dianne. The closest I've come to some hand on flying for a long time was a 10 minute fly in a 767 (big) sim last night. >I will play around with some approaches and watch the behavior>of the FMC to try to discern some of the autosequencing logic.I asked around and the general concensus was that the waypoints will not autosequence if you are flying more than 7nm from the track. Autosequencing will happen either abeam the waypoint or on the bisector of the included angle if not a straight path (being a Controller, you should know all about geometry ;-)).From someone who knows a great deal more than I know on the subject..."There are a lot of special rules have adopted over the years as (this) logic has been improved. Sometimes LNAV has to be on to effect the sequence and sometimes not. Sometimes you have had to have been on the side of the waypoint with the approaching leg or it will not sequence. In some of the boxes and I don't know which ones, you have to be within a certain distance of the waypoint to sequence it. There is a whole lot of special logic and I can not remember it all nor tell you about it here. There are also a lot of problems still hanging out that need to be found. It is kind of an optimization, you can not have it all your way because something else will suffer."So... basically, it sounds like the logic is proprietary.... so a lot of this stuff is hidden even from the pilots. The Honeywell and Smiths logic appears to be similar... so this covers Boeing and Airbus.Hope this helps.Cheers.Ian.

[Guest Dianne_S]

Ian,Thank you so much for taking the time to make such a detailed and thorough reply on this subject. I had never before realized the inherent complexity of some of these systems and it's really interesting to talk to someone who knows all of the P's and Q's, wow. You must really have such a cool job!Thank you again!