IXEG 737 Top of Descent Problem

[psimpson20]

Hi,

I'm new to the 737 and I've just come across a problem.I was flying a route from EDDH to EGCC.I was a cruise altitude and approaching T/D.However,on the MAP display,T/D was shown as being about 20 miles west of the actual LNAV path.Therefore,I was unable to reach T/D and start descending.Is this a known bug ? I have version 1.0.7 installed.

[Andrey Novikov]

It's a known bug. RNAV works ... sometimes. So it's better (and more realistic) to plan descends by yourself.

[psimpson20]

Just had another flight.I was able to reach T/D this time.However,I passed T/D and automatic descent failed to start.Is it just pot luck if VNAV actually works ?

[mmerelles]

did you reset the MCP before reaching T/D?

 

Can you share a video of your issues? or a detailed flight plan including airports, runways, sid, star, route, weight, fuel, ci, cruize, etc to reproduce?

 

[psimpson20]

I did reset the MCP before reaching T/D.At T/D,the altimeter moved slightly,but then very quickly stopped.

I can attach the PFPX flight plans that I used,if that's OK.

RYR 8451 EGCC-EHAM (18 May 2017) #1.pdf

RYR 3502 EDDH-EGCC (16 May 2017) #1.pdf

[mmerelles]

thanks for sharing the details. i will try one of those myself and see if i can reproduce

[mmerelles]

ok i did the flight #1 EGCC to EHAM, everything went just fine. no issues at T/D.

 

note: something to point out, when selecting SID SONE1R departure there is a waypoint D304H which is being parsed as mandatory altitude 0 constrain. This may interfere VNAV refusing to engage etc. I have seen this before, not sure this is an issue on the navigraph database or the ixeg bird while parsing the procedure.

When this happens you enter manually an altitude that makes sense. In this flight i just entered 2500A to match previous waypoint altitude (D296 - 2500A) and not to interfere next waypoint constrain WAL33 - FL050 mandatory.

 

All the rest went smooth. See pictures attached of the entire fmc programming before takeoff (LEGS, PERF, TAKEOFF). A few pictures inflight near T/C, then a few pictures reaching T/D and the aircraft descending via the STAR past T/D with no complain.

note: picture 1 has a red circle around the waypoint i had to edit for 2500A because it was set as 0ft MANDATORY.

 

 

[psimpson20]

Thanks for your response.I presume my problem was due to waypoint D304H.

I had a flight from EHAM to EGCC today,and the problem with T/D not being on the LNAV path was repeated.I have attached a screenshot to illustrate this.

Do you have an explanation for this ?

[mmerelles]

1 hour ago, psimpson20 said:

Thanks for your response.I presume my problem was due to waypoint D304H.

I had a flight from EHAM to EGCC today,and the problem with T/D not being on the LNAV path was repeated.I have attached a screenshot to illustrate this.

Do you have an explanation for this ?

 

will try this one...