VNAV fail

[AAN1718A 20]

<crickets chirping>

[Ephedrin 418]

he must be feeling like Denise Richards engaged with the Brain Bug...

 

besides that, I guess he‘s a troll to show-off his skills exposing the baaad pmdg stuff to a bunch of children at another forum. Btw: 6000ft at mach .886 is nothing the 747 would ever calculate. 

[Pricelss 2]

https://prnt.sc/i87fd8

Did it finally. The only reason Bedek isnt at 2500 is because I put that in before I started my descent. i try to edit the altitudes and it says "Invalid Entry"

[downscc 1,327]

This appears that you are on the OCK2F arrival into EGLL, BEDEK has an altitude constraint of 14000 and VNAV is expected to provide a descent to that constraint.  What is missing from that picture is how you got to this point.  What is your flight plan (this is important because the 777 has a bug with the OCK transition to 27L/R and I tested it during beta to make sure 747 fixed it)? What exact steps led to the picture, as in are you now past TOD and did the problem appear before TOD?  What is the FMA annunciating?  Give us enough to be able to reproduce the problem please.

[Pricelss 2]

I was in the 744 in the 1970s BA livery. This was taken past TOD. Before TOD I was able to put in the restraint at BEDEK (that's why it's there. It wasn't in there before for some reason.) FMA annunciating I'm unaware of. If I know what I'm looking for I can be sure to look out for it. As far as more info, once it happens again I will. Doing Brisbane to LAX so we'll see if its in the Quantas livery or just specific to that livery maybe? Unsure of how that works...

[Ephedrin 418]

3 hours ago, Pricelss said:

FMA annunciating I'm unaware of. If I know what I'm looking for I can be sure to look out for it. 

The FMA is the Flight Mode Announciation. While you talk to the airplane via the CDU (Control Display Unit (generally speaking FMS)) and the MCP (Mode Control Panel "the Autopilot") the Airplane talks to YOU via the FMA. It's the green letters above the artificial horizion on the Primary Flight Display. When you're on LNAV and VNAV during decent it should say sth like SPD | LNAV | VNAV PTH. I guess in your case it says VNAV SPD, as it clearly is not on its precalculated decend path. Of interest would be: Does it show LNAV in the middle section? Or maybe HDG or even LOC? Dan as a beta tester has a lot more experience in trouble shooting than me so better follow him, but wo be honest I am not convinced that a bug with a STAR would confuse the FMS of the 747 that much.. Your image looks to me like you have entered a cruise altitude of 2500 feet, actually travelling at FL380/38000feet and now on decent your FMS doesn't know where it actually is... can you please make sure that you have entered the correct crz alt on the PERF INIT page? top right corner.

[Christopher Low 5,324]

Ah, I wondered why he had a bunch of "2500s" surrounding his "14000" at Bedek.

[downscc 1,327]

10 hours ago, Pricelss said:

It wasn't in there before for some reason.

Because it is on the chart as an 'EXPECT 14000.'  The navdata rarely includes expected constraints, it is up to the pilot to review the chart just as you did and catch those.   Real world ATC will clear you for the descent with the altitude they want you at crossing BEDEK, it can be higher than 14000 if they are stacking up over OCK I suppose... the UK is not the backyard I play in often.

I set up a KIAH-EGLL flight in the GTI B744 yesterday using the OCK2F star and flew it for the first couple hours before I had to turn my attention to something else. At least for the first couple of hours there were no anomalies.

I asked you a couple of specific questions and you did not reply.  If you sincerely want so help finding the problem you are going to have to be forthcoming with information.  None of us here in the forum are looking over your shoulder to see what you are doing and if all you are going to do is complain that you have a problem we are not going to be able to help.

[Pricelss 2]

2 hours ago, downscc said:

Because it is on the chart as an 'EXPECT 14000.'  The navdata rarely includes expected constraints, it is up to the pilot to review the chart just as you did and catch those.   Real world ATC will clear you for the descent with the altitude they want you at crossing BEDEK, it can be higher than 14000 if they are stacking up over OCK I suppose... the UK is not the backyard I play in often.

I set up a KIAH-EGLL flight in the GTI B744 yesterday using the OCK2F star and flew it for the first couple hours before I had to turn my attention to something else. At least for the first couple of hours there were no anomalies.

I asked you a couple of specific questions and you did not reply.  If you sincerely want so help finding the problem you are going to have to be forthcoming with information.  None of us here in the forum are looking over your shoulder to see what you are doing and if all you are going to do is complain that you have a problem we are not going to be able to help.

I replied with the knowledge I had. As far as the FMA (Thanks to Epherin explaining it) IT was HOLD | LNAV | VNAV SPD 
as far as steps to get to that point I Implemented the restriction for BEDEK and then clicked DES NOW on the DES page as i was about 20 miles before TOD and wished to start my decent early. Then my 74 went pitch down about 15 degrees and an FMC message appeared that I do believe said "DES PATH UNACHIEVABLE" I cleared it and then a message saying "DRAG REQUIRED" appeared. At which point I noticed I was at a decent rate greater than -5k fpm and was approaching 300 knots. To counteract this I used V/S and manual throttles. What else do you want to know and Ill let you know to the best of my knowledge.

[Captain Kevin 586]

45 minutes ago, Pricelss said:

What else do you want to know and Ill let you know to the best of my knowledge.

What did you enter as your cruise altitude in the FMC. Looks like you may have somehow entered 2,500 based on your screenshot of the FMC.

[downscc 1,327]

I believe Kevin nailed it.  You probably set the MCP ALT to 2500 for the decent, which is not a problem but I would enter 7000 as the bottom of the STAR.  The error was pushing the ALT knob.... this resets your cruise altitude to that altitude and rather than a VNAV PATH pitch you get VNAV SPD, throttles go to idle and pitch down to hole whatever the MCP SPD is set at. You see you missed adding this to the step you took for the descent.  Every step is important.

[Captain Kevin 586]

5 minutes ago, downscc said:

I believe Kevin nailed it.

Give credit to Marc, actually. All I did was reiterate the question when Marc's question about the cruise altitude went unanswered.

[Pricelss 2]

Cruise before TOD was up to FL410 I believe. As far as resetting the MCP alt I set it to the 14k in case I reached it before BEDEK. And i didn't press the ALT knob. I went into the FMS on the VNAV DES page and clicked DES NOW. I clearly said I clicked "DES NOW" and on every flight i do this for the NG and T7 it does just fine. The 74 it doesn't. It did it this morning when I was flying the Quantas ER into LA. 

[downscc 1,327]

I did the complete KIAH-EGLL flight yesterday in the QOTSII with GTI livery and had no anomalies during descent and arrival on the OCK2F.  I didn't do an early descent but I saved the scenario a few minutes before TOD so I can rerun that and check out DES NOW.  I've used it before but I normally do not so I don't mind a quick check.

I assume your description is still adequate:

21 hours ago, Pricelss said:

clicked DES NOW on the DES page as i was about 20 miles before TOD and wished to start my decent early. Then my 74 went pitch down about 15 degrees and an FMC message appeared that I do believe said "DES PATH UNACHIEVABLE" I cleared it and then a message saying "DRAG REQUIRED" appeared. At which point I noticed I was at a decent rate greater than -5k fpm and was approaching 300 knots.

Interesting.... first I have to throw away the possibility that you inadvertently pressed the ALT knob thus resetting cruise altitude to 2500 not only because you say the MCP ALT was set to 14000 but also because when within 50 nm of TOD this press action starts an early descent (FCOM 4.10.11)

I loaded a scenario with B744F at FL350 28 nm before TOD, pre-descent flows done and 14000 entered at BEDEK on the OCK2F arrival into EGLL landing 27L ILS with OCK transition set up.

I pressed DES NOW on the CDU about 18 nm before TOD (descent speed set to .84/280) and she settled easily on a 1200-1050 fpm descent holding 280 KIAS as expected.  Wondering how in the world you saw 5000 fpm I pulled the thrust to idle such that in  HOLD | LNAV | VNAV SPD mode she would pitch down to maintain 280 KIAs but the descent rate increased to only 2100 fpm and of course the descent rate decreased as we entered thicker air.  I finished this little test by increasing thrust to maintain a shallow 500 fpm descent until we crossed the VNAV path and the mode changed to IDLE | LNAV | VNAV PTH and normal on-path descent continued to BEDEK where I quit the test run.

We are still missing something in your story that can explain how the FMS altitudes show 2500 and you are in an uncontrolled 5000 fpm descent.  I am 98% sure this isn't a bug because something like that would have been discovered during the many months of technical testing by actual pilots and mechanics and the several months of beta testing and the length of time this product has been released to market without this showing up as a bug.  There is a 2% chance in my opinion that you are doing something odd or unexpected that uncovers a bug and I'd sure like to find that if it exists because PMDG is working full time on the 748 that relies on the 744 and this is a perfect time to get something fixed quickly.

Or it could just be a corrupt panel state.

[Pricelss 2]

It is but what was your final cruise before TOD?