747 holding bug

[Guest fsindianpilot]

Hi,I wanted to practise the holding pattern on 747..and i faced this issue of 747 not wanting to hold ..I searched for this on PMDG forum and came across a post on " PMDG holding bug"..But the last reply was from Lefteris and they did identify this problem and were nailing it down..But that topic is locked after that post and i cant find to see any update on this problem.I followed the missed approach procedure at 34R at KSEA to hold at ANVIL at 5000ft and 161 inbound course..The aicraft flies to the hold properly and attempts to make a tear drop entry into the holding pattern by turning right .But when it is at right angle to the inbound course it forgets that hold and seems to fly at 90degrees to the inbound course..The LNAV was engaged after making the missed approach while climbing to ANVIL.Since it was flying at a different course i tried disengaging the LNAV and reengaging it..But FMC gave an error that "No active route".I haven't see any update on this issue later apart from Lefteris last post and cant find any reason for this topic being locked...Any idea whether this issue is being fixed because apart from sound update i dont seem to find any service updates on the bugs fixed for the past 1 year for 747..I am sure that the hold is programmed correctly in the FMC...WOuld highly appreciate any pointers..Thnx,Pankaj

[rsrandazzo 6,353]

Pankaj-I'm not able to fly the same MAP you describe at the moment to trouble shoot- but this sounds suspiciously as if the airplane passed the hold point, (which you left as the last fix in the flight plan?) and it then determined it had passed the last fix in the flight plan and thus ceased trying to hold since LNAV assumed it had nothing left to track...I cannot say for certain, as I'm unable to test the theory at this point- but generally speaking you wouldn't want to let the airplane fly past the last fix without having rubber firmly on the ground.This could be a legitimate bug- or it could be a procedure file problem- or it could be "correct operation." I'm not certain at the moment. ;-)I'll have to pull up some of our tech advisors to review what the airplane will do in such a scenario- but it won't be a quick answer...

[Guest fsindianpilot]

Hi Robert,Appreciate your early response..The airplane did not pass the holding point..The airplane was climbing and heading to ANVIL.The ANVIL holding point is on the same heading as the runway 34 R.So i am sure that it did not cross the holding point.The hold has a right turn holding pattern with inbound course of 161 and outbound of 341.The aircraft tracked straight to the hold and followed the track parallel to the inbound course(maintaining the runway heading of 341) and then started executing a right turn back to the holding point(as if it were executing a tear drop entry).I was expecting it to turn back to the holding point (to a heading of 161)and then start executing the right handed holding pattern with the outbound course of 341 and inbound of 161.But it executed the turn and tracked 90 degrees to the inbound course..I saw a post similar to my above mentioned problem of tracking 90 degrees to the inbound course and thought of reposting it again as the thread was locked.I will trying executing a hold at different holding points..And will try to get a screenshot of above scenario so that you have the pictorial inputs which can make it more clear...Pankaj

[brucek 38]

Sounds almost like a parallel entry to the hold, although the turn would be left for a rigth-turn (standard) pattern. I must try this too, I'm at work right now though.......:(Even though it would be rare to get the published miss, in any missed approach you are doing it becuase something didn't work out. Would a B744 pilot want to let the FMC do all the work, or would they want to enter the hold manually (maybe using auto-pilot but using heading and altitude capture instead of LNAV)? One reason to use LNAV is obviously you are busy figuring out what to do next, but one reason not to is that if LNAV doesn't work in the hold as it should, then you have nowhere else to go. And would you rely on LNAV to keep yourself in protected airspace in the hold? Looking forward to trying this with FS9 later.....Bruce.

[Guest fsindianpilot]

Hi Bruce,Yes as a pilot i should have other tools at hand when LNAV wouldn't work as expected.But my intention to fly the hold was to learn how to program and fly it using the FMC. Offcourse i did navigate the aircraft when i did find that LNAV didn't work as expected...Would be glad to know if the same situation at KSEA and hold at ANVIL worked for you.Keep us posted on your findings if you manage to get the time to work it out..Since i was out of home I couldn't get hand on the screenies...And thanks for pointing out that it is a parallel entry and not tear drop entry...:)Pankaj

[Guest fsindianpilot]

Screenies in order...Pankaj

[brucek 38]

I;m just home Pankaj, and have just had a chance to look at the IAP for ILS 34R. It's a hold on the north side of ANVIL, which is 11 DME on the extended LOC of ILS34R. And it's right turns (standard).As the hold "radial" is 341, the entry can be either a teardrop or a parallel entry, as far as the FAA standards go. Why someone would choose the parallel entry above a teardrop is beyond me, but I'm not sure what the logic in the FMC is for this (another reason not to trust it :) ).I have some "honey-dos" from the "Squadron Leader" here to do before I get a chance to try this. My FS9 is somewhat flakey now too, but since I almost always use FSX due to it's far superior flight environment modelling (offsets the lower fps for me :) ), I haven;t fixed it- so I may have to mess with that too. Back later hopefully with a report from of the missed using the PMDG B744.Bruce.

[brucek 38]

Ok, I tried this procedure with the PMDG B744.I engaged TO/GA just before minimums, and the a/c climbed very well, actually it missed the crossing altitude at DODVE, then I realized that both VNAV and LNAV were disengaged- is this normal on a GA, and if so maybe this is a part of what occured to you, Pankaj.Once L/VNAV were re-engaged, it did a teardrop by passing ANVIL then doing a hard left to 250, then a hard right to pick up the outbound track on the hold. Not the type of teardrop entry that the DE might approve :), but it worked well in keeping inside of the protected airspace.I tried several times (now knowing that I had to check L/VNAV for engagement), and it did this with good consistency. I had no winds or any wx at all engaged, so that may also be a factor.I saw your screenshots and wonder what happened- any luck in reproducing this? I think that Rob was going to try it too?Thanks, Bruce.

[Guest fsindianpilot]

Hi Bruce,Appreciate that you tried this out..But for me LNAV and VNAV did not disengage .On approach i plainly flew without LNAV and VNAV..Just armedd the APP.On minimums, disengaged the AP and pressed TOGA..While climbing out at 1000 ft , pressed LNAV , VNAV and A/P.The aircraft started steering itself to the hold which suggests that LNAV and VNAV were active.But lemme try this once again and have a look into the PFD annunciators to see if LNAV was really active even though the MCP may be showing LNAV on...Ah...Looking into the screenshots it shows the LNAV and VNAV are there on the annunciators...Yes Bruce, this situation is always reproducible on my machine.I will still give it a go..Pankaj

[brucek 38]

Thanks, this one is a strange one, esepcially since we both have reproducable results that are different. Maybe I should try what you did and use the method I usually do of activating the APP mode. Actually, I try and land the bird manually if I can, as this is the best part :)Bruce.

[Guest fsindianpilot]

Hi Bruce,This is one thread which is interesting and closely related to our topic.http://forums.avsim.net/dcboard.php?az=sho...30719&mode=fullJust to let you know that i have the default database and default FSUIPC..I will update the database and FSUIPC and try it once again..Else as the above thread suggests to fly the first leg using ALT and HDG and then use LNAV to make it hold correctly..Pankaj

[brucek 38]

Interesting, Tim does some great work.As I mentioned, I have always manually flown the missed, so was surprised that L/VNAV dropped out at GA. I also have the default database, and the registered FSUIPC (not sure which version).When re-engaging LNAV, I sometimes get the FMC error something like "no INTC course", and what I am doing is going to HDG SEL, and dialing in a heading that intercepts the track to the MAHP, then re-engaging LNAV. If I remmeber correctly, MAHP waypoints are "flyover" waypoints (I know the MA waypoint is), so this may be some of the issues, as it sounds like this is what Tim found too on the NG.Interesting subject!Bruce.