FMC Glitching out on EGLL arrival ILS27R with LAM transition

[maniamcool 75]

Hi,

 

I've recently noticed a bug when entering an arrival for the LAM3A STAR and LAM transition into ILS27R. Doing this would cause the FMC to flicker a few times before erasing all VNAV calculations. The leg page would have no speed or altitude data and the vnav page would be empty of information.

 

Is this a known bug or did I do something wrong? On the latest airac 1701 here. 

 

EDIT: I'm currently into my descend and I noticed that during the transition flight from LAM to the ILS, the route requires the aircraft to be at FL60A, however the fmc calculates the descend path to be below FL60 prior to that altitude restriction. I guess this probably caused the fmc to glitch out?

[skelsey 765]

This usually means that there is an unachievable (in the FMC's eyes) constraint somewhere. If you find it and delete it your VNAV calculations will come back.

 

The transitions are not flown IRL - it's always radar vectors, so you could just enter the STAR without a transition, leave the disco in after LAM and vector yourself to final with HDG SEL (or be vectored, if you are on VATSIM/have ATC software).

[spesimen 135]

 

 

EDIT: I'm currently into my descend and I noticed that during the transition flight from LAM to the ILS, the route requires the aircraft to be at FL60A, however the fmc calculates the descend path to be below FL60 prior to that altitude restriction. I guess this probably caused the fmc to glitch out?

 

a few other threads posted about this recently. you are correct..

it's a combination of factors...either a cost index that demands more speed than the restriction allows, combined with an altitude constraint that would be impossible with that combination of speeds, or that sort of thing..

 

some threads on it: 

http://www.avsim.com/topic/499897-somehow-lost-vnav-mid-flight/

http://www.avsim.com/topic/495968-vnav-disconnect-flying-the-coorz3-out-of-kden/

 

cheers

-andy crosby

[maniamcool 75]

Thanks for your replies Good to know that it isn't an inherent issue with the aircraft.

 

I'll take note of this behavior  when planning for future arrivals.

[lenhamlad 1]

In addition to Skelsey's post above here is the chart for ILS27R non radar controlled via LAM - http://www.ead.eurocontrol.int/eadbasic/pamslight-E20423FA4B7CF4086D6653E8BC0B279F/7FE5QZZF3FXUS/EN/Charts/AD/AIRAC/EG_AD_2_EGLL_7-16_en_2015-09-17.pdf

[cmpbellsjc 2,960]

I've had my computer completely crash when selecting some transitions to ILS on EGLL arrivals. Turns out it's a known issue with PMDG and thanks to Dan for letting me know.

 

The other day I was also flying into CDG and selected an ILS transition and the computer crashed when I was on final. Rebooted and flew the same route this time without selecting the transition and all was fine.

 

Seems to be something in the NGX and T7 at some airports where selecting transitions from ILS to a STAR waypoint either crashes the computer, sim or locks up the aircraft.

 

Sean Campbell