747 and grid navigation

[LeFreak 0]

hi folks,will the upcoming pmdg 747 support grid navigation?? would be cool to fly grid tracks on polar routes instead of having the fmc do all the work ;-)jan

[744pilot 0]

Grid???

[ps1flyer 9]

Jan,> would be cool to fly grid tracks on polar routes> instead of having the fmc do all the workwhere is the difference?Certainly, the 747-400 is capable of displaying GRID HEADING when in polar regions (that is, either North of 82

[LeFreak 0]

thanx for explaining that Markus .. do you know what would happen in the unlikely event that the IRS's fail (all 3 of them) and you are in the 6 micro tesla zone, where would the FMC get its position information from? does it continue on last know IRS position (supposing there is no GPS installed and no UHF/VHF navaids are in reach to crosscheck) ..Jan

[744pilot 0]

I think you would be in serious ####. :(

[ps1flyer 9]

Hi Jan,> do you know what would happen in the unlikely event that the> IRS's fail (all 3 of them) and you are in the 6 micro tesla> zone, where would the FMC get its position information from?> does it continue on last know IRS position you will have a problem and you are in serious trouble.If you would loose all 3 IRS system, you will loose:- all PFDs - all NDs- all autopilotsbecause the IRSs provide not only position data, but also attitude reference data and heading information.If the IRSs are still operational and only the alignement is lost, you should be able to re-align the IRSs to ATTitude mode. This can be done in-flight when flying straight, level and unaccelerated and takes some 30 seconds. Thus, you will get back attitude data for the PFD. The PFD heading needs to be entered manually but this is definitely a problem in polar areas where heading varies rapidly with position.Even if you get the IRSs back in ATT mode, you ND map is lost and no LNAV route will be displayed. Also, the autopilots will be inoperative. So, in any case, you have to fly manually and to navigate by dead-reckoning. The FMC will still be operational but since it does not receive any position update it will not be useful anymore for navigation purposes. Besides, it does no longer control the A/Ps e.g. for flying the LNAV route, obviously. Hope this helps, Markus

[LeFreak 0]

thanx markus ..sounds like an interesting situation ;-)Jan