Hi, I just finished my first transatlantic flight from EGLL to KJFK. Followed the real world NAT and everything and of course I enabled the drift-option looking foward for what would happen.What happened was, that the airplane actually drifted and when the automated radio switcher was able to bear the first American VOR, the FMC knew, it drifted. Now it turned in a steep turn to the right to recapture the real course.My Question: Does this happen the same way in the real world? I mean the aircraft banked up to 30

These days I'd expect all transoceanic aircraft to have GPS, and thus not be subject to drift. Real pilots?Lee Hetherington, PP-ASEL (KBED)

1 of the things I do at work on a daily basis is prepare a Pilot Briefing Package for a Major US airline flying back across the pond. Included in the package are the following:2 FP's ( These are prepared by the airlines's dispatch office - not myself )3 NAT TracksWX PackageNotams PackagePlotting ChartPosition Report Form.The Position Report Form is used to record the ETA/ATA for each waypoint, along with the Navigation accuracy for that waypoint when compared with the OFP. This way pilot's of aircraft not equipped with GPS can see if they are starting to encounter any drift from their course.

1 of two things Mark does in his spare time, is shear sheep.;)The other thing is drink inordinate amounts of scotch and fly the PIC767.Good to see you're about Mark - you gonna join us on the long haul event?Daryl ShuttleworthDS 3339http://vatsim.pilotmedia.fi/statusindicato...tor=OD1&a=a.jpg

Depends when it is - some of us work weekends currently.

Well...not exactly Mark. In an aircraft without GPS, you can't check the accuracy of an INU when outside range of ground navaids. There are no references to check the INUs against. The best you can do is to check the INUs against each other, (an agreement, or consistency check, not an accuracy check) so as to identify a bad one if it starts to head off into the twilight zone on you. In an airplane with triple INS, it's usually not a big deal, as one INU going astray will usually be significantly off from the two others. In a dual-INS bird, however, now you have to decide which one is bad...and on a really long flight, it could be that both have drifted significantly.With Litton 91 INUs we considered an error of ~2nm/hr of flying time acceptable. So, conceivably, if the INUs drift in opposite directions, you could have them disagree by as much as 20nm in a typical 5-hr Cat-I oceanic segment without being out of tolerances. 20nm will get you violated big as Dallas on the NATS, so you don't see many dual-INS birds flying in MNPS airspace any more unless they've been retrofitted with GPS update capability. And to answer the original question...if you find yourself off the course while in North Atlantic MNPS airspace, you'd better believe you'll be banking it up to beat cheeks back to centerline...hopefully before ATC radar figures it out.RegardsBob ScottATP IMEL Gulfstream II-III-IV-V L-300Washington, DC

Hello !The PIC version 1 does have an exaggerated IRU drift. But if MAP SHIFT does occurr, it's normal that the aircraft gets back to the course after it gets radio updates again.Tero