So me not being a real world 737 pilot, I am curious what exactly the vnav is lacking on the ifly max. And does the pmdg 737ng do a better more accurate job?

 

Any differences between the two in the real world?

6 hours ago, simsuper80 said:

So me not being a real world 737 pilot, I am curious what exactly the vnav is lacking on the ifly max. And does the pmdg 737ng do a better more accurate job?

 

Any differences between the two in the real world?

Two things come to mind very quickly:
1) The VNAV SPD mode is modelled incorrectly. E.g. when you're way above the path, VNAV should go to VNAV SPD and target the speed target you set. The iFly instead goes to VNAV PTH and dives down at 7000 feet per minute.
2) Again VNAV SPD: If you are on VNAV PTH and want to manually go below it (e.g. to prepare for a shortcut) you hit SPD INTV and dial the sped up. The VNAV should go to VNAV SPD now and increase the descent rate accordingly. The iFly instead will keep the descent rate and instead add thrust to reach the speed. [I know the latter is actually a software variant that exists in real life, but it's awful nonetheless]
3) If you enter an altitude restriction at a waypoint on your arrival or remove a waypoint, the rest of the waypoints should recalculate the new VNAV path *before* you hit execute. You could e.g. check what a possible shortcut would mean to your altitudes etc and then hit cancel/erase before executing, so you don't change the current flightplan for good. This doesn't work on the iFly, it just doesn't recalculate.