creates big questions about how crappy nav gear they have in [some] airliners
Its a statement of fact, its not uncommon for the old !!!! haulers to have one beam bar showing of to the right by half a dot and the other one showing half to the left in VOR mode and the GPS showing you going plumb up the middle. The VOR tracking mode on the AP is the work of satan and the thing wanders "S"ing up the radial. Everyone has a play with it and then never uses it apart from VOR approaches. And I could well imagine it deviating by 2-3 miles.
If your in heading mode, basically crew cockup, turn points are missed, wind changes arn't spotted and the tracking goes off. Alot of the machines you can't slave the AP to the GPS or if you do you use the VOR capture mode which I have already said is the work of satan and would make me feel sick never mind the punters in the back.
The only thing that will sort this is by tightening up the instrument limits and having a third party instrument C of A every 12 months which the airlines will lobby like
not to have. If say you report a 5 knts split between airspeed indicators they won't actually fix it because the limit is 6 knts each ASI is allowed +- 3 knts. And then you get the sodding machine does something different in the air than it does on the test rig on the ground.
There are several levels of LNAV in my experence.
1. Go get straight line only which the controllers will spot because they get to a point then turn if the crew are leaving the machine to do its own thing.
2.You get circular nav which means they can fly dme arcs and holds etc. But will still go to the point then turn
3. And then you get the predictive turn ones which have logic to swing by points and start turns before you get to the point and will also vary the distance to the point when the turn is wound in depending on the GS and angle to be turned through.
Sometimes it can be the same hardware but with a different software level. But they won't upgrade it because that would cost 50k.
Then there is training, some training folk say you can't start turning until you with x amount of a point this can vary between 0.5 miles and 5. I have looked for a reference for this years ago but couldn't find it. Then you have crews taking the piss and cutting the corner edging round it from 10 miles out.