Have you tried climbing to the target altitude. Will it intercept it?
No. For altitudes higher than current altitude, the autopilot does nothing based on VNAV (does not climb, does not intercept). Not surprising given there is no vertical deviation information displayed on the PFD. It works great in the descent.
I wonder if there is a different mode for turboprops? On those, one could do a climb in VNAV a lot better i.e. without running out of power.
denopa wrote:
The first surprise is that the constraint at DET appears as valid and active, despite requiring a climb. But that’s a good surprise. The second surprise is: why is the second constraint displayed as invalid (crossed)? In map view the first constraint is displayed, the second one is not.
I have a setup with GTN750 with VNAV enabled, and G500TXi PFD. The autopilot doesn’t talk with the G500 in terms of any altitude constraints (the GAD43e doesn’t support a connection to it). This is actually what I would suggest as a mental model when you try to understand the behaviour of the GTN, i.e. to consider the autopilot as completely separate from the navigation box, or to disregard it altogether. If anything, the AP is driven by the navigator and not vice versa.
One thing I noticed on my last flight is that as soon as you’re just 10 ft below the “At” target altitude and descending, you’ll get a flashing warning message on the GTN “Cannot reach vertical waypoint”. Which makes sense, you shouldn’t be below the target altitude before the waypoint if you’re following your VNAV profile.
To your question, if you consider the GTN as a separate entity, then the active leg determines the constraints (or rather the next waypoint in sequence with an altitude constraint). Since you didn’t have a lower constraint before your 8000ft at DET, it is valid and active; but you should have seen the flashing warning message mentioned above when flying towards DET with that leg active and below your target altitude. If you didn’t, that might be a limitation of the simulator implementation.
denopa wrote:
… the 9000 constraint becomes active and displays on the GTN map page…
That’s because your active leg is now “From present position to EGMC”, completely ignoring the prior leg with the prior (lower) altitude constraint at DET. “Present position” doesn’t have an altitude constraint, so you don’t have any climb in your navigator, and 9000 has become a valid constraint. Again, if flying below, you should get the flashing warning about inability to reach the target.
denopa wrote:
Edit: it’s keeping 3 degrees, I was going a bit fast in the sim.
When you’re within a certain time from your top of descent, you get a button with which to modify the angle on the VNAV utility page. I think it’s around 12 minutes before TOD. Interestingly, if choosing a steeper angle, that obviously pushes back your TOD and makes the button inactive again. If you choose something too steep you can’t easily get back your shallower descent angle, because once the button becomes active again you may be past the TOD point that would result from the shallower angle.
