VNAV

[jethound]

Why can we not engage the VNAV on a segment leg of a GPS approach. It will not engage until on the final approach. Example
the NOPT transition leg is 4400 from the IAF to the FAP your at 8000 decending why when established on an inbound leg of the approach can you not engage the VNAV so the plane will level off at 4400 feet then after you reach the 4400 you should be able to dial down the Minimums on the approach and the plane should fly all the way down to the MAP. If you started at 4400 feet at the IAF any time on the leg you should be able to dial the altitude down to Minimums with the VNAV engaged.

 

[skysailor]

That feature is coming for the HDX systems in a firmware update. My understanding is they are trying to make it the next one coming out. I am told the Classic and Touch will not get it due to lack of processor speed.

 

[jethound]

That is a shame all it has to do is recognize the decent limits on the plates no matter what you have set in to the altitude window.
guess I had better start saving my money for two HDX

 

[skysailor]

You can make the Classic (I have these just like you) do the entire approach on autopilot. Start in NAV mode and ALT hold. When you are level inbound to the first fix, set the next fix altitude restriction. When you reach the fix, use either Vertical Speed (500-700 FPM down) or IAS Hold mode to start the aircraft down. It will level at the next fix altitude. When you are level inbound to the final segment set approach minimums in the altitude window and arm VNAV for vertical mode. The autopilot will capture the vertical profile (glideslope on ILS or vertical profile on RNAV LNAV+V or LPV) and fly right to minimums.

 

[jchang10]

To continue what you wrote, what will happen at minimums? Seems like you are implying it will level off at your preset altitude setting. I could sworn the last time I tested this, VNAV mode, it will fly to the runway and ignore the preset altitude. I did this a while back, and that is what I thought it did for me. I will confirm this next time I think to test it.

 

[skysailor]

If the vertical mode is VNAV it should continue to descend while warning you as you pass the minimums you set. In IAS Hold or Vertical Speed it will level off. Your final segment in the example above will be flown in VNAV.

 

[jchang10]

I think we are on the same page now. VNAV is always to the runway. You need to hit ALT or VS climb with positive rate to stop the descent.

 

[airguy]

I think we are on the same page now. VNAV is always to the runway. You need to hit ALT or VS climb with positive rate to stop the descent.

Or the Go-Around button, which will prompt you to add power and the autopilot will assume the default climb rate and hold the current heading.

 

[jethound]

If you have min set in the window for the Vnav "MDA" the plane should not violate that MDA with the autopilot on. And once coupled on the Vnav portion of the approach you should be able to set your Miss approach altitude back into the Altitude window so when you tell it to miss and re-engage the nav function it should climb to the altitude set in the altitude window unless there is an altitude on the profile that is lower.

to imitate the jets we fly, the autopilot should never in a VNAV mode violate an Altitude window pre-select or an MINIMUM DH OR MDA. while flying a Vnav approach If you forget to set the altitude down prior to the aircraft capturing the VNAV then the plane will simply level off at the Altitude Window altitude. But once captured on the Vnav it should allow you to put in the miss approach altitude in the altitude window.

 

[skysailor]

I believe in VNAV mode it will continue through the MDA minimums you set so as to maintain a stable approach for you as you disconnect when you see the runway. The Go Around will be armed when VNAV is active so if you so not see the runway environment at minimums, you would activate the Go Around mode.

 

[jethound]

I believe in VNAV mode it will continue through the MDA minimums you set so as to maintain a stable approach for you as you disconnect when you see the runway. The Go Around will be armed when VNAV is active so if you so not see the runway environment at minimums, you would activate the Go Around mode.

I think you are correct about the plane descending to the runway. I think it ignores the altitude preset even if you would make that the same as minimums