744 'On approach mode'
 

Can any current 744 pilot tell me what happens to the MCP speed window when descending in VNAV SPD pitch mode and the aircraft then enters the "On approach mode" condition whereby the pitch modes changes to VNAV PTH?
Does the window remain open or does it close?
Thanks

Window remains open...

Thanks for that. Is my interpretation of the VNAV logic correct in that if you are descending in VNAV SPD for an RNAV approach and your vertical track is approximating the calculated path and you then meet the "On approach" transition will the pitch mode automatically change from VNAV SPD to VNAV PTH or do you need to close the speed window and then open it again to get it out of VNAV SPD and into VNAV PTH?

Once you've transitioned the on approach waypoint as long as you're within the VNAV PTH capture conditions it will catch with the window open, some airlines may consider that unstable being in VNAV SPD descending from above to catch the profile after the on approach waypoint.

The speed window closes when the pitch mode changes to VNAV from another pitch mode(such as having selected FLCH for descent where the speed window opened) which happens when you push the VNAV button. Happens as well at 400 feet on a typical departure when VNAV automatically engages from TO/GA pitch mode(because it was armed on the ground).

Is there a definitive waypoint on the approach whereby it transitions to the 'On approach mode"? Is it when sequencing the first waypoint associated with the approach ie. As selected from the without an approach transition. The FAF or the entered approach transition waypoint?

It is the point shown in the FMC on the DEP/ARR page at position 6R after you select the respective approach. It is not automatically the FAF.

In terms of an instrument approach, the FMC transitions to "on approach" when a published instrument approach has been selected and incorporated in
the active flight plan and the airplane has sequenced the first waypoint
on the published approach.

I respectfully disagree.

From the 744 FCOM:

Most of the time, on-approach logic will start at the Course Fix. But if you extend the centerline from the FAF, the on-approach logic will not start until the FAF sequences.

Thanks Buzzbox. I pretty much quoted the FCOM but left out the VFR stuff as it is not something done very often and seemed like a distraction. Basically, once by the first waypoint such as an IAF, "on approach mode".

So best for the earlier poster to respectfully agree.

Gotta admit though, I thought you needed at least flaps 1 prior to this thread.

As I'm sure you know, never bypass a stepdown fix when extending or you have lost the protection of that altitude which is almost always higher than the FAF. Guys have failed their rides doing such a thing. If on vectors, once turned inbound for intercept, then extend from the nearest fix in front of you.

I agree, JammedStab, that it is something that needs close attention. Guys have also busted check rides because they are vectored inside the CF on an ILS and they fail to extend the centerline from the FF. If you were on a downwind leg to base and you were vectored inside the wayline of the CF, the CF would never cycle, but you might not notice because you are intercepting the ILS and at that point most guys are concentrating on that. If you get to DA like this, it begs the check airman to command a go-around so he can enjoy the confusion as you get to 400' and select LNAV. Instead of following the missed approach route, it wants to do a 180 back to the CF. So, your last sentence is important -- Always make sure you have the right fix in front of you.

JammedStab:
You might be thinking of the Barbie Jet, whose "on approach" requirements are a little different to the somewhat ageing "Queen of the Skies".

From the 777 FCOM: