21 minutes ago, Christopher Low said:

Well, somewhat annoyingly my second test flight with the same parameters as last time (MCP altitude reset to 1000 feet before T/D) resulted in a flawless RNP 08 approach! I guess that something must have happened on the first flight that was different to this one, but I have no idea what that could have been.

I will just have to wait to see if it happens again on future flights, and try to isolate the reason why. Thanks for all of the suggestions, guys 👍

Chris, did I get it right? You had MCP ALT set to 1,000 ft before TD, but you didn't receive VNAV ALT at 1,000 ft? 

15 minutes ago, Stearmandriver said:

Oh certainly LNAV / VNAV / ability to conduct RNAV procedures is modeled and has been since FSX.  You're probably thinking of specific RF leg ability, which is only a recent addition (doesn't work great, but at least it's there now.)

Yeah, interesting!  Our rationale is to maintain stable flight guidance all the way to the runway, so we take the TDZE and round down.  I suspect the HGS may influence our decision in this; normally, it doesn't matter what the flight guidance does 100ft above the runway as a crew is visual by then, so I could see sticking with the standard of rounding up as we usually do with MCP altitudes.  But for a crew flying the HGS, it can be distracting to see the guidance cue all of a sudden jump up off the runway when in close, if it commands a level off.  I've seen crews reflexively start to follow it, especially captains that are new to a HUD.  We hammer them so hard to remain in the flight guidance and especially to follow the flare cue during an AIII that the suddenly rising guidance cue can cause a momentary reflexive back pressure.  Given the short and often contaminated runways we're doing these approaches to, any minor destabilization in close isn't great. 

Or it was someone's arbitrary decision 30 years ago.  That's... Equally possible.  😁

 

That's why I mentioned the difference in SOPs. I understand the reasoning behind the HUD scenario. Another SOP states that they will round down or round up the MCP, but after crossing the FAF (300 ft below the altitude), they will set the go-around altitude. HUD or non-HUD equiped. Such diversity in procedures.

2 hours ago, LRBS said:

Chris, did I get it right? You had MCP ALT set to 1,000 ft before TD, but you didn't receive VNAV ALT at 1,000 ft? 

It changed to VNAV ALT after I had disengaged the autothrottle and autopilot (which happened at around 1400 feet).

7 hours ago, Christopher Low said:

It changed to VNAV ALT after I had disengaged the autothrottle and autopilot (which happened at around 1400 feet).

Excellent, as it should be, respecting the MCP-set altitude. Just a note: disengaging the AT or AP should not activate VNAV ALT. It’s good to hear that it’s functioning as intended. 

 

Ah, so it changed to VNAV ALT on the FMA when I passed through that 1000 feet setting on the MCP?

4 hours ago, Christopher Low said:

Ah, so it changed to VNAV ALT on the FMA when I passed through that 1000 feet setting on the MCP?

Correct, in this instance (1,000 FT set on the MCP altitude window), when you get VNAV ALT, the computer is "telling you" that there is a conflict between the VNAV profile and the MCP altitude. The computer will give commands to maintain that MCP altitude, to get out of it, dial to a new altitude. The pitch mode will change with only one push of the altitude selector, and the VNAV profile will continue to the following programmed FMC restriction or MCP altitude. It gets more complicated, but this is the reason and the correct behavior.

P.S., I see you are looking for information about the 777. There are some short Boeing 777 CBT clips on YouTube, and some of us are qualified or previously type-rated in this airplane. We can answer questions with certain limitations. It can't explain everything as we do in a ground school, but it can point you in the right direction.

 

Edited April 28, 20251 yr by LRBS