Why does VS have to be 0 when activating APPR mode?

Hi All

When looking at a full approach procedure, ideally we would let the nav mode follow the STAR arrival, STAR approach, and then the ILS approach until we take manual control about 1000ft AGL before touching down.

But in infinite flight, you can’t activate APPR mode (for the AP to fly the glideslope and localiser) until the vertical speed is 0. This rarely happens when the autopilot follows most STARs, given the way points always follow a gradual descent instruction all the way to the runway, and so there’s always a -VS. The way I’m manually getting around this recently is to disable VNAV before reaching the way point that’s at the start of the final approach, meaning the plane eventually levels off, VS goes to 0, and I can activate APPR. But is this the correct way?

If you look here for example https://www.youtube.com/watch?v=l0KqBgJWqo8 … go to the 9 minute mark, a real A320 pilot is playing MS FS 2020 and is arming APPR when the plane is still gradually descending on the way to EGLL’s 09 final approach.

Can anyone clarify the correct procedure?

Thanks,
George

Your VS doesn’t have to be 0, it can be anything, it just means that once you activate APPR it can be a bit unstable to start with if it has to correct the descent rates,

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