Or the good old "BUFFET ALERT" - Where's my damn sandwich Boeing?
G-SPOT - We had one such moment into Lamezia this week. VNAV Non Precision Approach being planned, as we were being vectored for downwind VNAV insisted we were 4000" above path, even though we were at 8,000", 250kn with over 40 track miles.
We continue in using LVL CHG or V/S and get an extended downwind, with a turn at 12 miles, so we end up actually low. At 14 miles I start slowing down and ask for Flap 1, we intercept the profile and start a nice descent. I'm about to reduce when BANG, it says we're 2000" high again. What happens? It pitches to 2500 fpm at 10 miles, speed rapidly increases so we're doing Flap 5 240kn speedbrake out at 10 miles, with it in a dive. The speed stabilises but it took all of our effort to get Flap 10, Gear, and the rest out without busting placard speeds. What an effort!
VNAV is a great tool but it's just that. I'd take conventional MCP modes over FMC managed path anyday.
Horgy