Originally Posted by
FedElta
I spent a lot of time on A300/310, but none on the A320. I will assume similar architecture.
" Profile" cruise would limit autopilot pitch authority to +1.15/-.85 G. Pitch was used to maintain speed within these parameters. The real goal was to limit autothrottle movement and reduce fuel consumption. The book said a 1% reduction in consumption.
I never saw more than 50' variance in reasonablr air. RVSM compliance was never an issue, and ride smoothing for pax was a secondary benefit.
Moutain Wave, or moderate turb would necessitate an exit from "Profile" and restore full autopilot pitch authority.
320/330 drivers : is this similar in your jet ?
From the A330 manual:
When the aircraft is in ALT CRZ mode with the autopilot engaged, autothrust engaged in MACH mode, and is within a +/- 3 knot range of the target speed, the autothrust soft mode engages. This mode reduces the thrust variation in cruise, specifically in light turbulence. The autothrust soft mode disengages when the speed deviation fro the target becomes too large or is modified.
From the 320 manual:
SOFT ALTITUDE
On reaching the planned cruise altitude, ALT CRZ engages and the A/THR maintains the speed/mach target.
Two minutes after ALT CRZ engages, if the mach mode is operative, SOFT ALT mode engages. This allows the aircraft to deviate +/- 50 feet from the target altitude, thereby minimizing thrust variations and reducing fuel consumption.
Couldn’t find any numbers on the fuel savings, but 1% sounds reasonable.