Someone asked a great question concerning what we used on final approach for speed with the autopilot and flight directors turned off—pitch or power.
This question lead to many more:
- What does the airplane normally use for speed?
- How does the pilot know which is in use—Pitch or Power?
- More importantly—does it matter?
The A330 uses both Pitch and Power for airspeed. Heck yes it matters!
Two key points:
- In the “fixed thrust”—THR IDLE or THR CLB—Thrust is in a fixed position and the aircraft pitches to maintain the requested speed.
- In “variable thrust” mode—SPEED or MACH— the thrust maintains the speed.
In open descent the power is at idle—THR IDLE—Noted in column one on the FMA (Flight Mode Annunciator). If you’re in THR IDLE, how do you shift back to variable thrust—SPEED—so the thrust will control airspeed?
- Pull the V/S knob—noted in column 2.
- Capture the altitude selected in the FCU (Flight Control Unit).
- Capture the glideslope—noted in colum2. (Must be armed)
- Turn off the Flight Directors and the Auto Pilot.
This pulls us back full circle to the original question:
On approach if we disconnect the Autopilot and Flight Directors, what controls airspeed?
Remember turning off the Flight Directors and the Auto Pilot puts the plane into variable speed mode. This means that power controls the airspeed. A good thing to know if you ever think you might be locked into idle thrust. You really do have control.
Enjoy the Journey!