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?
Power!
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!
~ Karlene
Great information, even for us passenger-types. Love reading about this stuff.
ReplyDeleteThanks Linda. You can be the president of my fan club. :)
ReplyDeleteWhat would you do in a Boeing, Karlene?
ReplyDeleteFred, In the Boeing I "did" the exact same thing. I used pitch to fly the approach and power to fly my airspeed. I've always used the thrust for speed. Just makes sense... gives you a direct response. More power= faster. Less power = slow down.
ReplyDeleteKaren, this is a great post — thank you. It also goes a long way in contributing to the power vs. pitch debate among us "little" airplane flyers. If you hold pitch constant, the only way you can vary airspeed is with power. If you hold power constant, the only way you can vary airspeed is with pitch. In reality, however, as in life, everything affects everything.
ReplyDeleteMarc
Marc, you are so right. Everything does effect everything. I think if you visualize putting the nose of your plane where you want it to go... down, up... at the end of the runway, ie.,Pitch. And then figure out what power you need to give you the appropriate speed to fly ... you'll be golden.
ReplyDeleteWhich autothrootle modes does Boeing have.
ReplyDeleteHey Jet airliners.. Boeing has "on and off" I think. It's been a long flight. More thought and discussion coming if that's not correct.
ReplyDeleteon approach with the autopilot off, can you fly the final approach path with the flight directors on?
ReplyDeleteAbsolutely. Fly the flight directors. And, automthrust on or off. Either way.
ReplyDeleteif the flight directors are on and the autothrust is on, is it still possible for the plane to revert to speed mode?
ReplyDelete"Speed" is an autothrust mode. So yes... with the autothrust "on" the airplane can be in speed more. But it's not really a "reversion."
ReplyDeleteim sorry what i meant was if it was possible for the autothrust to revert to thrust idle mode.
ReplyDeleteJet Airliners, what you need to know is that idle thrust is not a "mode". It's idle thrust... or a position of power. When the auto thrust is on, the power will go from just "above" idle up to the selection that is selected. Example: In climb detent thrust goes from just above idle up to climb. And the power modulates in between per power requirement depending what you're doing. When the plane is landing it has the power to come to idle for the touchdown.
ReplyDeleteI hope this helps.