Weird airplane quirks
09-06-2021, 11:06 AM
#15
Gets Weekends Off
Joined APC: Dec 2005
Posts: 8,933
I was on the Bus for years but now on Fifi and already forgot. Can someone remind me, the logic of managed descent when pulling speed knob to maintain a new ATC airspeed. Say you had 280 kts set in the descent page and pushed to start a managed descent. I remember it would bracket +/- 20 knots, so bars at 260 kts and 300 kts. If it was getting high on profile, it would pitch down more up to 300 kts and try to stay on profile. Idle power.
Lets say it's doing 280 kts perfect in the managed descent. ATC says slow to 260 kts for descent. You pull speed to 260, it changes from magenta to blue. That much I remember. Plane will initially pitch up to get 260 knots, then come down. But I forget, what's the logic now? Will the plane keep coming down at 260 kts at idle, including going below Vnav deviation dot (magenta)? Or will it add some power once it gets back on the Vnav deviation dot and maintain the 260 knots and stay on Vnav dot?
Lets say it's doing 280 kts perfect in the managed descent. ATC says slow to 260 kts for descent. You pull speed to 260, it changes from magenta to blue. That much I remember. Plane will initially pitch up to get 260 knots, then come down. But I forget, what's the logic now? Will the plane keep coming down at 260 kts at idle, including going below Vnav deviation dot (magenta)? Or will it add some power once it gets back on the Vnav deviation dot and maintain the 260 knots and stay on Vnav dot?
09-06-2021, 11:26 AM
#16
Gets Weekends Off
Joined APC: Jan 2009
Posts: 1,269
I was on the Bus for years but now on Fifi and already forgot. Can someone remind me, the logic of managed descent when pulling speed knob to maintain a new ATC airspeed. Say you had 280 kts set in the descent page and pushed to start a managed descent. I remember it would bracket +/- 20 knots, so bars at 260 kts and 300 kts. If it was getting high on profile, it would pitch down more up to 300 kts and try to stay on profile. Idle power.
Lets say it's doing 280 kts perfect in the managed descent. ATC says slow to 260 kts for descent. You pull speed to 260, it changes from magenta to blue. That much I remember. Plane will initially pitch up to get 260 knots, then come down. But I forget, what's the logic now? Will the plane keep coming down at 260 kts at idle, including going below Vnav deviation dot (magenta)? Or will it add some power once it gets back on the Vnav deviation dot and maintain the 260 knots and stay on Vnav dot?
Lets say it's doing 280 kts perfect in the managed descent. ATC says slow to 260 kts for descent. You pull speed to 260, it changes from magenta to blue. That much I remember. Plane will initially pitch up to get 260 knots, then come down. But I forget, what's the logic now? Will the plane keep coming down at 260 kts at idle, including going below Vnav deviation dot (magenta)? Or will it add some power once it gets back on the Vnav deviation dot and maintain the 260 knots and stay on Vnav dot?
It will add power if you’re in selected speed and below the airspeed you selected. If you are faster than the selected speed it will ignore the profile and pitch up to slow down.
09-07-2021, 11:55 AM
#18
Gets Weekends Off
Joined APC: Jan 2009
Posts: 1,269
Plane will pitch up for 260 going off profile
can always select vertical speed at current rate,
dial selected speed down to 260 (new assigned)and use the brakes while meeting altitude constraints while slowing to the new assigned speed - not always possible - May have to tell atc it’s one of the other speed or altitude
can always select vertical speed at current rate,
dial selected speed down to 260 (new assigned)and use the brakes while meeting altitude constraints while slowing to the new assigned speed - not always possible - May have to tell atc it’s one of the other speed or altitude
Correct. Selected always trumps whatever is managed.
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09-07-2021, 12:00 PM
#19
Gets Weekends Off
Joined APC: Oct 2019
Posts: 439
I was on the Bus for years but now on Fifi and already forgot. Can someone remind me, the logic of managed descent when pulling speed knob to maintain a new ATC airspeed. Say you had 280 kts set in the descent page and pushed to start a managed descent. I remember it would bracket +/- 20 knots, so bars at 260 kts and 300 kts. If it was getting high on profile, it would pitch down more up to 300 kts and try to stay on profile. Idle power.
Lets say it's doing 280 kts perfect in the managed descent. ATC says slow to 260 kts for descent. You pull speed to 260, it changes from magenta to blue. That much I remember. Plane will initially pitch up to get 260 knots, then come down. But I forget, what's the logic now? Will the plane keep coming down at 260 kts at idle, including going below Vnav deviation dot (magenta)? Or will it add some power once it gets back on the Vnav deviation dot and maintain the 260 knots and stay on Vnav dot?
Lets say it's doing 280 kts perfect in the managed descent. ATC says slow to 260 kts for descent. You pull speed to 260, it changes from magenta to blue. That much I remember. Plane will initially pitch up to get 260 knots, then come down. But I forget, what's the logic now? Will the plane keep coming down at 260 kts at idle, including going below Vnav deviation dot (magenta)? Or will it add some power once it gets back on the Vnav deviation dot and maintain the 260 knots and stay on Vnav dot?
can always select vertical speed at current rate,
dial selected speed down to 260 (new assigned) and use the brakes while meeting altitude constraints while slowing to the new assigned speed - not always possible - May have to tell atc it’s one of the other speed or altitude
edit for punctuation
09-07-2021, 12:24 PM
#20
Gets Weekends Off
Joined APC: Apr 2016
Position: A320 CA
Posts: 723
the plane will pitch up for 260 going off profile
can always select vertical speed at current rate,
dial selected speed down to 260 (new assigned) and use the brakes while meeting altitude constraints while slowing to the new assigned speed - not always possible - May have to tell atc it’s one of the other speed or altitude
edit for punctuation
can always select vertical speed at current rate,
dial selected speed down to 260 (new assigned) and use the brakes while meeting altitude constraints while slowing to the new assigned speed - not always possible - May have to tell atc it’s one of the other speed or altitude
edit for punctuation
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