A320: min time for FDs to be off ?

[321XLR]

After landing flows / "cycle" the FDs

I seem to recalll hearing, or reading, that both FDs need to BOTH be off for like 5 seconds or they will not reset properly.

Where in the FCOM, or maybe Airbus bulletin, is this published ?

Thank You

[CW247]

It's not and don't think it ever was. It's an invented procedure that goes back to the old days when the FMGC/MCDU was running on older hardware and would timeout/crash. It was resolved by some pilots switching of the FDs as they thought that would place less demand on the computers and reduce the chance of a timeout. Some airlines have developed an SOP to switch off. Beats me.

[enzino]

Never heard of it, but I have noticed that some of the most senior A320 pilots in my company switch them off in their PM after landing flow.

[Amadis of Gaul]

Originally Posted by enzino

Never heard of it, but I have noticed that some of the most senior A320 pilots in my company switch them off in their PM after landing flow.

It's in our procedures to turn them off in the after landing flow. They don't get turned on again until the cockpit preparation procedures for the next flight.

[Rocket3837]

FDs are always ON regardless of the position of the FD PB.... You are only "Removing them from view" by the action of PB....
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[Fursty Ferret]

It's a hangover from the first-generation FMGS, where cycling the flight directors on the ground reset the FMS for the next flight. Nowadays (well, since the early 2000s really) this happens automatically once you leave the runway after landing.

[sonicbum]

Originally Posted by 321XLR

After landing flows / "cycle" the FDs

I seem to recalll hearing, or reading, that both FDs need to BOTH be off for like 5 seconds or they will not reset properly.

Where in the FCOM, or maybe Airbus bulletin, is this published ?

Thank You

Hi,

switching FDs OFF in the after landing flow is a homemade non standard procedure that is often brought in by people with previous experience on other types such as the 737 or the MD80.
Some airlines might add it in their after landing flow for some reasons but it is an unnecessary action.
Standard Airbus SOPs do not ask for FDs OFF during the after landing and during the Cockpit Preparation flow the wording is "FD....Check ON | PF-PM" meaning that it is supposed to be already on and you are checking the correct status.

[Check Airman]

My company resets the FD after each landing. Then again, we try to fly it the same we we flew the DC9.

[giggitygiggity]

Originally Posted by Rocket3837

FDs are always ON regardless of the position of the FD PB.... You are only "Removing them from view" by the action of PB....
​​​

Removing the FDs has other important functions such as forcing thrust to go into SPEED mode.

[Rocket3837]

Originally Posted by giggitygiggity

Removing the FDs has other important functions such as forcing thrust to go into SPEED mode.

Switching FDs OFF while AP is ON has no effect on neither the FDs nor A/THR modes but switching FDs OFF while AP is OFF makes FD engage in basic mode and that will force the A/THR to switch to SPD mode ....
Further, you can engage the AP while the FDs are already OFF.....
Thanks