I recently visited Frankfurt and noticed all the Lufthansa A320s were starting Engine 1 first on pushback. I looked into it and it seems Airbus changed their SOP at some point from Engine 2 first to Engine 1 first on the A320 family.

That got me curious about the A220, so I checked three different FCOMs and found the opposite is true there. It's strongly recommended to start Engine 2 first, to avoid

-Hydraulic pressure spikes

-FLAP SLOW / FLAP FAIL nuisance warnings

-Potential galley power load shedding & IFE issues

Made a video breaking this down with schematics and animations if anyone wants the visual explanation

https://youtu.be/VEebAVoOZNk

To understand why this was the case, I did some investigating into the A220's hydraulic system.

Basically, hydraulic System 2 powers both nosewheel steering and the slats. So if you're single-engine taxiing on Engine 1, System 2 is running on its electric backup pump only, and deploying the slats can starve pressure needed for nosewheel steering.

The FCOM recommendation is to keep the aircraft stationary while deploying flaps/slats in that scenario, to make sure there's enough power for steering.

The A220 never fails to surprise me the more I look into its systems :)

Always interesting to find out different stuff like this. 👍

do you have any sense of this is due to it really being a bombardier vs an Airbus? Seems like there’s good justifications for the difference

IIRC, it's the same on the Challenger 350 (it's been a while since I have flown one, so I could be wrong, but I vaguely recall that we always started Right Engine first)

7 hours ago, RJ_FO said:

IIRC, it's the same on the Challenger 350 (it's been a while since I have flown one, so I could be wrong, but I vaguely recall that we always started Right Engine first)

Thanks for the insight :)

8 hours ago, UrgentSiesta said:

Always interesting to find out different stuff like this. 👍

do you have any sense of this is due to it really being a bombardier vs an Airbus? Seems like there’s good justifications for the difference

Indeed! It certainly is. Yes, I believe the Bombardier aspect really explains the hybrid nature. Even the AFCS modes and hydraulic system naming (instead of Blue, Green, Yellow) is different to the rest of the Airbus Family.