Don't the coupled yokes on a conventional system provide "arithmetic summation" of the force applied by each pilot?
Not exactly the same.
Scenario: FO applies 10 lbs back pressure causing the plane to start pitching up. At 3 degrees nose up, the Captain applies
same magnitude forward pressure.
Airbus. Sum == 0, no commanded change, so the nose stops pitching up at 3 degrees ANU.
Conventional. Equal forces, so the yoke stops moving
rear-of-center. Plane continues to pitch up
past 3 degrees nose up.
Also note:
Airbus. FO's sidestick is now rear-of-center while the Captain's sidestick is front-of-center. But the plane continues "straight" -- contrary to
both pilots' natural expectation! See AF447 to see why this is bad.
Conventional.
Both pilots' yokes are at the
same rear-of-center position, and the plane behaves exactly as both would expect.
Active sidesticks will basically restore what's already natural to pilots / human beings.