Shore Guy
Didn?t have a lot to do with the 990 but Swissair used to fly them into our airport in the 70?s and I turned around many flights. Also got to look at some a US charter company sent some over for major overhauls etc (ex American Airlines aircraft I think). I did spend 6-7 years maintaining CV880-22M?s (with leading edge slats) and thought it a great little ship with some innovative systems and a strong structure. The engine (basically a civilian J79) was also interesting compared to the agricultural JT3 in the B707/DC8.
Black Dawn
You are correct. The aircraft manufacturers seem to invent their own names for things just to confuse us.
A Douglas CONTROL tab and a Convair FLIGHT tab, to use the manufacturers names, are both servo tabs being directly connected to the control column, rudder pedals or control wheel. I can?t recall what Boeing called the servo tabs on the 707.
A Douglas GEARED tab as fitted to the elevators was, I think more correctly called a balance tab and was linked to the rear spar of the horizontal stabilizer. Movement of the elevator away from neutral resulted in the tab deflecting in the opposite direction to assist the elevator movement reducing pilot forces. The DC8, and as far as I am aware, the DC9/MD80, had a control (servo) tab and a geared (balance) tab on each elevator.