(MLenoch) wrote:

"Paul Austin"

wrote:Something I saw raised a question in my mind: An MD-80's T-tail had
one half pitched up and the other half pitched about neutral.

This is a situation that is specific to the DC-9/MD-80 series airplanes. These
aircraft have elevators that are not connected to the control yoke in the
cockpit. Rather, the yoke drives the trailing edge tabs only, and thus the
elevators follow the "trim force" from the trailing edge tabs. Pitch trim, in
the usual sense, is attained by a trimable horizontal stabilizer. During
pretakeoff checks, the pilots will push forward on the control yoke to activate
the "stall recovery" (for lack of a better word at this moment) actuator; this
actuator will force the elevators down in unison, to produce a nose down
control input should a "stall recovery" be commanded by the aircrew. Just prior
to takeoff, the elevators appear in "harmony" to be connected together.

Therefore, seeing a split elevator on DC-9/MD-80 aircraft, while on the ground,
is normal, though visually disconcerting.

VL

That system was also used on all flight controls on the Canadair
Argus...most disconcerting to 'other type' crews (especially
civil airliners) following an Argus to see BOTH ailerons
deflected up, and then the elevators moving independently of each
other and the ailerons hanging down when the gust locks are
selected off.

I've heard literally dozens of comments like... "..ahh 739 from
Speedbird 665, be aware that your ailerons BOTH appear to be
deflected UP"..."Thank you Speedbird, that's normal for this
type".
--

-Gord.