727 autopilot behaviour

[celticmatrix 0]

This is a question I once posted somewhere else, but maybe you guys can help. Would like to know how the AP is normally (and realistically) used on the 727.My question is as follows: As far as I know the autopilot in the 727 is a pretty basic 2-axis autopilot. There are two separate "engage" switches for elevator and ailerons. Now, when I disengage the elevator AP in the CS (Captain Sim) 727 but keep the aileron control engaged (in order to keep a certain heading but control altitude manually) I notice that the elevator axis stays engaged, because there is elev trim movement by the autopilot which tires to level off the plane. This is a bit surprising since I switched the elevator AP to "disengaged". Is this the correct behaviour? Or am I missing something here? Maybe thats not exactly the way the 727 is flown and I should use the pitch control on the AP to make altitude adjustments, but I really like to have just one axis (lateral) engaged while controlling altitude. Hope this makes sense.

[CF104 0]

The SP-50 AP on the 727 is actually a three axis AP when the yaw damper is taken into account.Anyway, in real life you can't engage the Pitch channel unless the Roll channel is angaged first. Just engage the roll channel and you should have pitch under normal control. Our crews usually hand fly until cruise altitude and then angage both channels of the AP in HDG HOLD and ALT HOLD modes. When at TOD, they disengage ALT and HDG hold and fly using the turn and pitch wheel. The way you want to fly is perfectly normal for this AP on the 727 so give it a try and let me know if it works out for you. Cheers,JohnBoeing 727/737 & Lockheed C-130/L-100 Mechanichttp://www.precisionmanuals.com/images/forum/ng_driver.jpg