Had an interesting occurrence on takeoff this evening, and I'm wondering if it's something I did wrong, or some fluke I caused in the plane.I was taking off from KSDF - had everything dialed in, hit the Autoflight button once to arm ATS, and took the runway. PROF was armed. I had the heading knob set to the runway heading, as this was going to be a radar vectored departure and not a SID. Takeoff was normal, ATS clamped and off I went. At about 600 feet, I hit the Autoflight button again to engage what I thought would be heading select mode. Immediately the aircraft began to bank left, even though I had the runway heading set and it showed up properly "HEADING 168" in white on my PFD. I pulled the heading knob to perhaps command the proper heading, and yet the left turn continued. I disengaged the autopilot, and manually flew to the desired heading. I reengaged the autopilot, and again the aircraft wanted to roll to the left. I was finally able to remedy the situation by -pushing- the autopilot knob to set the current heading, and then pull to command. After my vectors, I engaged NAV mode and the aircraft tracked the flightplan as expected.Was I doing something wrong here? With a manual heading set upon takeoff the aircraft should track the manually set heading when the autoflight button is pushed, correct? Without NAV mode engaged (or armed prior to takeoff), it shouldn't try to navigate me to my first waypoint - and even if it were, I would've expected it to roll me to the right since It was only 40 degrees or so in that direction.Any suggestions?Brian Schwark / KBWI

The MD11 will turn in the same direction that the heading knob was turned, even if it means turning more than 180 degrees. The direction of the turn is indicated by the white dots on the outside of the heading arc. Here's what probably happened:You set the departure heading before you started taxi. As you moved to the departure runway, you probably made a few turns that confused the AFS a wee bit. By the time you lined up on the runway, the AFS wanted you to turn nearly 360 degrees in order to get to the heading you selected, in the direction that you turned the heading knob.The fix: Push the heading knob when you line up. That will set it to runway heading. If you were assigned a heading to fly after departure, you can then turn the heading selector in the appropriate direction.Paul

The MD11 will turn in the same direction that the heading knob was turned, even if it means turning more than 180 degrees. The direction of the turn is indicated by the white dots on the outside of the heading arc. Here's what probably happened:You set the departure heading before you started taxi. As you moved to the departure runway, you probably made a few turns that confused the AFS a wee bit. By the time you lined up on the runway, the AFS wanted you to turn nearly 360 degrees in order to get to the heading you selected, in the direction that you turned the heading knob.The fix: Push the heading knob when you line up. That will set it to runway heading. If you were assigned a heading to fly after departure, you can then turn the heading selector in the appropriate direction.Paul

When you put it that way, I can guarantee you this is exactly what happened. Me and my Boeing-experienced self need to spend a bit more quality time with the weighty tome that is the POH!Thanks. :)

LOL. The MD isn't that bad. Wait till you get into an Airbus!Paul

Brian,and should this ever happen again when airborne then you should PUSH the heading selector first before turning it again to the desired heading. If you pull the selector the AFS will just maintain the turn direction it got earlier.Regards,Markus