Something odd happened on autopilot yesterday...

Hi all,
I was flying the BAE 146 Avroliner (the red one in the gambling livery) north over the UK at 26000 ft. Air pressure was 3020mb, I was cruising at 300kts IAS on autopilot (with NAV switched on - basically the plane was flying itself 8-))
All of a sudden, the plane started swinging wildly across the sky, porpoising through 2000ft or so, and swinging through 90* left to right and more, basically it got so bad I had to disengage autopilot and drop down 10000ft before the wing stalled. Very odd.
I was using the 15min update real-life weather, it was cold and fairly windy, pressure was as I said earlier. Basically, was this just a glitch, or something I was doing wrong? As a last resort before dropping out of autopilot and descending I switched on the Yaw Dampener, but it had no effect.
Thanks for replies, I'd like to know what killed my 80 or so passengers
Cheers
Seb
I was flying the BAE 146 Avroliner (the red one in the gambling livery) north over the UK at 26000 ft. Air pressure was 3020mb, I was cruising at 300kts IAS on autopilot (with NAV switched on - basically the plane was flying itself 8-))
All of a sudden, the plane started swinging wildly across the sky, porpoising through 2000ft or so, and swinging through 90* left to right and more, basically it got so bad I had to disengage autopilot and drop down 10000ft before the wing stalled. Very odd.
I was using the 15min update real-life weather, it was cold and fairly windy, pressure was as I said earlier. Basically, was this just a glitch, or something I was doing wrong? As a last resort before dropping out of autopilot and descending I switched on the Yaw Dampener, but it had no effect.
Thanks for replies, I'd like to know what killed my 80 or so passengers

Cheers
Seb