The autopilot was not at fault in the level off.
It was the trim system which was slow to react, so the 'frame would climb slightly above alt and eventually find itself back to datum.
The easy way of overcoming this was to use the trim wheel gently in the nose down direction during altitude acquire, until the mini indicator showed it was in trim.
Problem solved without expensive mods!
Yes, it had was known as 5 APUs in close formation, but I had the pleasure of hearing the relieved comments from SLF counting the "donks" as they boarded, in the weeks following the tragic Kegworth accident.
A great plane to start ones airline career, simple unsophisticated auto system which had to be watched, thereby inculcating a way of operating which stood me in good stead when subsequently I became "Boeing'd".............
