Thanks,
So it looks like every FAR 25 aircraft is required to have surge tanks.
I see from the ATR-42 manual that they follow the regulation for 2%...."An additional volume in each tank allows a 2% thermal expansion of fuel without spillage."
It would be interesting to know if there are surge tanks on an of the non-FAR 23 aircraft. I wonder how it worked for the large piston airliners back in the day.