Pins
BCAL: DC10 had a hockey stick downlock pin with a steering bypass pin on a chain - both used for pushbacks and towing. On 747 and A310 A320, used only bypass pin for pushbacks, downlock pin inserted (with open log book entry) for tows. On 1-11 - no pins for pushbacks but sys 2(?) hyd pump off during eng start, downlock pin inserted (with open log book entry) for tows.
My current co (not hard to work out who that is then):
747 - only bypass pin for pushbacks, downlock pin inserted (with open log book entry) for tows (again - we have ground use only hocky stick types)
The aircraft carry thie own full compliment of gear pins.
A340 - only bypass pin for pushbacks, downlock pin inserted (with open log book entry) for tows.
The thinking behind any company that does not require downlock pins for push backs is - manufacturers advice! and that you are primarily driving the gear in the "extend" direction during the push (okay - not when the tug is slowing the aircraft, or when a slight "pull forward abeam XYZ" is required).
A tow is a prolonged force in the direction of gear downlock "breaking" and retraction.
Paul