A unit is unloaded?

there is a event for 'a unit is loaded into a transport' but is there one for unloaded?
if there isn't, how would i find a unit that has been unloaded?

Example
Events
Unit - A unit Is issued an order targeting an object
Conditions
(Issued order) Equal to (Order(unload))
(Issued order) Equal to (Order(Goblin Zeppelin))
Actions
Do nothing



the condition thing is under: "Order Comparison"

^^