SELECT avg(T3.Total_Passengers) FROM aircraft AS T1 JOIN airport_aircraft AS T2 ON T1.Aircraft_ID  =  T2.Aircraft_ID JOIN airport AS T3 ON T2.Airport_ID  =  T3.Airport_ID WHERE T1.Aircraft  =  "Robinson R-22"
What is the average total number of passengers for all airports that the aircraft "Robinson R-22" visits?
SELECT avg ( T3.Total_Passengers ) FROM aircraft AS T1 JOIN airport_aircraft AS T2 ON T1.Aircraft_ID = T2.Aircraft_ID JOIN airport AS T3 ON T2.Airport_ID = T3.Airport_ID WHERE T1.Aircraft = `` Robinson R-22 ''
select avg ( t3 . total_passengers ) from aircraft as t1 join airport_aircraft as t2 on t1 . aircraft_id = t2 . aircraft_id join airport as t3 on t2 . airport_id = t3 . airport_id where t1 . aircraft = value
What is the average total number of passengers for all airports that the aircraft `` Robinson R-22 '' visits ?