Below is the list of tables from the database along with their columns and datatype. Need to generate an accurate SQL query for the question.
Only use the columns present in the respective table. Only use the columns which are required to generate the SQL query. Only use table joins if required and not otherwise.

### Tables ###
TABLE: CREATE TABLE airport_aircraft ( Aircraft_ID VARCHAR, Airport_ID VARCHAR )
TABLE: CREATE TABLE aircraft ( Aircraft_ID VARCHAR, Aircraft VARCHAR )
TABLE: CREATE TABLE airport ( Total_Passengers INTEGER, Airport_ID VARCHAR )

### Question ###
What is the average total number of passengers of airports that are associated with aircraft 'Robinson R-22'?

### Accurate SQL ###

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"