A300
Flight Crew Air Transport Pilot (ATP)
Troubleshooting; Situational Awareness; Confusion
Aircraft Equipment Problem Critical
Flight Crew Returned To Departure Airport; General Maintenance Action
Aircraft
On takeoff; unable to retract gear.  Selected 2nd system; gear retracted.  Then; multiple failures occurred: CAPT ADC; CAPT F/D; AT System; Transponder 1&2; Pitch Trim #1; etc...  Captain gave aircraft to me to fly while he discussed with Maintenance.  ATC stated that our destination airport would not accept aircraft without operable transponder.  Therefore; we returned to the departure airport without incident.
The Reporter stated that the second system selector is call Position System Selector 1 or 2. He did not know for certain what caused the gear retraction failure but he suspected an air ground switch failure.
An A300 landing gear would not retract after takeoff until the Landing Gear Position Detector System 2 was selected. Then with gear retraction; the #1 ADC; #1 Flight Director; the autothrottle system and both transponders failed so the flight returned to the departure airport.