What was found
AFTER DEPARTURE VMO NEVER EXCEEDED 260 KTS CAUSING RETURN TO E WR. FOUND S591 ALTERNATE VMO/MMO SWITCH IN THE "ALTN" POSITION. POSITIONED SWITCH TO "NORM" AND LOCKWIRED. AIR SPEED NOW CHECK GOOD UP TO 420 KNOTS ,ALSO PERFORMED LOW LEVEL LEAK CHECKS ALL GOOD OK TO CONTINUE.RE CHECKED SWITCH S591 SWITCH N VERIFED ITS IN NORMAL N LOCK WIRED PERFORMED PITOT -STATIC CHECK AS PER AMM 34-11-00-862-045 ALL ALSO C/W TASK 34-12-00-715-001. OPERATIONAL TEST-AIR DATA COMPUTING SYSTEM. A/C OK FOR SERVICE.