B737-300 CREW DISCOVERED 'A' FLT CTL HYD PRESSURE WARNING LIGHT ILLUMINATED. PRESSURE OK. DEFERRED PER MEL. INFLT; GOT FEEL DIFFERENTIAL LOW PRESSURE WARNING LIGHT. CREW ELECTED TO DIVERT.

Narrative

FLT TAXIED OUT ON 1 ENG (#2). FO STARTED #1 ENG WHILE ON TXWY E. WHILE PERFORMING THE AFTER START FLOW; FO NOTICED LOW PRESSURE LIGHT (A FLT CTL) WAS ILLUMINATED. CAPT CALLED FOR TAXI CHK. THE FLOW AND CHKLIST WERE COMPLETED; NOTING THAT THE FLT CTL LIGHT REMAINED ILLUMINATED AFTER RECALL; THEN IT WAS CANCELED. TAXIED TO CARGO RAMP; CAPT SET BRAKES. CAPT POSITIONED 'A' FLT CTL SWITCH TO STANDBY RUDDER (STANDBY RUDDER CHKED GOOD); CHKED HYD QUANTITY AND PRESSURES (BOTH NORMAL). READ THROUGH THE AMBIGUOUS AND MISLEADING MEL 27-5 CONDITION 1 AND CONCLUDED IT WAS A FALSE INDICATION. CALLED MAINT CTL TO VERIFY COMPLIANCE AND GOT THE OK TO GO BY BOTH MAINT AND DISPATCH. CAPT WAS THE PF. AFTER TKOF AT 3000 FT; AFTER FLAP RETRACTION; THE ACFT ROLLED TO ONE SIDE THEN THE OTHER (BTWN 20-30 DEGS EACH DIRECTION). VERY SIMILAR TO WAKE TURB FROM A HVY ACFT; BUT THERE WAS NO HVY JET IN FRONT OF US. CAPT STATED THAT THE FLT CTLS DID NOT FEEL RIGHT. FO AND CAPT LOOKED UP AND NOTICED THAT NOT ONLY WAS THE LOW PRESSURE LIGHT ILLUMINATED BUT THE FEEL DIFFERENTIAL LIGHT WAS ON AS WELL. AT THIS TIME; CAPT MADE THE DECISION TO RETURN TO ZZZ. FO NOTIFIED ATC THAT A RETURN TO ZZZ WAS NECESSARY FOR A PRECAUTIONARY LNDG. THE APCH AND LNDG WAS UNEVENTFUL. WT AND RATE OF DSCNT WAS NOTED FOR THE OVERWT LNDG.