What was found
LEVEL AT FL 340, BOTH CA & FO STBY AIRSPEED INDICATORS INDICATED 125 KTS. BOTH CA & FO PRIMARY A/S IND. ON EFIS INDICATED 275 KTS. TAS 470 KTS. TAT -12. VMC CONDITIONS. APPROX 40 MINUTES LATER, WITH NO CHANGE IN CONDITIONS, BOTH STBY A/S IND. RETURNED TO NORMAL, MATCHING PRIMARY A/S INDICATORS. PERFORMED CAPTAINS AND FIRST OFFICERS STANDBY AIRSPEED BACK FLUSH PROCEDURE WITH DRY NITROGEN AS PER M/M 34-10-00-03 PROCEDURE C - [1] A & B . RECONNECTED PRESSURE LINES. SYSTEM NEEDS PITOT STATIC VERIFICATION WITH TEST SET. TEST SET BORROWED FROM HANGAR AVIONICS DEPT.