COMMUTER SMT RWY EXCURSION DURING TKOF. TKOF ABORT RETURN TO BLOCKS ACFT DAMAGED.

Narrative

DURING A WATER AUGMENTED TKOF THE ACFT DEPARTED THE RWY ON THE LEFT SIDE AFTER AN UNCONTROLLED SWERVE LEFT WHICH DEVELOPED AFTER 50 KTS AIRSPD DURING THE TKOF ROLL. ALTHOUGH THERE WERE NO SUSPICIONS OF ANY ACFT NOSEWHEEL STEERING MALFUNCTION I CONSIDER THE ONLY POSSIBLE REASON FOR THIS RWY INCIDENT IS THAT SOMETHING IS NOT PROPERLY DESIGNED OR ALWAYS PREDICTABLE IN THE STEERING SYS. SUBSEQUENT MAINT INVESTIGATION OF THE NOSE STEERING/CASTERING SYSTEMS APPEARS TO INDICATE NO DISCREPANCY. THE ACFT HAD BEEN WRITTEN UP SOME DAYS BEFORE AS HAVING AN ERRATIC NOSE STEERING PERFORMANCE. THE NORMAL METHOD OR PROC OF OPERATION SHOULD BE REVIEWED AS THE STEERING SYS IS UNNECESSARILY COMPLICATED WITH A SWITCH ON THE LEFT PWR LEVER. A SWITCH IN THE RIGHT SPD LEVER 2 ANNUNCIATOR LIGHTS AND SEVERAL MORE ON THE CONTROL PANEL. THIS MISHAP I BELIEVE WOULD NOT HAVE HAPPENED IF THE NOSE WHEEL STEERING WERE NOT USED ABOVE NORMAL TAXI SPDS. AS PREVIOUSLY DONE WITH THE EARLIER MODELS. AFTER THIS INCIDENT WHICH ENDED WITH THE ACFT DEPARTING THE RWY WITH THE LEFT MAIN GEAR AND RETURNING TO THE PAVEMENT WITH NO INDICATION OF ANY DAMAGE. THE STEERING WAS NOTED TO BE OK FOR TAXI BACK TO THE TERMINAL AND THIS WAS DONE. UPON SHUTDOWN THE LEFT PROP WAS DISCOVERED TO HAVE TIP DAMAGE PLUS THE UNDERSIDE OF RIGHT NACELLE HAD SOME SHRAPNEL DAMAGE IN 2 SMALL PLACES. THE BULK OF CONCERN TO DATE IS THAT I SHOULD HAVE EVACUATED THE PAX RATHER THAN RETURN TO THE TERMINAL. I WOULD LIKE SOMEONE TO GET THE PROCS/OR HARDWARE CHANGED SO THE SITUATION DOESN'T HAPPEN AGAIN. SUPPLEMENTAL INFO FROM ACN 98110: TO SAVE TIME; THE CAPT DECIDED TO USE RWY 2R. AT 40% TORQUE; THE CAPT CALLED FOR THE AWI SYS TO BE TURNED ON. BOTH TORQUE METERS READ APPROX 40%. WHEN I MOVED THE SWITCH TO ON; I GOT THE 2 AWI PUMP LIGHTS AND A RISE IN BOTH TORQUE METERS TO ABOUT 70%. THESE INDICATIONS ARE NORMAL. I FOLLOWED THE CAPT THROUGH ON THE PWR LEVERS. TKOF PWR WAS TO BE 107%. AS BOTH TORQUE METERS PASSED ABOUT 90% I FELT THE CAPT RETARD BOTH PWR LEVERS TO FLT IDLE.