A STUDENT PLT IN A PA28-181 ENCOUNTERED A STORM GRATE WHILE TAXIING AT LWS WITH HIS CFI. UNBEKNOWNST TO BOTH PLTS; THE NOSE GEAR SUNK INTO THE GRATE CAUSING A PROP STRIKE.

Narrative

ON APR/XA/00; AT OR ABOUT XA30 AM LCL TIME; THE RENTED PIPER ARCHER THAT I WAS RECEIVING DUAL INSTRUCTION IN; STRUCK AN UNMARKED TXWY HAZARD; CAUSING MINOR DAMAGE. MY INSTRUCTOR AND I HAD JUST LANDED AFTER A BRIEF JAUNT TO THE LCL PRACTICE AREA. FOLLOWING THE LNDG; WE TAXIED OUT FROM THE ACTIVE RWY 11 ON TXWY E. WHILE WE WERE TAXIING; THE NOSEWHEEL OF THE AIRPLANE SUNK INTO TO A STORM GRATE. THIS STORM GRATE WAS IN THE BOTTOM OF AN APPROX 6 INCH DEEP DEPRESSION IN THE BLACKTOP. THE GRATE AND THE DEPRESSION WERE IN THE MIDDLE OF THE TXWY AND WERE COMPLETELY UNMARKED. AS SUCH; IT WAS COMPLETELY INVISIBLE. THE PROP STRIKE WAS A MINOR ONE -- WE EVEN FLEW AROUND THE PATTERN AGAIN; UNAWARE THAT IT HAD HAPPENED. AT THE OTHER ARPTS; I'VE FLOWN OUT OF (RNT; BFI; 536; PUW); SUCH HAZARDS ARE CLRLY MARKED; USUALLY WITH ORANGE OR YELLOW PAINT. THIS HAZARD COULD BE SIMILARLY MARKED; AND AT MINIMAL COST OR THE HAZARD COULD SIMPLY BE REPAIRED. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THAT HE HAD NOT FLOWN IN SEVERAL MONTHS. HE REVEALED THAT THIS CFI DID NOT SEEM COMFORTABLE WITH TOUCH AND GOES AND INSISTED THAT THEY MAKE FULL STOPS AND TAXI BACK FOR EACH TKOF. AFTER THEY HAD LANDED ON RWY 11; THEY EXITED AT TXWY E; WHICH HE DESCRIBED AS A HIGH SPD TXWY. IN THE RPTR'S OPINION; THERE WAS FRESH BLACKTOP ON TXWY E AND THE GRATE WAS DEPRESSED INTO THE BLACKTOP BY APPROX 8 INCHES. HE DESCRIBED THE DAY AS SUNNY AND THAT THE RADIATION COMING UP FROM THE BLACKTOP WAS CAUSING AN ILLUSION THAT CAMOUFLAGED THE DEPRESSION SO THAT IT WAS INDISCERNIBLE. AT FIRST; THE RPTR AND HIS CFI DID NOT KNOW THERE HAD BEEN DAMAGE DONE TO THE AIRPLANE. THEY TOOK OFF AGAIN AND LATER THE CFI DECIDED TO MAKE A FULL STOP TO INSPECT THE PROP. THEY FOUND THAT THE PROP WAS BENT APPROX 1 INCH. DURING THEIR TRIP AROUND THE PATTERN; THEY DETECTED NO VIBRATION NOR WERE THERE ANY COCKPIT INDICATIONS OF A PROB. THEY NOTIFIED ARPT MGMNT AND ARE EXPECTING REIMBURSEMENT FOR THE DAMAGE THEY INCURRED.