ACR LTT PF HIT FLAP SWITCH ON APCH CAUSING FLAPS TO RETRACT TO TKOF POSITION RESULTING IN ILLEGAL LNDG.

Narrative

AT 500' DURING APCH TO LAND THE CAPT REQUESTED STAND IFR CALLS. I MADE THE STANDARD CALLS AS OUR BEFORE LNDG CHK WAS COMPLETE (FLAPS WERE SET TO 50 DEGS). AFTER I CALLED 'DECISION HEIGHT--RWY IN SIGHT;' THE ACFT BEGAN TO RAPIDLY SINK. I CALLED 'WIND ;' AS I NOTICED THAT THERE WAS NO REAL SIGNIFICANT LOSS OF AIRSPD ON FINAL. THE CAPT CONTINUED THE APCH AND LANDED THE ACFT WITH A VERY NOSE HIGH ATTITUDE AND HIGH PWR SETTING. SEVERAL ACFT WERE ON APCH BEHIND US SO THE CAPT RPTED A 20 KT WINDSHEAR OVER THE RWY THRESHOLD. ACCORDINGLY; THE TWR ISSUED WINDSHEAR ADVISORIES ON ATIS. AFTER WE PARKED AT THE GATE THE CAPT ADMITTED THAT THIS HAD HAPPENED TO HIM SEVERAL DAYS EARLIER AT ANOTHER ARPT. I VERIFIED THAT I HAD VISUALLY CONFIRMED THE FLAPS AT 50 DEGS AS I ALWAYS DO BEFORE CALLING 'BEFORE LNDG CHK COMPLETE.' THE CAPT THEN ADMITTED THAT HE MUST HAVE ACCIDENTALLY HIT THE FLAP SWITCH WHILE MANUALLY TRIMMING THE ACFT TO LAND. THE CAPT CALLED THE TWR AND RPTED THAT 'ONE OF US;' MUST'VE HIT THE FLAP SWITCH AND WE DID NOT LAND WITH FULL FLAPS. WE ARE NOT APPROVED FOR ANY OTHER THAN FLAP 50 DEGS (FULL) LNDGS. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING: ON THIS MODEL LTT; THE FLAP SWITCH IS A SPRING LOADED TOGGLE TYPE WITH 3 POS--UP; 20 DEGS FOR TKOF AND FULL DOWN; 50 DEGS FOR LNDG. THE SWITCH IS LOCATED ON THE AFT CENTER PEDESTAL RIGHT NEXT TO THE TRIM CONTROLS FOR THE AILERON AND RUDDER AND VERY EASY TO HIT WHEN ADJUSTING THE TRIM. RPTR FEELS IT IS A BAD LOCATION AND THE SWITCH IS A BAD DESIGN AS IT DOES NOT HAVE A VERY POSITIVE DETENT AND IS CHEAPLY CONSTRUCTED.