LOW WINGED SMA ACROBATIC TYPE ACFT LOSES ITS CANOPY DURING DSCNT AFTER ACROBATICS.

Narrative

DEPARTING THE AEROBATIC PRACTICE AREA; WHILE IN A WINGS LEVEL DSCNT; MY ACFT EXPERIENCED COMPLETE; SUDDEN DEP OF THE CANOPY. AFTER ASCERTAINING THAT NO DAMAGE TO THE ACFT WAS VISIBLE OR OTHERWISE APPARENT; AND AFTER DOING A LOW- SPD LNDG CONFIGN CTLABILITY CHK; I ATTEMPTED TO DETERMINE THE CAUSE OF THE LOSS OF THE CANOPY. (AIRSPD AT THE TIME OF LOSS WAS APPROX 170 KIAS; VNE IS 235). A SERIES OF RETRACTABLE METAL PINS HOLD THE SLIDING CANOPY TO BOTH SIDES OF THE FUSELAGE; AND WHEN FULLY CLOSED THE CANOPY IS LOCKED WITH A LATCH AT ITS TOP FORWARD CTR PART (WHICH SECURES IT TO THE WINDSCREEN FRAME). THE CANOPY CAN BE JETTISENED BY PULLING ONE OF THE 2 EMER RELEASE HANDLES; WHICH RETRACT THE SECURING PINS FROM THE CANOPY RAILS. THE 2 EMER HANDLES ARE LOCATED ON THE OUTBOARD SIDES OF THE COCKPIT; JUST AFT OF THE RUDDER PEDALS. THEY NORMALLY ARE SAFETY-WIRED FORWARD TO THE LOCKED POS. AFTER THE CANOPY DEPARTED; I FOUND THE CANOPY RAIL PINS TO BE HALFWAY RETRACTED; ALTHOUGH IT APPEARED THE RELEASE HANDLES WERE IN THE FORWARD (LOCKED POS; AS THEY HAD APPEARED PRE-TKOF). HOWEVER; AFTER MARKING AN UNEVENTFUL LNDG; I FOUND THAT THE EMER RELEASE HANDLES (WHICH ARE CAMMED TOGETHER) WERE INDEED PARTIALLY MOVED TOWARD THE AFT UNLOCKED POS; WITH THE SAFETY WIRE BROKEN. THE TRUE CAUSE OF THE RELEASE HANDLES BEING PARTIALLY ACTUATED IS UNKNOWN TO ME. A POSSIBLE CAUSE IS THAT A PAX ON ONE OF SEVERAL RECENT FLTS MAY HAVE INADVERTENTLY CAUGHT THEIR FOOT ON THE LEVER ON THEIR SIDE. IT IS POSSIBLE THAT I MAY HAVE DONE THE SAME THING ON MY SIDE; DURING THE AEROBATICS. IN THE FUTURE I WILL EMPLOY HEAVIER GAUGE SAFETY WIRE; CAUTION PAX ABOUT THIS POSSIBILITY; AND BE MORE AWARE OF MY OWN FOOT POS DURING FLT. BY THE WAY; THE CANOPY DEPARTED OVER RUGGED MOUNTAINOUS TERRAIN WHICH APPEARED DESERTED. IT HAS NOT BEEN RECOVERED.