Narrative:

Departing the aerobatic practice area, while in a wings level descent, my aircraft experienced complete, sudden departure of the canopy. After ascertaining that no damage to the aircraft was visible or otherwise apparent, and after doing a low- speed landing confign ctlability check, I attempted to determine the cause of the loss of the canopy. (Airspeed at the time of loss was approximately 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 center part (which secures it to the windscreen frame). The canopy can be jettisened by pulling one of the 2 emergency release handles, which retract the securing pins from the canopy rails. The 2 emergency 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 position. 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 position, as they had appeared pre-takeoff). However, after marking an uneventful landing, I found that the emergency release handles (which are cammed together) were indeed partially moved toward the aft unlocked position, 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 passenger 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 passenger about this possibility, and be more aware of my own foot position during flight. By the way, the canopy departed over rugged mountainous terrain which appeared deserted. It has not been recovered.

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Original NASA ASRS Text

Title: 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.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.