Narrative:

I was performing the first leg of a ferry of an L-39 aircraft. The preflight and strap in was performed individually by both myself and my back-seater; a company mechanic; while the aircraft was still in the hangar. I had us close both canopies in the hangar shade to ensure we had the cockpit to cockpit volume set correctly before we were pulled out to the ramp for a dry start to ensure proper oil service. The oil service level was verified by FBO personnel and after being given the thumbs up; I continued the start with the APU still running. Subsequent after start checks and engine run ups were uneventful. Takeoff and initial climb seemed normal; but in retrospect the noise level in the aircraft was probably higher that normal. I attributed the increase noise level due to not wearing my earplugs as is my normal habit pattern. Climbing through 10;000 ft I observed a cabin altitude warning and notified the mechanic. I checked the canopy handle; the canopy unlock light; the bleed switch; the ecs and cabin pressure switch; and they were all normal. I reset the cabin pressure lever which depressurized the canopy seal. The canopy immediately rose about 4 inches on the left side and was still attached on the right side. I asked the mechanic to take the aircraft and I pulled down on the canopy with both hands. It came down about 2 inches and then separated from the aircraft. I took back control of the aircraft; started a descent and turn back to the departure airport and declared an emergency. I asked ATC to mark my position so that I would know the approximate position of the canopy. The engine and aircraft were running fine and I made an uneventful landing. The aircraft was secured and impounded pending an investigation. I received the coordinates and time of the incident after landing. I believe the cause of this incident was due to improper locking of the canopy. Although the canopy lock handle was locked and canopy unlock light was out; the canopy was not locked properly. The company is currently doing an investigation.

Related reports:

Google
 

Original NASA ASRS Text

Title: A L-39 Canopy departed in flight climbing though 11;000 FT with air conditioning and indicating systems operating normally.

Narrative: I was performing the first leg of a ferry of an L-39 aircraft. The preflight and strap in was performed individually by both myself and my back-seater; a company Mechanic; while the aircraft was still in the hangar. I had us close both canopies in the hangar shade to ensure we had the cockpit to cockpit volume set correctly before we were pulled out to the ramp for a dry start to ensure proper oil service. The oil service level was verified by FBO personnel and after being given the thumbs up; I continued the start with the APU still running. Subsequent after start checks and engine run ups were uneventful. Takeoff and initial climb seemed normal; but in retrospect the noise level in the aircraft was probably higher that normal. I attributed the increase noise level due to not wearing my earplugs as is my normal habit pattern. Climbing through 10;000 FT I observed a cabin altitude warning and notified the Mechanic. I checked the canopy handle; the canopy unlock light; the bleed switch; the ECS and cabin pressure switch; and they were all normal. I reset the cabin pressure lever which depressurized the canopy seal. The canopy immediately rose about 4 inches on the left side and was still attached on the right side. I asked the Mechanic to take the aircraft and I pulled down on the canopy with both hands. It came down about 2 inches and then separated from the aircraft. I took back control of the aircraft; started a descent and turn back to the departure airport and declared an emergency. I asked ATC to mark my position so that I would know the approximate position of the canopy. The engine and aircraft were running fine and I made an uneventful landing. The aircraft was secured and impounded pending an investigation. I received the coordinates and time of the incident after landing. I believe the cause of this incident was due to improper locking of the canopy. Although the canopy lock handle was locked and canopy unlock light was out; the canopy was not locked properly. The company is currently doing an investigation.

Data retrieved from NASA's ASRS site as of July 2013 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.