Temecula, CA, USA
N601KS
ZENITH Zodiac CH601XL
About seven minutes after departure, following what appeared to be an uneventful takeoff and initial climb, the airplane began a 180° turn toward the departure airport. A few minutes later, witnesses heard a loud bang, and the airplane pitched down aggressively, rolled inverted, and impacted the ground in a steep, nose-down attitude. During the descent, the pilot’s flight bag and other cabin contents fell out of the airplane, and the sound of buffeting wind noise and the pilot struggling were heard on the airport’s common traffic advisory frequency. Examination did not reveal any anomalies with the flight controls or engine that would have precluded normal operation, and all components from the airplane were found in the immediate vicinity of the impact site. There was no evidence of bird strike. The owner/builder of the airplane stated that he had once experienced the canopy opening on takeoff but was able to land safely. As a result of this event, he disabled the standard lock and installed a set of two small over-center latches, each mounted to the rear sides of the canopy frame with two soft aluminum rivets. Examination of the canopy system revealed damage signatures that appeared to indicate that the rivets of one latch had separated in shear, and the other latch had twisted away from the airframe. It is likely that the accident was initiated by the failure of the mounting rivets in one latch, which caused the canopy to partially open on one side, then twist the latch away from the other side, resulting in an open and possibly deformed canopy. The reason for the initial failure could not be determined; however, the owner of the airplane was shorter than the pilot and had raised the seat and moved it forward during construction. The modification would have resulted in the accident pilot having to lean inboard, or sit with his head tilted, to avoid touching the canopy. It is possible that the airplane encountered turbulence that caused the pilot to hit the canopy, resulting in the failure of one of the latches. Multiple instances of canopies opening in flight were reported for this airplane model. Because an open canopy disturbs airflow over the horizontal stabilizer, flight control difficulties can result in a loss of control nose-down pitching motion, often accompanied by a loud banging sound and cabin contents being sucked out, all which were observed in this accident. Although the Pilot Operating Handbook (POH) provides instructions for continued flight with an open canopy, evidence from both this and previous accidents suggests that both the nose-down motion and associated negative G-forces can be hard for pilots to maintain airplane control. The airplane’s POH suggested the installation of a secondary backup latch system, and 2 weeks following the accident, the manufacturer issued a safety alert recommending such. The accident airplane was not equipped with a secondary latch.
HISTORY OF FLIGHTOn November 23, 2021, about 1033 Pacific standard time, an experimental, amateur-built Zenith Zodiac 601XL, N601KS, was destroyed when it was involved in an accident in Temecula, California. The pilot was fatally injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. Data from an onboard Appareo Stratus GPS/ADS-B receiver showed that the airplane departed from runway 18 at French Valley Airport (F70) at 1020 and began a climbing left turn to the southeast, reaching an altitude of about 3,600 ft mean sea level (msl) about 7 minutes later. After reaching the shores of Vail Lake, 10 miles southeast, it began a 180° descending right turn to a heading of about 320° back in the direction of F70. Over the next three minutes, the airplane gradually descended from 2,800 to 2,400 ft msl, while maintaining an airspeed of about 100 knots (kts). The airplane then pitched about 60° nose-down while rolling about 90° right as it began descending at a rate that reached 9,600 ft per minute before the data ended. About that time, a witness, who was in the front yard of a residence about 3 miles southeast of F70, reported hearing a loud bang, then looked overhead to see an airplane flying to the northwest. The airplane rolled inverted while diving diagonally into the ground. After impact, debris started falling from the sky almost directly above her. Multiple other witnesses within the area of the housing development recounted similar observations of hearing a loud booming sound followed by observing an airplane dive toward the ground while debris fell from it. The FAA does not record the common traffic advisory frequency (CTAF) transmissions at F70 airport; however, CTAF audio was being recorded by a public audio streaming service at the time of the accident. The recording indicated that, shortly before 1033, a sound consistent with buffeting wind noise was captured, along with a person in distress, possibly shouting, “help.” Family members later confirmed that the recording sounded like the pilot. PERSONNEL INFORMATIONThe last entry in the pilot’s logbook was for a flight review six days before the accident, which was conducted in a Piper PA23-250. At that time, his total flight experience was 855.1 hours. Most of his recent flight experience was in the multi-engine Beech D95A airplane, and he attained his helicopter rating on September 9, 2021. His total flight experience in the accident airplane was 10.3 hours, which took place during 12 flights between December 12, 2020, and January 10, 2021. The pilot had an arrangement with the owner that he could fly the airplane at any time. The owner was not aware that he was going to fly the airplane on the day of the accident, and the reason for the flight could not be determined. AIRCRAFT INFORMATIONConstruction of the airplane was completed by the owner in 2007, and its special airworthiness certificate was issued in November of that year. The airplane was then involved in a hard landing event, which necessitated replacement of both wings and repairs to the fuselage, along with replacement of the canopy. The airplane was taken out of service in 2014 for an engine rebuild after 45 total flight hours. The rebuild was completed on September 1, 2020, along with a condition inspection. The logbooks indicated that the owner then performed a series of flights in accordance with “Phase I” flight testing, and on December 20, 2020, he documented that the airplane had accrued 54 total flight hours and was authorized for “Phase II” flight. The accident pilot then flew the airplane six more times through January 10, 2021. The Zodiac CH 601 series was the subject of an FAA Special Airworthiness Information Bulletin (SAIB) CE-10-08, dated November 7, 2009, that identified a concern with the airplane’s wing structure following a series of in-flight structural failures. To address the SAIB, the kit manufacturer provided a wing upgrade modification package. The airplane’s maintenance logbooks indicated that the modifications were accomplished in June 2012, along with the addition of aileron balance weights. Although the airplane was equipped with an autopilot, it had been disabled by the owner and had never been used. AIRPORT INFORMATIONConstruction of the airplane was completed by the owner in 2007, and its special airworthiness certificate was issued in November of that year. The airplane was then involved in a hard landing event, which necessitated replacement of both wings and repairs to the fuselage, along with replacement of the canopy. The airplane was taken out of service in 2014 for an engine rebuild after 45 total flight hours. The rebuild was completed on September 1, 2020, along with a condition inspection. The logbooks indicated that the owner then performed a series of flights in accordance with “Phase I” flight testing, and on December 20, 2020, he documented that the airplane had accrued 54 total flight hours and was authorized for “Phase II” flight. The accident pilot then flew the airplane six more times through January 10, 2021. The Zodiac CH 601 series was the subject of an FAA Special Airworthiness Information Bulletin (SAIB) CE-10-08, dated November 7, 2009, that identified a concern with the airplane’s wing structure following a series of in-flight structural failures. To address the SAIB, the kit manufacturer provided a wing upgrade modification package. The airplane’s maintenance logbooks indicated that the modifications were accomplished in June 2012, along with the addition of aileron balance weights. Although the airplane was equipped with an autopilot, it had been disabled by the owner and had never been used. WRECKAGE AND IMPACT INFORMATIONThe airplane came to rest inverted and nose down in a field. The airframe was compressed aft, such that the engine and firewall were in line with the trailing edge of the wings. Both wings sustained crush damage through to the aft spar, both fuel tanks were breached, and the smell of fuel was present in the soil surrounding the site. A 70-ft-long debris field consisting of aluminum fragments, flight instruments, and significant quantities of clear canopy acrylic shards emanated west from the main wreckage. The pilot’s flight bag, an iPad, seat cushion, sun visor, and a fuel sump jar were located about 400 ft east of the main wreckage, dispersed in the general area below the descending segment of the flight track. The flight controls and corresponding control surfaces sustained impact damage and were severely deformed and separated in multiple locations. Examination did not reveal any preimpact failures. Similarly, the fuel system sustained multiple breaches, but all fittings were tight, and the fuel selector valve appeared to be in the right tank position. A significant quantity of canopy fragments were dispersed west of the initial impact point. Remnants of the canopy frame were comingled with the main wreckage. The canopy sides remained attached to the rear bow, and the forward bow had broken away from the left side structure. The engine sustained extensive impact damage, detaching sections of the intake manifold and most accessories. The firewall had formed around the rear of the engine. There was no evidence catastrophic internal engine failure or oil leak. The propeller hub remained attached to the crankshaft, and both composite propeller blades had detached at their roots. One blade exhibited leading edge knicks, dents, and chordwise scratches consistent with rotation at impact. The other blade was bent about 6 inches from the root, but otherwise intact. Both a ground and overhead drone search of the area below the flight track leading up to the initial upset did not reveal any other cabin contents, airplane parts, or canopy material. TESTS AND RESEARCHThere was no evidence of bird strike to any of the airframe structure. Samples recovered from windshield fragments, both propeller blades, and the vertical and horizontal stabilizer were examined by specialists from the Smithsonian Institution’s Feather Identification Lab using DNA and microscopic analysis. None of the samples contained bird material. Canopy The airplane was equipped with a forward hinging, tip-up canopy that comprised an aluminum and steel frame structure and an acrylic bubble with a thickness ranging between 1/16 and 1/8 inch. Gas struts supported the canopy when open, and the original design used an automotive-style latch within the frame that locked into a striker-pin on either side of the cabin sidewall canopy sill. The airplane’s pre-flight inspection section of the Pilot Operating Handbook (POH), dated March 2010 (revision) 2, stated: Check that your canopy closes and latches properly on both sides. If in doubt, add a secondary latching system as recommended by the Australian CAA. Zenair Ltd, published the “MANDATORY ACTION – SAFETY ALERT” document on December 6, 2021, about two weeks after the accident. The alert documented a series of events where canopies had opened in flight and recommended the installation of a secondary canopy latch. The alert referenced the “Recreational Aircraft Airworthiness Notice AN 070109-Issue 1” issued by Recreational Aviation Australia in January 2009. This notice documented the compulsory fitment of a secondary canopy locking device on Zodiac/Zenair/Zenith aircraft models fitted with a forward hinging canopy. AN 070109-1 stated that the canopy was of relatively light construction, and was prone to distortion during flight, which can cause the latches to release. It also revealed that the locking mechanism can be latched without adequately locking the canopy. It cited reports where the canopy had opened in flight, and while those airplanes remained capable of flight, a speed or power reduction resulted in increased turbulent airflow over the elevators and a sudden nose-down attitude. FAA regulations do not mandate compliance with safety alerts, nor are there provisions for issuing airworthiness directives to experimental airplanes. The NTSB has investigated seven accidents that occurred after the canopies of Zenith 600 series airplanes opened in flight. Review of international accident reports, along with various Zenith internet forums, also revealed that multiple pilots had encountered similar events. The openings all resulted in control difficulties in flight, often leading to high negative G-forces, aggressive nose-down pitch movements, and cabin contents being sucked out of the airplane. The owner of the accident airplane stated that the canopy had once opened during takeoff. It was accompanied by a very loud bang sound, and then loud wind noise as the flight progressed. The canopy opened to about 6 inches, and he was able to maintain aircraft control and return to the airport to land. He stated that, following that event, he disabled the airplane’s standard lock by removing the striker-pins mounted on the canopy sill. He then installed a lock that consisted of two 2 ½-inch-long, over-center latches mounted to the rear of the canopy frame. He did not install a secondary latch. The canopy over-center latches installed by the owner were held in place with two 1/8 inch aluminum blind rivets per side. Both latches had separated from the airframe and were found with the main wreckage. The canopy latch hooks remained attached to the sides of the rear canopy structure. For one latch, the 7/32 inch head of the blind rivet was still in place and appeared to have sheared from the rivet shank, which was not located. The other rivet was missing. The inboard side of the over-centering arm and the corresponding threaded portion of the hook exhibited scratches and paint transfer marks. The mating side of the mounting plate exhibited scratches and grooves in the vertical plane (canopy tilt direction), that were not present on latch the second latch. Both rivets were missing from second latch. Its over-centering arm had deformed inward, and its mounting plate was twisted. The owner stated that, because of his height, he moved the seat 4 inches forward and raised it by 2 inches to enhance forward visibility, and that during turbulence, his headset often touched the canopy. He surmised that the pilot, who was 8 inches taller, would have needed to lean inboard to avoid touching the canopy. He further stated that turbulence was not uncommon in the accident area. The POH contained a section entitled “Canopy Opening in Flight,” which stated: -Concentrate on flying the airplane. -REDUCE SPEED TO 60 KNOTS -RAISE FLAPS -Ignore the canopy and wind noise -Fly a normal approach and landing without flaps, including completing the landing checklist. -The canopy will remain raised in an open position about 1 foot -If the canopy opens after lift-off, do not rush to land. Climb to normal traffic pattern altitude, fly a normal traffic pattern, and make a normal landing. -Do not release the seat belt and shoulder harness in an attempt to reach the canopy. Leave the canopy alone. Land as soon as practicable and close the canopy once safely on the ground. -Do not panic. Try to ignore the unfamiliar wind. Also, do not rush. Attempting to get the airplane on the ground as quickly as possible may result in steep turns at low airspeeds and altitude. -Complete all items on the landing checklist. -Remember that accidents are almost never caused by an open canopy. Rather, an open canopy accident is caused by the pilot's distraction or failure to maintain control of the airplane.
The failure of the airplane’s canopy latch system, which resulted in the canopy opening in flight and a loss of airplane control. Contributing to the accident was the lack of a secondary canopy latch as recommended by the kit manufacturer.
Source: NTSB Aviation Accident Database
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