CZECH SPORT AIRCRAFT SportCruiser

Full Narrative

HISTORY OF FLIGHTOn August 2, 2023, about 1036 Pacific daylight time, a Czech Sport Aircraft SportCruiser, N384SC, was destroyed when it was involved in an accident in Van Nuys, California. The flight instructor and student pilot were fatally injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 instructional flight.
 
ADS-B flight track data revealed that the airplane initially departed runway 16L at the Van Nuys Airport (VNY), Van Nuys, California, about 1021:33. The airplane then entered the left traffic pattern and performed a touch-and-go landing at 1027:39. The airplane entered the left traffic pattern again, following a similar flight path as before (see figure 1). The airplane touched down about 1033:57 and then became airborne about 1,700 ft down the runway, in nearly the same place as the previous takeoff. After a 14-second gap in the data, the flight path continued above taxiway K, and the ground speed decreased from 60 to 50 kts. The flight path continued at that speed and the altitude increased.
 

Figure 1. Accident flight path (magenta) and previous circuits in the traffic pattern (purple, green).

At 1035:09, the airplane made a left turn onto the crosswind leg of the traffic pattern while climbing to an altitude of about 315 ft agl. The airplane then turned to the downwind leg; these turns were conducted closer to the runway and at a lower altitude than in the first two takeoffs. After a 15-second data gap, the airplane’s track continued at 1035:42, with a ground speed of 71 knots and an altitude of 430 ft agl; this marked the highest altitude attained during this flight segment.
 
The airplane turned left toward the airport while the altitude gradually decreased. Around 1036:12, about 830 ft from the runway, the airplane made a slight right turn to parallel the runway. About 22 seconds later, abeam the runway 16L threshold, the airplane was traveling at a ground speed of about 55 kts. The airplane then turned left at an altitude of about 195 ft agl. The last flight track data point was recorded at 1036:39 and located 255 ft east-northeast of the accident site; it showed an altitude of 170 ft agl.
 
Numerous security cameras captured footage of the airplane's movements leading up to the impact. After the airplane turned onto the downwind leg of the traffic pattern for runway 16L, it maintained a steady altitude. Around 1035:42, the airplane performed a complete 360° turn, during which it fluctuated in altitude. (The time and location of this turn corresponded to a gap in the ADS-B track data.) Toward the end of the turn, the airplane climbed. The airplane briefly flew toward the runway, descending before turning to fly parallel to the runway (see figure 2 below).
 

Figure 2. ADS-B flight track (bottom) and composite image of flight path (top). (Composite image source: Jet Aviation video footage.)

At 1036:35, the airplane initiated a left bank that steepened aggressively. As the bank angle increased, the nose of the airplane dropped. The airplane impacted the ground in a near-vertical attitude; the parachute did not deploy, and the flaps appeared to be retracted (see figure 3). 


Figure 3. Composite image of airplane attitude before impact. (Source: Helinet video footage.)
 
The pilots were in communication with the Van Nuys airport traffic control tower during the flight. The exact times of the audio transmissions could not be verified and are estimated to the minute. The student pilot was making the transmissions for the beginning portion of the flight. On the third takeoff, around 1735, the flight instructor said to the controller, “we are having some power loss.” The controller asked if they required assistance. The instructor stated, “priority landing,” which he repeated several times. About 30 seconds following the transmission indicating a "power loss," the controller issued a clearance for the airplane to land on runway 34R. This runway corresponds to the departure runway, but in the opposite direction.
 
The controller asked again if the pilot required assistance, and the instructor replied, “negative, we are landing right now.” About one minute following the transmission indicating a "power loss," the controller issued a clearance that the airplane could land on any runway. About 10 seconds later, the controller asked what the nature of their emergency was, to which the instructor responded, “we are having exhaust gas temperature issues.” AIRCRAFT INFORMATIONA review of engine logbooks revealed that the last maintenance performed was a 100-hour inspection on July 30, 2023, at a tachometer time of 925.0 hours. The engine was built in October 2014 and started regular operation in 2018.

No maintenance was conducted on the engine between February 2021 and February 2023. On January 19, 2021, at a tachometer time of 565 hours, the carburetor floats were replaced, in compliance with a service bulletin. No logbook entries indicated any further maintenance on either of the carburetors prior to the accident. The engine manufacturer stated that the carburetor piston slides would not have been removed as part of the service bulletin.

According to the airplane’s pilot’s operating handbook, at the maximum takeoff weight of 1,320 lbs and an estimated bank angle of 30°, the stall speed would be about 38 knots indicated airspeed, with 270 ft of altitude loss during recovery.


Avionics

The airplane was equipped with a Dynon Skyview system and one Dynon SV-D1000 screen, both of which were burned beyond the possibility of recovering any non-volatile memory. The Dynon alert system provides non-flightpath alerts through a flashing Alert Notification Indicator. This indicator flashes red for warnings, yellow for cautions, and gray for messages.

In the event of high EGT in the red range, the system is designed to display a flashing red warning. If audio alerts have been activated in the setup menu, it will also audibly alert the pilot in their headset with the phrase “EXHAUST GAS TEMPERATURE.” The EGT red range is configured by the airframe manufacturer to start at 1,616°F, which is the maximum EGT for the engine.

Carburetors

The engine was equipped with two Bing constant depression carburetors. The cross-draft butterfly valve carburetors had a variable venturi and a double float system arranged centrally, below the venturi. The variable venturi is actuated by a carburetor piston, which is suspended on a rubber diaphragm and protrudes into the venturi throat. The piston adjusts the smallest cross-section ("air funnel") of the venturi, using vacuum controlled by the position of the throttle valve.

In the Rotax Heavy Maintenance Manual procedure for assembling the carburetor, under "Insert Diaphragm," Step 1 notes, “The index tabs on the diaphragm must fit into the indentation of the carburetor piston.” Step 2 notes, “The position is determined via the index tabs of the diaphragm.” A highlighted notice also states, “While installing the chamber top be careful not to turn the carburetor piston assy. out of position.” AIRPORT INFORMATIONA review of engine logbooks revealed that the last maintenance performed was a 100-hour inspection on July 30, 2023, at a tachometer time of 925.0 hours. The engine was built in October 2014 and started regular operation in 2018.

No maintenance was conducted on the engine between February 2021 and February 2023. On January 19, 2021, at a tachometer time of 565 hours, the carburetor floats were replaced, in compliance with a service bulletin. No logbook entries indicated any further maintenance on either of the carburetors prior to the accident. The engine manufacturer stated that the carburetor piston slides would not have been removed as part of the service bulletin.

According to the airplane’s pilot’s operating handbook, at the maximum takeoff weight of 1,320 lbs and an estimated bank angle of 30°, the stall speed would be about 38 knots indicated airspeed, with 270 ft of altitude loss during recovery.


Avionics

The airplane was equipped with a Dynon Skyview system and one Dynon SV-D1000 screen, both of which were burned beyond the possibility of recovering any non-volatile memory. The Dynon alert system provides non-flightpath alerts through a flashing Alert Notification Indicator. This indicator flashes red for warnings, yellow for cautions, and gray for messages.

In the event of high EGT in the red range, the system is designed to display a flashing red warning. If audio alerts have been activated in the setup menu, it will also audibly alert the pilot in their headset with the phrase “EXHAUST GAS TEMPERATURE.” The EGT red range is configured by the airframe manufacturer to start at 1,616°F, which is the maximum EGT for the engine.

Carburetors

The engine was equipped with two Bing constant depression carburetors. The cross-draft butterfly valve carburetors had a variable venturi and a double float system arranged centrally, below the venturi. The variable venturi is actuated by a carburetor piston, which is suspended on a rubber diaphragm and protrudes into the venturi throat. The piston adjusts the smallest cross-section ("air funnel") of the venturi, using vacuum controlled by the position of the throttle valve.

In the Rotax Heavy Maintenance Manual procedure for assembling the carburetor, under "Insert Diaphragm," Step 1 notes, “The index tabs on the diaphragm must fit into the indentation of the carburetor piston.” Step 2 notes, “The position is determined via the index tabs of the diaphragm.” A highlighted notice also states, “While installing the chamber top be careful not to turn the carburetor piston assy. out of position.” WRECKAGE AND IMPACT INFORMATIONThe accident site was located about 425 ft from the edge of runway 16L with all the wreckage found within the same area on a ground track of 300°. The farthest wreckage was part of the rocket from the parachute system. There were small plexiglass shards in front of the main wreckage. There was no evidence of soot or oil on the airframe.

The wreckage was consumed by fire. The propeller was in front of the wreckage and there was a divot in the concrete pad consistent with that being the first impact. The wings and tail remained attached. The flap position could not be ascertained due to the thermal damage, but video footage suggested that they were extended. The fuselage body was bent down at the empennage (adjacent to the step) with the tail resting on the ground. The rocket had been deployed and was found ahead of the wreckage.

An external examination of the engine revealed that the crankcase was fractured in numerous areas around the casing, with many accessories broken from their mounting flanges. The engine sustained thermal damage and numerous fuel and oil lines were completely consumed. The ignition system was consumed by fire, precluding testing. Firefighters reported using fire suppressant and water to extinguish the fire.

The top spark plugs appeared in normal condition and all electrodes were similar in shape. The combustion chambers and internal case were examined using a lighted borescope, and no evidence of valve-to-piston face contact was observed. The camshaft lobes did not appear rounded, and no material deformation was observed on the lobes.

Carburetors

The Nos. 1/3 carburetor was found with its piston slide misaligned when viewed through the venturi. The half-moon curve at the bottom of the slide was not aligned with the bore of the carburetor. The carburetor top was removed, and the piston was extracted from the housing. The diaphragm's index tabs were not aligned with the corresponding slots in the carburetor top, indicating an incorrect assembly.

The Nos. 2/4 carburetor piston slide was observed to have more misalignment than the No. 1/3 carburetor when viewed through the venturi. After the removal of the carburetor top, the piston was extracted. The diaphragm had been consumed in the post-impact fire, preventing confirmation of proper alignment between the index tabs and housing slots.

According to the engine manufacturer, this misalignment can result in vibrations (experienced as a rough running engine), excessive decreases in rpm when operating on a single magneto (for example, during a before-takeoff engine run-up), and a reduction in overall engine performance.


Figure 5. Carburetor piston slides.