Accident Overview
On January 7, 2021, at approximately 1430 local time, a Flight Design CTLSi ultralight vehicle registered AJ2199 crashed in a mountainous area of Sandimen Village, Sandimen Township, Pingtung County, Taiwan. The aircraft, operated by the Kaohsiung Aviation Sports Promotion Association, was on a 20-minute introductory flight with one instructor and one passenger. Both occupants died in the accident. The aircraft was destroyed by impact and subsequent fire.
Aircraft and Operator Information
The ultralight was a fixed-wing CTLSi manufactured by Flight Design (Germany), serial number F-18-02-02, with a Rotax 912is engine. It held a valid inspection certificate (CAA-108-006) issued by Taiwan's Civil Aeronautics Administration. The aircraft had undergone a 100-hour maintenance check on December 22, 2020, with 100.7 engine hours, and had flown 8 hours 40 minutes since then. The empty weight was 382.7 kg, maximum takeoff weight 600 kg. For the accident flight, fuel load was 40 kg and each occupant weighed 80 kg, giving a takeoff weight of 582.7 kg.
The 59-year-old male operator held a valid ultralight instructor certificate (category: fixed-wing, class: AP-5). He was a member of both the Kaohsiung Aviation Sports Promotion Association and the Taiwan Flying Players Association. His flight experience prior to the accident included 471 hours 59 minutes in non-CTLS aircraft at the Taiwan Flying Players Association and 67 hours 10 minutes in CTLS aircraft at the Kaohsiung Association. Post-accident toxicology tests found no alcohol in the operator's blood or urine.
Weather Conditions
The accident occurred during a cold front affecting Taiwan, with light rain in parts. At 1430, weather at Pingtung North Airport (16 km west-southwest of the accident site) recorded: wind 340° at 2 knots, visibility 3,200 meters, light rain with mist, scattered clouds at 600 ft, overcast at 1,600 ft, temperature 16°C, dew point 15°C. Precipitation from 1400 to 1500 was 0.4 mm. At the Sandimen automatic weather station (2.2 km south of the accident), wind at 1400 was 300° at 1 knot, precipitation 1400-1500 was 1 mm.
Ground witnesses at the Jiehao activity site reported that weather deteriorated in the afternoon: low clouds, drizzle, poor visibility, and the eastern mountains (about 2.5 km away) were not visible. A video taken by a friend of the passenger showed the aircraft becoming invisible 27 seconds after takeoff. Based on the aircraft's best climb speed (123 km/h at sea level and max takeoff weight), the distance flown in 27 seconds is about 0.92 km, indicating visibility of about 1 km. The Kaohsiung Association's operations manual required a minimum visibility of 5 km and cloud ceiling of 1,500 ft for visual flight.
Flight Sequence
The aircraft departed from runway 26 at the Jiehao activity site at approximately 1420. According to witnesses, the operator arrived at about 1349 and was asked about the poor weather. The operator replied affirmatively. During taxi, the windshield fogged, and the aircraft returned to clean it. The witness again advised against flying, but the operator decided to proceed. After takeoff, the operator reported a left turn to the southern airspace. About 10 minutes later, radio calls went unanswered. At approximately 1600, another pilot launched to search but encountered clouds with a ceiling below 500 ft about 2 km from the field and returned immediately.
Accident Site and Wreckage
The wreckage was located at approximately 2200 on the same day by rescue personnel at coordinates E120°38'35.24", N22°43'46.62", elevation 327 meters, on a 70-degree slope. The aircraft struck the ground at a heading of about 120 degrees. Except for parts of the wings and tail, the engine, cockpit, and fuselage were completely burned.
Investigation Findings
The investigation concluded that the operator failed to comply with regulations requiring ultralight vehicles to be operated under visual meteorological conditions (VMC). The flight was conducted in instrument meteorological conditions (IMC), which was the primary cause of the accident. The Kaohsiung Association's operational manual prescribed VMC minima but lacked procedures to prevent intentional violation. The association's real-time position reporting system relied on pilot radio reports, which failed when radio contact was lost, hindering timely search and rescue.