What happened
On July 21, 2019, a Montaer MC01 ultralight, registration PU-ETD, was performing a local flight for training purposes at the Atibaia Aerodrome (SDTB) in São Paulo, Brazil. The flight, operated by a flight school, involved two crew members: a pilot instructor and a second in command (SIC) who was performing the maneuver to gain recent experience.
During a touch-and-go training procedure, the aircraft encountered a sudden crosswind gust originating from the east. This gust caused the aircraft to lose directional control, veering to the left side of the runway. The aircraft exited the operational area and came to rest in an inverted position on irregular, sloped terrain approximately 90 meters from the runway centerline. The impact resulted in substantial damage to the aircraft, while both crew members sustained minor injuries.
The investigation
CENIPA's investigation examined the meteorological conditions, the aircraft's operational limits, and the crew's performance. Investigators noted that the Atibaia Aerodrome lacks an official Aerodrome Flight Information Service (AFIS), meaning pilots must rely on a windsock to estimate wind speed and direction. The local topography, specifically the Serra de Atibaia, is known to create orographic winds that can cause significant crosswind components and gusts.
The investigation reviewed the operator's safety manual, which permitted instructional flights in crosswinds up to 25 kt, a threshold investigators considered high for a light experimental aircraft. Furthermore, the Pilot's Operating Handbook (POH) for the MC01 did not specify a demonstrated crosswind component for takeoff or landing. The investigation also looked into the crew's coordination, noting reports that the SIC's control inputs during the gust were contrary to those of the instructor.