What happened
On May 17, 2017, an Aerospool Dynamic WT9 ultralight, identified as 68-US, departed from Mulhouse-Habsheim aerodrome for a flight toward Strasbourg-Neuhof. Shortly after takeoff, the aircraft's radar contact was lost. The aircraft struck trees and collided with the ground before catching fire. The impact occurred at a 45-degree nose-down attitude with the wings nearly level. The engine was still producing power at the time of impact, as evidenced by damage to the propeller and vegetation.
The investigation
The investigation focused on the wreckage and the aircraft's canopy mechanism. The Aerospool Dynamic WT9 features a single-piece canopy that pivots forward, assisted by gas struts, and is secured by a latch. Investigators found debris from the canopy at the crash site, but no canopy fragments were found upstream of the impact point, suggesting the canopy was already open before the collision.
Evidence from the flight path showed components such as a part of the elevator and the pilot's personal items (cap and backpack) scattered along a trajectory leading to the impact. While the flight manual provides emergency procedures for an improperly locked canopy, the investigation could not determine the exact state of the locking mechanism or the gas struts at the moment of failure.
Findings
Investigators concluded that the canopy opening in flight was the primary catalyst for the accident. It is highly probable that an inadequate closure of the canopy prior to takeoff led to its unexpected opening during the flight.
Several factors contributed to the loss of control following the opening:
- The sudden influx of airflow into the cockpit likely caused pilot surprise and loss of concentration.
- The aerodynamic performance and controllability of the aircraft were significantly degraded by the increased drag.
- The pilot's attempt to manage or close the canopy likely distracted from essential flight controls.
Notably, the investigation highlighted that between 2005 and 2018, the BEA recorded 18 accidents involving unexpected canopy openings in ultralight aircraft, three of which were fatal.