What aircraft was involved and where did it happen?

The accident on 1999-09-25 involved a aircraft, registration 75-OV, at Meaux, FR.

What was the probable cause of the accident?

The exact cause of the loss of control during the initial climb could not be definitively established, though a sudden pitching moment was the primary phenomenon observed.

Fatal loss of control during initial climb of Mignet HM1100

A Mignet HM1100 ultralight aircraft crashed during a training flight at Meaux-Esbly, resulting in two fatalities.

What happened

On September 25, 1999, at 17:25 UTC, a Mignet HM1100 ultralight aircraft, identified as 75-OV, was performing a local flight at Meaux-Esbly aerodrome for the purpose of flight instruction toward a passenger-carrying qualification. The aircraft was occupied by an instructor and a student.

After completing two circuits, the aircraft performed a touch-and-go maneuver. During the initial climb, witnesses observed the aircraft suddenly pitch forward and dive abruptly toward the ground. The aircraft struck a clearing surrounded by trees, resulting in two fatalities and the destruction of the aircraft.

The investigation

Investigators examined the wreckage and found significant damage, including frontal impacts and damage to the leading edge of the front wing. The front wing had separated from the fuselage, and the left rear wing was torn away. While the control surfaces and various linkages were recovered, the control tube for roll was found broken due to static failure. The engine sustained heavy damage, and the airspeed indicator was frozen at 210 km/h.

Regarding the aircraft's configuration, the investigation noted that the doors of this specific model could potentially exert pressure on the underside of the front wing if not properly secured. While the manufacturer later identified that an improperly locked door could cause a pitching moment, no evidence was found to confirm that a door had opened during this flight.

Analysis of the aircraft's weight and balance showed an estimated takeoff mass of 470 kg. Although this slightly exceeded the 450 kg limit in effect at the time, updated regulations had since increased the allowable mass for similar aircraft, and the manufacturer's test flights had demonstrated a higher capability. The investigation also confirmed that the emergency parachute system remained undeployed and the cockpit canopy did not break during flight.

Findings

The aircraft experienced a sudden and loss of control during the initial climb.
There was no evidence of a structural failure of the control systems or an uncommanded power reduction that could be recovered from.
While the potential for a door opening to cause a pitching moment was noted as a design vulnerability, no factual evidence supported this occurring in this instance.
The precise cause of the loss of control could not be determined from the available facts.