What aircraft was involved and where did it happen?

The accident on 2018-06-10 involved a Grob G109B, registration G-KHEH, at Near Raglan, Monmouthshire , GB.

What was the probable cause of the accident?

The collision was most likely caused by the crew failing to see the dead tree until it was too late to avoid it, potentially exacerbated by a loss of engine power due to carburettor icing.

Fatal collision with tree during field landing training

A Grob G109B touring motor glider crashed near Raglan, Monmouthshire, resulting in two fatalities after striking a dead tree during a practice landing exercise.

What happened

On 10 June 2018, a Grob G109B, registration G-KHEH, was conducting a training flight involving a practice field landing near Raglan, Monmouthshire. The flight, which included an instructor and a student, departed Usk Airfield at approximately 0947 hrs. After performing an orbit over nearby fields, the aircraft commenced a descent toward a target landing area.

As the aircraft approached the field, witnesses observed it flying at a very low altitude. Some observers reported hearing the engine spluttering or misfiring, while others noted the engine sounded sluggish. During the final stages of the approach, the aircraft's right wing struck a dead oak tree located on the perimeter of the field at an altitude of approximately 57 ft agl. The impact caused the aircraft to roll and invert, eventually coming to rest in the field. The collision resulted in 2 fatalities.

The investigation

The AAIB examination of the wreckage and engine revealed that the engine was producing power at the moment of impact, as evidenced by the fragmented propeller and the location of a propeller blade tip. While the engine showed no mechanical defects, investigators noted that the carburettor heat baffles were in the hot position, and the ambient conditions were conducive to carburettor icing.

Flight data recovered from a tablet computer showed the aircraft's descent included significant fluctuations in vertical and ground speeds. The investigation also noted that the aircraft had flown below the 500 ft altitude limit prescribed by the Rules of the Air when passing near residential buildings. The investigation could not definitively conclude if an engine issue, such as icing, caused the low altitude or if the descent was a deliberate part of the training maneuver.

Findings

The aircraft's right wing struck a dead tree, causing an immediate roll and inversion.
The pilots likely did not observe the dead tree until it was too late to take evasive action.
The engine was under power at the time of the collision.
Environmental conditions were suitable for the development of carburettor icing, which may have affected engine performance during the descent.
The aircraft was operating at an altitude below 500 ft agl near structures and people during the training exercise.