Incident Overview
On May 16, 2017, at 08:25 local time, a Robin DR400-180R with registration F-GLKA departed from Vinon-sur-Verdon (83) for Château-Arnoux Saint-Auban (04). The aircraft was operated by a general aviation school and carried one pilot. During the initial climb to approximately 3,500 feet at a speed of 150 km/h, the pilot experienced severe vibrations followed by a loud bang and observed an object passing on the left side of the aircraft.
Pilot Actions and Landing
Recognizing the likely loss of a propeller blade, the pilot immediately reduced airspeed to maximum glide, set the throttle to full rich, and shut off both magnetos. The vibrations ceased upon engine shutdown. The pilot declared an engine failure, requested landing on runway 16, turned off the battery, and closed the fuel valve. The aircraft landed safely without further incident, resulting in damage to the airframe but no injuries.
Technical Investigation
The aircraft was equipped with a DUC H-FLR2_5-D-I_C "FLAIR-2" propeller, certified on July 7, 2016. At the time of the incident, this specific unit had accumulated 80 hours of use since March 20, 2017. The propeller featured two aluminum alloy (2017A T4) half-hubs and five carbon fiber composite blades.
Examination revealed that one blade had separated at the hub, while a second blade fractured at mid-height, likely due to impact with the first detached piece. The remaining blades were intact. Laboratory analysis determined that the assembly of the two half-hubs failed at the retention zone of the missing blade's foot due to the propagation of two fatigue cracks.
Root Cause Analysis
The first fatigue crack initiated on the inner side of the rear half-hub within a connection fillet specified with a 1 mm radius. It propagated perpendicular to the blade's longitudinal axis until reaching the outer surface (Rupture A). A second crack initiated near the joint plane on the front half-hub and similarly propagated to the outer surface (Rupture B).
Further inspection identified another crack in the retention zone of a different blade (Rupture C). Micrographic examination of this area revealed a machining defect: two radii were present where only one was specified. This defect increased stress concentration, initiating the fatigue crack. While similar anomalies were found on other blades, the specific zone for the missing blade could not be examined due to lost fragments. However, it is probable that a similar machining anomaly existed there, leading to the hub failure.
Regulatory Response
Following the incident, the European Union Aviation Safety Agency (EASA) issued an urgent airworthiness directive (AD N°2017-0092-E) on May 19, 2017, requiring the removal of this type of propeller from service. DUC Hélices also temporarily suspended other five-blade aluminum hub propellers used on 180 hp aircraft.