What happened
On December 3, 2020, a Dassault Falcon 900EX, registration OE-IMI, was performing a landing at Kangerlussuaq Airport (BGSF) under Instrument Flight Rules. The flight had originated from Vienna (LOWW). During the landing roll, the aircraft experienced a significant loss of directional control, with one main wheel deviating approximately 19.4 meters from the runway centerline. The incident resulted in minor damage to the aircraft, specifically the rupture of hydraulic brake unit lines and damage to main wheels #1, #2, and #4. There were no injuries to the crew.
The investigation
Investigators from AIB Denmark examined the aircraft's maintenance history, flight crew training, and meteorological conditions. The investigation focused on the operation of the aircraft's optional brake heating system. Evidence from tire rubber skid marks on the runway confirmed that three of the main wheels were blocked upon touchdown. The inquiry also reviewed the interaction between the Airplane Flight Manual (AFM) and the operator's specific flight procedures regarding the use of the heating system. Technical inspections of the brakes and hydraulic lines were conducted to determine the mechanism of the damage.
Findings
- The primary cause of the incident was the presence of frozen main wheel brakes at the moment of touchdown.
- Weather conditions at the departure airport (LOWW) presented a significant risk of brake freezing, justifying the use of the brake heating system.
- The flight crew activated the brake heating system for only about three minutes after departing Vienna, failing to meet the recommended ten-minute duration.
- The crew did not activate the brake heating system during the descent into Kangerlussuaq.
- Inconsistencies were identified between the AFM and the operator's procedures; the use of the word "recommended" in operational documentation may have led the crew to treat the safety system as optional rather than a necessary preventive measure.
Safety action
Following the investigation, the aircraft manufacturer updated and corrected the procedures regarding the use of the brake heating system and distributed these to all operators. The AIB issued two safety recommendations: one requesting EASA and the manufacturer to make the AFM procedures more directive and explicit to prevent subjective decision-making, and another urging a reevaluation of airworthiness reviews regarding the risks of blocked wheels and subsequent hydraulic line ruptures.