What happened
On June 7, 2011, at 9:35 local time, a Bell 407 helicopter, registration EC-IMZ, operated by INAER, crashed into a steep mountainside at Puerto de Angulo, in the municipality of Valle de Mena, Burgos. The aircraft was performing aerial maintenance inspections for Red Eléctrica de España (REE), flying at low altitudes and speeds to check high-voltage power lines for corrosion and wear.
The flight originated from the La Jara substation. Although the crew noted that weather conditions had improved since the previous day, they were aware of potential difficulties due to clouds and drizzle in the higher elevations. The mission was being conducted under Visual Flight Rules (VFR). As the helicopter progressed through the valley, the terrain elevation increased. While the aircraft had been flying safely in clear conditions earlier in the flight, the meteorological situation at the accident site was characterized by intermittent fog and low cloud bases.
Witnesses near the area reported seeing the helicopter through the fog shortly before an explosion was visible. The aircraft struck a nearly vertical rock wall at an elevation of approximately 7-55 meters, about 450 meters before reaching the summit of the pass. The impact caused a significant fuel deflagration and the total destruction of the aircraft. Both the pilot and the specialist technician on board were killed instantly.
The investigation
The CIAIAC investigation examined the flight records, maintenance logs, and meteorological data. GPS tracking from the fleet monitoring system confirmed the flight path and indicated that the aircraft was maintaining a relatively uniform altitude relative to the power lines until the final moments. The investigation also reviewed witness statements from local residents and motorists who observed the aircraft in marginal visibility conditions.
Investigators analyzed the terrain, noting that while the slope appeared moderate at lower elevations, it transitioned into a steep, vertical cliff at the point of impact. The investigation also looked into the operational procedures of the operator, specifically regarding how pilots evaluate visibility during specialized inspection tasks.
Findings
- The aircraft was fully airworthy, with all maintenance requirements up to date.
- The pilot held a valid commercial license with appropriate type ratings.
- The flight was being conducted within the planned area of operations under VFR.
- Meteorological conditions at the time of the accident were marginal, with intermittent fog and low clouds at terrain level.
- The pilot attempted a right-hand turn and climb, likely seeking to regain visual references or avoid obstacles, but failed to correctly assess the available space due to the reduced visibility.
- The pilot conducted the flight in areas of very low visibility, leading to a loss of visual references and subsequent spatial disorientation.
- The terrain feature struck by the aircraft was a steep, vertical wall that the crew likely did not anticipate would be so abrupt.