What happened
On July 30, 1990, at approximately 20:30 local time, a Hughes 500D helicopter (registration D-HOBO) operated by Deutscher Helicopter Dienst GmbH crashed into the ground at Baltar, Portugal. The aircraft had spent the day conducting aerial surveillance for forest fires in the Valongo, Trofa, and Baltar areas. After returning to its base at the Baltar Fire Station around 20:00 to disembark firefighters, the pilot initiated a local flight over the station grounds without prior maintenance reporting or specific operational requests.
During the approach to the landing pad, the helicopter flew laterally from the right, crossing perpendicular to its longitudinal axis with its tail facing north. As it passed in front of the fire station tower, the aircraft climbed and rotated port-side around its vertical axis. Witnesses reported a change in engine noise, suggesting contact with the tower. The helicopter subsequently entered an uncontrolled descent, striking the ground violently at the edge of the landing pad. The impact caused the main rotor blades to detach and scatter within a 100-meter radius. The pilot sustained fatal cranioencephalic trauma and was ejected from the aircraft due to the force exceeding the seatbelt's 6 G rating.
The investigation
The GPIAAF investigation established that there were no specific meteorological observations for the exact moment, but conditions were clear with visibility over 10 km and calm winds. The aircraft was not equipped with a flight data recorder. Forensic analysis of metal shavings found on the fire station tower at a height of approximately 4.35 meters confirmed they matched the fixed balance weight material from one of the main rotor blades. The trajectory of the scraping indicated a counter-clockwise path relative to the horizon.
Medical examination confirmed the pilot, a 29-year-old commercial helicopter pilot with 130 hours of experience, died from multiple brain injuries. Testimony from firefighters indicated the final flight was solely the pilot's initiative to check an unspecified item in the aircraft before handover. No maintenance technician was present, and no anomalies were reported prior to the flight.
Findings
The primary cause of the accident was the main rotor blade tip striking the fire station tower, which resulted in a sudden imbalance of the rotor system and loss of control. The impact with the tower altered the pitch of the affected blade, leading to violent vibrations and structural failure. Contributing factors included the low altitude of the approach relative to the tower height and the lack of adherence to standard operating procedures for helipad operations.
Safety action
The investigation recommended that helipads used for forest fire fighting operations must comply with ICAO Annex 14, Volume II requirements. Additionally, pilots engaged in such operations were advised to strictly follow approved operational manuals.