Robinson R44 N881KE accident near Houston, Texas

Probable cause

The pilot’s failure to maintain clearance from a lighted radio tower during a visual night flight. Contributing to the accident was the air traffic controller’s failure to issue a safety alert notifying the pilot of the flight’s unsafe proximity to the tower.

NTSB analysis

The pilot of the commercial air tour helicopter was conducting a night sightseeing flight under visual meteorological conditions. Shortly after departure, the pilot established communication with the Houston Hobby Airport air traffic control tower local controller and requested the “downtown loop.” The local controller identified the helicopter on radar, approved the request, and issued the current altimeter setting. Several minutes later, the controller issued a traffic advisory for another company air tour helicopter. The accident pilot reported that she observed the traffic on her ADS-B display but had not visually acquired it. The controller instructed the accident pilot to maintain visual separation from the traffic, and the pilot was reading back the instruction when her transmission abruptly ended. The helicopter then struck a 1,003-ft-tall radio tower about 100 ft below its top. The air traffic control operations supervisor looked out the air traffic control tower window and witnessed the accident. Video and photographic evidence showed that the tower’s middle and top flashing beacons were operational at the time of the accident; the lower beacon was not visible in any available imagery.

The radio tower was depicted as an obstruction on applicable aeronautical charts and on the air traffic controller’s radar display. Flight data showed that the helicopter maintained a straight flightpath toward the tower at an altitude below the top of the tower until impact.

An FAA safety review found that traffic volume at the time of the accident was light, with routine complexity, and identified no unusual factors that would have distracted the controller. FAA Order 7110.65, “Air Traffic Control,” paragraph 2-1-2, “Duty Priority,” requires controllers to give first priority to separating aircraft and issuing required safety alerts. Further, FAA Order 7110.65, paragraph 2-1-6, “Safety Alert,” requires a controller to issue a safety alert when the controller is aware that an aircraft is at an altitude that, in the controller’s judgement, places it in unsafe proximity to terrain, obstructions, or other aircraft. The order further notes that “while a controller cannot see immediately the development of every situation where a safety alert must be issued, the controller must remain vigilant for such situations and issue a safety alert when the situation is recognized.”

Although the pilot remained responsible for maintaining clearance from terrain and obstructions while operating under visual flight rules, air traffic control (ATC) safety alert requirements applied once the controller was aware that an aircraft was at an altitude that, in the controller’s judgment, placed it in unsafe proximity to an obstruction. The tower was depicted as an obstruction on the controller’s radar display, and the helicopter’s flight track proceeded toward the tower at an altitude below its top. Traffic volume was light, the controller’s workload was routine, and the FAA safety review identified no unusual factors that would have prevented the controller from monitoring the helicopter’s flightpath. Nevertheless, the controller did not issue a safety alert before the helicopter struck the tower.

Text from the NTSB. Open the NTSB docket for CEN25FA019 for the full record.