A survey identifies power lines crossing the planned flight path at roughly 60 feet AGL. What is the best mitigation?

Power lines are among the most dangerous obstacles a small unmanned aircraft encounters, and the reason is visibility. Conductors are thin, often unpainted, frequently seen against a bright sky or a cluttered background, and essentially invisible on a camera feed until the aircraft is on top of them. They also carry induced electrical fields that can disturb the magnetometer and degrade position holding near them. Obstacle avoidance sensors are unreliable against wires for the same reason a pilot cannot see them — there is very little surface for a sensor to return. So the only dependable mitigation is planning: identify the crossing during the site survey, set a route and altitude that keep the aircraft well clear, mark the hazard on the flight plan, and brief every crew member on where the wires are and what the abort action is. Flying beneath them trades a very small risk for a very large one, and no authorization is involved because the hazard is physical rather than regulatory.

Wires are nearly invisible in flight and poorly detected by sensors, so the dependable mitigation is planning a route and altitude that keep the aircraft well clear, with the crew briefed on the hazard.

Power lines are difficult to see in flight and are poorly detected by obstacle avoidance sensors. Conductors can also induce magnetometer interference. Site survey, route planning and crew briefing are the effective mitigations.

You Will Not See the Wire, and neither will the sensors. Plan around it before you launch.

Note the magnetometer effect too. Compass errors and unstable position holding near high-voltage lines are a separate hazard from the collision risk.

• •Trusting obstacle sensors against thin conductors
• •Flying beneath lines to stay clear of traffic
• •Overlooking magnetometer interference near high-voltage lines