New Delhi, Aug. 3 -- SPOKANE, Wash. - While pilots were being ordered to pull their helicopters and aerial tankers out of the fire zone over the weekend, the problem was not weather. Unauthorized drones were occupying the restricted airspace the Federal Aviation Administration had declared over the fires, grounding the aircraft that fire managers depend on most heavily when a blaze is moving at zero percent containment through residential streets.

Fire officials confirmed that unauthorized drone incursions were forcing aerial assets to stand down. FAA temporary flight restrictions designate mandatory no-fly corridors over active wildland fire zones. The restrictions are standard procedure for any significant suppression operation, establ...