A commercial airliner was on final approach to San Francisco’s international airport in November when the crew spotted a drone outside the cockpit window. By then it was too late “to take evasive action,” the pilots reported, and the quadcopter passed by their windshield, not 300 feet away.

A month earlier, a jetliner was flying at an altitude of 4,000 feet near Miami’s international airport when its pilots reported a “close encounter” with a drone. In August, a drone came within 50 feet of clipping the left wing of a........

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