Was it bad piloting and an overworked controller?

Maybe so. NY times excerpts:

The controller who was handling helicopters in the airport’s vicinity Wednesday night was also instructing planes that were landing and departing from its runways. Those jobs are typically assigned to two controllers, rather than one, the internal F. A. A. report said. This increases the workload for the air traffic controller and complicates the job.

The helicopter did not follow the intended route, the people briefed on the matter said. Rather, it was above 300 feet, when it was supposed to be flying below 200 feet, and it was at least a half-mile off the approved route when it collided with the commercial jet. The helicopter was supposed to be flying closer to the bank of the Potomac River and lower to the ground as it traversed the busy Reagan National airspace, four people briefed on the incident said.

The duties of handling air traffic control for helicopters and for planes at Reagan National on Wednesday night were combined before the deadly crash. That left an air traffic controller handling dual roles, according to a person briefed on the staffing and the report.

The controller who was handling helicopters in the airport’s vicinity Wednesday night was also instructing planes that were landing and departing from its runways. Those jobs are typically assigned to two controllers, rather than one, the internal F. A. A. report said. This increases the workload for the air traffic controller and complicates the job.

The helicopter flew outside its approved flight path. The American Airlines pilots most likely did not see the helicopter close by as they made a turn toward the runway. And the air traffic controller, who was juggling two jobs at the same time, was unable to keep the helicopter and the plane separated.

Was it bad piloting and an overworked controller?
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