Aviation regulators are investigating a flurry of collisions and close calls between consumer drones and aircraft, encounters they say pose significant risks to the flying public.

Canadian authorities released a report Wednesday on a collision there with a small charter plane while U.S. regulators said they are trying to confirm whether an air-tour helicopter in Hawaii clipped one as well. The incidents come just days after leading aviation-industry groups urged Congress to tighten regulations on hobbyist drones because of a video showing one flying feet from an airliner near Las Vegas.

“The use of drones near an aerodrome or within controlled airspace poses a serious risk to aviation safety,” Canada’s Transportation Safety Board said in the report. “For this reason, all recreational and non-recreational drone users must be knowledgeable about and comply with the regulations, including the requirement to operate within line of sight.”

So far, none of the confirmed collisions has triggered a crash or even led to serious damage. Still, the Federal Aviation Administration in a study based on computerized models last fall concluded that drones would cause more damage than birds of similar size because they contain metal parts. Significant damage to windshields, wings and tail surfaces was possible, the study found.

The surging number of incidents combined with a regulatory system that makes it difficult to monitor drone flights has alarmed by traditional aviation groups.

“The likelihood that a drone will collide with an airline aircraft is increasing,” said a letter to U.S. lawmakers earlier this week from Airlines for America, a trade group representing large carriers, and the Air Line Pilots Association and the National Air Traffic Controllers Association, the unions that represent pilots and controllers.

In the latest report, the U.S. FAA said it is investigating whether an air-tour helicopter in Hawaii struck a drone on Friday.

The incident occurred over the island of Kauai, the agency said in an emailed statement Wednesday. The pilot reported scratches to the helicopter’s belly, but no significant damage. No one was injured, according to the FAA.

If confirmed as a drone collision, it would mark the second such case involving an aircraft in the U.S. A drone struck an Army helicopter near in New York City on Sept. 21, according to the National Transportation Safety Board. The helicopter landed safely. The drone’s operator had flown the device out of his sight and didn’t see the helicopter, the NTSB found.

Quebec Incident

A small drone that struck a charter plane carrying eight people above Quebec City highlights the need for people to follow legal restrictions, an investigation by the Transportation Safety Board of Canada concluded.

The TSB couldn’t find debris from the drone or its operator after the Oct. 12 collision. It called on operators of the devices to better educate themselves on the rules and safety hazards. The plane, a twin-turboprop, was able to land safely with only minor damage to its left wing, the report found.

Even groups that have traditionally defended the rights of hobbyists to fly drones have been raising increasing alarm.

The Academy of Model Aeronautics, which represents hobbyists who fly at clubs around the country, issued a statement Tuesday saying “some rogue flyers choose to operate in an unsafe manner despite existing drone laws.”

It called on the FAA and local police to “hold these people accountable.”

In the U.S., drones are typically restricted to flights within 400 feet of the ground and within sight of the operator. But in the thousands of FAA reports of possible drone safety incidents, many involved apparent illegal flights.