On March 5, the pilot of an Alitalia flight on its final approach to Runway 31 R at New York's JFK International Airport spotted something odd in the air—a small, black flying machine with four propellers flying too close for comfort. The aircraft, likely a "quadrocopter" style drone, passed within 200 feet of the Alitalia airliner at an altitude of about 1,750 feet.

Yesterday, the FBI issued a call for help from the public, requesting anyone with information about the drone or its operators to contact the FBI's New York field office. An FBI spokesperson told Ars that there had been no new developments in the case. While investigators believed the drone was a quadrocopter, they had not officially confirmed this detail. But given the size of the drone—less than three feet across—and the pilot's report that it had four propellers, the vertical-takeoff quadrocopter design is the most likely suspect.

Commercial drones in the "microdrone" class, such as the Microdrones quadrocopter recently snatched up by an Italian university student, are expensive and not widely available to individuals. They are, however, available used on the aftermarket for about $20,000. More traditional radio-controlled commercial drones used in film and video production, such as those made by Quadrocopter, sell for slightly less.

But kit quad-rotor drones, like the ArduPirates drones built using Arduino programmable microcontrollers and ArduCopter code, can be built for around $300 and use GPS to navigate on a programmed course. The Parrot AR Drone, controllable by mobile devices based on Apple's iOS and Google's Android, is also in that price range. Though while that drone could operate at 1,750 feet, it would need modification to be controlled from the ground at that altitude.

There's been some speculation that the drone may have been flown out of Brooklyn's Floyd Bennett Field, a popular spot for model aircraft hobbyists. But given the size of the drone (under three feet across, according to the pilot who spotted it) and its type, it's more likely the device was launched somewhere east of the airport in the Five Towns area in Nassau County, a collection of affluent suburbs on Long Island's South Shore.

This drone could simply have been flying into commercial airspace by accident or malfunction. But small drones could just as easily be launched with malicious intent. While a quadrocopter drone of the size described in the March 5 incident would weigh no more than about 12 pounds (and much less if it was a hobbyist's kit drone), it could still do serious damage to an airliner during takeoff or landing.

A collision with a small drone could have an effect on a jetliner similar to a birdstrike. Birds colliding with aircraft have broken windscreens of jets and have even, in the case of US Airways Flight 1549, taken out engines. In January of 2009, just a few days before the geese took down Flight 1549, a helicopter carrying oil platform workers in Louisiana hit a red-tailed hawk and crashed, killing eight of its nine passengers.

A drone intentionally GPS-guided into an airport's approach or takeoff airspace could do more than just crash into aircraft. If a drone was built with the intent of causing damage to a plane or distracting its crew at a crucial moment, it might carry a small explosive or a camera-aimed laser pointer, for example.

Given how easily small drones can be built or obtained and how difficult it is to track them, it will require a lucky break for authorities to track down the drone and its operator. And this isn't a problem that regulation will solve—drones of this size can be assembled by someone with fairly basic technical skills. You can already download and 3D-print most of the parts for a quadrocopter drone, much like you can with firearms.