Some pilots aboard a Southwest flight landing at Oakland International Airport Saturday evening reported seeing a "fairly good-sized drone" in restricted airspace, just off to the plane's right side, flying at about 2,000 or 3,000 feet with a red beacon on top of it. This is highly illegal under FAA regulations, not to mention potentially dangerous, and police may still be investigating the situation.

As ABC 7 reports, Alameda police were subsequently called to a beach not far from the airport, perhaps in search of the drone's remote flyer, but no drone was located there. It's unclear if this was a quadcopter drone or something larger and more sophisticated.

Drones of any size could cause "catastrophic" problems for commercial planes, as one expert explains, if they get accidentally sucked into a plane's engine. It does not seem this particular drone got very close to the Southwest aircraft, however.

Per new FAA rules, you're not allowed to fly a drone with a five-mile radius of an airport, nor can you fly one above 400 feet. Those rules are laid out on the website KnowBeforeYouFly.org, which is geared toward recreational drone flyers.

Also a problem recently, as drone flying has become a more popular pastime, are drone fly-bys of the Golden Gate Bridge, which present security concerns when they take footage of restricted areas of the bridge not generally accessible to the public.

Related: Stop Flying Your Drones Around The Golden Gate Bridge!