When a small plane collided with a sightseeing helicopter over the Hudson River last week, it was only the second time in decades that crowded skies near Manhattan led to a midair crash.

But an Associated Press review of pilots' safety reports found many more near-misses in the airspace in recent years, including several between small planes and helicopters flying the busy river corridor near the Statue of Liberty.

Almost all the incidents involved small aircraft flying at low altitude in an area where pilots pick their own routes and watch for conflicts without help from air traffic controllers.

In 2006, the pilot of a prop plane headed south for a sightseeing swing around the Statue of Liberty said he may have inadvertently passed just 50 feet above a helicopter flying a similar route.

In 1998, the pilot of an air taxi headed to LaGuardia Airport from a heliport on Manhattan's West Side reported that he came within 200 to 300 feet of being clipped by a Cessna.

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One pilot complained about a harrowing 1996 flight down the Hudson to his home airport in Linden, N.J. He had three close calls in 20 minutes.

"Do we need another midair before the FAA ... gets its act together?!" he wrote.

Pilots provided the accounts of near-misses through the Aviation Safety Reporting System, which allows fliers and air traffic controllers to voluntarily and anonymously disclose incidents they felt involved a safety risk.

A database of those reports reviewed by The Associated Press included at least 11 incidents filed since 1990 that described aircraft coming dangerously close over the Hudson.

Those reports only involve a tiny fraction of incidents within that corridor, and experts say most near misses, regardless of where they happen in the U.S., go unreported, meaning the actual number of close calls is probably much higher.

There were additional close calls between helicopters and planes reported in 2001, 2000, 1995, 1994 and 1996, when a plane on another sightseeing flight near the statue descended to avoid a helicopter and came within 300 feet of the water.

"I'm surprised we haven't had more incidents," said Chris Meigs, an assistant professor at Embry-Riddle Aeronautical University who became familiar with the Hudson River airspace while flying for a commercial airline out of Newark, N.J.

"It's a really, really busy airspace," she said. "You need to be a fairly skilled pilot to handle it. There isn't much margin for error."

Saturday's crash has renewed old questions about the safety of the Hudson River flyway for general aviation aircraft.

The Federal Aviation Administration said late Thursday that it had removed from duty an air traffic controller who was talking on the phone during the crash and a supervisor who had stepped away. It said that while there was no reason to believe that the employees' actions contributed to the accident, such "conduct is unacceptable."

The National Air Traffic Controllers Association, the labor union representing controllers, said it supports a full investigation of the allegations "before there is a rush to judgment."

The crash was the first midair collision between two pilots near the city's waterfront since 1983, when a seaplane coming in for a landing near Wall Street collided with a police helicopter over Brooklyn.

Air traffic above the East River was placed under tighter restrictions in 2006 after New York Yankees pitcher Cory Lidle and his flight instructor were killed when their plane failed to execute a proper turn in the tight airspace and plowed into a skyscraper.

But the Hudson River is still governed by fewer rules.

It is often bustling with helicopters and small planes, all of which must stay under 1,100 feet and stick to the river to avoid straying into airspace reserved for big jets taking off and landing at two big airports nearby, LaGuardia and Newark Liberty International.

According to Meigs, the close calls over the Hudson mirror a pattern that can be seen nationwide: Most near collisions are in uncontrolled airspace involving general aviation aircraft.

According to FAA statistics, more than twice as many general aviation aircraft have been involved in near collisions in the U.S. over the last 10 years as aircraft operated by commercial air carriers.

A majority of aircraft involved in close calls were operating under visual flight rules, where they were can pick their own routes as long as they avoid other aircraft. A smaller number were operating by instruments with clearance from air traffic control.

Only 164 of the 1,638 near collisions reported during the past decade involved two aircraft flying on instruments under controllers' supervision.

Some of those many conflicts, including the few that lead to deadly crashes, might be avoided with customized GPS technology that can perform some of the same functions as air traffic controllers.

The equipment, called Automatic Dependent Surveillance-Broadcast systems, are not cheap, running $12,000 to $16,000 per airplane, but they can be of great value in a congested area.

Pilots using the systems can see any other aircraft equipped with one of the devices on a screen in their cockpit.

"Our pilots swear by it," said Frank Ayers, another professor at Daytona Beach, Fla.-based Embry-Riddle, who leads the flight training department.

"We don't use it to avoid the collision that is going to occur five seconds from now. We use it to avoid the conflict that could occur five minutes from now."

By 2020, the FAA plans to require all aircraft to be equipped with ADS-B systems capable of transmitting their positions to other aircraft.