Passenger jet had to abort takeoff to avoid runway collision at New York's LaGuardia Airport

Federal officials are investigating why two planes got dangerously close on a runway at New York's LaGuardia Airport earlier this month despite the airport being equipped with an advanced surface radar system that's designed to help prevent such close calls.

Both the Federal Aviation Administration and the National Transportation Safety Board said Monday that they are investigating the May 6 incident when a Republic Airways jet had to abort takeoff and slam to a stop because a United Airlines plane was still taxiing across the runway.

In audio from the tower that ABC obtained from the website www.LiveATC.net, the air traffic control said to the pilot of the Republic Airways jet: ''Sorry, I thought United had cleared well before that.''

At the time that controller was directing the Republic Airways jet to takeoff, a ground controller on a different radio frequency was directing the United plane to a new taxiway after it missed the first one it was supposed to use to exit the runway.

Both the airlines and the airport referred questions to the FAA.

The number of close calls in recent years has created serious concerns for the FAA, NTSB and other safety experts. The NTSB's investigation of a February 2023 close call in Austin highlighted the concerns, but there have been a number of other high-profile near misses. In one case, a Southwest Airlines jet coming in for a landing in Chicago narrowly avoided smashing into a business jet crossing the runway.

LaGuardia is one of just 35 airports across the country equipped with the FAA's best technology to prevent such runway incursions. The ASDS-X system uses a variety of technology to help controllers track planes and vehicles on the ground. At the other 490 U.S. airports with a control tower, air traffic controllers have to rely on more low-tech tools like a pair of binoculars to keep track of aircraft on the ground because the systems are expensive.

Expanding the systems to more airports is something Transportation Secretary Sean Duffy would like to do if Congress signs off on his multi-billion-dollar plan to overhaul the nation's aging air traffic control system.

But it's clear the technology is not perfect because close calls continue happening. The FAA is taking a number of additional steps to try to reduce the number of close calls, and it plans to install an additional warning system at LaGuardia in the future.

But the rate of runway incursions per 1 million takeoffs and landings has remained around 30 for a decade. The rate got as high as 35 in 2017 and 2018. But generally there are fewer than 20 of the most serious kind of incursions where a collision was narrowly avoided or there was a significant potential for a crash, according to the FAA. That number did hit 22 in 2023 but fell to just 7 last year.

To help, there are efforts to develop a system that will warn pilots directly about traffic on a runway instead of alerting the controller and relying on them to relay the warning. That could save precious seconds. But the FAA has not yet certified a system to warn pilots directly that Honeywell International has been developing for years.

The worst accident in aviation history occurred in 1977 on the Spanish island of Tenerife, when a KLM 747 began its takeoff roll while a Pan Am 747 was still on the runway; 583 people died when the planes collided in thick fog.