WASHINGTON, March 3 (Reuters) - The Federal Aviation

Administration is investigating why several flight crews on

Saturday received faulty alerts of potentially nearby aircraft

on arrival at Washington's Reagan National Airport.

The FAA said Monday that some of the crews executed

go-arounds as a result of the alerts that aim to prevent

collisions and is investigating why the alerts occurred. A

go-around is when a plane aborts a landing as it nears the

airport.

There has been intense focus on traffic at the airport after

a January 29 fatal collision between an Army helicopter and an

American Airlines ( AAL ) regional jet near the airport that

killed 67 people.

Reagan National has the single busiest runway in the United

States.

Airplanes use alerts to warn of potential collisions, with

pilots using various Traffic Alert and Collision Avoidance

System alerts. The system functions independently of

ground-based air traffic control.

In October, the FAA said it

was opening an audit into

runway incursion risks at the 45 busiest U.S. airports.

The FAA has taken a series of steps since the fatal

incident including

limiting helicopter traffic

around the airport,

barring airplanes from taking off

when a presidential helicopter is present and

slowing the rate of arrivals

.

Over the last two years, a series of troubling near-miss

incidents has raised concerns about U.S. aviation safety and the

strain on understaffed air traffic control operations.

A persistent shortage of controllers has delayed flights

and, at many facilities, controllers are working mandatory

overtime and six-day weeks to cover shifts.

The FAA, which has aging technology and facilities and

needs billions of dollars to modernize, is about 3,500 air

traffic controllers short of targeted staffing, prompting the

aviation industry and lawmakers to call for action.