Magnetic rockets have the ability to track planes or weapon emplacements over a short distance.

Also on Thursday, the aviation agency said it had begun using a new system to track planes flying over water, beyond the reach of radar.

The F.A.A.'s radar cannot track planes below 600 feet at that point on the Hudson River.

Primary reliance remains with the controllers, who track planes on radar and issue traffic guidance instructions to pilots.

But some American officials doubted Mexico's ability to accurately track planes.

Air traffic control uses radar to track planes both on the ground and in the air, and also to guide planes in for smooth landings.

The system will use radar to track the movement of incoming and outgoing planes as well as planes on runways and taxiways.

In a radar system, for example, the system would track planes but ignore false signals caused by electronic interference.

Radar could be used to track planes in the air and determine distance, direction, speed and even type of aircraft.

One was requiring devices only on larger planes and enabling those devices to track smaller private planes by picking up their radar signals.