NTSB Identification: NYC99IA036.
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Scheduled 14 CFR CANADIAN AIRLINES
Incident occurred Tuesday, December 08, 1998 in NEW YORK, NY
Probable Cause Approval Date: 04/20/2000
Aircraft: Boeing 737, registration: GCPX
Injuries: 52 Uninjured.

NTSB investigators used data provided by various sources and may not have traveled in support of this investigation to prepare this aircraft incident report.

The Boeing 737 was on downwind for La Guardia's runway 4, at 4,000 feet msl, when the crew caught a glimpse of three lights. The lights were red, white, green, and aligned vertically with the red light on the bottom. The first officer saw the other airplane, and had enough time to realize they were not going to collide, but not enough time to execute an evasive maneuver. In addition, the airplane's traffic alert collision avoidance system went from 'TRAFFIC' to 'MONITOR VERTICAL SPEED' to 'CLEAR OF CONFLICT' in approximately 2 seconds. The other airplane was a Cessna 172, IFR, at 5,000 feet msl. The pilot of that airplane saw the Boeing 737 at his 12 O'clock position, and perceived it to be at the same altitude. To avoid a perceived collision, the Cessna pilot executed a descent, and at 4,000 feet msl, the two airplanes passed 0 feet vertically and 500 feet horizontally from one another.

The National Transportation Safety Board determines the probable cause(s) of this incident to be:

The Cessna pilot's incorrect visual identification of the Boeing 737's altitude, and decision to take evasive action that was not required, which resulted in the two airplanes coming within 500 feet horizontally, and 0 feet vertically of one another.

Full narrative available

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