Two commercial airlines almost failed earlier this month south of San Juan in Puerto Rico. An Air France jet and an American Airlines jet flew over the Caribbean Sea and approached before TCAS was activated to help prevent a collision safely. The incident occurred in the middle of the night on Sunday, December 13, 2020.
A potential collision between two passenger jets avoided
According to Simon Hradecky’s report in The Aviation Herald, the incident involved a Boeing 777-300 from Air France and a Boeing 737-800 from American Airlines. The Air France jet, registered as F-GZNN, was on its way to Lima from Paris. The American Airlines jet, registered as N926NN, was going to Miami after leaving St George in Granada.
Air France’s Boeing 777 is seven and a half years old and is painted in the distinct colors of SkyTeam. The American Airlines jet is six and a half years old. This is the first recorded incident for the Air France plane and the second incident for the American Airlines jet.
Air France’s Boeing was operating flight AF480. This is Air France’s regular departure at 10:30 am from Charles de Gaulle straight to Lima, arriving later that day. American Airlines flight was AA1546, departing at 16:17 from the Maurice Bishop International Airport in Granada bound for Miami.
According to The Aviation Herald, Air France’s Boeing 777 was 220 nautical miles south of San Juan, Puerto Rico, and was rising to FL380 from FL360. American Airlines’ Boeing 737 was already on the FL380 and converging quickly with the Air France jet at right angles.
The Traffic Alert and Collision Prevention Systems (TCAS) on both aircraft were then activated. American Airlines’ Boeing 737 went up, and Air France’s Boeing 777 went down to FL374. The report says that the American Airlines jet crossed the flight path of the Air France jet at 38,800 feet, approximately four nautical miles ahead of the AF480. Air France’s Boeing 777 crossed the Boeing 737’s flight path at 37,400 feet.
The incident highlights the value of TCAS
Having passed each other without further incident, both aircraft resumed their originally planned flight paths and continued on to their destinations.
This incident highlights the value of TCAS (known as Airborne Collision Avoidance
System or ACAS in some other jurisdictions). TCAS works independently of the land base
air traffic control system and provides anti-collision protection for commercial passenger jets.
TCAS uses the same radar beacon transponders installed on aircraft to operate with ground air traffic control radars. The level of protection provided by TCAS equipment depends on the type of transponder the aircraft is carrying. TCAS is a safety net of last resort that works independently of any separation standards.
Contemporary TCAS systems use secondary surveillance radar transponder signals. An aircraft’s TCAS examines the Mode C and Mode S transponders of nearby aircraft. It can read the altitude and range of nearby aircraft and, if necessary, issue an alert.
While the mid-December incident involving Air France and American Airlines jets is a good example of how TCAS works, TCAS works in a short time. TCAS goes into action less than a minute before any potential conflict. Although four nautical miles may seem like a safe distance, when aircraft are each traveling at hundreds of miles or more an hour, things will happen very quickly.
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