An Air India flight bound for San Francisco returned to Delhi after a technical failure affected its collision avoidance systems [1, 2].

The incident highlights the critical nature of redundant safety systems on ultra-long-haul flights, where a total failure of traffic monitoring tools necessitates an immediate return to base.

Flight AI173 [1], a Boeing 777-300ER [2], was carrying approximately 230 passengers [2] when the crew decided to abort the journey. The aircraft had been in the air for over eight hours, roughly nine hours in total [1, 2], before the decision to divert was made.

The return was prompted by the failure of both Traffic Collision Avoidance System (TCAS) units [1]. TCAS is designed to provide pilots with alerts regarding the proximity of other aircraft to prevent mid-air collisions. Because both units failed, the crew determined that continuing the flight to the U.S. was unsafe [1, 2].

The aircraft originated from Indira Gandhi International Airport in Delhi [2]. After the prolonged flight and subsequent U-turn, the plane returned to its point of origin for technical inspection, and passenger disembarkation [1, 2].

Air India operated the flight using the long-range Boeing 777-300ER, which is typically used for the airline's most demanding international routes [2]. The failure of both redundant systems is a rare occurrence in modern commercial aviation, though safety protocols mandate a return if minimum equipment requirements for the destination are not met [1].

“The aircraft had been in the air for over eight hours, roughly nine hours in total.”

The total failure of both TCAS units represents a significant loss of situational awareness for a flight crew. While air traffic controllers provide separation services, TCAS serves as the final automated layer of protection against collisions. For an ultra-long-haul flight, the lack of this redundancy makes the aircraft ineligible to operate in high-traffic corridors, leaving the crew with no choice but to return to the origin airport regardless of the flight time already elapsed.