Two planes from Chennai waiting to land at Chattrapati Shivaji International Airport breached their separation limit leading the Traffic Collision Avoidance System (T-CAS) in both aircraft to issue an alert. An airport official said the incident could have been a result of a minor error in judgement and congestion at CSIA. The aircraft,a Jet Airways Boeing 9W 2119 and Air Indias IC 174,came within 4.75 nautical miles of each other when the T-CAS in both aircraft issued an alert. In India two aircraft must maintain a standard separation of five nautical miles. The Directorate General of Civil Aviation is probing the incident. Both aircraft were on the radar when there was a breach by 0.25 nautical miles. An advisory was issued immediately and separation between the aircraft was increased, an airport official said. Nearly all aircraft have the T-CAS. Airline officials said with so many warning systems in place,a mid-air collission was quite impossible. Jet Airways flight 9W 2119 (Chennai - Mumbai) of 10th July,2010,had a Resolution Advisory,an alert message advising of another aircraft in the vicinity. This incident took place while holding over Mumbai under ATC instructions, said a Jet spokesperson. Our commander has filed a report about observing another aircraft while approaching Mumbai airspace, said an Air India spokesperson. The Air India flight had 70 passengers while the Jet flight was carrying 142 passengers. The TCAS alert was a resolution advisory which means that the aircraft were 25 seconds from impact. A traffic advisory would have been 40 seconds from impact. Airport officials said that while Airports Authority of India norms stipulate five nautical miles seperation but there are airports that operate with two nautical miles or 2.5 nautical miles seperation. Reducing the separation standards would be one way to increase capacity which has been talked about at aviation circles at different levels, said an official. At present the CSIA can handle upto 32 to 34 movements in an hour.
