TCAS RA triggered by high rate of climb in HAL Bengaluru airspace

Casualties unknown • IN

Two IndiGo Airbus A320 aircraft experienced a serious airprox incident in Bengaluru airspace after one aircraft climbed at a rate exceeding regulatory limits.

What happened

On July 10, 2018, two Airbus A320 aircraft, registered as VT-IFP and VT-ITP, operated by IndiGo, experienced a serious loss of separation within the HAL Bengaluru airspace. The aircraft VT-IFP was en route from Coimbatore to Shamshabad, climbing through various flight levels toward FL360. Simultaneously, VT-ITP was traveling from Bengaluru to Cochin, climbing toward FL280.

Initially, the radar controller maintained a vertical separation of over 5,000 feet between the two jets. However, as both aircraft climbed, the separation rapidly diminished. At 17:28 UTC, the Traffic Collision Avoidance System (TCAS) issued Resolution Advisories (RA) to both crews. The aircraft VT-IFCO received a level-off instruction, while VT-ITP received a climb instruction. During the encounter, the vertical separation dropped to just 300 feet, with a lateral distance of 4 NM.

The investigation

The AAIB investigation examined radar transcripts, flight data recorder (DFDR) information, and cockpit voice recordings. The investigation established that the radar controller had issued climb instructions to both aircraft but failed to provide traffic information to either crew. Furthermore, the controller was preoccupied with other traffic in the sector and did not monitor the specific climb rates of the involved aircraft.

Data from the DFDR revealed that while the crew of VT-IFP maintained a standard climb rate of approximately 1,500 to 1,600 feet per minute, the crew of VT-ITP climbed at roughly 3,000 feet per minute. Additionally, the investigation found that the controller issued a heading instruction to VT-IFP while it was still performing RA maneuvers, which deviates from standard air traffic services procedures.

Findings

  • The primary cause of the incident was that the crew of VT-ITP maintained a high rate of climb that exceeded the limits prescribed in DGCA Operations Circular 7 of 2010.
  • The radar controller failed to provide necessary traffic advisories to the pilots.
  • There was a lack of effective surveillance by the radar controller due to high workload from other traffic.
  • The controller provided an avoiding heading instruction to an aircraft already executing a TCAS RA, contrary to established protocols.

Probable cause

The incident was caused by the crew of VT-ITP climbing at a rate of 3,000 feet per minute, violating regulatory guidelines, compounded by the radar controller's failure to monitor the separation and provide traffic information.

Frequently asked questions

What happened in the 2018-07-10 aircraft accident near IN?

Two IndiGo Airbus A320 aircraft experienced a serious airprox incident in Bengaluru airspace after one aircraft climbed at a rate exceeding regulatory limits.

What aircraft was involved and where did it happen?

The accident on 2018-07-10 involved a aircraft, registration VT-ITP, at IN.

What was the probable cause of the accident?

The incident was caused by the crew of VT-ITP climbing at a rate of 3,000 feet per minute, violating regulatory guidelines, compounded by the radar controller's failure to monitor the separation and provide traffic information.

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