Mumbai: The misinterpretation of instructions from the air traffic control (ATC) by Air India Express crew likely caused a runway incursion during a naval aircraft's take-off at the Goa Dabolim Airport in April, according to the Aircraft Accident Investigation Bureau (AAIB). Following the probe, the investigation body has urged the aviation regulator to set-up a joint-investigation system with defence authorities to carry out seamless evidence sharing during such instances.
Air India Express Plane With 171 Passengers Entered Active Runway
The incident, which occurred at 8.17am on April 3, involved an Air India Express’ Boeing 737 aircraft carrying 171 passengers which taxied onto an active runway at Dabolim Airport directly into the path of an accelerating Indian Navy fighter jet, leading to a critical runway safety event. However, the tragedy was averted by the quick reaction of the military fighter pilot, who pulled his aircraft into an early lift-off, clearing the civilian airliner by less than 1,000m while flying overhead.
Dabolim Airport operates under a unique arrangement as a military airbase managed by the Indian Navy (INS Hansa) while civilian passenger flights use its passenger terminal. Ground taxiing for civilian airliners is directed by the Airports Authority of India (AAI), while the actual runway and airspace are managed by Naval Air Traffic Control (ATC).
Runway Change And 'Expect Backtrack' Instruction Cause Confusion
On April 3, the ground controllers initially instructed the Air India Express flight to prepare for departure on Runway 26. Minutes later, control informed the pilots that the active runway had been switched to Runway 08 and told them to "expect a backtrack" – an advisory meaning they would likely need to taxi down the active runway to reach the starting point for takeoff.
As the airliner taxied toward the runway via Taxiway N2, the ground controller instructed: "Taxi via N2, hold at holding point Runway 08". However, the co-pilot – a trainee undergoing line training – read back the instruction as "Taxi via N2 Runway 08", completely omitting the critical order to "hold at holding point". The ground controller failed to catch this incomplete read-back, creating a classic operational miscommunication.
Captain Mistakenly Assumes Clearance To Enter Active Runway
Believing they were already cleared to enter the runway, the Captain instructed the trainee to inform controllers they were entering. When the co-pilot transmitted "entering runway", the ground controller assumed the airliner had already switched radio frequencies and received clearance directly from Naval ATC.
At 8.17am, when the passenger jet taxied past the holding line and onto the active runway, the Naval ATC – unaware that a civilian airliner was entering the runway – had issued takeoff clearance to a naval fighter aircraft operating on a separate radio frequency. It was only after the fighter accelerated past 100 knots, the tower controllers spotted the airliner intruding onto the runway from the opposite end.
Runway Slope Prevents Pilots From Seeing Each Other
Due to a natural slope in Dabolim's runway terrain, neither pilot could visually see the other at ground level. The Naval ATC immediately radioed an emergency alert to the fighter pilot, warning of an "unidentified aircraft on the runway". Recognising he lacked sufficient runway distance to abort his takeoff safely, the fighter pilot initiated an immediate, steep lift-off abeam Taxiway N5.
The military jet passed over the runway at an altitude of approximately 450 feet, clearing the Air India Express jet by a horizontal distance of just 900 to 1,000m.
Investigators identified a chain of human-factor lapses and communication breakdowns. It found that the AIX Captain was overly eager to expedite taxi procedures to minimise runway occupancy time. Hearing "expect backtrack" led the crew to wrongly believe they had been cleared to enter the active runway. The AAIB noted that the Captain was occupied monitoring the trainee since the flight was a training mission.
The final investigation report highlighted that the ground controller did not verify that the pilots accurately repeated the instruction to hold short of the active runway. It also noted that the in-pavement red stop bar lights at the taxiway intersection were not illuminated, which the Captain mistakenly interpreted as an implicit signal to proceed.
Following the investigation, safety authorities issued several binding recommendations to all the stakeholders involved in the incident. It asked the commercial carrier to carry out a corrective retraining of the Captain, counseling for the First Officer and an operational circular to all its pilots regarding radio discipline and runway entry protocols. On the other hand it directed the Airports Authority of India (AAI) – which handles the ATCs – to issue strict guidelines requiring controllers to enforce precise radio phraseology and eliminate ambiguous phrases like "expect backtrack".
The AAIB also recommended the Indian Navy to officially publish stop-bar lighting rules and standardise how civil traffic transitions to military control towers. On the other hand, it urged the Directorate General of Civil Aviation (DGCA) to establish a formal joint-investigation protocol with Defence authorities to ensure seamless evidence sharing during future civil-military airport incidents.
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