New Delhi: A video of an IndiGo flight landing on a runway, only a short distance behind an Air India (AI) flight that was taking off, was widely shared on social media Saturday.
The video sparked discussions over whether this was a safety lapse that could have led to a serious accident. ThePrint takes a look at what happened, what the airlines said, whether it was a lapse, and what the authorities are doing.
What happened
On Saturday evening, AI 657 got the clearance to depart at the same time as IndiGo 5053 got the clearance to land on the Mumbai International Airport’s Runway 27.
According to aeroplane tracker Flightradar24, the flights were 1,671 feet apart at their closest point — the AI flight was still on the ground while the IndiGo flight was airborne — the Automatic Dependent Surveillance – Broadcast (ADS-B) data from the flights showed.
AI 657 began its take-off roll at 00:45:05 UTC (coordinated universal time) when the IndiGo 5053 was approximately 5,700 feet away, according to Flightradar24. Then, at 00:45:27, IndiGo entered the runway area as the AI flight accelerated through 90 knots of ground speed.
The smallest recorded distance between the two flights was at 00:45:36 UTC when the lateral separation was 1,671 feet, and at 00:45:39, AI 657 began its rotation when the distance between the flights was 1,679 feet. Three seconds later, IndiGo touched down, said Flightradar24.
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What the parties involved said
In their statements, IndiGo and Air India said the Air Traffic Control (ATC) cleared the respective flights for landing and take-off.
“On June 8, 2024, IndiGo flight 6E 6053 from Indore was given landing clearance by ATC at Mumbai Airport. The pilot in command continued the approach and landing and followed ATC instructions. At IndiGo, passenger safety is paramount to us, and we have reported the incident as per procedure,” IndiGo said.
Meanwhile, the aviation regulator, the Directorate of Civil Aviation (DGCA), initiated a probe into the incident while also de-rostering the Air Traffic Controller (ATCO) involved in the incident. ATCOs are responsible for coordinating the movement of flights to maintain safe distances between them during take-offs, landings, and ground movement. In India, the Airports Authority of India (AAI) under the Ministry of Civil Aviation is responsible for managing air traffic control (ATC) services.
There was no “air prox situation” in the incident, the association representing ATCOs — Air Traffic Controllers’ Guild — said in its statement posted on Twitter. The International Civil Aviation Organisation (ICAO) defines air prox or aircraft proximity as a situation in which the pilots or the ATC personnel think the distance between two flights or their relative positions and speed might compromise safety. The DGCA probe, the guild further said, will check whether the ATC and the pilots followed all norms.
“…the visibility was good, and there was no air prox situation, with respect to the landing IndiGo flight and the taking off Air India flight. This may be a ‘wow’ moment for out-lookers, but (for) those who perform this safety critical task daily, (it) comes under part of their duty, for which they are trained rigorously,” the ATC guild said.
The guild also highlighted the demanding nature of the job. “The ATCs are under significant pressure when there is high-density traffic at airports…We hope, with this, at least some more awareness will come to people at large about why ATC is called one of the most stressful jobs in the world.”
It also pointed out that the Mumbai airport is one of the busiest in terms of traffic density and that on a single runway RW27 — where Saturday’s incident occurred — there are at least 46 arrivals and departures per hour.
“The ATC has the discretion to allow arrival and departure within a few minutes on the same runway, especially in high-density airports,” the guild said, adding that the separation minima between two flights can be lesser if the visibility is good.
“Had there been a safety risk for landing, the pilot himself would have initiated a go-around. Media trials put extra stress on working controllers, as the nature of (the) job itself comes with risk at every clearance, which is done under acceptable limits of safety,” it said.
While the guild issued a statement on behalf of ATC, no comments have come from the Airport Authority of India (AAI), which manages air traffic control in the country.
Mumbai is one of the busiest airports in the country, often seeing airspace congestion when flights hover over the city for a long duration of 40-60 minutes. An analysis conducted by AAI found that excessive slot allocation and poor slot adherence majorly contributed to traffic congestion, prompting intervention by the Ministry of Civil Aviation.
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What do the rules say
Shantanu Gangakhedkar, senior consultant of aerospace & defence at Frost & Sullivan, said every airport has different specifications for the minimum distance or time allowed between two flights. These specifications depend on the runway location, the ATC technology at the airport, local civil aviation authority rules, weather conditions, and the aircraft type.
Using the same runway for landing and take-off is quite a common practice across the globe at airports where the traffic is high and runways are limited, Gangakhedkar said. He added that the International Civil Aviation Organization (ICAO) lays down general guidelines, which are then adapted by a country or an airport as suited for operations.
The ATC guild’s website mentions standards such as separation minima, which could go up or down depending on the facility available to the controller.
“While only 5 miles between two aircraft is considered sufficient in case of radar controlled airspace, a minimum 15 minutes are required between two aircraft if no navigational facility (which allows the reduction in separation) is available,” it noted, adding that separation applies to all three dimensions — vertical, lateral and longitudinal.
There are different sets of rules for these three dimensions.
The ATC guild site said that the controller has to apply the separation minima that best suits the situation. “…but he must ensure that the separation between two flights should only increase and not reduce subsequently, and for that, he has to take into consideration flight time till flights in question enter into the jurisdiction of the next controller, where from next controller will take over,” it added.
Meanwhile, a 2009 circular by the DGCA noted the definition and classification of air proxima by ICAO and stated the body has not quantified these categories.
The circular said that while investigations into several air prox incidents in India revealed breaches of separation, the incidents did not classify as ‘critical’ or ‘serious’.
It said, “For example, if the required standard longitudinal separation between two aircraft in an ATS route is 10 minutes and the separation reduces to 9 minutes, the chances of a midair collision is impossible, regardless of any evasive action taken by the pilot or the air traffic controller… in India, such cases are termed as ‘air prox incident’.”
The four categories of air prox in India are ‘critical’ (risk of collision), ‘serious’ (safety not assured), ‘no hazard’ (no risk assured), and ‘unclassified’ (no risk determined).
The aircraft separation should be 250 feet vertically and 500 feet laterally for an incident to be critical. Serious incidents occur when the flights have more than 250 feet vertical separation but less than 500 feet lateral separation or when their lateral distance is more than 500 feet but vertical plunges below 250 feet.
(Edited by Madhurita Goswami)
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