In 2017 only the Jeju-Seoul Gimpo route (with over 64,991 flights) and Melbourne-Sydney (54,519 departures and arrivals) were busier than Mumbai-Delhi.
It is the third-busiest air route in the world, with as many as 47,500 departures and landings last year.
Yet despite reaching this position, the Mumbai-Delhi route could face serious challenges in sustaining or improving it this year.
The reason? Hardly any additional capacity is now available at Mumbai airport to deploy more flights on this route.
But with the demand growing by 10-12 per cent annually, and with no possibility of adding more flights, flyers will soon face a hike in air fares this year.
According to OAG, an air travel intelligence firm based in the UK, the Mumbai-Delhi air route was the third-busiest in the world last year, with an average of 130 flights between the two cities every day.
In 2016, India was number six in the pecking order of the busiest routes, and this calculation was based on the capacity deployed on the route one way.
In 2017 only the Jeju-Seoul Gimpo route (with over 64,991 flights) and Melbourne-Sydney (54,519 departures and arrivals) were busier than Mumbai-Delhi.
Airlines say the route makes up about 10 per cent of their capacity and revenues, making it by far the biggest market.
And, at an average passenger load factor on this route of 80-90 per cent, this is a lucrative route, on which the demand is growing.
It also reflects the skew that these two markets have in the aviation business in the country as it constitutes more than 35 per cent of the domestic traffic.
Over 10,000 passengers depart every day from Mumbai for Delhi and vice versa and 70 per cent of them are corporate travellers, and this makes the situation even worse as they travel only during the peak hours (6am-8am and 5pm to 7pm).
That is why IndiGo and Jet Airways, each of which has 17 departures from Mumbai, top the list, followed by Air India (11), Vistara (10), GoAir (7), and SpiceJet (4). Yet the writing is on the wall. While most airlines are pushing for more capacity on the route, none is available.
Says a senior executive of a leading airline: “If slots are available, we can achieve a growth rate of 10-12 per cent on this route every year.
"But as slots are not available, the only possibility is to deploy bigger planes. But everyone does not have that flexibility, especially the LCCs. What you will see is fare increases”.
Last year, for instance, only Vistara and IndiGo were given additional slots on the route.
According to estimates of the Centre for Asia Pacific Aviation, the airport, which has a maximum capacity of 50-52 million per annum, is handling 46-50 departures an hour, which pretty close to the global best of around 55.
Currently the airport handles over 45 million passengers a year.
The agency says that the airport would reach its full capacity either by FY18 and surely by 2019, which makes the development of the new airport in Navi Mumbai so important.
Photograph: Adnan Abidi/Reuters
