While outgoing flights are allotted places in the departure queue, the aerodrome control tower officers, hunched over their radar screens in Palam's air traffic control tower, are telling the pilots of incoming aircraft the order in which they will land.
It is a tense but well-practised procedure. With one of Palam's runways handling incoming traffic and the other being used for take-offs, no plane spends more than twenty minutes in the queue.
That is when the supervisor calls out, "Hindon airspace, closed below 150."
In layman terms, it means that Indian Air Force fighter aircraft at Hindon airbase, on the north-western edge of New Delhi, are starting their flying and that no civil airliner may enter Hindon airspace below 15,000 feet.
With one quarter of the airspace around New Delhi now unavailable for civil traffic, the supervisor might just as well have called out, "Triple the delay for all civil flights."
The first complication comes almost immediately: Jet Airways flight DKN627 from Leh, already descended to 8,000 feet, can no longer circle around from the north-east, its usual route to land. Instead, it needs to fly in a wide circle from the west and the south of New Delhi.
As long as Hindon's fighters are flying, all airliners flying in from places to the north and north-west, like Jammu and Kashmir, Punjab, and all European and American cities, will not just have to cover extra distance around the south of Delhi, but will be flying across the paths of other aircraft coming in from Rajasthan, Maharashtra, Gujarat and the southern states. Severely complicating matters will be aircraft taking off from Palam, straight into their paths.
Air traffic controllers are skilled at the tense and complex jugglery of separating fast-flying aircraft from one another by keeping them at different altitudes and areas. But it takes time and causes delays.
Forced by burgeoning air traffic into streamlining its ground systems in Delhi, the Airports Authority of India has brought a second runway into service and built rapid exit taxiways to enable landing aircraft to quickly vacate the runway.
That brought delays down from an hour to just a third of that time. But Hindon-type restrictions on freedom of airspace in a dense traffic environment is a problem the AAI says can only be resolved through moving IAF bases further away from metro cities.
Expert committees on airspace like the Roy Paul Committee and the Naresh Chandra Committee of 2004 have also pointed the finger at Hindon.
AAI Director K Ramalingam puts it bluntly: "It will be much better for civil aviation if the air force bases themselves move some distance away from cities with airports. That will greatly ease the congestion over metro airports, which is partly caused by having to share the airspace with air force operations."
For the IAF, this will be an unacceptable step in what they see as a decades-old process of creeping acquisition. Since before independence Palam Airport belonged to the IAF; Safdarjang Airport handled civil flights, including those to international destinations.
Fighters flying from Palam traditionally protected the capital's airspace; it was from here that the Kashmir airlift in 1948 was mounted. In the 1950s, the IAF moved all its operations to Hindon, leaving only a VIP transport squadron in Palam. This year, says the IAF, it will vacate Palam entirely.
But vacating Hindon as well, says former Air Chief Marshall SP Tyagi, is out of the question. "Hindon is meant for the air defence of Delhi. It cannot be shifted to somewhere far away. Besides, the IAF has put thousands of crores of rupees into assets (in airfields like Hindon). I can make procedural adjustments to accommodate civil airlines."
The IAF has, in fact, made many adjustments; Hindon is now freer with its airspace than ever before. But airspace bottlenecks have grown despite this because the IAF's generosity has been neutralised by a new paranoia.
In the wake of 9/11, when images of airliners ploughing into landmark buildings fanned fears in New Delhi, a committee headed by former Director General of Civil Aviation HS Khola framed regulations to keep civilian aircraft away from the so-called VIP areas of central and south Delhi. Those regulations add to the delays.
Civil aviation in other metro cities suffers equally from having to share airspace with IAF installations. A new international airport is coming up in Bangalore, but it is surrounded on three sides by IAF airspace.