Delays at Delhi airport: Apart from the fog, what else is causing the chaos

Fog at one busy airport can cause widespread disruptions as airline networks and operations are complex, with aircraft and crew serving on multiple flights across sectors through the day. Complications like crew duty time limits being exceeded due to delays and lack of parking stands for incoming aircraft due to congestion compound problems.

Sunday blues at Delhi airport

On Sunday, as many as 508 outbound flights from the IGI airport were delayed while 87 were cancelled, as per data from flight tracking service Flightradar24. As for inbound flights, 414 were delayed while 42 were cancelled. Dense fog hit operations on Monday too, but the situation appears to have improved with the weather clearing up and visibility improving.

In addition to the fog, the fact that one of the runways equipped to handle aircraft movements in low visibility is currently inoperative worsened matters. The Delhi airport has four runways in all, of which two are Instrument Landing System (ILS) CAT IIIB-compliant, which means they are equipped to handle aircraft in extremely low visibility. One of the two such runways is under maintenance for recarpeting, and therefore, has not been in operation for weeks.

The problem was further complicated as the only operational CAT IIIB-compliant runway was reportedly recently downgraded in category from one end due to construction activity close to the runway. This meant that CAT IIIB landings could only operate from one side of that runway.

At one point, even this portion of the runway was rendered ineffective as visibility dipped to zero.

It is worth noting that having CAT IIIB-compliant runways is not enough in low visibility. Airlines are also required to deploy aircraft equipped for ILS CAT IIIB and pilots trained to handle low-visibility operations. These requirements could also have added to the woes.

Cascading effect on airline networks

For the sake of understanding, let us consider the example of a courier delivery vehicle, which is supposed to deliver a planned number of orders during the day at different locations. If it gets inordinately delayed at any of the locations, subsequent deliveries will also be delayed, or worse, cancelled for the day, unless the courier service is able to quickly deploy another delivery vehicle. But what if a large number of delivery vehicles get stuck at the same location? Surely, the operations would see a cascading impact.

This cascading effect on the network was apparent at the Mumbai airport, the country’s second-largest, which was unaffected by fog but had 362 delayed departures and 30 outbound flight cancellations on Sunday, as per Flightradar24 data. Delhi-Mumbai is the busiest aviation route in India with over 700 weekly flights between India’s political capital and financial capital.

In instances of such disruptions, airlines with large and dense networks and high aircraft and crew utilisation levels tend to suffer more. While such parameters reflect efficiency in operations, finding and deploying spare aircraft and crew at a short notice can be hugely problematic.

Beyond the fog

With numerous flights delayed or cancelled on Sunday, the congestion build-up at the Delhi airport also led to long queues for departure, leading to passengers being stuck in aircraft for hours before take-off. Often in such cases, passengers get restless and demand to be deplaned instead of spending hours inside the aircraft. However, deplaning passengers after boarding is not a simple process and requires clearances from airport security, as boarding is completed and luggage is already loaded onto the plane. Deplaning the passengers so they can wait at the terminal may also require them to go through airport security and be checked in again by the airline.

A number of incoming aircraft also bore the brunt of the congestion. For instance, an Air India aircraft operating a flight from Frankfurt to Delhi was able to land a little before 8 am on Sunday, but took almost two-and-a-half hours to find a parking bay.

As a consequence of delays due to heavy congestion at airports, pilots (flight crew) and cabin crew might exceed their Flight Duty Time Limitation (FDTL), after which they are not allowed to operate a flight till they have been through adequate rest periods. FDTL guidelines include limitations on duty time as well as flight time. This means that if the crew exceed the maximum permissible duty time for the day even if they have not been able to operate any flight in that period, they have to be taken off duty.

The Directorate General of Civil Aviation (DGCA) has increasingly turned stricter on FDTL compliance as fatigue is a major risk factor in aircraft operations. With hours wasted awaiting take-off or finding a gate after arrival, in addition to previous delays due to bad weather at major airports, crew shortage can hit airlines fairly quickly due to the FDTL norms.