Hundreds of flights were delayed at Delhi airport, one of the busiest in the world, after a technical issue with an air traffic control messaging system on Thursday evening, according to India's airport authority and a source familiar with the situation.

The malfunction, which caused average delays of an hour for departures, had the potential to create further disruptions and lead to congestion at other airports across India. Arrival delays also increased due to the growing backlog on the ground, as indicated by Flightradar24 data.

Shares of IndiGo fell by 2% on Friday, while SpiceJet dropped by 1%, as the airlines, alongside the Air India Group, warned of continued delays. The airlines are expected to incur additional costs from passenger care and refunds due to the delays, which are likely to extend into Saturday.

The Airports Authority of India (AAI) explained that the issue stemmed from the Automatic Message Switching System, which generates flight plans. The malfunction forced controllers to manually create flight plans, resulting in the delays.

The problem began on Thursday evening local time, the source added.

"Technical teams are working to restore the system as soon as possible," the AAI stated in a post on X. The agency did not provide further details about the cause of the malfunction.

Some airlines, including Air India Express, have assigned their own personnel to assist air traffic control in manually generating flight plans, another source said.

CNN NEWS 18 reported that authorities were investigating whether computer malware might have caused the issue, although Reuters could not independently confirm this claim.

This incident follows a ransomware attack in September that disrupted automated check-in systems at some of Europe's largest airports, leading to flight delays.

The technical issue in India caused approximately 25 flight departures to be delayed on Thursday, and over 175 on Friday at Delhi airport, the first source said. Delhi airport typically handles 60-70 aircraft movements per hour. Flightradar24 data showed that average departure delays were around 60 minutes.

The glitch also affected several international flights, with an ITA Airways flight to Rome delayed by nearly two hours and a Virgin Atlantic flight to London delayed by more than an hour. The AAI has not provided an estimated time for when the issue will be resolved, according to two airline sources.

Delhi airport, which handled around 78 million passengers in 2024, is the ninth busiest airport in the world, according to Airports Council International. The airport operator is majority-owned by GMR Airports, while air traffic control is managed by the AAI.

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