IndiGo will cancel around 500 flights on Friday in India, with all departures from New Delhi grounded, amid a deepening crisis at the country’s largest airline that has admitted it failed to plan for new flight duty timings imposed on pilots.

The crisis, in its fourth day, has jolted the airline which has over 60% market share and left thousands of passengers stranded across the country, in what has emerged as the biggest challenge for the carrier ever.

IndiGo plans to cancel 104 flights in Mumbai, 102 in Bengaluru, 92 in Hyderabad, airport sources familiar with the developments told Reuters. They declined to be named because they were not authorised to share the information.

Delhi airport announced all IndiGo departures were cancelled for the day, a number a source put at 235 flights.

On Thursday, IndiGo told the regulator its operations would be fully restored by February 10. It asked for relief from some provisions that limit pilot duty hours at night.

Indigo said the disruptions have arisen primarily from “misjudgment and planning gaps” in implementing the new pilot duty rules which increased the amount of mandatory rest per week for pilots by 12 hours to 48 hours, effective November 1.

In addition, pilots are now only allowed to make two night-time landings per week, down from six under the old rules.

Shares of IndiGo dropped nearly 3% on Friday, taking their weekly slump to 10.3%.

IndiGo’s on-time performance further dropped to 8.5% on Thursday from 19.7% on Wednesday, government data showed. On Thursday more than 250 flights were cancelled by the airline and on Wednesday around 150.