New Delhi, Dec 7 (PTI) IndiGo - the airline that once redefined punctuality and scale in India - cancelled hundreds of flights nationwide, undone by its biggest operational crisis yet: a potent mix of misjudged pilot requirements under new rules and a risky "lean-staffing" or "buffer-deficit" model.

Regulatory changes to pilot duty-time limits, combined with tight staffing and an aggressive winter schedule, exposed deep cracks in IndiGo's crew-planning model this month. The airline's use-every-aircraft, maximise-night-flying strategy - the backbone of its low-cost dominance - collapsed as large segments of its pilot roster were pushed into mandatory rest periods.

India's largest airline has been for the past six days cancelling hundreds of flights, including more than 650 on Sunday out of around 2,300 daily flights it operates, throwing travel plans into disarray for tens of thousands of passengers.

The disruption left many missing critical meetings, job interviews and even their own wedding receptions, while some stranded travellers were reportedly dealing with medical emergencies.

With IndiGo commanding over 65 per cent of India's domestic market, the disruptions set off a nationwide domino effect, overwhelming airports and leaving rival carriers unable to absorb the surge of displaced travellers.

Terminals were flooded with desperate, angry passengers, while thousands of pieces of baggage lay strewn across arrival and departure halls.

Regulators have stepped in, arguably belatedly, with fare caps, advisories and oversight, while the airline has rolled out fee waivers, refunds and a phased restoration plan. The steps in the near-duopoly market - IndiGo and Tata Group-owned Air India control over 91 per cent of the market share - will take time to restore normalcy.

Here is an explainer on the crisis: TRIGGER: The Directorate General of Civil Aviation (DGCA) introduced revised Flight Duty Time Limitations (FDTL) rules in phases, with full enforcement by November 1, 2025, to combat pilot fatigue and align Indian aviation with global safety standards.

Under the new rules, weekly rest for pilots was raised from 36 to 48 hours; weekly number of landings a pilot can make from midnight to early morning cut to two from six earlier, maximum time pilots can fly in flights that stretch into the night capped at 10 hours, no more than two consecutive night duties and night flights defined more tightly (00.00 - 06.00 instead of earlier 00.00 - 05.00) - all of which dramatically reduced the number of flights a pilot can operate per week.

DGCA had originally notified the revised limits in January 2024. The revised rules were notified with immediate effect on May 31 last year, with airlines initially required to comply by June 1, 2024, but their implementation was deferred to a phased roll-out starting July 1, 2025, and completing by November 1 this year.

POOR PLANNING: IndiGo reportedly underestimated how many additional pilots were needed under the new rules. For its large Airbus A320 fleet, IndiGo said it needed over 2,422 captains to operate smoothly, but had only 2,357 and a similar shortfall among first officers.

Also, adding to the problems was IndiGo's "lean-staffing" or "buffer-deficit" strategy - limited pilot hiring, thin roster reserves and an operating model heavily reliant on night flights and high aircraft utilisation. That formula worked under the old rules, but it left the airline with virtually no cushion once stricter crew-rest requirements kicked in.

CANCELLATIONS: Mass flight cancellations were reported first on December 2.

On December 3, at least 150 flights were cancelled, spread across Delhi, Bengaluru, Hyderabad, and Mumbai. And chaos only escalated thereafter.

Major airports - Delhi, Mumbai, Bengaluru, and Hyderabad, among others - turned into scenes of chaos: long queues, stranded passengers, missing baggage, cancellations even after boarding or check-in, and very poor communication from airline staff.

For thousands of passengers, the disruption was far more than an inconvenience: missed weddings, business meetings and medical emergencies, alongside costly last-minute rebookings and days of uncertainty with no clear timelines.

INITIAL AIRLINE RESPONSE: IndiGo acknowledged widespread problems for the first time on December 3, and attributed it to a multitude of factors - minor technology glitches, schedule changes linked to the winter season, adverse weather conditions, increased congestion in the aviation system and implementation of updated crew rostering rules (Flight Duty Time Limitations).

The airline said all these factors worked together to have a "negative compounding impact on our operations in a way that was not feasible to be anticipated".

IndiGo also said it would provide refunds or alternate travel arrangements.

It said the cancellations arose primarily from "misjudgment and planning gaps".

BOOKINGS: Despite problems taking root, IndiGo continued to take fresh bookings for same-day and near-future flights and checked-in passengers, later informing them that the flights were delayed and communicating cancellation after hours of wait at the airport.

Even after six days, IndiGo does not provide a clear status of flights it is operating during the day or the ones that are cancelled. It is left to passengers to find out if their flights are scheduled or cancelled, often after they reach the airport.

APOLOGY: The airline officially apologised to passengers on December 4, following three days of long airport queues and stranded travellers left waiting for flights that never took off.

The next day, IndiGo CEO Pieter Elbers issued an apology and outlined three lines of action to solve the crisis, expecting the airline to "return to a full, normal operation" between December 10 and 15.

On Sunday, IndiGo said it will operate 1,650 out of around 2,300 flights and expects to stabilise operations by December 10.

IndiGo had also announced several measures to support the affected passengers - full refunds for all cancelled flights, processed automatically to the original mode of payment; complete waiver on cancellation and rescheduling fees for travel between December 5 and December 15, 2025; hotel rooms and ground transport arranged across cities for stranded passengers; complimentary meals and snacks to be provided at airports; and lounge access for senior citizens, wherever possible.

RULES SUSPENDED: Facing public outrage and massive disruption, DGCA on December 5 granted a temporary one-time exemption for IndiGo's A320 fleet from certain night-duty and night-landing restrictions, effective until February 10, 2026.

At the same time, DGCA has opened a formal inquiry. IndiGo must submit fortnightly progress reports on crew utilisation, propose a concrete roadmap to plug staffing gaps, and generally rebuild its roster resiliency.

FARE CAPS: The crisis at IndiGo led to a surge in domestic airfares across several important cities. For example, the cheapest fare for December 6 for a Delhi to Bengaluru flight crossed Rs 40,000, with some options exceeding Rs 80,000. Minimum fare for Delhi-Mumbai touched Rs 36,107, with the highest over Rs 56,000. Last-minute fare for Delhi-Chennai surged to Rs 62,00-Rs 82,000.

The government stepped in on December 6, capping fares. The Ministry of Civil Aviation ordered all airlines to maintain strict adherence to prescribed fare caps.

SHOWCAUSE: DGCA on December 6 issued show-cause notices to IndiGo CEO Pieter Elbers and Accountable Manager Isidro Porqueras, seeking explanations within 24 hours on the massive flight disruptions.

The notices mentioned that the primary cause of the flight disruptions is the non-provisioning of adequate arrangements to cater to the revised requirements for smooth implementation of the approved FDTL scheme for the airline.

BOARD COMMITTEE: IndiGo on Sunday said its board of directors has set up a Crisis Management Group (CMG) comprising its chairman Vikram Singh Mehta and directors Gregg Saretsky, Mike Whitaker, and Amitabh Kant.

CEO Pieter Elbers is also part of the group that has been meeting regularly to monitor the situation and is being constantly updated by the management on the measures being undertaken to restore normal operations. PTI TEAM ANZ BAL BAL