Explained | Why Pilots Need Rest, How Fatigue Grounded Flights, And Why Indigo Struggled to Implement New FDTL Rules

By Surabhi Gupta

New Delhi: Pilot alertness is the invisible safety net of aviation. Every commercial flight depends not only on technology, training and procedures, but on the physical and mental readiness of the human beings at the controls. While pilots undergo rigorous training, medical screening and recurrent checks, experts warn that fatigue, especially chronic and unmitigated fatigue, remains one of the most under-recognised threats to flight safety.

Recent cases of pilot illness, in-flight incapacitation, diversions and sudden flight cancellations have forced India’s aviation regulator to confront a long-delayed issue: whether airlines are pushing pilots beyond safe limits in pursuit of tight schedules and lower costs. At the centre of the debate are the Flight Duty Time Limitations (FDTL) rules, and the operational disruptions that followed their stricter enforcement, particularly at IndiGo, the country’s largest airline.

Why Rest Matters: The Science Of Fatigue And Circadian Rhythm

Former aviation veteran Captain Shakti Lumba explains that pilot fatigue is not simply about feeling tired. It is rooted in human biology. “The period between 4–6 AM is known as the WOCL, the window of circadian low,” Lumba told ETV Bharat. “Any sleep disruptions during this period leave the body tired. Repeated disruptions of the WOCL cause fatigue, which is a mental state of mind when a person becomes less alert, loses concentration and is likely to make mistakes.”

According to Lumba, regular sleep disruption between midnight and 6 AM leads to what is called transient fatigue. “This gets mitigated by weekly rest of at least 48 hours, including two local nights,” he said. “If transient fatigue is not mitigated with rest, it leads to the more dangerous cumulative fatigue.”

Cumulative fatigue, aviation experts warn, cannot be fixed with a single day off. It builds silently over weeks of disrupted sleep, night operations and extended duty hours, increasing the risk of errors, slow reactions and even sudden medical incapacitation in the cockpit.

Recognising this, the Directorate General of Civil Aviation (DGCA) redefined “night” for fatigue management purposes from 12 midnight to 6 AM, restricted night operations infringing this period to no more than two times a week, and limited night landings during this window to two per flight. “These restrictions are not arbitrary,” Lumba said. “They are based on how the human body actually functions.”

Medical Reality: Fatigue Is A Health Risk, Not A Motivation Issue

Doctors underline that fatigue is a physiological and neurological condition, not a matter of discipline or willpower.

Dr Rajesh Sagar, Professor of Psychiatry at AIIMS, told ETV Bharat, "Chronic fatigue represents a neurobiological state rather than a subjective complaint. Night flying disrupts circadian regulation, impairing executive function, vigilance, emotional control and insight, often before the individual is aware of the deficit. Fatigue affects the brain, cardiovascular system and metabolic balance simultaneously, increasing vulnerability to microsleeps, judgment errors and sudden functional incapacitation.”

Dr Sagar cautioned against relying on stimulants or medications. “Pharmacological countermeasures may mask sleepiness but do not restore higher-order cognitive capacity essential for safe flight operations,” he said, stressing that fatigue must be treated as a preventable medical risk factor.

Senior psychiatrist Dr Deepak Raheja described the danger more starkly. “Humans are simply not designed to operate at 35,000 feet while the rest of the world sleeps,” he said. “Repeatedly fighting circadian rhythm is chronic biological stress. It keeps cortisol levels high and puts immense strain on the heart.”

“The scariest thing about fatigue is that it mimics intoxication,” Raheja added. “A sleep-deprived pilot often has the same delayed reaction times and poor judgment as someone over the legal alcohol limit.”

Pulmonologist Dr Meet Ghonia warned that fatigue also interacts with hypoxia. “Chronic fatigue and irregular sleep impair oxygen utilisation and increase stress hormones, leading to reduced alertness, microsleeps and cardiac rhythm disturbances,” he said. “Fatigue reduces reaction time and emergency response capacity, similar to flying with mild hypoxia.”

Dr Rachana Awatramani, PhD, counselling psychologist, said chronic fatigue, irregular sleep patterns and night flying can seriously affect a pilot’s physical and mental health. Disrupted rest disturbs the body’s circadian rhythm, leading to impaired cognitive performance, slower reaction times and reduced motor skills. Over time, sleep deprivation can weaken immunity, increase cardiovascular risks and affect metabolic health.

From a psychological perspective, fatigue reduces alertness, focus and judgment, increasing the likelihood of errors during critical phases of flight. “A fatigued brain processes information more slowly and inaccurately, which can compromise decision-making, especially in emergencies. In severe cases, extreme fatigue may even result in in-flight incapacitation. Adequate rest, she stressed, is essential for maintaining alertness, memory recall and the ability to respond effectively to unexpected situations in the cockpit,” she explained.

Trigger Events That Forced Regulatory Action

According to aviation experts, recent incidents involving pilot illness and incapacitation acted as a tipping point. “They were the trigger that made the DGCA stand up and take action to manage fatigue,” Captain Lumba said.

An ALPA (Air Line Pilots’ Association) official said two serious cases, one in August 2023 before a flight, and another in April 2025 after a flight, exposed the risks of fatigue being under-managed. “Many cases are suppressed by airlines,” the official said. “But these incidents hastened the 20-year-long struggle for FDTL implementation, which airlines had successfully lobbied against in pursuit of lowering costs.”

Why Airlines Resist: Economics Versus Safety

Captain Lumba argues that the resistance to FDTL is rooted in airline economics. “Airlines are bottom-line focused and consider regulatory safety as a hindrance to efficiency, revenue and profits,” he said. “They keep a lean workforce to reduce costs.”

Airline performance is measured using ASKMs (Available Seat Kilometres), while costs and revenue are calculated as CASK and RASK per seat kilometre. “As a business, airlines try to reduce CASK and increase RASK,” Lumba explained. “Safety is expensive. Some airlines like IndiGo are not willing to pay for safety since it results in higher CASK.”

“Only the country’s safety regulator can ensure airlines adhere to safety regulations,” he added. “That is done all over the world, except India.”

The ALPA official echoed this, pointing to flawed rostering and pay structures. “Pilots are paid only when they are flying,” the official said. “They are not paid when waiting at airports or during delays. Airline software is designed to squeeze maximum flight time from each pilot, without adequately accounting for total duty time.” Night flights, especially between 2 AM and 6 AM, are “especially susceptible to fatigue”, the official said, adding that airlines increased night operations in December 2025 compared to December 2024 without adequately supplementing pilot numbers.

Why IndiGo Struggled Despite A Long Warning Period

As India’s largest airline, IndiGo had the longest preparatory window to comply with Phase-2 FDTL rules. Yet it saw widespread delays and cancellations once enforcement tightened.

Captain Lumba says the reason was strategic confidence, not lack of awareness.

“Simply, they were confident that Phase-2 FDTL implementation would be rolled back due to lobbying and the clout they have because of their monopoly,” he said. “They got what they wanted by hook or by crook.”

The ALPA official pointed to deeper structural problems: “Artificially low salaries, long notice periods of six to twelve months, inability to train novice pilots fast enough to replace experienced pilots leaving IndiGo, lack of retention measures, and even non-poaching agreements.”

When DGCA enforced schedule reductions, however, the official said operations stabilised. “They are already operating with minimum cancellations and delays. The reduction of flight schedules has expedited normalcy.”

Till When Will Disruptions Continue?

According to Captain Lumba, the duration of disruptions depends entirely on the government’s stance. “It depends on whether the government keeps giving concessions or comes out with a fresh FDTL catering to airline economics at the cost of air safety,” he said. “Or whether it keeps public safety paramount and gives no further concessions.”

If safety rules remain firm, IndiGo will have two choices: reduce flights to match available captains, or significantly increase pilot strength. “Both will increase costs,” Lumba said.

Doctors and pilot bodies argue that this cost is unavoidable if safety is to be preserved.

“FDTL is one of the things that assures safety,” the ALPA official said. “But other systemic changes are also needed, fair pay structures, just culture, non-punitive fatigue reporting, and proper regulation of cadet pilot training.”

Fatigue is not an inconvenience to be managed around; it is a biological limit that cannot be negotiated away. As Dr Tarun Kumar of Medanta Moolchand Heart Centre warned, irregular sleep and extended duty degrade everything from reaction time and judgment to memory and motor skills, increasing accident risk.