Delhi airport fog delays arrivals across north India every winter, filling the board with "Delayed" and "Diverted" the moment the season's fog sets in. Someone waiting at the curb usually asks the same question: doesn't Delhi have CAT III landing systems for exactly this? It does, and CAT III is genuinely why Delhi still lands flights on mornings that would have shut a lot of airports down completely. It is not why the board clears fast once fog sets in. Those are two different problems, and the gap between them is worth understanding before you plan a pickup in December or January.
What CAT III actually means
CAT III, short for Category III, is an instrument landing classification that lets an aircraft land using ground-based radio guidance instead of the pilot seeing the runway. Skyfarer Academy's rundown of the categories, working from the U.S. regulations it describes, puts Category I at a runway visual range (RVR) of 2,400 feet, or 1,800 feet on runways with enhanced touchdown-zone lighting, roughly 730 meters or 550 meters; Category IIIA down to 700 feet, roughly 210 meters; and Category IIIB, the most capable version flying commercially today, down to 150 feet, roughly 45 meters.
India runs its own operating minimums for CAT III flying, and these are the ones that actually govern a Delhi landing. Under the rules Indian carriers fly to, a CAT III(B) landing needs an RVR of at least 75 meters, and a CAT III take-off needs at least 125 meters, reported by Business Today in December 2025. Landing and take-off are treated separately for a reason worth remembering at the curb: an aircraft already in the pattern can often still land in conditions that will not let the next one leave the gate.
Why the board still backs up even with CAT III
CAT III solves the physics problem of landing blind. It does nothing for the traffic problem underneath it, and that is the part that actually produces the delayed and diverted rows on the board.
Delhi normally lands or launches roughly one aircraft a minute across its runways. In dense fog, even with every CAT III procedure running, that rate can stretch to closer to one flight every three minutes, because of the extra separation and taxiing caution low visibility forces on controllers and pilots alike, per the same Business Today report. A three-times slowdown does not sound catastrophic on paper. Run it for the five or six hours a serious fog bank can sit over Delhi and the backlog compounds fast: every flight that lands late pushes its own departure late, and every departure that slips pushes the next arrival into a longer holding pattern. CAT III keeps the airport open. It does not keep the schedule intact.
DGCA's fog window and what it requires of airlines
India's civil aviation regulator, the DGCA, does not leave fog season to chance. For the 2025-26 season it set the low-visibility window at December 10, 2025 to February 10, 2026, and inside that window airlines carry specific obligations rather than a general expectation of caution.
Two of those obligations do most of the work. Airlines must roster cockpit crew who are specifically trained and current on Low Visibility Operations through CAT III B or the relevant Instrument Landing System procedure, with standby crew available rather than a single qualified pilot per route. And airlines must deploy CAT III B-certified aircraft to the stations most exposed to fog, so the right airframe is already sitting at the right airport before the fog rolls in rather than being flown in after, according to the fog-season plan Air India published ahead of that window. An airline that shows up to December without either piece in place is the one whose flights get cancelled first, not because its aircraft cannot land, but because it has no crew cleared to try.
Which other Indian airports have CAT III, and where diversions actually go
Delhi is not the only Indian airport carrying this infrastructure. Six airports currently have CAT III capability: Delhi, Lucknow, Jaipur, Amritsar, Bengaluru and Kolkata, per Business Today's December 2025 reporting. Amritsar's Sri Guru Ram Dass Jee International Airport is the one that matters most for Punjab-bound travellers, since it sits in the same north-India fog belt as Delhi and carries the same seasonal exposure.
That six-airport list is not the same as the list of airports Delhi flights actually divert to. The same Business Today reporting names the destinations for Delhi fog diversions directly: primarily Jaipur, Ahmedabad, Lucknow, Nagpur, Bhopal and Indore. Only Jaipur and Lucknow appear on both lists. Ahmedabad, Nagpur, Bhopal and Indore have no CAT III capability at all, which means a diverted flight can face a longer wait on the ground once it lands there, not just a longer wait in the air getting there.
An airport without CAT III has a much shorter fog tolerance of its own: once RVR drops much below Category I minimums, that airport simply stops accepting or releasing traffic until conditions lift, with no landing-system workaround available.
What to watch on the board if you are waiting
Two things on the arrivals or departures board matter more than the rest during fog season. The status word itself is the first: "Delayed" during a fog event usually means the flight is genuinely airborne or on the ground somewhere, working through the slower movement rate rather than sitting cancelled, while "Diverted" means it has gone to an alternate airport, most likely Jaipur, Ahmedabad, Lucknow, Nagpur, Bhopal or Indore, and a new plan for reaching you is now needed. The second is the estimated time itself, which will move more than once during an active fog bank as the airline updates it against the actual movement rate rather than the schedule filed months earlier. Treat an estimate from two hours ago as expired, not as wrong, and refresh before you leave the house rather than after.
How TrackMyWings helps
TrackMyWings™ is a live flight-tracking platform in development, India-first in its go-to-market with worldwide coverage in view. A private beta shipped on 2026-08-24, Android only, on the Play internal testing track, with a small group of named testers. Public launch has no fixed date yet.
Delhi and Amritsar both have airport pages in our directory, Delhi and Amritsar, alongside an IndiGo airline page. Gate and status alerts and a live map are planned for launch and do not exist yet, so for this winter's actual fog delays the sources to check are DGCA's own notices and your airline's status page, not any app, including ours.
Questions people ask
Does CAT III mean fog delays should not happen at Delhi anymore? No. CAT III lets aircraft land and depart in visibility that would ground a non-equipped airport entirely, but it does not restore Delhi's normal one-flight-a-minute movement rate. The slower, more cautious pace fog forces on controllers is what actually produces the delays on the board.
Why do some flights land while others at the same airport are diverted? Landing and take-off have different minimum visibility requirements, with take-off typically needing more runway visual range than landing. An aircraft already lined up to land can sometimes get in under conditions that will not let a different flight depart, which is why the board can show both outcomes within minutes of each other.
Which other airports could my diverted flight land at during Delhi fog? Business Today's December 2025 reporting names Jaipur, Ahmedabad, Lucknow, Nagpur, Bhopal and Indore as the airports that actually take Delhi's fog diversions. Only Jaipur and Lucknow among them also have CAT III capability; the others do not, so a diverted flight can face a longer wait on the ground once it lands.
Is the DGCA fog window the same dates every year? Not exactly, though it lands in the same general stretch. For the 2025-26 season DGCA set it at December 10 to February 10; check the current season's notice each winter rather than assuming the same dates repeat.
Sources
- Travel Trade Journal, "Air India activates fog-season plan as DGCA sets Dec 10-Feb 10 low-visibility window", https://traveltradejournal.com/air-india-activates-fog-season-plan-as-dgca-sets-dec-10-feb-10-low-visibility-window/, captured 2026-09-23
- Business Today, "Explained: Why even CAT III compliant flights get hit by low visibility during fog", https://www.businesstoday.in/india/story/explained-why-even-cat-iii-compliant-flights-get-hit-by-low-visibility-during-fog-507230-2025-12-18, captured 2026-09-23
- Skyfarer Academy, "How Low Can You Go? Understanding ILS Categories I, II, and III", https://blog.skyfareracademy.com/2026/04/16/how-low-can-you-go-understanding-ils-categories-i-ii-and-iii/, captured 2026-09-23
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