Explained: Why even CAT-III compliant flights get hit by low visibility during fog

Delhi airport on December 18 said that due to dense fog, flight operations were under the CAT III conditions (low visibility operations) but in a sub-zero visibility, flight operations are completely stopped.  

Only six airports in India — Delhi, Lucknow, Jaipur, Amritsar, Bengaluru and Kolkata — currently have the infrastructure and technology to support CAT III operations during dense fog.

“Majority of the new aircraft are equipped with CAT III technology but airport infrastructure needs upgrade to facilitate the same,” says the Captain of a major airline.   

In a zero visibility scenario, even the airport with instrument landing systems (ILS) has to stop operations. The zero visibility in the aviation parlance means anything (even 1 meter below) the mandatory requirement of 75 meters for CAT III (B) landing and 125 meters for take-off. The ILS helps in landing but not taxing on the runway during fog.   

Air India and IndiGo have majority of their pilots’ compliant to CAT (III) landing which means a Captain having 500 hours of flying and first officer having 300 hours of flying. However, things go haywire as pile up happens during dense fog.  

“Delhi airport’s all four runways are equipped with CAT III landing but with over 1500 flight moments daily where every 1 min a flight takes off/land, during fog the duration shifts to 3 min per flight. If the visibility goes down below zero for 5-6 hours, the capacity gets blocked and pile up happens,” adds the Captain.

About 40 airports in the northern and northeast regions of the country facing the issue, badly impacting the flights during winter season. Delhi being the major domestic hub sees several flight disruptions during fog.

When Delhi airport is enveloped in dense fog, several alternate airports divert flights primarily, Jaipur, Ahmedabad, Lucknow, Nagpur, Bhopal and Indore.  

Airports in India are upgrading their instrument landing systems (ILS) to improve safety and efficiency as dense fog has been a recurring issues in the northern and northeasters regions of the country during winter months.