Why flights are cancelled during rain: it is not just visibility

On Monday, heavy rain and thunderstorms caused disruptions in flight operations at Delhi's airport, with 26 flights cancelled and 15 diverted. Despite modern commercial aircraft being built to operate in poor weather, heavy rain can still disrupt flights. While reduced visibility is a concern, it is not the primary issue. Pilots are trained in instrument flying and can navigate guided by cockpit instruments, making heavy rain less of a problem once the aircraft is high enough.

The main issue arises during take-off and landing. Rain can create runway spray, while rain and low cloud can reduce pilots' ability to see lights, markings, and obstacles on the runway. This is where runway visual range (RVR) comes into play - the distance a pilot can see markings or lights over the runway. If the RVR is too low, the plane faces a higher risk of sliding off the runway, hitting a ground vehicle, or colliding with another plane due to reduced braking and directional control.

Airlines and airports closely monitor runway conditions, with the American government's Federal Aviation Administration (FAA) advising pilots to be vigilant about potential changes in braking conditions on wet runways. Strong winds, thunderstorms, and lightning are other threats posed by heavy rain. Thunderstorms can produce rapid changes in wind speed and direction, turbulence, hail, and lightning. Strong crosswinds can make landing and take-off difficult, as pilots have to adjust the plane's path in relation to the wind.

Despite these challenges, commercial aircraft are designed to withstand severe weather conditions. They have systems to remove rain from the windshield, protect against icing, and handle lightning strikes. Pilots, crew, and ground personnel are highly trained to ensure safe flight operations in poor weather, using systems like the Instrument Landing System (ILS) and the CAT system for low-visibility operations.