Wednesday, August 23, 2017

When dark clouds beckon

Heavy rainfall, en route icing, moving cloud, severe turbulence, strong gusty winds, severe thunderstorms, and lightning inside the cloud... These are only some of the challenging scenarios that a pilot has to contend with while flying during a monsoon.

Many a time, these scenarios are beyond the range of the weather radar installed on board the aircraft. The pilot is expected to 'fly around' these types of severe weather to ensure safety of not just the passengers and crew but also the aircraft.

In meteorology, monsoon signifies directional shifting of winds from one season to another. In summer, warm and moist wind blows in from the ocean towards the land (South-West monsoon). During the winter months this is reversed: cold and dry wind originating from land blows into the sea (North-East monsoon).

Together, they involve a change of 180 degree in the wind direction. And herein lies the trigger to the entire chain of risky weather events ranging in type and severity from location to location.

Capt Paresh Nerurkar, a senior commander in Air India, says the presence of a low-pressure area (a weather system over sea or land, signifying active monsoon conditions) could throw up its own challenges.

He specifically pointed the corridors along the coasts — South Gujarat to Kochi on the West Coast and Kolkata to north of Chennai on the East Coast – in this connection. They are challenging for a variety of reasons, including proximity to the sea and associated weather events that they can throw up.

Also, during a monsoon, avoiding the clouds can be challenging. "At high altitudes, they are very destructive and dangerous. Once you enter them, it is very difficult to save yourself," he says.
While taking off/landing, it is generally the high winds that engages the attention of a pilot. It becomes difficult to control the aircraft. "A thunderstorm is generally associated with strong and variable winds. It can be extremely tough here," Captain Nerurkar says.

In general, heavy rain is known to affect depth and distance perception. Rain on the wind-shield creates refraction effects that can lead a pilot to believe that the aircraft is too high, with the risk of an unwarranted nose-down correction and flight below the desired flight path.

Rain at night increases the apparent brilliance of the Approach Light System making the runway appear to be closer than it really is. The risk is that a pilot will land short of the runway threshold. Runway surface conditions can also induce illusions. As a wet runway reflects very little light, a pilot may think that the aircraft is further away, contributing to the risk of a late flare and hard landing.
Flying in haze too creates the impression that the runway is further away, inducing a tendency to shallow the glide path.
23/08/17 Vinson Kurian/Business Line

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