Peak winters spell doom for the aviators, operators and fliers on account of poor visibility conditions at the airports. Indo- Gangetic plains are more vulnerable for thick fog disrupting air operations. National capital Delhi, is the hub center, operating hundreds of daily flights, both, in and out. The city also is one of the most vulnerable and susceptible airport for disturbing the winter schedule, subjected to low visibility conditions. Fog may disrupt flight operations anytime between November to February. However, period from 15 December to 31st January is frequented by thick and dense fog. Incidents of thick fog can not be ruled out in February as well. Visibility range of 200 mtr or less is termed as thick fog and reaching threshold of 50 mtr is called dense fog. Anything less than 50 mtr is practically considered ‘Nil’ visibility and termed as ‘very dense fog’.
There is inter dependence of three players for tackling fog hit operations. Firstly, the airline machines ( aeroplane) need to be well equipped and should be constantly upgraded. Secondly, ground based aviation aids in terms of landing system is quite important. There are different versions of landing equipment used, one of them being CAT- III (A,B,C) which is used at Indian airports. Thirdly, the most important being training and qualification of pilot. Compatibility of man and machine to the prevailing meteorological conditions holds the key , for authorised operations.
In poor visibility conditions, all the airports resume Instrument Landing System ( ILS), facilitating landing and take-off, popularly called CAT-III procedure. At Palam airport, 3 runways are equipped with ILS, namely runway 11, 28 & 29. Only, CAT-III compliant pilots are permitted to carry out marginal visibility operations during landings and take-offs. The CAT-III compliant pilot may land in visibility, as low as 50 mtr, with a decision height of 15 mtr. However, for take off, the threshold visibility requirement goes up to 125 mtr. All this is subject to visibility range along the runway in use, called RVR.
CAT-III system comes in to play when the visibility drops to 200 mtr or less. CAT-III A operations are done in visibility (RVR) >/= 175mtr. CAT-III B operations are adopted when the RVR is >/= 75 mtr. And finally, CAT-III C procedure is followed when the airport visibility drops to less than 50 mtr. However, when the RVR for the runway in use drops below 50 mtr, the airfield is shut for air operations.