Heavy fog engulfing the national capital today stranded thousands of air and rail passengers leading to the cancellation of numerous flights and train delays.<br/><br/>A fault in the landing system at the Indira Gandhi International (IGI) Airport and "tripping" of the northern grid further added to the problems of the people.<br/><br/>The visibility dropped to less than 100 metres in the city early today and continued to remain low till 1200 hrs.<br/><br/>Around 50 domestic flights and 20 international flights were delayed for hours and many were cancelled due to low runway visibility at the IGI Airport.<br/><br/>An DIAL official informed that the CAT III B instrument landing system that provided visibility data to Air Traffic Control (ATC) could not be used due to fault in the Runway Visibility Range (RVR) instrument.<br/><br/>The minimum temperature in the capital was recorded at 8.4 degrees Celsius, a notch above the normal for this time of the season.<br/><br/>The India Meteorological Department (IMD) has forecast dense fog and clouds in Delhi tomorrow with a minimum temperature hovering around 9 degrees.<br/><br/>The situation was no better at the city's railway stations, where over 50 incoming trains were delayed by more than five hours.<br/>