Indian Weather and the Runway Conditions

Rain is a major factor. Operating flights in heavy rain emphasizes the importance of numbers and runway conditions. Flight manuals mandate the numbers to be flown by the pilots. The performance Regulations restricts the precise weight of the aircraft allowable for a particular condition and allowances are made by human factor errors. Eg: WHEN A RUNWAY IS REPORTED TO BE WET operational calculations are based on the amt of water being less than 3mm on the runway surface. When it exceeds that figure, the condition is based on what is termed as “Contaminated or Slippery” When water exceeds 13mm on the runway surface, take-off and landing are not permitted.

The Data given by the manufacturers for take-off and landing distances are based on the numbers flown by extremely test pilots. The data obtained from the test flights are multiplied by 1.67 to allow human factor errors – the experience levels and the flying skills of average pilot. This figure applies when the runway conditions are DRY. When the runway is reported wet, this corrected figure is multiplied by 1.15 to allow for additional safety margin. Hence, a dry runway figure is multiplied by 1.92times to cater for a landing on a wet runway, almost double if you see.

Runway Reported "WET"

A perfect landing at 1000 feet from the beginning of the runway at a precise speed, an immediate application of brakes within ONE second and deployment of Thrust Reversers and spoilers within TWO seconds of touchdown. The average pilot is unlikely to match these numbers. The margin of 1.92 is calculated to cater for the performance of an average pilot.

In adverse weather conditions, speeds are likely to vary due to wind conditions and also the flying skill of the pilot. During an approach in heavy rain, the visual illusions due to the film of water on the windscreen in spite of powerful wipers that aircrafts have, can create judgment errors.

The fatigue factor of a pilot comes into play when pilots are required to take off and land during rain. Obviously the runway condition is gonna be “WET” in reality they are flooded but no action is taken and the pilot takes off or lands in the belief that the depth of water is only 3mm!!


~ by anand213 on February 23, 2009.

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