sunilwings
24th Aug 2008, 00:37
WET VERSUS CONTAMINATED R/W
“More stopping power is needed when the R/W is contaminated”
On 1 Jun 2008, A-320 of Guatemala went off the R/W and broke into 3 pieces. 6 dead 31 injured. On 2 Aug 2005, an Air France A-340 over-ran the R/W at Toronto. The a/c was destroyed in a post accident fire. Exactly a month earlier a Bangla Desh a/c Biman DC-10 over-ran the R/W at Chittagong. The a/c suffered extensive damage. An Air India Boeing 747 which went off the R/W. on Mumbai, on 30 July 2005 and was lucky to escape with no damage except reputation. Even before the enquiry started several arm chair pundits blamed the pilots. Question that emerged was “Were they aware of what is involved in a wet runway landing?
All the accidents mentioned took place while landing in heavy rain. All the aero planes involved experienced x-wind component and tail wind component. This combination is very dangerous. During a heavy down pour the water depths can vary along the R/W depending upon the condition and slope. The a/c wheels can hydroplane (explained in later paragraphs) if the depth is sufficient to prevent making proper contact with the R/W.This makes it very difficult to stop the a/c within the confines of the R/W.
Why do accidents happen on wet R/W?
Main reasons are that the pilots do not get the correct information on the Actual R/W condition. The only information the pilot gets is that the R/W is “WET”.
Obviously, what is a wet R/W? For a pilot a R/W is considered “WET” when the depth of water on it is less than 3mm. that is what the Flight Manuals state. If the depth is more than 3mm, the R/W comes into the category of “SLIPPERY” or “CONTAMINATED”. These differences in water depths will change the actual landing distance by a very large amount.
The a/c requires 40% more R/W to stop on a wet R/W, on a contaminated R/W the figure increases to 300%. Thus if an a/c requires 6000’ feet of R/W for landing on dry R/W, it will require 8400 ft on wet R/W and more than 18000ft if the R/W is contaminated!
Thus when a pilot receives a report that says that R/W is wet, he assumes that the depth of the water is less than 3mm and after a 40% addition to the landing distance, will make for a safe landing. In reality the actual depth of the water on the R/W can be as much as 3 inches during a heavy monsoon downpour. This would bring it into CONTAMINATED CATEGORY. In 33 years of my flying I have never heard the R/W condition report other than WET (An issue for contemplation).
Accidents on wet Runway’s are on the increase. Experience levels of the pilots in the airline are dropping due to rapid expansion in Aviation Sector. Unfortunately Training and regulations are not in pace with time. Adequate back up training on simulators is found wanting. Furthermore many accidents in recent past have involved a/c with old technology, without modern safety features that are inbuilt into new generation aircrafts.
The answer to it,
Building Grooved Runway’s, investing in Modern Runway’s friction system and proactive R/W conditions are essential for making landings safe.
Therefore it is important to understand the various aspects on a/c performance when it comes to land on wet/contaminated R/W.
“More stopping power is needed when the R/W is contaminated”
On 1 Jun 2008, A-320 of Guatemala went off the R/W and broke into 3 pieces. 6 dead 31 injured. On 2 Aug 2005, an Air France A-340 over-ran the R/W at Toronto. The a/c was destroyed in a post accident fire. Exactly a month earlier a Bangla Desh a/c Biman DC-10 over-ran the R/W at Chittagong. The a/c suffered extensive damage. An Air India Boeing 747 which went off the R/W. on Mumbai, on 30 July 2005 and was lucky to escape with no damage except reputation. Even before the enquiry started several arm chair pundits blamed the pilots. Question that emerged was “Were they aware of what is involved in a wet runway landing?
All the accidents mentioned took place while landing in heavy rain. All the aero planes involved experienced x-wind component and tail wind component. This combination is very dangerous. During a heavy down pour the water depths can vary along the R/W depending upon the condition and slope. The a/c wheels can hydroplane (explained in later paragraphs) if the depth is sufficient to prevent making proper contact with the R/W.This makes it very difficult to stop the a/c within the confines of the R/W.
Why do accidents happen on wet R/W?
Main reasons are that the pilots do not get the correct information on the Actual R/W condition. The only information the pilot gets is that the R/W is “WET”.
Obviously, what is a wet R/W? For a pilot a R/W is considered “WET” when the depth of water on it is less than 3mm. that is what the Flight Manuals state. If the depth is more than 3mm, the R/W comes into the category of “SLIPPERY” or “CONTAMINATED”. These differences in water depths will change the actual landing distance by a very large amount.
The a/c requires 40% more R/W to stop on a wet R/W, on a contaminated R/W the figure increases to 300%. Thus if an a/c requires 6000’ feet of R/W for landing on dry R/W, it will require 8400 ft on wet R/W and more than 18000ft if the R/W is contaminated!
Thus when a pilot receives a report that says that R/W is wet, he assumes that the depth of the water is less than 3mm and after a 40% addition to the landing distance, will make for a safe landing. In reality the actual depth of the water on the R/W can be as much as 3 inches during a heavy monsoon downpour. This would bring it into CONTAMINATED CATEGORY. In 33 years of my flying I have never heard the R/W condition report other than WET (An issue for contemplation).
Accidents on wet Runway’s are on the increase. Experience levels of the pilots in the airline are dropping due to rapid expansion in Aviation Sector. Unfortunately Training and regulations are not in pace with time. Adequate back up training on simulators is found wanting. Furthermore many accidents in recent past have involved a/c with old technology, without modern safety features that are inbuilt into new generation aircrafts.
The answer to it,
Building Grooved Runway’s, investing in Modern Runway’s friction system and proactive R/W conditions are essential for making landings safe.
Therefore it is important to understand the various aspects on a/c performance when it comes to land on wet/contaminated R/W.