The Phenomenon of Lightning Continued...
...Lightning is always associated with thunder storms (Jeppesen pg. 6-43), but can also occur within the ash clouds from volcanic eruptions, or can be caused by violent forest fires which generate sufficient dust to make a static charge. Although, in the last 100 years or so we have found out what lightning is; the greatest mystery yet to solve is how a simple cumulus cloud comes to produce one of nature’s most devastating phenomenon. Like most things, lightning has very humble beginnings in the water cycle.
What makes Lightning?
In the process of the water cycle, moisture can accumulate in the atmosphere. This accumulation is what we see as a cloud. Although scientists don’t agree on how clouds gain the charges to create lightning, many different theories exist. This one shows a possible explaination: Clouds can contain millions upon millions of water and ice droplets suspended in the air. As the process of evaporation and condensation continues, these droplets will eventually collide with other moisture that is in the process of condensing as it rises. The importance of these collisions is that electrons are knocked off of the rising moisture, thus creating a charge separation. (How Lightning Works pg. 2)
The newly separated electrons fall to the bottom of the cloud where they gather, while the water droplets carry the positive ions to the top of the cloud. This creates a strong electric field within the cloud. (Figure 1) As you can see, the electrical field becomes more and more intense till the electrons at the earth's surface are repelled deeper into the earth by the negative charge of the cloud. Since the negative electrons in the Earth are rebelled away, the ground acquires a strong positive charge.
Now the electrical field wants desperately to neutralize itself with the positive Earth. As the field grows in volts it begins to ionize, breaking down, and the air around the cloud. The importance of this ionization is that the electrons are now free to move much more easily than they could before. (Figure 2) “So, in other words, this ionized air (also known as plasma) is much more conductive than the previous non-ionized air.”(How Lightning Works pg. 3) You can see this process with I a high-speed camera as it “burns” a path to the ground. The path that is ionized will be the path the lightning will follow.
A path is not created instantaneously; in fact, there are many separate paths of ionized air stemming from the cloud. All the paths are referred to as step leaders. The air does not all ionize at the same time; any sort of pollution of impurities in the air will speed of the breaking down of the air. Step leaders don’t always follow the shortest path; they will follow the path of least resistance. Just as the step leaders form from the cloud heading toward the ground, a positive streamer reaches for the cloud. (Figure 3 & 4) However, once the positive streamer is formed they it doesn’t grow, as it is the job of the step leader to connect the all the way to the ground.
As soon as the two meet the connection between the ground and the cloud, the current flows to neutralize the charges. An electrical current, always has heat associated with it. Since there is an enormous amount of current in a lightning strike, there is a vast amount of heat. “In fact, a bolt of lightning is hotter than the surface of the sun.” (How Lightning Works pg. 5) The heat is the actual cause of the white-blue flash that you see.
In an effort to escape the heat, the oxygen expands so rapidly it creates a shock wave. This is best known as thunder, which give a thunder storm its name. Thunder, however, is not harmless. If you are too close you can feel the shock wave and it can cause you to go temporally deaf.
Impacts and Effects in Aviation
A commercial airliner is on the average struck by lightning twice per year. For all its power, lightning rarely causes crew injury or substantial damage to aircraft structures. (Figure 5) However, lightning can cause temporary loss of vision, puncture the aircraft skin, or damage electronic navigation and communications equipment. (Jeppesen pg. 6-43) The weather associated with lightning has more of an impact on flying, i.e. thunderstorms, because of the rarity of lightning strikes causing damage. If struck by a bolt of lightning, the current is largely directed around the outside of the aircraft's metallic skin. The last major U.S. commercial airliner crash caused by lightning was more than 35 years ago and was the worst lightning related aviation disaster. It occurred over Elkton, MD on 8 December 1963. Lightning struck and penetrated the reserve fuel tank. (How safe are you from lightning inside an airplane?) I will go over this accident in more detail in the Accident section of my paper. What happens is, when an airplane is struck by a thunderbolt, the electrical charges just traverse the length of the aircraft and exit through the static wicks at the trailing edges of the flaps or tail plane. The next time you happen to sit by a window seat behind the wings, just look out for these static wicks. They are like painting brushes with fine hairs sticking out at the end of the flaps.
How best to avoid Lightning and its effects
When you think of lightning you typically think of thunderstorms, although lightning can appear in other places. Lightning can also occur within the ash clouds from volcanic eruptions, or can be caused by violent forest fires which generate sufficient dust to create a static charge. (Volcanic Lightning)(Figure 6) So, logically, if you avoid things that cause lightning you will avoid lightning.
So the best way to avoid lightning and its effects is to constantly check weather and know the signs of developing thunder storms. Thunderstorms are results from the rapid upward movement of warm, moist air. They can occur inside warm, moist air masses and at fronts. As the warm, moist air moves upward, it cools, condenses, and forms cumulonimbus clouds that can reach heights of over 20 km. As the rising air reaches its dew point, water droplets and ice form and begin falling the long distance through the clouds towards the Earth's surface. As the droplets fall, they collide with other droplets and become larger. (Jack Williams) As the water droplets collide the particle separation creates the lightning.
Keeping up on the weather that is going on is a good way to avoid lightning and its various sources. One of the earliest ways to detect a thunderstorm is an unstable air mass. The unstable air mass lifts the air creating, given the right conditions, storm clouds that will eventually lead to the formation of lightning. The installations of static wicks are also a good way to ground the lightning as well.
Accidents Due to Lightning
According to NLSI, National Lightning safety Institute, there have only been a few aviation accidents that have cause fatalities. (NLSI) This number actually surprised me, for how long planes have been in and around lightning the number seems very small; although, I don’t believe that they have every accident relating to lightning. The accident that I choose to talk about was a devastating tragedy that ended with the plane crashing into the ground in a fireball. The accident killed all 81 of the crew and passengers. The Guinness Book of world records said that it is “The Largest Lightning Strike Death Toll,” not exactly the best record.
Pan American Flight 214 departed San Juan, Puerto Rico for a flight to Philadelphia with a stop at Baltimore. (Figure 7) The aircraft arrived at Baltimore and took off again after refueling. As they contacted approach control the crew chose to wait in a holding pattern along with 5 other aircraft because of extreme winds at their destination. Flight 214 entered a holding pattern west of the New Castle VOR, and there it suffered a lightning strike. This caused the ignition of the flammable fuel vapors inside the left reserve fuel tank. The ignition set off a chain reaction in the center and right reserve fuel tanks as well causing them to explode as well. As the fire spread over the wing the left wingtip separated. The aircraft was then seen to crash in flames. (Figure 8) The Philadelphia Approach only received one “mayday” call as the plane was descending out of the sky in a fireball.
Today you can see the result of this accident on every commercial jet/aircraft today. The FAA ordered that static wicks be installed to prevent such an accident from occurring again. Shortly after the crash of flight 214, Leon H. Tanguay, director of the Civil Aeronautics Board (CAB) Bureau of Safety at the time, sent a letter to the FAA recommending several safety modifications to be a part future aircraft design. One of the modifications he wanted was related to volatile fuel vapors that can form inside of partly empty fuel tanks, which as the accident showed can ignited by various potential sources and cause an explosion. The letter suggested reducing the volatility of the fuel mixture by introducing an inert gas, or by using air circulation.
Thirty-three years later a similar recommendation was issued by the NTSB (the CAB Bureau of Safety's successor) after the TWA Flight 800 crashed on July 17, 1996, with 230 fatalities, which was also determined to have been caused by the explosion of a volatile mixture inside a fuel tank.( 800 NTSB AAR-00/03 Final Report)
Wrapping it Up
We may know about lightning, but the raw fury and power that displays still captures the imagination of people today. Although we as humans have tried to lessen the effect of lightning in aviation, we will never be able to completely avoid it. I hope that you enjoyed reading my paper as much as I like writing it; I learn so many interesting facts about lightning. In conclusion, lightning should never be taken lightly and the more you know the more you can come to respect this amazing phenomenon.
What makes Lightning?
In the process of the water cycle, moisture can accumulate in the atmosphere. This accumulation is what we see as a cloud. Although scientists don’t agree on how clouds gain the charges to create lightning, many different theories exist. This one shows a possible explaination: Clouds can contain millions upon millions of water and ice droplets suspended in the air. As the process of evaporation and condensation continues, these droplets will eventually collide with other moisture that is in the process of condensing as it rises. The importance of these collisions is that electrons are knocked off of the rising moisture, thus creating a charge separation. (How Lightning Works pg. 2)
The newly separated electrons fall to the bottom of the cloud where they gather, while the water droplets carry the positive ions to the top of the cloud. This creates a strong electric field within the cloud. (Figure 1) As you can see, the electrical field becomes more and more intense till the electrons at the earth's surface are repelled deeper into the earth by the negative charge of the cloud. Since the negative electrons in the Earth are rebelled away, the ground acquires a strong positive charge.
Now the electrical field wants desperately to neutralize itself with the positive Earth. As the field grows in volts it begins to ionize, breaking down, and the air around the cloud. The importance of this ionization is that the electrons are now free to move much more easily than they could before. (Figure 2) “So, in other words, this ionized air (also known as plasma) is much more conductive than the previous non-ionized air.”(How Lightning Works pg. 3) You can see this process with I a high-speed camera as it “burns” a path to the ground. The path that is ionized will be the path the lightning will follow.
A path is not created instantaneously; in fact, there are many separate paths of ionized air stemming from the cloud. All the paths are referred to as step leaders. The air does not all ionize at the same time; any sort of pollution of impurities in the air will speed of the breaking down of the air. Step leaders don’t always follow the shortest path; they will follow the path of least resistance. Just as the step leaders form from the cloud heading toward the ground, a positive streamer reaches for the cloud. (Figure 3 & 4) However, once the positive streamer is formed they it doesn’t grow, as it is the job of the step leader to connect the all the way to the ground.
As soon as the two meet the connection between the ground and the cloud, the current flows to neutralize the charges. An electrical current, always has heat associated with it. Since there is an enormous amount of current in a lightning strike, there is a vast amount of heat. “In fact, a bolt of lightning is hotter than the surface of the sun.” (How Lightning Works pg. 5) The heat is the actual cause of the white-blue flash that you see.
In an effort to escape the heat, the oxygen expands so rapidly it creates a shock wave. This is best known as thunder, which give a thunder storm its name. Thunder, however, is not harmless. If you are too close you can feel the shock wave and it can cause you to go temporally deaf.
Impacts and Effects in Aviation
A commercial airliner is on the average struck by lightning twice per year. For all its power, lightning rarely causes crew injury or substantial damage to aircraft structures. (Figure 5) However, lightning can cause temporary loss of vision, puncture the aircraft skin, or damage electronic navigation and communications equipment. (Jeppesen pg. 6-43) The weather associated with lightning has more of an impact on flying, i.e. thunderstorms, because of the rarity of lightning strikes causing damage. If struck by a bolt of lightning, the current is largely directed around the outside of the aircraft's metallic skin. The last major U.S. commercial airliner crash caused by lightning was more than 35 years ago and was the worst lightning related aviation disaster. It occurred over Elkton, MD on 8 December 1963. Lightning struck and penetrated the reserve fuel tank. (How safe are you from lightning inside an airplane?) I will go over this accident in more detail in the Accident section of my paper. What happens is, when an airplane is struck by a thunderbolt, the electrical charges just traverse the length of the aircraft and exit through the static wicks at the trailing edges of the flaps or tail plane. The next time you happen to sit by a window seat behind the wings, just look out for these static wicks. They are like painting brushes with fine hairs sticking out at the end of the flaps.
How best to avoid Lightning and its effects
When you think of lightning you typically think of thunderstorms, although lightning can appear in other places. Lightning can also occur within the ash clouds from volcanic eruptions, or can be caused by violent forest fires which generate sufficient dust to create a static charge. (Volcanic Lightning)(Figure 6) So, logically, if you avoid things that cause lightning you will avoid lightning.
So the best way to avoid lightning and its effects is to constantly check weather and know the signs of developing thunder storms. Thunderstorms are results from the rapid upward movement of warm, moist air. They can occur inside warm, moist air masses and at fronts. As the warm, moist air moves upward, it cools, condenses, and forms cumulonimbus clouds that can reach heights of over 20 km. As the rising air reaches its dew point, water droplets and ice form and begin falling the long distance through the clouds towards the Earth's surface. As the droplets fall, they collide with other droplets and become larger. (Jack Williams) As the water droplets collide the particle separation creates the lightning.
Keeping up on the weather that is going on is a good way to avoid lightning and its various sources. One of the earliest ways to detect a thunderstorm is an unstable air mass. The unstable air mass lifts the air creating, given the right conditions, storm clouds that will eventually lead to the formation of lightning. The installations of static wicks are also a good way to ground the lightning as well.
Accidents Due to Lightning
According to NLSI, National Lightning safety Institute, there have only been a few aviation accidents that have cause fatalities. (NLSI) This number actually surprised me, for how long planes have been in and around lightning the number seems very small; although, I don’t believe that they have every accident relating to lightning. The accident that I choose to talk about was a devastating tragedy that ended with the plane crashing into the ground in a fireball. The accident killed all 81 of the crew and passengers. The Guinness Book of world records said that it is “The Largest Lightning Strike Death Toll,” not exactly the best record.
Pan American Flight 214 departed San Juan, Puerto Rico for a flight to Philadelphia with a stop at Baltimore. (Figure 7) The aircraft arrived at Baltimore and took off again after refueling. As they contacted approach control the crew chose to wait in a holding pattern along with 5 other aircraft because of extreme winds at their destination. Flight 214 entered a holding pattern west of the New Castle VOR, and there it suffered a lightning strike. This caused the ignition of the flammable fuel vapors inside the left reserve fuel tank. The ignition set off a chain reaction in the center and right reserve fuel tanks as well causing them to explode as well. As the fire spread over the wing the left wingtip separated. The aircraft was then seen to crash in flames. (Figure 8) The Philadelphia Approach only received one “mayday” call as the plane was descending out of the sky in a fireball.
Today you can see the result of this accident on every commercial jet/aircraft today. The FAA ordered that static wicks be installed to prevent such an accident from occurring again. Shortly after the crash of flight 214, Leon H. Tanguay, director of the Civil Aeronautics Board (CAB) Bureau of Safety at the time, sent a letter to the FAA recommending several safety modifications to be a part future aircraft design. One of the modifications he wanted was related to volatile fuel vapors that can form inside of partly empty fuel tanks, which as the accident showed can ignited by various potential sources and cause an explosion. The letter suggested reducing the volatility of the fuel mixture by introducing an inert gas, or by using air circulation.
Thirty-three years later a similar recommendation was issued by the NTSB (the CAB Bureau of Safety's successor) after the TWA Flight 800 crashed on July 17, 1996, with 230 fatalities, which was also determined to have been caused by the explosion of a volatile mixture inside a fuel tank.( 800 NTSB AAR-00/03 Final Report)
Wrapping it Up
We may know about lightning, but the raw fury and power that displays still captures the imagination of people today. Although we as humans have tried to lessen the effect of lightning in aviation, we will never be able to completely avoid it. I hope that you enjoyed reading my paper as much as I like writing it; I learn so many interesting facts about lightning. In conclusion, lightning should never be taken lightly and the more you know the more you can come to respect this amazing phenomenon.