We have all come to fear and respect thunderstorms. Probably the one element that visibly strikes fear in pilots and passengers alike is the lightning associated with thunderstorms. When not in IMC, it’s easy to see where the lightning is emanating from, and if you are a safe distance away. However, once in the clouds, you can only approximately discern azimuth but not how close it may be. You can approximate the distance by counting the seconds between the visible flash and the clap of thunder and divide by five to get the distance in miles. Note that most lightning occurs within the clouds and not cloud-to-ground.
If you don’t see lightning but hear thunder, you can be sure lightning is present—thunder is its by-product. However, where lightning can be seen 100 miles away, thunder is typically only heard at about 20 miles and in the confines of an airplane significantly less.
How dangerous is the lightning to aircraft? Consider the energy in a bolt of lightning—it can be up to one billion volts of electricity, 10,000 to 200,000 amperes of current and has a temperature far higher than the surface of the sun. Surprisingly, lightning strikes on light aircraft are not common. However, it’s still not something to toy with. Keep at least 20 miles from thunderstorms for a variety of good reasons; one is that lightning can strike out of clear air more than ten miles from the thunderstorm cell.
While there are no statistics on general aviation lightning strikes, the Federal Aviation Administration estimates that commercial jet airliners in the US are struck by lightning once every 1000 flight hours, or once each year, on average. Airplanes are capable of triggering lightning themselves just by flying through ionized clouds.
Reviewing NTSB records, there were few accidents related to a lightning strike and none in recent years. Structural damage to aircraft is atypical but does occur, though rarely of a nature that threatens the safety of the occupants or aircraft. Most damage is constrained to small puncture holes associated with entry and exit points of the lightning.
Typical Aircraft Damage
Lightning typically strikes an aircraft’s outer boundaries and then the current exits via another extremity, such as the tail. Damage to control mechanisms and surfaces is a possibility. In 2014, a SAAB-Scania SAAB 2000 lost elevator control following a lightning strike on approach to Sumburgh Airport, in the United Kingdom.
A serious situation occurred in March 2010 to an Embraer EMB-145LR. The aircraft sustained a lightning strike while on approach. The flight crew subsequently encountered elevator control binding, although they were able to land without further incident. A post-accident inspection of the airplane revealed that the tailcone was damaged. Examination of the damage disclosed that the tail cone’s light assembly wiring harness and its respective over braid shielding were thermally damaged. A bulkhead frame was dislodged from its location due to the thermal damage present on the wiring harness. The dislodged bulkhead came to rest on the elevator’s bellcrank, which restricted the flight crew’s ability to control the elevator.
In June 2011, a Beech B200 descending from 16,000 feet was being vectored for an approach when struck by lightning. The strike caused minor damage to a propeller blade on the left engine. The left wing flap and the right elevator were substantially damaged. The pilot stated they had passed an area of convective activity and were in instrument meteorological conditions with smooth air at the time of the lightning strike.
Note that FAA Advisory Circular (AC) 20-37, Aircraft Propeller Maintenance, states that a detailed propeller inspection must be completed at each annual inspection or as required by the aircraft maintenance procedures. The visual examination is to look for excessive wear and erosion, damage, nicks, cracks, corrosion, or ground strike but also any evidence of a lightning strike.
Lightning is bright, especially when close. Momentary blindness from the flash, especially at night, is not uncommon. In 2010, the flight crew of a Beech 1900 saw buildup of static electricity near the nose of the airplane (known as St. Elmo’s fire) during an instrument approach. The first officer reported that the light from the static electricity was so bright he wisely decided to keep his eyes focused on the instruments. Shortly after that, lightning struck the nose of the airplane, and the associated flash temporarily blinded the captain. The first officer continued to fly the approach without difficulty.
During a post-accident inspection, the flight crew discovered substantial damage to the right elevator. When lightning is in the vicinity, turn up cockpit lighting to the fullest at night, pull down sunshades (day or night) and, as this first officer did, stay focused on the instruments.
Aircraft Electrical Systems
Lightning and electronics don’t get along well so expect some interference with avionics and communications gear and even the compass. With today’s glass cockpits, lightning strikes do take on more seriousness. In October 2014, a Boeing 787-8 flight crew lost the use of three of the five head-down displays available to them following a lightning strike. No procedures existed for a power reset while in flight, which most likely would have resulted in a restoration of the displays.
The FAA has determined that electrical transients can be present during certain lightning strikes. Although the displays passed the required certification testing, it was determined that certain environmental conditions could exist, resulting in a loss of the display. If lightning can affect certified systems, then you can be sure uncertified systems are susceptible.
A complete loss of electronics will force the use of the frequently small, limited, and inconveniently placed backup analog instruments. Have you ever tried flying IFR on your backup instruments? Do you know how to reset your electronics in flight?
Intense precipitation is usually a clue that lightning is not far away. FAA directives require air traffic controllers to issue precipitation location and intensity information to pilots for this and other reasons. At some point climbing through 12,000 feet for FL190 In Jan 2012, an Embraer EMB-145LR was struck by lightning. It sustained damage requiring repairs to the left-wing skin and rivets and replacement of the left wingtip and aileron. There was moderate to extreme intensity precipitation along the aircraft’s route of flight. Unfortunately, in this case, the pilots were not notified of the precipitation.
Lightning strikes on aircraft are generally known to occur within 5000 feet of the freezing level. Flying at warmer levels not only reduces the chances of a lightning strike but also limits any potential for icing. Lightning is also more prevalent over land than large bodies of water.
Sometimes our concern should be to things on the ground. Power outages are frequently associated with lightning strikes, which could render ground facilities inoperative. In 2009, a Cessna T210 pilot attempted to activate the runway lighting via the pilot-activated system. However, the system was inoperable due to a recent lightning strike. A resident partially illuminated the runway using headlights from an automobile. The pilot came in high and lost control of the airplane while executing a missed approach with fatal consequences.
A plane might be safer in the air than on the ground. In 2011, A Cirrus SR-22 sustained substantial lightning airframe and avionics damage while tied down. How many other aircraft have been damaged on the ramp with a tail and antennas acting like lightning rods? In 2014, a Grumman G164 had a landing gear collapse. A fatigue crack was found that originated at the site of electrical arc damage to the gear leg, perhaps caused by a lightning strike.
You are also probably safer in your airplane when it comes to lightning than you are on the ground. Lightning kills an average of 47 people in the United States each year, and hundreds more are severely injured. Next time you are out in the rain with an umbrella, know your odds of being struck has just increased.
Richard Lanning Ph.D. is a graduate of the U.S. Naval Academy and a pilot for more than 30 years. He is an ATP, CFII and is glider/gyroplane CFI.