Posted by: harrisonjones | April 15, 2012

United Flight Struck By Lightning

A United Airlines flight was struck by lightning shortly after takeoff from SFO this week.  The crew returned to SFO safely and found little or no damage to the aircraft. Actual lightning strikes to aircraft are uncommon because there is normally not a path for the electricity to travel to ground. Even during taxi the aircraft is insulated from the ground by the rubber tires, just as an automobile is. The more common occurrence is what is called a static discharge. While flying in cloud, and usually near thunderstorms, static electricity can build up on the aircraft and then discharge to a nearby cloud (similar to cloud to cloud lightning). This can be quite a thrilling experience as most of the static builds up around the nose of the airplane and then travels aft in the form of a fireball accompanied by a loud bang as it discharges into the atmosphere. Explaining this phenomenon to the passengers can be a challenge and a test of your credibility; especially if you’re considering the need for a change of linen yourself. 

The more common, and less thrilling, form of static is St. Elmo’s fire. As the atmosphere at the nose of the airplane ionizes, a bluish glow forms and little streaks of electricity dance across the windshield.

                

This can cause an adrenalin rush the first time you see it, but after that it becomes a pleasant diversion unless it evolves into a static discharge. There are several good You Tube videos of St. Elmo’s if you do a search.  

The only problem associated with St. Elmo’s is that it is accompanied by radio static. In fact, if you’re flying in cloud and experience unexplained radio static, you can anticipate St. Elmo’s shortly. This is a nice thing to know because it gives you the chance to invite the flight attendants to the cockpit beforehand. St. Elmo’s accompanied by screams can be quite entertaining if properly orchestrated. Of course this requires a brief timeout from the accepted CRM protocol, but as long as you swear you didn’t know it was going to happen… 

Fortunately, our friends in engineering have afforded us design protections from lightning and static discharges and normally little or no damage occurs during these events. Numerous static discharge wicks are installed on the airframe to prevent excessive static buildup. These are usually found near the wingtips and at the tail and provide a path for electrical discharge.

Another safety feature is called bonding straps. All adjacent metal parts of the airplane have these metal straps between them to provide a path for static electricity to flow; thus preventing arcing and the possibility of a spark causing a fire danger.

These design features are more important than ever now that we depend so heavily on electronics to fly the airplane. I’m thinking a huge surge protector for the autopilot might be in order…

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Responses

  1. Captain…

    A common misbelief is that the rubber tires insulate a car (airplane) from the ground so a lightning strike can not strike a car. This is incorrect. The all metal body of a vehicle forms a Faraday cage around which the electricity is directed. The air is a lot better insulater than rubber and it doesn’t stop lightning.

    This is true for an airplane. Usually the lightning is directed around the body so no damage is done.

    Mike

    • Thanks for the comment, Mike, and for the additional insight. I’ve concluded that lightning should be studied from as far away as possible and static discharges are more excitment than I can stand. Please visit again, soon and often.

  2. Surge protectors are very important if you want to protect all your electronic equipements from electrical surges. surge protectors may be expensive but it can really save you from a lot of headache due to equipment malfunction. :.’`: Regards

    • I couldn’t agree more, Keely. Thanks for stopping by.

  3. Lightning strikes are quite common actually. When I worked in operations it was not rare to have one or two a day on average during the summer months, with the associated maintenance write up, inspections and often damage (usually to the composites on the winglets or tail). I think the kind of discharge you describe is rarer and cannot remember a flight attendant ever reporting one on one of our aircraft. Just sayin.

    • Thanks for sharing your experience, Mike. Static discharges are definitely more rare and require certain atmosphereic conditions, and for that I’m gtareful. The last one I experienced occured over Brazil in the ITCZ (Inter Tropical Convergence Zone) near the equator. The fat part of the earth is a wierd weather area.


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