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…