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To the Letter

Re: Struck by Lightning

Dear Mr. Schonberg,

As an interested and appreciative reader of the Aviation Safety Letter, and a professional pilot for the past 12 years, I was somewhat taken aback by the tone of the article on lightning strikes in Issue 3/97. The article insinuates that many highly trained and experienced airline crew members flew aircraft near a lightning storm merely to meet a schedule. The article also suggests that the on-board weather radar would have indicated this hazard, and that the crews either didn't use the radar or didn't care about the returns. I feel that both of these comments are inaccurate at best.

As you know, weather radar indicates returns from precipitation and is consequently very useful in avoiding turbulence, windshear and hail, but gives a pilot no indication of the electrical activity in a storm cell. Recent research suggests that many lightning strikes occur when the aircraft is abeam a storm cell, rather than under or in a cell, and that they can occur at distances up to 20 NM from the edge of a storm cell. In addition, the lightning-strike potential around a storm cell is highly variable and topography-dependent; an area that is safe at one point can quickly become unsafe, and vice versa.

While I am not saying that, with hindsight, the situation could not have been better managed, I feel that it is somewhat unfair to be so quick to judge. If all aircraft avoided thunderstorms by 20 NM at all times, most western Canadian airports would be closed every afternoon in the summer months! Conventional thought and practices seem to indicate that pilots can safely circumnavigate such storms using many sources of information. That is using weather radar, stormscopes (if the aircraft is so equipped), air traffic control, and pilot weather reports, and merely by looking out the front windshield. Thus, lightning strikes are a fairly rare occurrence and, when they do occur, the design of the aircraft does what it is supposed to do and damage is usually minimal. In light of the above, to suggest that several dozen professional pilots jeopardized their passengers' safety to make a schedule is somewhat rash.

Thank you once again for the Aviation Safety Letter. I find it to be a truly useful and educational resource that is very easily understood.

Kevin Maher
Vancouver, British Columbia

 

More Lightning

The article states that "The lightning could easily have fried the aircraft's electronics...."

Transport category aircraft certified to the Federal Aviation Regulations in the United States, Joint Aviation Requirements in Europe, or Canadian Aviation Regulations in Canada have to meet stringent airworthiness standards for protection against the effects of lightning strikes. Two types of effects have to be considered:

  1. direct effects: The aircraft must be shown to be able to withstand a direct lightning strike and not suffer structural or significant surface damage, nor shall any fuel in tanks, lines, and so on, be ignited by the strike; and
  2. indirect effects: The aircraft avionics and electrical systems, including electronic controls for systems such as landing gear, flight controls, and fuel management, must be able to withstand electrical impulses induced in the aircraft wiring as a result of the electromagnetic field created by a lightning strike.

As you can see from the above, there should be no risk of the electronics being fried. The aircraft may suffer minor surface damage from the lightning-strike attachment or discharge points, and the carrier should conduct a post-strike inspection of the exterior surface to determine the extent of any damage.

A few years ago, I was in a Canadian B-737 that was struck by lightning on approach to Vancouver International Airport. After disembarking, I stood by the window at the gate and was pleased to see a mechanic walking around the aircraft, looking carefully at the radome and rear lower fuselage, including antennas. Obviously, the flight crew had reported the strike to the ground crew.

John Carr
Principal Engineer
Avionics and Electrical Systems Engineering
Aircraft Certification Branch
Transport Canada

Originally Published: ASL 4/1997
Original Article: To the Letter - Re: Struck by Lightning

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