Sunday, May 13, 2007

Static Wicks

Part of the reason the airplane had to have maintenance this week was because we had a broken static wick. According to our MEL (Minimum Equipment List), we have to have at least one static per moveable surface on the airplane.
Why and what are static wicks...?

According to Wikipedia:

Static dischargers are commonly known as static wicks or static discharge wicks. They are used on aircraft to allow the continuous satisfactory operation of onboard navigation and radio communication systems. During adverse charging conditions, they limit the potential static buildup on the aircraft and control interference generated by static charge. Static dischargers are not lightning arrestors and do not reduce or increase the likelihood of an aircraft being struck by lightning. Static dischargers are subject to damage or significant changes in electrical resistance as a result of lightning strike to the aircraft, and should be inspected after a lightning strike to ensure proper static discharge operation. Static dischargers are fabricated with a wick of wire or a conductive element on one end, which provides a high resistance discharge path between the aircraft and the air. They are attached on some aircraft to the ailerons, elevators, rudder, wing, horizontal and vertical stabilizer tips.
So now you know!

6 comments:

  1. After a coworker saw a video clip of an airplane being struck by lightning I pointed him to this blog to explain static discharge wicks. I'm an ex-F-16 tech so I knew what they were but couldn't explain it as clear. Thank you.

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  2. Anonymous6:33 PM

    I'm working on preparing for my CFI check-ride. I was told that the examinar I was going with liked to ask if the static wicks were missing, could we still go on the flight. I will be taking my check ride in a Piper Arrow. We have no MEL. I they are not required by the regs, Aircraft Certificating, or type of operation. They may be part of AD's. But the big question is does it affect safety of flight? Maybe it does if you static wicks were required by your MEL.

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  3. Anonymous8:54 AM

    You can still go on the flight.

    No MEL, so we are just left with the part 91 requirements for the flight.

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  4. Check 14 CFR 23.867

    Once I had found that, I performed a search of the Arrow Type Certificate Data Sheet. That showed certain situations where that CFR applied. If you have any of the equipment listed that applies to 23.867, it is likely that you are required to have those static wicks.

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  5. Annon:

    It's always been my contention that the more electrically complex the aircraft and the more the aircraft flies at high altitude, the more the airframe benefits from static dissipation via the wicks. The Arrow, even if it did have a MEL, likely wouldn't require static wicks on every surface given the altitudes it operates in.

    As for safety of flight, I am no electrical engineer and can't answer with authority. My basic understanding (and what I share with others) is that there must be a path for the static to discharge or static will build up, but on metal aircraft placement is not as important as on composite aircraft that may not pass electrical charges well if a wick goes missing.

    Simplified: having more on an arrow might be better but is not a requirement and missing one would not pose a serious threat as the other wicks will compensate.

    Putting my money where my mouth is: I flew this weekend in a steam C182 with two missing wicks and didn't bat an eye.

    The real question: I'm betting the examiner doesn't really care about any of this. They are likely looking to see of you can address the existence (or lack thereof) of the MEL. I'd stick to your answer you gave above: "yes we can fly because they are not on an MEL (because there isn't one), they are not directly addressed in the regs, and we will be low enough that we won't need them in our type of operation. Unless they are a part of an emergency AD that came up since the last inspection, I we would be legal."

    I'm not sure that I'd bring up the "they were not required for airframe certification" unless you know how you back that up. Remember, one of the things examiners look for is your ability to avoid "digging your own grave" by answering more than the question requires thus giving them an opportunity to take you down a rat-hole towards an answer that puts you in over your head. I've seen folks struggle with oral exams strictly by trying to throw too much out there during an answer. Think answers through. Be prepared to say "that's not something I would get into too much detail with a student at the private pilot level" (or some such thing).

    My favorite moment during my CFII ride was when I said, "my understanding is that when altitude increases... (technical answer)... Is that not how you would explain it?" By turning it around, they had to either go into more detail themselves (and many love showing they know more than you do) or agree and move on. Mine actually said something like "that sounds right to me, but I'm not really sure." This confirmed that they were looking not for the actual answer but how I handled/controlled the situation.

    Your "student" may be an expert in real life but they are pretending to be a new Private Pilot candidate. You are the CFI during the ride. Be prepared to limit what you share with them so that you don't overwhelm them... at least that is how I spun my responses when giving the basics rather than an encyclopedic answer.

    I hope it helps. Good luck!
    -H. Michael Miley, CFII

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  6. Anonymous10:57 PM

    Well said. Really well said. Thank you Miley.

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