Let's say you discover that your landing light is inoperable during the preflight. Your aircraft doesn't have a MEL, so you follow 14 CFR §91.213(d). Assuming you do everything else required (placard, etc.), would placing a collar around a circuit breaker be considered deactivation?

If not, is there anything that a private pilot can do that would be considered deactivation?

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    $\begingroup$ The humorous absurdity of pulling & collaring a breaker (interrupting the circuit) for a failed landing light (usually because the incandescent filament has burned out, interrupting the circuit) is not lost on me. Though on a serious note, if we're talking about a fault in a HID landing light system or LED landing light the potential failure modes certainly warrant "preventing the operation" of the system until you know what caused the fault... $\endgroup$ – voretaq7 Dec 28 '13 at 8:36
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    $\begingroup$ It does seem a bit absurd. I asked this question because it's one that seems to come up in checkrides. During my checkride I was asked what I would do in this situation. I answered that I would collar the circuit breaker, and the DE told me that would not be enough and I would have to have a certified mechanic repair the light or disconnect the power to the circuit breaker to be legal. I didn't argue, but I'm pretty sure he's wrong and the collaring is deactivation. $\endgroup$ – kevin42 Dec 28 '13 at 15:33
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    $\begingroup$ I would think collaring qualifies as deactivation too - certainly as lnafziger pointed out it's what manufacturers recommend, and I'm pretty sure it's what airlines do for non-critical equipment that needs to be "tagged out" because it's broken. For that matter taping a bent index card cover over the switch so you can't turn it on it would also seem to qualify, albeit a somewhat inelegant solution. $\endgroup$ – voretaq7 Dec 28 '13 at 21:55

Based on this Advisory Circular, the answer is yes.

g. Deactivation means to make a piece of equipment or an instrument unusable to the pilot/crew by preventing its operation

Collaring the circuit breaker prevents it from being pushed in, and therefore prevents its operation.

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    $\begingroup$ This is consistent with MEL M&O procedures that in some cases specify doing exactly this. $\endgroup$ – Lnafziger Dec 18 '13 at 21:24

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