That answer is mostly wrong.
If the item qualifies as a "rotable spare part, temporary spare part, or standby emergency spare part" (which have specific definitions), you may have the option to depreciate those.
Otherwise, the Regulations say "If a taxpayer elects to apply the de minimis safe harbor ... then the taxpayer must apply the de minimis safe harbor to amounts paid for all materials and supplies that meet the requirements".
<a rel="nofollow" target="_blank" href="
https://www.law.cornell.edu/cfr/text/26/1.162-3">https://www.law.cornell.edu/cfr/text/26/1.162-3</a>
