It&#x27;s not <i>strictly</i> true that aircraft age is measured in takeoff and landing cycles and YoY depreciation is pretty huge for new aircraft even holding condition constant, but I&#x27;d agree that it might make commercial sense to keep a &gt;10 year old 717 on standby. More likely to be short term fluctuations in demand or a short term airworthiness issue than any intent to have a &quot;spare&quot; aircraft though.