Amusing if you are interested in percentages: after arriving from Oz, travelling DFW-JAX twice in the last 6 months on AA's last flight out [AA2296], with 1845 scheduled departure, I've achieved 100% success in having delayed departures, with 'amusing', if you believe them, excuses:
29Sep13 ~ boarding delayed due non-arrival of operating crew; pre-flights checked, all good, except minor brake line leak, for which Maint have been summoned; half-an hour later decision is made that "pax must disembark, whilst comprehensive checks are carried out, so come back to gate in an hour please". An hour later all ready to re-board, and do so, happy; Biggles duly arrives and re-starts pre-take-off checks, looks at his watch, and laughingly advises pax that "notwithstanding telling 'em so, we're now out of crew duty time, but we think we have another Biggles available, so all off, thanks". Amusement factor is quickly dissipating ... finally departed 2-and-half-hours later than scheduled.
30Mar14 ~ airframe sitting at departure gate, Bewdy! But, boarding delayed due non-arrival of cabin crew, expected in 45" from inbound flight; ah, no operating crew, who arrived about 30" later. All aboard: then during push-back/safety demonstration "a senior airline person" came forward and spoke to the operating crew re some perceived problem, and Biggles announced that they'd "have to check a minor electrical problem", which became a "need to return to the gate for Maint, but something-else had already been moved onto the gate we'd vacated so we needed to wait for another"; cue first round of G&Ts being served in the plush end! We'd moved off Gate D-something, and of course when the new gate was ready it was A-something, necessitating a long transit taxi around half of central Texas; 2nd G&T and hot nuts, why, thank you! Parked at new Gate, and Maint arrived, and Maint looked, and Maint advised that it'd be a few minutes, then that it was an airframe change required, so everybody off. The gate agent was confident that there'd be an airframe available, in 30"; then 45"; and there was, in 60" plus time to transfer bags etc from broken to unbroken airframe. Departed 4-and-a-half hours late. The minor electrical turned out to be a 50% DC power lack!
The good thing: sitting in the soft seats and being G&T'd, and almost nil traffic on the road from JAX international to NoKs at such a late hour!