The maiden commercial flight in January 1970, Pan Am from JFK to London (already delayed a month), got this on startup and they had to transfer to a backup aircraft which meant they were 4 hours late at London.
The maiden flight by Pan Am was actually 27 hours late at London. The flight was already boarded with pax and VIPs when the problem surfaced and the flight was cancelled. When they tried again the next day at least they had provided a back-up 747 this time.