- " 'You've made unauthorized entry into commercial transport airspace,' the angry voice [from air traffic control] went on. 'Why the hell wasn't your transponder on? Over!' / Doc grinned at Marty and Jennifer before he replied. / 'Roger. We're experiencing minor technical transponder difficulty. We're descending now for repair. Over and out!' / Marty admitted it; he was more than shaken up, and not just with that huge, flying truck. Commercial transport airspace? Transponder? / It was time for some answers. "
- —From Back to the Future Part II by Craig Shaw Gardner (quote, page 14)
When the DeLorean time machine appeared in the middle of Skyway C25 in the wrong lane and facing oncoming traffic on its arrival in 2015 from Lyon Estates in 1985, Emmett Brown had to tell an angry air traffic controller that their transponder had developed a fault to cover for this mistake.
However, it is unclear as whether the DeLorean had a transponder fitted in the first place, bearing in mind that Doc later said that many of the modifications he had made to the DeLorean — specially the installation of a Mr. Fusion Home Energy Reactor — were not exactly considered "street legal".
- Back to the Future Part II novelization (Mentioned only)