From the Gizmodo article (which is also the source of the above image). The Piper Pawnee is an agricultural aircraft or, in more common parlance a crop duster. Yes, just like Dusty from Pixar’s Planes, although Dusty is more representative of a far more advanced Air Tractor-type. It could be something else like a Cessna Agwagon, though the rear fuselage and engine cowl are very subtle giveaways to someone who has spent all of his free time staring at pictures of airplanes instead of dating women. Either way, the Pawnee and Agwagon all date from the same general time period, originally developed during the 50s and 60s using components from Piper’s and Cessna’s passenger offerings wrapped around a new fuselage comfortably seating two people (typically a pilot and on-site mechanic) and of course more bug spray than you can shake a Lowe’s at.
What’s interesting is that the Pawnee (I’ll just stick with this assumption) clearly has a phone number listed on the side of its fuselage implying an aircraft for hire. Other than for carrying passengers (not exactly something you’d do with a Pawnee) or its original, intended cropdusting mission there’s really only two things you’d hire an airplane for - aerial towing or skywriting. Again, it’s not likely a Pawnee would be a prime choice for a skywriting platform but the same properties that make it a great aerial spray applicator (namely just having a really powerful engine, all the way up to an air-cooled flat-8 in the Pawnee’s successor - take that, Porsche!) also make for a great towplane, whether it’d be gliders or (most likely the case over LA) advertisement banners. Therefore, I’m going to guess it probably experienced engine problems while, I don’t know, telling Los Angelenos about the virtues of taking 15 minutes to switch to Geico and had to make the choice of either the LA river or the roof of a Hummer stretch limo on the 405.
It’s probably a safe bet that it just didn’t have enough fuel left to make it to the Hummer.