A Delta flight was recently forced to turn around an hour after take-off when maggots fell from the overhead compartment onto passengers sitting in the economy seats.
The flight on Tuesday 13 February was transporting travellers from Amsterdam to Detroit, Michigan, when a passenger’s suitcase containing rotting fish was in the overhead bin and opened up resulting in maggots falling onto passengers and the plane turning around.
After the plane landed all passengers were instructed to de-board the aircraft and the suitcase containing the fish was placed in a bag to be destroyed. The plane itself was also deeply cleaned.
When I fly to the US from Toronto I clear US customs in Pearson Airport, before getting on the plane. If I were to sign up for a Nexus pass I’d be able to pass through US customs even faster, but I don’t travel often enough for it to be worthwhile. Not sure if either of those matches what you mean by pre-clearance.