TLDR: I’m wondering if the below explanation makes sense. Maybe depends on the definition of “early”, but my feeling is that “trap doors” like for bales of hay were not a super common way of exiting aircraft.
evokes the image of letting a bundle out through a trapdoor, which is how those early aviators escaped from their planes before opening their parachutes.
Uhm… Which early planes (or even later ones) had “trap doors” for people emergency exiting? As far as I understand, parachutes were coming into common use (common issue) in aircraft in the last year of WW1. Observation balloons used them earlier, throughout the war. Anyway, at that time aircraft (or balloons) generally didn’t even have closed canopies, meaning people just got in/out through the open cockpit hole on top of the plane.
So a trap door would not seem to be common in WW1 (and possibly neither the "opening their parachutes - the Rip cord seems to have been invented later, at that time parachutes mostly seemed to have been automatically opened by a cord attached to the balloon or airplane).
And later? I’m not very familiar with the inter bellum years’ planes, but in WW2 trap doors in airplanes might have been a bit more common. At least on some bigger multi-engined bomber planes with closed canopies, which were partly (for certain positions) entered and possibly exited through doors and ladders in the bottom of the fuselage. Example B17, where part of the crew was supposed to also exit through the “trap door”-like bomb bay doors.