exactly what it says on the tin, be it flight gear or a uniform proper. if he and/or his partner are fully kitted out, it could literally just be an instance of being caught up in the moment and not wanting to wait through the 3000 step process to doff all of that gear before getting off.

or lapsex in the cockpit? copilot reaching across the center console at cruising altitude or while waiting to taxi on the hardstand to jack him off? there are options.

getting out of combat and/or a very close scrape and more or less immediately having sex because every nerve in his body is lit up at the moment. variations on this could be the partner having been on the same mission and this being a mutual thing, or maybe the partner's on the ground and for them it's more "thank god you're alive" sex.

john has a dom lean and likes to push boys around a little, give orders, etc. he'd definitely get off on the power rush of (consensually) commanding around someone he outranks in the bedroom, especially considering that in the grander scheme of things he's lowish on the totem pole in his daily life.

sexual tension between guys assigned to the same plane as himself, UST finally boiling over, sex as a coping mechanism, etc. he's not really in acceptance of his sexuality and sort of sees the interest in other men as being war-related/purely situational, so arrangements he can rationalize as being a matter of utility are very appealing to him. "we both have needs and with each other we know we aren't going to get VD from some girl off base", generalized stress relief, etc are all options here. if there are any castmates out there, i'd love to ship him with a croz or (in the stalag era and later) hambone.

some kind of slight au in which humans go through more pronounced, detectable hormonal cycles, and whatever the army has for controlling that isn't 100% effective, or he/his partner can't tolerate the side effects, or maybe a dose gets missed or there's just not availability, period. interested in playing out the negative physical effects and general mental/physical discomfort in addition to an overwhelming urge to mate - sex with a 'please help me get through this misery, it doesn't MEAN anything about the two of us' bent.

i would love to write him fucked UP, be it because of sickness, (air)sickness, drinking, or some fourth thing i haven't thought of. he's never been airsick in his life and has a navigator who famously gets severe airsickness, so there could be an interesting role reversal there. not interested in bodily fluid play.

nothing too pronounced - just small shifts with changes in life circumstance that catch him/his partner off-guard, be it in response to finally getting out of the POW camp he ends up in, spending a month on leave, any number of the medications a soldier might get put on during that time, stress, or something similar. particularly love the trope of the partner being like "you look so much better like this" and being quite fond of a neutral or (in john's eyes) negative change. potentially down to work feeding into this if it's while he's recovering from the stalag.

pretty impressive career already, but he manages to fly this thing while getting shot at. he's also exceptionally talented as a pilot, enough to stick a landing in a field with no landing gear down with notably minimal damage to the plane and nobody getting hurt. would love to play out a partner being horny about his general profession and him getting off on the ego boost.

receiving only - interested in the discomfort/mild swelling/"holy shit this feels weird" angle. water, or for an added pain element—maybe it's cathartic for him?—soapy water or sth.

the one situation in which i'd be interested in writing him bottoming at this point, probably with a handwaved serious romantic relationship - tell him they're going to get him pregnant, really get into the "this will ruin your career and body" element, etc. idk if he'd be into the giving end of this and it would involve a lot of (non-kinky) catholic boy religous introspection (sex for procreation but not really...) but i'm down to try it!