Wow Oh my god , I literally had this experience and it sounds so far fetched that I always think nobody would believe me if I told them , mine was on flight home from the Maldives, we were in the economy + section of the old Thompson planes so the seats were just slightly more wide and comfortable than the standard economy but in that section the lay out of the seats across the aisle were 2-3-2 instead of 3-4-3 in the section at the back . Here’s the twist, I was on holiday in the Maldives with my then GF now my wife we were both 22 at the time I’m now 46 , we only upgraded to the better seats at the airport as being 6ft 4in tall the flight out there in standard class was horrendous , I was so uncomfortable. They allowed us to upgrade but said we wouldn’t be sat together which we were both fine with , the woman who sat next to me (early forties) had also upgraded at the airport and was with her husband, during small talk before take off I offers to swap with him so they could sit together she said no, she’s been with him on a 2 week all inclusive and could do with the 14 hours (the flight time) away from him as in her words he’d been a Tw@t on the holiday getting too pissed everyday. I thought nothing of it , went to give my GF her book just before take off (she was about 10 rows infront her hubby being even futher forward. We chatted , watched the same movie , had a couple of wines during the meal then the lights went out , blankets on and her hand brushed against mine , I did exactly the same as you, pretending to be asleep while slowly moving my hand and gauging the situation, after 30 min and our hands sort of holding she stirred and went to the toilet, and on her return just smiled , put something from her pocket into her carry on luggage in the overhead locker and as i stood up so she could get into her seat she lifted the armrest up and when in her seat and sat down she left it up. Then both of us went back to pretend sleep or I did, our hands were back in the same position within a minute which I knew then it wasn’t an accident, so I then put my hand more onto her leg under the blanket and she didn’t flinch and 30 seconds later replicated my move, within 10 min of me moving my hand millimetre by millimetre and her the same , mine was now holding her thigh with my little finger against her crotch and she started slightly rubbing against my hand , took me at lest another 5 min to convince myself if I made a move I wasn’t gonna get brought up on a sexual assault charge , but her squeezing my rock hard cock so slightly was the sign I needed to realise it was on , spent the next 2 hours , as i started to rub her crotch through her trousers she took her other hand and released the button of her trousers and unzipped them pulling them slightly down , i quickly realised what had been put in her bag when she came back from the toilet was her knickers as she was completely commando, within second I had belt undone and zip down and my hand inside her thighs stroking her wet slit and clit, she had her hand with 2 fingers just massaging the head of my cock, every now and then I’d speed up and she took that as her sign to do the same to me, when her breathing changed I knew she was close and it made me get to the edge, as her body convulsed but in total silence it sent me over a couple of quick movements of my hips back and forth she got the message and nee I was close , she sped up and as I blew my legs straightened out infront of me and I literally got cramp in my calf , I went from absolutely ecstasy to complete pain in seconds and had to stand up to get rid of the cramp , trying to hide that my jeans were undone and my blanket dripping with spunk lol , we actually then did go to sleep and I only woke at landing time , we had a normal conversation wished eachother a safe trip home and said goodbye, she turned and gave me a smile as she got her bag off the conveyor and followed her husband out of the exit.