SpazSinbad
Unclear if different types of engine blanks are used ashore/at sea, most probably the fabric blanks at sea (it would appear they are ‘foldable’ and space is a at a premium) also in very adverse weather they would flex but not detach if fitted correctly; it would appear from the image that they are secured by 1980’s vintage pip pins, possibly with a Royal Warrant
It would appear that the F35 engine compressor is situated some way back from the intakes via a bifurcated duct, I am unsure if there is a direct line of sight for aircrew/engineers to make a quick inspection for FOD without opening an inspection hatch.
If indeed the FAA/RN Aircraft ZN152 was fitted with these type of blanks it poses the question on how could one detach without leaving some tell-tale signs of distress on the aircraft skin, or was it removed left in the intake to collect later and forgotten about as people sometimes do!
I do remember a F4 Phantom being ranged on HMS Ark Royal post engine change, the cumbersome and heavy toolbox needed moving from the hangar to the deck so it was positioned in the engine exhaust for a ‘ride’ unfortunately during an unusual engine start there was a poofff and the toolbox was lost to the Mid Atlantic