Complex sentence: Flying shots in films were of a model; the aircraft itself was grounded by the studio's insurance company and was thought to have been scrapped in 1943, becoming a backlot relic, the model was used in several later films.
Split into simpler sentences: Flying shots in films were of a model; the plane itself was grounded by the studio's insurance company. The airplane itself is thought to have been scrapped in 1943, becoming a backlot relic, the model was used in several later films.