As the corenor stated at the summing up, there was a conflict of evidence between what the sciencific evidence from the remains of the seat and the aircraft portion of the system (such as the inner cylinder of the ejection gun had witness marks consistant with the TLP locking device being dragged across its surface) and RAF technicians (stating that the TLP was servicable and that the spring possibly have failed). The MMPs were clear on checks but training did not include ensuring the two point TLP checks were mandatory. Spring failure could not be discounted (because the mechanism was never found) but the witness marks to the BOI seem to suggest that the plunger spring pressure marks on the tube were consistant with it being intact (and the BOI did trials on other seats to confirm that). However no MB seat has ever fallen out on a military aircraft before this incident (examples of civilian owned seats have, due to incorrect fitting of the latch plunger). Without the TLP, proving a manslaughter charge beyond any reasonable doubt is impossible (and rightly so). Hard copy documents illustrating a neligence of duties in regards to airworthiness is also dodgy ground due to DMS and the way CMU interacted with the MAE. I'm not surprised the Provo's didn't pursue things on that score, but I reckon it was a closer thing than the more serious charges.