With the chopper crash mentioned by Dave Reid, that now makes two attempts at manslaughter charges in both of which the CPS failed to secure a conviction. Here is an extract from the CPS The Code for Crown Prosecutors:
"The Decision Whether to Prosecute
4.5 The finding that there is a realistic prospect of conviction is based on the
prosecutor’s objective assessment of the evidence, including the impact of
any defence and any other information that the suspect has put forward or on
which he or she might rely."
In both the Tiger Moth and the chopper cases they must have thought that there was a realistic prospect of conviction. But the expected was not the outcome . Will they now try for a third.