Because of the limited amount of evidence available, the investigating Board were unable to determine the cause of the accident, and so concluded that it was impossible to find that the pilots had been negligent to any degree. The Reviewing Officers, on the other hand, concluded on the same evidence that both pilots had been negligent to a gross degree.
I still cannot accept that it was just the 'inadequate legal advice' provided to the Reviewing Officers which caused them to fail to apply the standard of proof correctly.