@jcj:
But civil servants are not politicians - by and large they just do the job that they have been asked to do. Accident investigation has always been something of a unique case in that regard, because the purpose must always be to find what went wrong and prevent it from happening again.
The one time in living memory when it was proven that an aviation authority colluded with politicians and a manufacturer to soft-pedal design problems (overriding the accident investigators in the process), it ended up blowing up in their faces, and condemning the airliner involved (the DC-10) to a chequered reputation in perpetuity. To do so is clearly not worth the risk.