One of the circumstances leading to the VSS Enterprise crash was the fear of the pilot to unlock the feather system too late, thus the ascent would have had to be aborted. The feather system must have been unlocked between a speed of Mach 1.4 and Mach 1.8. If not unlocked before Mach 1.8 the flight would be aborted, this was the rule in the VSS Enterprise flights (I dunno whether it still is in the modified VSS Unity), why was it like this? Note I'm talking of unlocking the feather system, not activating it (going into feathered mode). The unlock is to happen during ascent of the SpaceShipTwo.
The poor pilot didn't know that when unlocking the feather system too early the spaceplane would go into feather mode by air drag (they didn't make it clear to the pilots). He wanted to avoid abortion of the flight so he unlocked the system before Mach 1.4 and still in subsonic flight. So why was there the rule to abort the ascent if the feather system isn't unlocked before Mach 1.8 in the first place? What would have been the threat if the feather system is unlocked too late?