@OG - check the Wiki link.
Originally Posted by Wiki
The spoilers [were] only activated if at least one of the following two conditions is true:
- there must be weight of at least 6.3 tons on each main landing gear strut
- the wheels of the plane must be turning faster than 72 knots (133 km/h)
Followed up with:
Originally Posted by Wiki
As a result of the accident, Airbus Industrie changed the required compression value from 6.3 tons to just 2 tons per main landing gear.
I remember the timing issue because the left gear touched down 9s after the right - it was the delay in the left gear getting the required compression value that caused the delay in spoiler deployment.
[EDIT : I'm aware that it's a totally different application, I was simply trying to distinguish the air/ground mode criteria, which are not relevant to AF447, from the AoA vane maker's specified NCD threshold of 60kts, which is. ]