Found some details in
http://www.rvs.uni-bielefeld.de/publ...aw-report.html for the A320:
3. The aircraft automatics comprises, for basic landing configuration if the
aircraft (i.e. with flaps extended to FULL position), the programme which
subjects actuation of all braking devices to some specific conditions. Ground
spoilers, when selected, will extend provided that either shock absorbers are
compressed at both main landing gears (the minimum load to compress one
shock absorber being 6300 kgs), or wheel speed are above 72 kts at both main
landing gears. Engine reversers, when selected, will deploy provided that
shock absorbers are compressed at both main landing gears.
Such a logics result in the lack of possibility of immediate actuation of two
mentioned above aircraft's braking devices without meeting the conditions
described.
4 In emergency, the crew is unable to override the lock-out and to operate
ground spoilers and engine thrust reversers.
Cheers