bmi F100 - Cat 3
safetypee
Cat 3a - fail passive.
2 aircraft have the additional equipment required for Cat 3b, triple instead of dual IRS and electrical system mods. Those are the main differences, there are some other minor ones.
The 2x3b capable aircraft were acquired after the rest of the fleet, 3 F70s and 4 F100s at the time. To obtain 3b approval would have meant additional dedicated sim training for all crews just to utilise the capability of 2 out of 9 aircraft.
YS