Whilst on ground school for the 146 some 20+ yrs ago we were told that regulatory requirements did not take into account reverse thrust for landing distance requirements, it was an unaccounted stopping bonus. Thus on the 146 the landing distance required was increased by 10% as it didn't have RT.
https://flightsafety.org/files/alar_bn8-3-distances.pdf
When discussing landing distance, two categories must be considered:
- Actual landing distance is the distance used in landing and braking to a complete stop (on a dry runway) after crossing the runway threshold at 50 feet; and,
- Required landing distance is the distance derived by applying a factor to the actual landing distance.
Actual landing distances are determined during certification flight tests without the use of thrust reversers.