Full thrust varies with airfield elevation and temperature. On the 146 fleet I operate, we use rated thrust in the following circumstances:
- Once a week to confirm that rated thrust is achievable,
- When the runway is wet,
- If the crosswind is greater than 25kt from 55° or more off the runway bearing,
- If the BRW is such that for the given airfield elevation/temperature/climb gradient required/TODA/TORA combination, there is no scope to conduct a flexible (reduced) thust take-off,
- If the Captain/crew believes rated would be best, for example turbulence expected in the take-off flight path,
- 3 Engine ferry flights, which are operational crew only positioning flights.
On all other occasions we use Flex Thrust.