Originally Posted by
vilas
PENKO
Quoted below from FCTM NO-110 P4/10
The flight crew should sequence the F-PLN first, and then press the APPR pb. When the LOC mode is armed or engaged, the flight crew should not perform a DIR TO, in order to sequence the F-PLN as this will result in the FMGS to revert to the NAV mode. In this case, the LOC mode will have to be re-armed and re-engaged, increasing workload unduly.
This is why you ask to sequence the FPLAN BEFORE the approach is armed.
Quite logical.