Substitute FO for FA and the problem reduces to one already solved
Agreed, provided the training, background & medical checks, all reveal that:
- The FA has an equal, or lesser risk to the substituted pilot
- The adding of extra people does not increase the risk
It all comes down to the risk assessment, and which crucially EASA and the CAA say, the risk of having 2 on the Flt Deck must be assessed and allowed for.
Each airline's risk assessment will no doubt differ... but others as well as me have pointed out the FA "risk" has issues - and very specific ones to do with mental illness / depression / associated medication / self diagnosis (as well as separate security ones).