FAL is an acronym, so it would be wrong to correct anyone for saying it F-A-L, as pronouncing the individual letters of an acronym is always correct. However, in cases like NASA, ASAP, MOLLE, and AWOL, when an acronym resembles common vowel-consonant construction seen in most English words, it is pronounced as such.
It is true that nobody vocalizes IBM as ibbum, but the vowel-consonant construction isn't comparable to that of an English word.
It would be weird to hear someone vocalize NASA as N-A-S-A, but correct nevertheless. It's just never spoken that way, so it goes against what people are used to.
FAL is like ASAP. I hear both spoken either way. Anyone who corrects you on your choice is being pretentious.