Not quite. Bow wave and Bank were two different things.
Bow Wave automatically went towards you filling up in the next month, ie. if you had a 3hr. bow wave, and your line next month was 72, the 3 hour bow wave would spill forward to fill you up.
Bank was if you wanted to 'save' that 3 hours for a rainy day some months into the future. But you had to elect to deposit it into your bank, which I think maxed out at +60 hours. Anything above that had to continue as a bow wave.
You could also go negative bank. If you wanted to fill up say a 68hr. month (to 75) you could borrow (up to 20 hours) from the bank to fill up. If in later months you developed a bow wave, the first 5 hours of it was automatically used to pay back your negative bank.
There was also a 'spill back' provision, where if you had a short month, you could take some time out of your next month's line and spill it back to fill up (to 75) the previous month.
OR...you could take some time out of your positive bank and use that to fill up.
The typical strategy was to fill your bank up before you bid up to a higher paying seat, then take some out every month to fill up, at the higher rates.
The bow wave strategy was used to push time forward into the choice summer months, drop your trips and stay home, while your bow wave got you paid. Between 60 hour banks, huge bow waves, and dropping any trips that touched your vacation months, you could go all summer without flying a trip, if you worked it right, and many did.
When I was hired in 1985, they had not hired since 1981, so most of the flight engineers had huge bow waves (200 hours), but the company was short of pilots so they 'froze' their bow waves, ie. they wouldn't let them use them to drop trips!
They were in contract negotiations when I interviewed, one of the big sticking points was the B Scale. American Airlines had just started that nonsense in 1984, so in typical "Me Too" fashion, all the other airlines wanted to have one... "To Compete with American"
Of course everyone you spoke with at the interview had to ask you how you would feel if you were put on a B Scale. They even had pay charts they showed us, "Here's what your pay rates might be, are you OK with that?"
