Actually, the 16% increase in RASM was comparing 1st quarter 2006 TO 1st quarter 2007.
JetBlue's preliminary passenger revenue per available seat mile for the month of March increased 16 percent year over year.
Average fare in 2006 was $106 (Q1 2006)... so a 16% increase would be $122.96 for Q1 2007. Not to bad but not quite the $139 that would be in average fare was $120.
Still, CASM is the key!
If you charge the same for ticket, have the same number of passengers per departure, but remove the number of seats in your aircraft, PRASM goes up accordingly, as does CASM, since the number of ASMs has diminished in both cases.
I don't think that the reduction in the available seats accounts for all the improvements in PRASM, but it does have an effect.
A bigger effect might be from reaching out to higher yield markets with the 190s.
Whatever the reason, it is certainly good news for the industry whenever revenues go up.