As legacy carriers are retrenching on the domestic front, low-cost carrier JetBlue Airways ( JBLU) is plotting a major offensive on the East Coast. The New York-based airline, which made its inaugural flight in 2000, announced Tuesday it will add a slew of new routes between Nov. 8 and April 6, including as many as 10 daily flights between New York's John F. Kennedy Airport and Boston's Logan. JetBlue will also start flying from those two airports to Austin, Texas, and Richmond, Va., and from Boston to Nassau in the Bahamas and West Palm Beach, Fla. On the new routes, JetBlue will fly brand-new 100-seat Embraer 190 planes, which the airline officially began taking delivery of Tuesday. The 100-seat jets fill a gap between smaller 50- to 70-seat regional planes and larger single-aisle planes like the Airbus A320 and Boeing 737. The Embraers enjoy lower unit costs than the regional jets because they spread fixed costs over more paying customers. But they also allow airlines to fill planes on secondary or high-frequency routes where a 150-seat A320 or 162-seat 737 would be overkill. JetBlue, which so far has flown only Airbus A320s, has 99 firm orders for the Embraer planes. Like other low-cost carriers, JetBlue continues to expand, sometimes filling voids left by larger network carriers, which have been slowing or cutting back domestic capacity and focusing instead on more lucrative international flights. JetBlue has been profitable for 18 straight quarters, but that streak could end when the carrier reports third-quarter results Oct. 20. The average estimate of analysts surveyed by Thomson First Call is for JetBlue to break even. JetBlue shares fell 19 cents, or 1%, to $18.63.