The old Jefferson Airplane is ready for takeoff again. Original members Grace Slick, Paul Kantner, Jorma Kaukonen and Jack Casady will start recording an album of new material in the next few weeks and a spokesman says they will be on a major label. There's no word yet on whether Marty Balin, another key original member of the '60s psychedelic band, will be on board. Slick says the reunion came about when she went to see a performance by Hot Tuna, the Kaukonen-Casady group, with Kanter in San Francisco. She ended up singing a few songs with them and now it's back to the future.