The year 1979 was the last big year of aircraft shipments. Almost 18,000 were sold that year. About 3,000 of those airplanes were piston twins. Today, any single that sells 534 units a year is red hot. In 1979, that's how many Seneca twins Piper sold. If the piston single business looks lethargic when compared with the good old days, the piston twin is practically extinct. Beech builds a few Barons, and Piper some Senecas and Seminoles, mostly on special order. The Diamond Twin Star, which is a diesel twin, and the Adam 500 are just coming on line. In 1979 there were 33 different piston twins on the market.