In 1965, a new feature was introduced to the M20. It was called "positive control" and was a single-axis autopilot produced by Brittain Industries. It maintained the wings of the airplane in a level position unless a button on the control wheel was depressed for turns and banks. It was a controversial feature, liked by some pilots and disliked by others. Production and sales of the M20 continued to increase. In 1966, a total of 760 units were delivered, including 280 of the M20C Mark 21 planes and 473 of the M20E Super 21s. A new model, the M20F Executive 21, offered more legroom due to a increase in cabin length which also allowed for a third fuselage side window. It had of fuel capacity compared to in earlier models, and grossed an additional . This year, the company exceeded $1,000,000 in profits.