Disagreements also ensued over whether to have a co-pilot,

The major drawback of the Monomail was that its design was too advanced for the engines and propellers that were available. The airplane required a low-pitch propeller for takeoff and climb and a high-pitch propeller to cruise. By the time the variable-pitch propeller and more powerful engines were available, newer, multiengine planes were replacing it.

The co-pilot was added.

the plane was designed so that there would be sufficient propeller clearance if a variable-pitch propeller was added later.

The first 247 didn't fly until February 8, 1933, a year later than planned. It went into service with United on March 30, and most of the first 25 planes were delivered during April and May.

The modern twin-engine 247 demonstrated new aerodynamic qualities. It was a low-wing, all-metal monoplane with retractable landing gear and powered by two 550-horsepower (410-kilowatt) Pratt & Whitney Wasp radial engines. Lightweight alloys reduced its weight. It had enough power to climb on one engine with a full load, and it was also the first airliner to use wing flaps. Its final version, the 247D, had variable-pitch propellers and improved performance at higher altitudes to compete with the Douglas DC-2. It had room for 10 passengers, two pilots, and a stewardess (as flight attendants were then called), plus mail and baggage.