Updated by Howard Aero as the Howard 250, the conversion was to prove popular with about 22 aircraft modified in the early 1960s in San Antonio Texas.
- Some of the upgrades include:
- Increased fuel capacity to 1100 gallons
- Gross takeoff weight increased to 22,500 lbs.
- Extended wing tips
- Specially developed square tip propellers
- Engine cowling to nacelle streamlining
- High flow exhaust system
- Two speed superchargers
- Engine fire extinguishers
- Electric elevator trim
- In-flight fuel dump system
- Streamlined flap and wing trailing edges
- Fully enclosed landing gear doors
- 12 place oxygen system
- Stretched cabin picture windows
- Curved glass windshields
- Extended cockpit side windows
- Extended nose for Bendix weather radar
- Freon air conditioning
- Stinger tail for streamlining
- Deice boots
Lockheed began to develop a larger and updated version of the Model 14 Super Electra in 1939 after the earlier design did not prove a commercial success.
The company modified the fourth Super Electra by adding two more rows of seats in a fuselage stretched by 5ft 6in to 49ft 10in. The first of three altered aircraft flew on September 21, 1939, with the first true Model 18 following on February 2, 1940.
(Information From Golden Age Flight Museum)