Development of the DC-1 can be traced back to the 1931 crash of TWA Flight 599, due to the failure of a wooden strut, which in turn was caused by water which had over time seeped between the layers of the wood laminate and dissolved the glue holding the layers together. All metal wings and structural members Retractable landing gear Capable of remaining in flight, even if one engine failed. TWA accepted the model with a few modifications (mainly increasing seating to 14 passengers and adding more powerful engines) and ordered 20 aircraft. The production model was called the Douglas DC-2.