the model cs quickly earned an unenviable reputation when six of the eight passing their acceptance flights crashed between july 8, 1913, and february 9, 1914, with all but one of the crashes involving fatalities. the fifth crash on november 24, 1913 killed the army's chief instructor and a new pilot. as a result, the wright company factory manager, grover loening, concluded that the wright c was flawed by a design defect. orville wright disagreed, maintaining that pilot error was to blame, specifically unfamiliarity with the more powerful engine. he theorized that pilots stalled the aircraft by applying full power that in level flight made angle of attack critical. he proposed that full power be used only to climb and invented an angle-of-incidence indicator sensitive enough to warn a pilot that his climb or dive was too steep. he also completed work on an autopilot which he patented in october 1913, and successfully demonstrated in december, but a gyroscope-operated autopilot patented by lawrence sperry proved more immediately practical and became standard.