Investigators found that if the throttle lever was pulled back too far, it would cause the propeller to reverse—a feature designed to slow the aircraft upon landing.

Since the plane was so close to the ground, the suddenness of the bank and dive meant the flight crew had no chance to recover the aircraft before impact.

In the aftermath of the accident, the Civil Aeronautics Administration (CAA) issued an Airworthiness Directive ordering all DC-6 and DC-6B aircraft to be fitted with a manual device which could prevent the inadvertent reversal of the propeller blades.

The climbing bank continued to increase at a rate which alarmed witnesses, and soon after the aircraft rolled through 90° (at which point the wings were vertical to the ground).

Moments later the right wing and nose impacted the ground, causing the fuselage to cartwheel over, before the aircraft came to rest, with the correct side up.

[3][5] The Civil Aeronautics Board (CAB), charged with investigating the accident, examined the wreckage at Long Island MacArthur Airport.

[3][5] They could not conclusively determine the amount of power being produced, but stated there was no evidence found in the wreckage that suggested the engines might have suffered an operational failure.

The pilot then retards the throttle levers to a point below idle speed and that directs the electric mechanisms in the propeller hub to rotate the blades to a position in which they will provide reverse thrust.

When the aircraft took off, electrical power would be cut to the mechanisms so that the propeller blades could not be inadvertently reversed, and the red flag swung out of sight.

They found that if the propellers were reversed prior to take-off they would not, if the flag was not raised, be rotated automatically again in the air to produce forward thrust if full power was applied.

[5][7] One aviation author wrote of the crash, "The flight tests showed conclusively that, at take-off configuration, a DC-6 becomes uncontrollable with an outboard engine at full power with its propeller in reverse pitch.

[5][8] The investigation concluded the accident sequence began when the check pilot, while the aircraft was on the ground, retarded the throttle lever for No.

[5][8] The final accident report concluded there wasn't sufficient time for the crew to react, since the dive began suddenly while the plane was so close to the ground.

4 throttle into the reverse range just before breaking ground, with the other three engines operating at high power output, which resulted in the aircraft very quickly becoming uncontrollable once airborne.

"Following the accident, the Civil Aeronautics Administration (CAA) issued an Airworthiness Directive ordering all DC-6 and DC-6B aircraft to be fitted with a sequence gate latch, known as a Martin bar.

According to the CAB report, a United Air Lines engineer told investigators the Martin bar should make propeller reversal "a more reliable and safer device [than the system fitted to Mainliner Idaho] ... with its numerous switches, relays, and automatic operation.

The signals, fitted in the cockpit of the aircraft, would have warned the flight crew that the thrust lever had been pulled back too far, and the propellers had been reversed.

A Douglas DC-8 operating United Air Lines Flight 859 crashed in 1961 when the first officer attempted to reverse all four engines during the landing roll.

[10][11][12][13] In 1991, Lauda Air Flight 004, operated by a Boeing 767, crashed after the left engine thrust reverser deployed in-flight for reasons that could not be determined, killing 223 people.

The aircraft rolled to the right and crashed in a populated area of São Paulo, Brazil, killing all 95 occupants onboard and 4 on the ground.