New York-LaGuardia

The Board determines that the probable cause of this accident was a loss of control of the aircraft in extreme turbulence resulting in an involuntary steep descent following which aerodynamic loads from high airspeed, recovery, and turbulence exceeded the design strength of the aircraft.

The Board determines that the probable cause of this accident was the pilot’s descent below his allowable minimum altitude and his inattention to flight instruments while attempting to locate the runway visually. The Board concludes that this accident was brought about by the captain’s disregard of the minimum altitude during instrument flight. It is evident that he was attempting visually to locate the runway tile flying at a low altitude under conditions of restricted visibility.

The Board determines the probable cause of this accident was premature descent below landing minimums which was the result of preoccupation of the crew on particular aspects of the aircraft and its environment to the neglect of essential flight instrument references for attitude and height above the approach surface. Contributing factors were:
- Limited experience of the crew with the aircraft type,
- Faulty approach technique in which the autopilot was used in the heading mode to or almost to the surface,
- Erroneous setting of the captain's altimeter,
- Marginal weather in the approach area,
- Possible misinterpretation of altimeter and rate of descent indicator,
- Sensory illusion with respect to height and attitude resulting from visual reference to the few lights existing in the approach area.

The Board determines that the probable cause of this accident was the deficient judgment and technique of the pilot during an instrument approach in adverse weather conditions in failing to abandon the approach when a visibility of one-eights mile was reported, and descending to a dangerously low altitude while still a considerable distance from the runway.

The Board determines that the probable cause of the accident was the failure of the captain to (1) properly observe and interpret his flight instruments and (2) maintain control of his aircraft. The following findings were reported:
- The weather at the time of takeoff was above the prescribed company minimums,
- The aircraft, immediately following takeoff, made a left turn of approximately 119 degrees and a descent,
- The pilot and flight crew did not observe or interpret any instrument indication of a left turn or descent,
- The heading indications of both fire-seized course indicators corresponded closely to the impact heading of the aircraft,
- These instruments had been functioning properly until the time of impact,
- There was no failure or malfunction of the powerplants,
- There was no airframe failure or control malfunction,
- There was no electrical power failure or malfunction of instruments prior to ground impact,
- There was no fire prior to ground impact,
- As a result of fuselage deformation the main cabin door jammed, hindering evacuation of passengers,
- The main cabin lighting system became Inoperative during deceleration and the emergency inertia lights did not actuate.

The Board determines that the probable cause of this accident was unintentional movement of No. 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. The following findings were reported:
- No evidence of failure or malfunctioning of the structure powerplants, propellers, or electrical system was found,
- In reducing power to zero thrust during an instrument takeoff with a simulated engine out, No. 4 propeller was unintentionally reversed before the aircraft became airborne,
- Evidence indicated that No. 4 throttle was moved out of reverse by the pilot into the forward position in an attempt to unreverse, but the reverse warning flag was not lifted, resulting in increased reverse thrust,
- An outboard propeller on a DC-6 reversing as the aircraft becomes airborne, in conjunction with high power output of the other three engines, at takeoff configuration and airspeed causes the aircraft to become almost immediately uncontrollable,
- There was insufficient time and altitude for any pilot corrective measures to become effective.

The Board determines that the probable cause of this accident was that after failure of the right engine, accepted single-engine procedure was not followed, which resulted in the aircraft losing altitude and striking the ground. The following findings were reported:
- Weather was not a factor in the accident,
- A structural failure occurred in the power section of the right engine that necessitated feathering of the right propeller,
- Failure to attain single-engine performance resulted in loss of altitude,
- Mechanical difficulties in the left engine reduced power but remaining available power was sufficient for single-engine performance.

The Board determined that the probable cause of this accident was the failure of the captain in command to monitor the copilot's approach and take corrective action when the aircraft first went appreciably below a normal approach path. The following findings were pointed out:
- The weather data included a coiling of 1,700 feet and visibility of 1 1/2 miles,
- Authorized minimum ceiling and visibility for the subject approach were 500 feet and one mile, respectively,
- Instrument weather was encountered during the approach,
- The approach was continued visually, despite the instrument weather,
- Air speed was decreased and the aircraft settled rapidly to the water at 0903,
- There was no malfunctioning or failure of the aircraft, or any of its components.

The Board determines that the probable cause of this accident was the reckless conduct of the Navy pilot in performing acrobatic maneuvers on a Civil Airway and his failure to notice the presence of an air carrier aircraft with which he collided.
The following findings were noted:
- The Navy pilot was performing acrobatics on the airway immediately prior to and at the time of collision,
- Neither aircraft was seen by the crew of the other in time to avoid collision.

The Board determines that the probable cause of this accident was the incapacitation of the crew by a concentration of CO2 gas in the cockpit.
The following factors were considered as contributing:
- A fire warning caused the crew to discharge at least one bank of the CO2 fire extinguisher bottles in the forward cargo pit (the forward underfloor baggage compartment),
- Six 15-pound CO2 bottles and six discharge valves were found in the wreckage, however, both the bottles and the valves (which had become separated from their respective bottles upon impact) were so damaged that no conclusions could be drawn as to how many of such bottles had been discharged prior to impact,
- At the time of impact, the emergency cabin pressure relief valves were closed, and the control mechanism for such valves was in the closed position,
- Except for the apparent failure of the fire detection instrument referred to in finding No. 5, supra, the investigation revealed no mechanical failure of the aircraft or fire in flight,
- The emergency procedure for the operation of the DC-6 fire extinguisher system was established after flight tests were conducted in a descent configuration of 300 miles per hour, with landing gear and flaps up, no flight tests were conducted prior to the accident in a descent configuration of 160 miles per hour with gear and flaps down, which configuration was also approved for DC-6 operations,
- At the time of impact the landing gear was in the “up" position, thus indicating that the aircraft had descended in the configuration of 300 miles per hour. The extensive breakage of the aircraft precluded any positive determination as to the position of the flaps,
- After the release of CO2 gas hazardous concentrations of the gas entered into the cockpit,
- Due to the physiological and toxic effects of high concentrations of CO2 gas in the cockpit, which would probably not have occurred had the cabin pressure relief valves been open, the members of the flight crew of the aircraft were rendered physically and mentally incapable of performing their duties.
The following comment was added to the conclusion:
A fire in flight permits little opportunity for the exercise of detached and thoughtful consideration of emergency procedure. Immediate action is required if a fire is to be controlled. Too little consideration has been given to the psychological and physical limitations of crew members in time of stress and danger as related to the complexity of emergency fire procedure. It is not safe to assume that the pilot and co-pilot, under emergency pressure, will always adhere rigidly to the sequence of steps outlined in the CAA Approved Airplane Operating Manual. The possibility of human error under great mental stress is well documented in air transport experience and the design of aircraft controls, especially those of an emergency character, should take into consideration the natural limitations of human nature. These limitations argue against involved procedures applicable in emergencies. In harmony with this objective, the Douglas Aircraft Company has designed and is testing a modified fire extinguishing system which will permit all necessary steps to be executed by the movement of one control. An additional vent is also being designed to reduce CO2 concentration in the cockpit. Seven days after the Mt Carmel accident, the Director of Aviation Safety of the CAA directed telegrams to all CAA regional administrators calling attention to his telegram of June 10, 1948, referred to above, and advising that further investigation had disclosed the existence of the CO2 concentration condition found in Constellation aircraft by the Chillicothe tests in other makes of aircraft. The telegram concluded "Hence, flight crews of all aircraft should be advised to wear oxygen masks and utilize emergency cockpit smoke clearance procedures when carbon dioxide is released into any fuselage compartment from other than portable extinguishers.” All scheduled U S air carriers operating DC-6s have equipped the airplanes with demand type full face oxygen masks for the use of the crew.