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The reconstruction of the flight path accomplished in the foregoing paragraphs might well be adjusted for some additional altimeter error not previously indicated or disclosed during the investigation. However, we are of the view that if such an error did in fact exist it need not have been of great magnitude to permit rationalization of the factors involved.
CONCLUSIONS
The Board concludes there is no one factor so outstanding as to be considered as the probable cause of this accident. On the contrary, the Board has found that the accident was an accumulation of several factors or errors, which, together, comprised the safety of the flight.
The Board believes, after exhaustive and detailed investigation, that Flight 320 flew at an average ground speed of 130 knots between New Rochelle and the La Guardia Range Station. Using winds aloft data and time-over-fix data received from aircraft that preceded Flight 320, the Board has determined its indicated airspeed over this area to be approximately 150 knots. The aircraft passed over La Guardia Range Station at a low altitude, possibly as low as 300 feet, but probably not higher than 500 feet. The crew had limited visual reference following the range passage; the first officer and flight engineer observed lights just prior to impact. During the instrument approach, the captain's altimeter was indicating at least 80 feet, and possibly as much as 125 feet above the altitude at inch the aircraft was flying owing to calibration and setting errors.
Just prior to impact, the aircraft was in a shallow descent, in approach configuration except for landing flaps and landing light extension, and was maintaining approximately 130 knots groundspeed. Captain DeWitt was flying the aircraft on auto-pilot "heading mode" during which he was controlling altitude by manipulating the pitch trim wheel with his right hand and controlling direction by rotating the CDI cursor with his left hand. Impact occurred within seconds after the crew received and acknowledged clearance to land. The testimony of the first officer and flight engineer concerning the simultaneous misindication of both drum altimeters could not be substantiated by the evidence of record. The possibility of failure of the captain's altimeter was examined. However, the Board believes there is insufficient evidence available to substantiate this.
The Board believes that even though the accident probably resulted from the captain's neglect of certain essential instrument references, it could have been prevented had the first officer followed prescribed operating procedures, and been fully alert and attentive to all his cockpit duties throughout the approach.
As a result of this accident, the Federal Aviation Agency, on February 8, 1959, as a "precautionary measure," raised Electra minimums. Upon the installation of the conventional three-pointer type sensitive altimeters, the restrictions were lifted.
During this investigation considerable testimony was presented concerning American Airlines' procedures and techniques employed in the operation of autopilots. The Federal Aviation Agency testified that it had not issued any policy directives with respect to the use of autopilots in the various possible types of installment approaches for an air carrier.
While the Board considers that fully automatic front course ILS approaches using an autopilot coupler may be basically sound, it is the Board's opinion that
