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The aircraft had been flown 238 hours by the owner, including three training flights, following its return by EAL.
1.17 Modifications
Following this accident, and as a result of further testing of the DC-8, the FAA approved several aircraft modifications, and new maintenance and operating procedures. The AND travel limit of the horizontal stabilizer was reduced from two degrees to one-half degree to minimize the effects of mistrimming. The elevator load-feel and centering spring assembly was modified to properly adjust tolerances, and eliminate the possibility of a heavy compression spring in the assembly producing a preset in the assembly. The PTC actuator bellcrank arm was replaced to modify the aft force on the control column to provide an increase in longitudinal stability under all flight conditions, and an amber warning light was installed to warn of 80 percent full extension. The operating procedures for the aircraft were also changed to restrict the climb speed to 250 knots maximum when the PTC was inoperative and the aicraft c. g. exceeded 30 percent. Because trimming against an unwanted PTC extension will result in (1) decreasing the elevator available for landings, and (2) decreasing the stability of the airplane the procedure for overcoming the condition was changed to: "…the elevator should not be trimmed to zero, but the stabilizer should be positioned to maintain a slight push force (approximately 10 pounds)…"
EAL has also modified their Collins 105 Approach Horizon to provide a more realistic presentation of altitude to the pilot.
2. ANALYSIS AND CONCLUSIONS
2.1 Analysis
In this case there is a meager amount of information regarding the events immediately prior to the accident plus an immense collection of data and testimony of a general, or background nature. The Board has been faced with two basic questions, (1) Is there sufficient evidence as to conditions and circumstances of the flight on which to make casual determinations? (2) Are the background data too general to be applicable to this case or are they in reality symptoms of underlying factors which led to the accident?
Three factors contribute to the lack of specific information about the flight. First, air traffic was extremely light, negating the usual departure requirements of limiting altitudes, specified navigational fixes, and constant radar surveillance. This reduced the radio conversation to the minimum; hence, no references were made by the crew to altitude, speed, or position at any given time following takeoff. Similarly, neither controller, ARTCC, or Departure had definitive information for the last one-third of the flight, and, of course, no altitude references at all. Second, the failure to recover certain meaningful components from Lake Pontchartrain had made it difficult to draw many positive conclusions. Third, the failure to recover the pertinent portion of the flight recording tape eliminated perhaps the best means of accurately defining the final phases of Flight 304.
To properly assess the evidence at hand, the Board found it necessary to construct by analytical methods a facsimile of the type of plot normally gained
