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is doubtful that the 2-degree position would normally have been reached following the takeoff at New Orleans, the Board believed that the history of this aircraft reflects a possible condition which could have caused trim position more AND than usual. To see how this could come about, it is first necessary to examine the history and characteristics of another DC-8 which was leased to Eastern Air Lines from January 15 to March 4, 1964.
On April 1, 1964, twenty-seven days after return of the leased DC-8 to the owner, the crew of a training flight noted control difficulties following takeoff. An inspection of the control system subsequently revealed that the PTC actuator on installation had been adjusted so that it was extended 1/2 inch when at its most retracted position. Normally this amount of extension would have caused the indicator on the first officer's column to be partially extended. In this case the sleeve from which the indicator plunger extends, had been raised to the degree that it was flush with the plunger at the minimum position of the actuator as installed. Additionally, because of a mechanical malfunction in the linkage as found, the indicator was inoperative. A check into the maintenance records showed that on February 13, while the aircraft was on lease to EAL, the PTC actuator was replaced because of a failure of the installed unit, a new actuator was obtained by EAL from the owner's stock, and installed in the aircraft by EAL maintenance personnel at Kennedy International Airport.
The EAL foreman in charge of this work testified to the Board on his activities in this regard. He stated that he had examined the old and new units, assuring that the replacement actuator measured the same as the old one with respect to "eye-bolt to eye-bolt" length and to number of threads showing on the rod end-fitting. Investigation has revealed, however, that both of these conditions could not exist simultaneously since the old unit, DACO P/N 17989-2, and the new one, DACO P/N 17989-3, differed in configuration. With the same number of threads showing on a -2 as on a -3, the eye-bolt to eye-bolt distance will differ by about 1/2 inch, the -3 being the longer. So installed, the fully retracted position would be the equivalent of the programmed extension for 386 knots EAS[1] below 20,000 feet or at 0.84 Mach number at higher altitudes.
It is extremely interesting to note the effects this misrigged PTC system had on the aircraft. Pilots commented that nosedown trim was required following takeoff to the point that the warning light was illuminated.[2] There was no reference made to how much additional AND trim was used. Also of interest is the fact that the c. g. was at 26 percent, or approximately the same as that of N8607. The weight was considerably higher, however, weight effects on trim are minimal.
The Board discovered a parallel to the above case in the history of N8607. The PTC actuator in the aircraft at the time of the accident had been installed
