Page:CAB Accident Report, Eastern Air Lines Flight 304.pdf/17

 on May 6, 1963, as a replacement for a malfunctioning actuator. As with the leased DC-8, the new unit was a -3, whereas the one removed was a -2, and the change had likewise been accomplished by EAL maintenance personnel. With reference to the PTC problems encountered at Philadelphia on the day before the accident, the Board can find it nowhere indicated that anyone, either maintenance or flight personnel, ascertained that the actuator was in fact retracted. The only determination made was that the unit was inoperative and an election was made to utilize the airplane in that condition until the following day. Failure to positively ascertain the true position of the actuator was most probably brought on by its inaccessibility, removal of the first officer's seat was necessary to view the actuator. This has since been corrected by the installation of an access panel in the nose wheel well. The captain of the flight to Mexico City testified that the PTC was also checked in flight after departure from Washington and found to be still inoperative. While this information further verifies the static condition of the system, it offers no enlightenment on the PTC actuator position.

Further, the Board believes it sees in the possibility of a partially extended PTC, an explanation for the many autopilot difficulties which remained, for the most part, uncorrected. The pilot write-ups and maintenance records reflect that N8607 had been plagued with autopilot difficulties, many of which were longitudinal. Several write-ups had been for automatic disconnects. The autopilot trim system is limited in positioning the stabilizer in the AND sense (1.25 to about 1.5 degrees AND) and if more nosedown moment is required to keep the aircraft in trim while utilizing the autopilot, the attendant loads must then be carried by the elevator servo. The circuitry of the autopilot will automatically disengage. These disconnects occur along a force-time curve extending from heavy-load/short-time to light-load/long-time. The recorded history of the autopilot difficulties does not contain, for the purposes of this report, the detail necessary to arrive at specific values of any meaning, however, the recorded disconnects and other longitudinal problems, despite repeated autopilot component replacements, indicate a problem lying without the autopilot system.

In summary, the work performed by EAL maintenance personnel on the leased DC-8 and the similar change in actuator models in N8607 establish the possibility of a partially extended PTC actuator, and the autopilot difficulties in N8607 are symptomatic of this condition. Furthermore, if the indicator system failed, as occurred on the leased aircraft and on this one earlier in the day preceding the accident, it is also possible that the PTC actuator could have become inoperative at any position. Apparently the indicator was the only basis used at Philadelphia to determine that the actuator was retracted. Therefore, the Board must accept the possibility that N8607, at departure from New Orleans, as well as earlier, was being operated with a PTC actuator extension (although inoperative) ranging from 0.5 inch to 2.15 inches (normal full extension of 1.65 inches plus the 0.5 inch misrigging).

If this condition existed, it is very likely that full AND stabilizer could have been employed shortly after takeoff. Failure of the chain sprocket on the next attempt to trim noseup would result in ever increasing pull forces on the column as airspeed was accelerated toward en route climb. In its consideration of this as a casual factor, the Board has found reasons both to support and to reject the probability.