Page:CAB Accident Report, Southeast Airlines Flight 308.pdf/10

- 10 - intersect the localizer at the middle marker and then to turn to a 90-degree heading to track outbound past the outer marker. It is probable that the crew, thinking they were in the vicinity of Gray, followed the normal procedure for intercepting the localizer. From the position it has been shown N 18941 was over when it reported Gray, a course of 65 degrees to the localizer would pass south and east of the outer marker. Thereafter, without receiving the outer marker and without the use of the low frequency receivers or the No. 2 navigation receiver, the flight would be unable to determine its position along the localizer.

From the calculations which were mentioned above, the time interval from the Grey report to the beginning of the procedure turn was found to be 5 minutes and 45 seconds. Normally, a procedure turn would have been started approximately 3 minutes and 30 seconds after passing Gray. Even if the flight had been over Gray, as it reported, to continue 2 minutes and 15 seconds beyond the normal flying time to the outer marker would place the procedure turn well beyond the authorized 5-mile limit and probably beyond the 5-mile buffer area which is provided as a safety zone east of the procedure turn area. Actually, Flight 308 flew for a period of 5 minutes and 45 seconds from the position, which was erroneously reported as Gray, before starting its procedure turn. Had a procedure turn been started 3 minutes and 30 seconds after this report, as is normal, it is probable the accident would have been avoided.

It is apparent that the flight finally realized it had missed the outer marker and must have realized they were east of it, because they started their turn. Both crew members were familiar with the Tri-City Airport and facilities, and both must have been well aware of the terrain variations in the area. When they realized they were east of the outer marker an unknown distance, the first and only proper action was to execute a missed-approach procedure, climbing to 5,500 feet on the west course of the localizer.

It is assumed that the flight did receive the localizer indications. However, it did not receive an indication of the outer marker. The transmission from the flight asking if the glide slope was operating indicates that this instrument was not operating properly or that they could not rationalize the indication from it with their supposed geographic location. If the localizer had been intercepted to the west of the outer marker, the glide slope indicator would have been at a full fly-down deflection because the aircraft would have been above the glide slope. It would have changed from full fly-down to full fly-up as the aircraft proceeded eastward on the localizer past the outer marker.

It is possible that either the glide slope indicator or the outer marker beacon did not function properly. It may be that the crew concluded they were inoperative. In this event they were wrong in continuing the approach.

Actually, the aircraft intercepted the localizer east of the outer marker. At this point, the glide slope indicator would have been at a full fly-up deflection because the glide slope was above the aircraft. It may be that the crew was confused when, thinking they were west of the outer marker, they received an indication opposite to that expected. It is also possible that high terrain intervening between the transmitter and the aircraft may have blocked the signal (which is VHF and line-of-sight) from being received by the aircraft, causing a flag to appear in the deviation indicator of the aircraft. In either case the Board believes the crew had a clear duty to discontinue the procedure immediately and execute the approved missed approach.