Page:CAB Accident Report, Southeast Airlines Flight 308.pdf/9

- 9 - rate turns throughout, it was possible to calculate, mathematically, this airspeed. These calculations revealed that N 18941 would have had to have had an airspeed of 180 knots or a groundspeed of 191 knots to travel from Gray intersection to the accident site in the eight minutes. Obviously, this speed is much too high for a DC–3, especially while maneuvering prior to an ILS approach. From the calculations it is evident that N 18941 could not have been over Gray at 2024, as it reported.

The Board therefore selected two airspeeds, 130 knots and 110 knots, as representative maneuvering speeds at which an ILS procedure would be flown. Substituting each of these speeds in the computations, and starting at the crash site working back toward Gray, it was possible to determine two lines of position along one of which N 18941 had to be located eight minutes before the crash. (These are displayed graphically on attachment A.) It was immediately discerned that the 110-knot line of position could not, in all probability, be correct because it was impossible to correlate the en route reporting times to it. However, the 130-knot line of position appears to be consistent with all the known facts.

From the position report over Piedmont at 1958 and the report over Bulls Gap, which is 30.5 miles from Piedmont, at 2010, it can be seen that the ground-speed of the aircraft was 152 knots. The next position report was over Gray, 32 miles from Bulls Gap. At a groundspeed of 152 knots, this segment should have taken 12.5 minutes. However, the flight did not report over Gray until 2024, 14 minutes after passing Bulls Gap. At this same groundspeed the airplane would have traveled 35.5 miles, or at least 3.5 miles closer to the accident site than Gray. In other words, when the flight reported over Gray it was actually 3.5 miles or 1.5 minutes beyond Gray. By plotting this distance (35.5 miles from Bulls Gap) on a chart, it was found to cross the 275-degree radial of the Tri-City omni at the same approximate point as the line of position calculated for a maneuvering speed of 130 knots. Again referring to attachment A, it can be seen that a course from Bulls Gap to this point would pass approximately two miles east of Gray.

As stated before, the Board believes that the ADF was inoperative as reported by Captain Bond. It further believes that the flight from Knoxville to Tri-City was made in instrument weather conditions without using the low frequency radio aids which define Green Airway 5. There was evidence at the public hearing that in some instances pilots were using the intersection of the 65-degree radial of the Knoxville VOR and the 275—degree radial of the Tri-City VOR as Gray intersection. The intersection of these radials is very indefinite because of the distance from Knoxville and it is possible to receive an indication which could place it several miles east of Gray.

On the basis of all this evidence the Board believes that the crew of N 18941 flew from Knoxville to Tri-City, utilising the Knoxville VOR, and attempted to locate Gray without the aid of the low frequency radio. As will be recalled, the winds aloft were reported to be from the north-northwest and would tend to drift the aircraft east of its course. It is clear that all of these factors combined to cause the airplane to arrive at the position which was reported as Gray intersection.

Had the aircraft been at Gray the correct procedure would have been to continue on the same heading as the low frequency range leg (65 degrees) to