Douglas DC-9-15 accident at Gulfport, Mississippi, 17 Feb 1971

Accident narrative

On February 17, 1971, at approximately 0809, a Southern Airways Douglas DC-9-15 struck an electric transmission line static cable during a VOR/DME approach to Runway 13 at the Gulfport, Mississippi, Municipal Airport. The crew executed a successful missed approach and landed the aircraft safely on Runway 31. Of the seven passengers and four crew members aboard, one passenger received a scratched hand from flying glass. The aircraft sustained substantial damage, but there was no fire.

### The flight

Southern Airways Flight 41 originated at Moisant Airport in New Orleans, Louisiana. It departed at 0745 and took off at 0751 for the 67-mile flight to Gulfport. The first officer was operating the controls from the right seat. The flight was conducted on an IFR flight plan, though both pilots stated they maintained visual ground contact at all times and did not encounter instrument weather en route.

Approaching Gulfport, the flight was cleared to descend to 4,000 feet. At approximately 0804, the crew reported 15 miles west and was cleared to 1,800 feet for a straight-in VOR approach to Runway 13. Gulfport Approach Control reported the weather as a partial obscuration with one-quarter mile visibility in fog. The crew advised that they required at least one-half mile visibility to commence the approach. Two and a half minutes later, the controller advised that the visibility had improved to three-quarters of a mile.

### The approach

The cockpit voice recorder indicated that the crew spent much of the time between the initial weather report and the update checking the captain’s flight manual for visibility minimums. During this period, the flight intercepted the 7-mile arc toward the final approach path. At four miles out, the flight contacted the Gulfport Tower and was cleared to land.

The minimum descent altitude (MDA) for the approach was 420 feet. During the final descent, the captain told the first officer, "Tom you're cheating, you got full flaps." The first officer then retracted the flaps to 30 degrees.

Shortly after, the captain said, "Bring it back up you're one hundred fifty feet---. Don't want to hit that tower over there." The crew stated the first officer then added power and rotated the nose upward. Sounds of impact were recorded nine seconds later.

The aircraft struck a powerline static cable 8,900 feet northwest of the runway threshold at an elevation of about 140 feet. The tower controller observed the aircraft over the runway threshold executing a missed approach. The flight requested to land on Runway 31, was cleared for a contact approach, and landed without further incident.

### What the investigation found

The Board found no evidence that a failure or malfunction of any aircraft system or component was related to the accident.

The aircraft's left main landing gear had contacted the static cable, pulling 1,000 feet of wire from the supporting towers. The broken wire whipped over the leading edge of the wing and struck the aft fuselage, pulling through the left main tire and causing foreign object damage to the left engine.

The Board noted that the sun was fairly low in the southeast, which would have restricted forward visibility as the aircraft descended into the fog. This lighting would have reduced the ability to perceive objects ahead while providing a deceptive degree of visibility to the side and downward, leading the crew to believe visibility was better than it actually was.

The investigation found that the initial one-quarter mile visibility report diverted the crew's attention from their normal arrival routine. Checking the manual delayed the prelanding checklist until well into the final approach, preventing the captain from continuously monitoring the instruments. The Board noted that the cockpit workload, the distraction of retracting the flaps, and the crew's attempts to locate the runway visually detracted from their instrument scan.

The flight data recorder showed a nearly constant rate of descent that continued well below the 420-foot MDA. The Board evaluated the aerodynamic effect of retracting the flaps from 50 degrees to 30 degrees and found it would decrease the rate of descent at a constant airspeed; the flight data recorder showed no significant change in the rate of descent attributable to the flap retraction.

The Board found no indication that the altitude was being monitored as required. No altitude calls, including the minimum descent altitude, were recorded on the cockpit voice recorder. The captain's recorded statement of "one hundred fifty feet" was evaluated by the Board as either 150 feet below the MDA or a direct reading from the radio altimeter; in either case, the MDA was exceeded by a considerable amount before the crew detected their error. The captain stated he observed low-altitude warning lights on the radio altimeter and flight director just before telling the first officer to pull up. The aircraft's barometric altimeter also had an altitude warning capability, but the Board found it was not functional at the time of the accident.

### Probable cause

The National Transportation Safety Board determined that the probable cause of this accident was "inadequate monitoring of the approach. The captain was preoccupied with the prelanding checklist during the final approach and the first officer, who was flying the aircraft, was devoting his attention to an attempt to establish visual contact with the runway in low visibility. These activities resulted in an improperly executed VOR/DME approach during which the aircraft descended below the minimum descent altitude before the crew acquired visual contact with the runway environment."