Douglas DC-9-32 accident at Louisville, Kentucky, 8 Sept 1970

Accident narrative

On September 8, 1970, at approximately 2114 eastern daylight time, Delta Air Lines Flight 439 touched down 156 feet short of Runway 29 at Standiford Field in Louisville, Kentucky. The Douglas DC-9-32 struck an upward-sloping incline, bounced onto the runway, and slid 4,457 feet before coming to a stop. The aircraft was substantially damaged. All 89 passengers and five crewmembers evacuated safely, with one stewardess and 14 passengers sustaining minor injuries.

**The flight** Flight 439 was a scheduled domestic passenger service from Chicago, Illinois, to Atlanta, Georgia, with intermediate stops in Louisville and Lexington, Kentucky. The aircraft departed Chicago at 2013 on an instrument flight rules plan.

The crew was experienced. The captain had 5,600 total flying hours, including 1,663 in the DC-9, and had been flying into Louisville for eight years. The first officer had 3,485 total hours with 638 in the DC-9.

**The approach** At 2101, Louisville Approach Control established radar contact and provided vectors to intercept the inbound instrument landing system (ILS) localizer for Runway 29. The flight was subsequently cleared for an ILS approach. The weather was reported as a visibility of seven miles with scattered and broken cloud layers, and winds from 310 degrees at eight knots.

The crew computed a landing weight of 92,000 pounds, establishing an approach reference airspeed of 123 knots, and extended the flaps to 50 degrees. The captain stated that the approach appeared normal in all respects and that he last observed an airspeed of 130 to 132 knots. He believed the aircraft did not flare properly, resulting in a hard landing and a bounce. The first officer also thought the approach was normal, noting an airspeed of 130 knots and normal instrument indications when the aircraft was about 2,500 feet from the runway end.

However, a witness who saw the aircraft pass over a toll road approximately 1,000 feet from the runway threshold thought the airplane was low. The witness noted that airplanes approaching low usually increased engine power over the road, but Flight 439 did not.

The ground leading to the Runway 29 threshold sloped upward at a gradient of approximately five percent (2 degrees, 44 minutes). The aircraft made initial ground contact on this incline 156 feet short of the threshold, rolled forward 73 feet, and became airborne again. It touched down a second time on the runway, 262 feet beyond the threshold, and skidded 4,457 feet before coming to rest. The fuselage fractured and buckled between stations 737 and 794, and the tail cone was worn flat from runway contact.

**What the investigation found** Investigators found no aircraft system or component malfunctions. Tests of the flight instruments, pitot-static systems, and anti-skid components showed they operated within manufacturer limits.

A structural analysis by the Douglas Aircraft Company concluded that the primary cause of the fuselage damage was the increased effective sink speed caused by landing on the inclined surface short of the runway. The manufacturer noted that damage would not likely have occurred had the aircraft landed on the runway itself.

The cockpit voice recorder yielded no pertinent information due to an extraordinary amount of background noise on the cockpit area microphone. The flight data recorder, however, provided a clear profile. After correcting a constant calibration error in the altitude trace to match the known ground elevation at impact, investigators plotted the approach path. The plot showed that the aircraft was constantly below the ILS glide slope throughout the final approach. The descent rate was uniform, with no indication of a sudden "duck under" maneuver. The Board noted that if the aircraft had been stabilized on the glide slope, its wheel-path would have crossed approximately 50 feet above the runway threshold.

The Board believed the pilot did not use the ILS glide slope, but instead relied upon visual ground references. Standiford Field's Runway 29 had no approach lighting installed at the time. While residential and commercial lights provided visual cues further out, the upward-sloping area between the toll road and the runway threshold was devoid of lights. The Board concluded that this lack of lighting, combined with the deceptive sloping terrain, caused visual illusions that led the pilot to misjudge the aircraft's altitude.

**Probable cause** The National Transportation Safety Board determined that "the probable cause of this accident was the pilot's misjudgment of altitude due to the absence of sufficient lights in the approach area, misleading information produced by deceptive sloping terrain, and that the pilot did not position the aircraft on the ILS glide slope while he was establishing the final approach profile."