1973 DeKalb–Peachtree Airport Learjet crash

The remains of 15 cowbirds were found at the end of Runway 20L.

Upon reaching the accident site, investigators from the NTSB found both engines, the wings and empennage had separated from the fuselage, which had largely been consumed by fire. It was clear to investigators the aircraft had encountered a bird strike upon take-off.[7] One pilot who landed at around the time the Learjet took off told the Gadsden Times, "Just as we came across the runway it was almost black with birds. They swarmed and parted as we went through them."[9]

Analysis of the cockpit area found there was bird residue and feathers on the windshield and center post. The remains of 15 cowbirds were found within 150 feet (46 m) of the end of Runway 20L.[7] These birds, the NTSB found, had collided with the aircraft structure.[10] Examination of the two engines found evidence of foreign objects, which consisted of minute fragments of feathers. The objects had blocked cooling ports, and had damaged the rotor assembly inside the engine. It was found the left engine had encountered 14 separate bird strikes and the right engine had encountered five.[7] When the birds entered the engine, they caused the compressors to stall; these were the two loud bangs the witnesses heard as the aircraft took off. As the aircraft passed over the perimeter fence, the left engine flamed out, and the trail of smoke was unburned fuel passing through the hot combustion and turbine sections. Investigators determined it was possible the flight crew had managed to restart the left engine.[10]

To pass certification, the General Electric CJ610 turbojet engine underwent bird strike testing, during which chloroformed birds are passed through a test engine.[11] However, the damage to both engines was, according to the NTSB, "considerably heavier" than it had been in the test engine. Because of the failure of the left engine, and the severe damage to the right engine, the aircraft was unable to remain airborne.[10]

Formerly a military base, DeKalb–Peachtree Airport came under control of the DeKalb County government in 1960 for use as a civil airport. The County government told the FAA they would "take action to restrict the use of land adjacent to or in the immediate vicinity of the airport to activities and purposes compatible with normal airport operations including landing and take-off of aircraft."[11] However, in the summer of 1962, ten years before the accident, a sanitary landfill site was opened in the vicinity of the airport. The NTSB report suggests birds were regularly attracted to the landfill site.[10]

An image showing the proximity of the landfill site to aircraft departing from Runway 20L, and the number of birds that were attracted to the area

In 1970, the FAA contacted the County government and alerted them to the potential risk of a bird strike at the airport. "In February 1971, the FAA was advised by the County that the dump would be closed by August 1972," as stated in the NTSB accident report.[10] However, the landfill site was not closed in 1972, and remained open at the time of the accident. Investigators concluded it was likely the dump was a factor in the accident: "There is little doubt that the municipal dump located adjacent to the airport property attracts birds which are a serious hazard to aircraft."[12]

Furthermore, the NTSB concluded the FAA had not intervened to take action with regards to the dump. "In following up on the compliance requirements for airports developed or improved with Federal funds, the FAA did not take adequate measures, in accordance with existing statues, to assure that the hazard was removed from the vicinity of the airport."[12] The NTSB was reportedly "concerned because responsible authorities had not taken due cognizance of the bird hazards to aircraft at the DeKalb–Peachtree Airport."[12] The final report stated,

Many airports are confronted with perennial or seasonal bird problems, and all such airports should employ methods to minimize the hazard. Public and private studies have shown that the elimination of food and water sources in the vicinity of airports is the most effective means of combating the bird hazard. Open garbage dumps attract birds, and the location of these facilities around airports is not compatible with normal airport operations.[12]

The final NTSB accident report concluded the probable cause of the accident was the loss of power due to a bird strike to both engines. The risk of bird strikes was, the Board found, magnified by the landfill site located adjacent to the airport. The FAA and airport authorities were both aware of the danger, and did not act on the information.[12] The final report stated,

The National Transportation Safety Board determines that the probable cause of this accident was the loss of engine thrust during take-off due to ingestion of birds by the engines, resulting in loss of control of the airplane. The Federal Aviation Administration and the Airport Authority were aware of the bird hazard at the airport; however, contrary to previous commitments, the airport management did not take positive action to remove the bird hazard from the airport environment.[12]

In the aftermath of the accident, the NTSB made several recommendations. They recommended the FAA "develop and implement a procedure for more stringent and continued surveillance" of airports which develop properties adjacent to the flight paths of aircraft, and "impose timely sanctions against operators of facilities which receive Federal aid and do not fully comply with the requirements imposed upon them."[12] They also advised the FAA to circulate material around airports warning authorities of the dangers posed by landfill sites in the vicinity of runways.[13]