Delta Air Lines Flight 9570
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On May 30, 1972, Delta Air Lines Flight 9570 crashed while attempting to land at the
Greater Southwest International Airport Greater Southwest International Airport , originally Amon Carter Field, was the commercial airport serving Fort Worth, Texas, from 1953 until 1974. Dallas/Fort Worth International Airport opened in 1974 a few miles north to replace Greater Southw ...
(GSW) in
Fort Worth, Texas Fort Worth is the fifth-largest city in the U.S. state of Texas and the 13th-largest city in the United States. It is the county seat of Tarrant County, covering nearly into four other counties: Denton, Johnson, Parker, and Wise. According ...
during a training flight. All four occupants aboard the training flight were killed. The crash was determined to be caused by the aircraft flying through
wake turbulence Wake turbulence is a disturbance in the atmosphere that forms behind an aircraft as it passes through the air. It includes variety of elements, the most significant of which are wingtip vortices and jetwash. Jetwash refers to the rapidly moving g ...
, and led to sweeping changes in procedures for maintaining minimum safe distance behind aircraft that generate substantial wake turbulence.


Aircraft and crew

Delta Air Lines Delta Air Lines, Inc., typically referred to as Delta, is one of the major airlines of the United States and a legacy carrier. One of the List of airlines by foundation date, world's oldest airlines in operation, Delta is headquartered in Atla ...
Flight 9570 was a training flight operated using a
McDonnell Douglas McDonnell Douglas was a major American aerospace manufacturing corporation and defense contractor, formed by the merger of McDonnell Aircraft and the Douglas Aircraft Company in 1967. Between then and its own merger with Boeing in 1997, it produ ...
DC-9-14 (registration (registration '). The aircraft was manufactured in 1965, and had operated for 18,998 hours at the time of the accident. The purpose of the flight was to flight check three Delta pilots. Flight 9570 had a total of four occupants, including the two-man flight crew actually flying the aircraft, an additional pilot awaiting his flight check, who would have been riding in the rear, and an FAA air carrier operations inspector, who was on board for proficiency checking, and was riding in the “jump seat”, a fold down seat between the pilot and co-pilot. Also involved in the accident was
American Airlines American Airlines is a major airlines of the United States, major US-based airline headquartered in Fort Worth, Texas, within the Dallas–Fort Worth metroplex. It is the Largest airlines in the world, largest airline in the world when measured ...
Flight 1114, a training flight conducted using a
McDonnell Douglas DC-10 The McDonnell Douglas DC-10 is an American trijet wide-body aircraft manufactured by McDonnell Douglas. The DC-10 was intended to succeed the DC-8 for long- range flights. It first flew on August 29, 1970; it was introduced on August 5, 197 ...
. Flight 1114 was not damaged or affected by the accident.


Accident

On May 30, 1972, Flight 9570 departed Dallas Love Field in
Dallas, Texas Dallas () is the third largest city in Texas and the largest city in the Dallas–Fort Worth metroplex, the fourth-largest metropolitan area in the United States at 7.5 million people. It is the largest city in and seat of Dallas County w ...
at 06:48
Central Daylight Time The North American Central Time Zone (CT) is a time zone in parts of Canada, the United States, Mexico, Central America, some Caribbean Islands, and part of the Eastern Pacific Ocean. Central Standard Time (CST) is six hours behind Coordinate ...
, and proceeded to GSW to perform training approaches and landings. Flight 9570 requested an ILS approach to GSW's Runway 13. The clearance was granted, and Flight 9570 was advised that the American Airlines DC-10 was already in the traffic pattern to perform " touch-and-go landings" at GSW. Flight 9570 landed without incident. After landing at GSW, Flight 9570 received new takeoff and climb-out clearances, made training maneuvers including an ILS missed approach. Flight 9570 then requested approval for landing on Runway 13, behind the American DC-10 which was also inbound for a landing on the same runway. The
air traffic controller Air traffic control specialists, abbreviated ATCS, are personnel responsible for the safe, orderly, and expeditious flow of air traffic in the global air traffic control system. Usually stationed in air traffic control centers and control ...
gave Flight 9570 clearance to land on Runway 13 with an advisory "caution, turbulence." The controller did not advise the DC-9 that they were following a "
heavy Heavy may refer to: Measures * Heavy (aeronautics), a term used by pilots and air traffic controllers to refer to aircraft capable of 300,000 lbs or more takeoff weight * Heavy, a characterization of objects with substantial weight * Heavy, ...
," though the controller did advise that they were following a DC-10 which experienced pilots should have known was a "heavy" aircraft. On approach to the runway, the DC-9 began to oscillate about the roll axis, then rolled rapidly to the right. After rolling 90 degrees to the right, the right wingtip struck the runway. The airplane continued to roll to the right, until the fuselage struck the runway in a nearly inverted position. The aircraft was damaged by impact forces, and destroyed by a subsequent fire. All four occupants were killed.


Investigation

The
National Transportation Safety Board The National Transportation Safety Board (NTSB) is an independent U.S. government investigative agency responsible for civil transportation accident investigation. In this role, the NTSB investigates and reports on aviation accidents and incid ...
(NTSB) investigated the accident. The manner of the crash suggested to the NTSB that the accident was caused by wake turbulence from the DC-10 it had followed. Prior to the Flight 9570 accident, the
Federal Aviation Administration The Federal Aviation Administration (FAA) is the largest transportation agency of the U.S. government and regulates all aspects of civil aviation in the country as well as over surrounding international waters. Its powers include air traffic m ...
had no specific wake turbulence based aircraft separation standards in place. Instead, separation was determined by air traffic control radar resolution limits and, in some cases, runway occupancy restrictions. However, the rapidly increasing use of large jets that cause substantial wake turbulence, such as the
Boeing 747 The Boeing 747 is a large, long-range wide-body airliner designed and manufactured by Boeing Commercial Airplanes in the United States between 1968 and 2022. After introducing the 707 in October 1958, Pan Am wanted a jet times its size, t ...
, DC-10, and Lockheed L-1011 TriStar in recent years had increased the risk of wake turbulence related accidents. However, prior to Flight 9570, most accidents involving wake turbulence involved smaller aircraft than the DC-9. Recognizing wake turbulence as a potential cause, the NTSB performed test and research activities to confirm their hypothesis. The NTSB performed wake vortex testing at the
National Aviation Facilities Experimental Center The National Aviation Facilities Experimental Center (NAFEC) was founded July 1, 1958, by the Airways Modernization Board (AMB) and located in Galloway Township, New Jersey, near Atlantic City, New Jersey. On November 1, 1959, after passage of the ...
at Atlantic City Airport in
New Jersey New Jersey is a state in the Mid-Atlantic and Northeastern regions of the United States. It is bordered on the north and east by the state of New York; on the east, southeast, and south by the Atlantic Ocean; on the west by the Delaware ...
, initially using a Lockheed L-1011 (a
trijet A trijet is a jet aircraft powered by three jet engines. In general, passenger airline trijets are considered to be second-generation jet airliners, due to their innovative engine locations, in addition to the advancement of turbofan technology. ...
similar in size to the DC-10) and then later using a DC-10 loaned to the NTSB. Colored smoke was emitted from the airport control tower, and observations of the smoke as a L-1011 or DC-10 aircraft flew by the tower provided information about the length of time a vortex would remain after the aircraft was clear. The NTSB's tests demonstrated that the wake turbulence caused by an aircraft the size of the DC-10 was sufficient to upset the flight of a following DC-9 to the magnitude experienced by Flight 9570. Following these tests, the probable cause of the accident was determined to be:


Impact

While the risk to small aircraft was already known, the crash of Flight 9570 demonstrated that medium-sized aircraft such as the DC-9 were also vulnerable to wake turbulence. As a result, the investigation into Flight 9570 prompted changes to the minimum distance that all small and medium sized aircraft must maintain when following "heavy" aircraft, and the procedures for maintaining those distances. The NTSB recommended that the FAA develop new minimum aircraft separation standards that take into account wake separation effects of larger aircraft on following aircraft. In response, the FAA developed mandatory minimum separation requirements based on maximum takeoff weight. All aircraft weighing more than 300,000 pounds would be classified as "heavy". Under the new rules, any plane lighter than a "heavy" must maintain at least five miles of separation behind a "heavy" aircraft; a "heavy" behind another "heavy" must maintain four miles of separation. These regulations became the standard for maintaining minimum safe distance between aircraft; the definition of "heavy" was revised downward to aircraft weighing at least 255,000 pounds in 1994.


References


See also

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Aviation safety Aviation safety is the study and practice of managing risks in aviation. This includes preventing aviation accidents and incidents through research, educating air travel personnel, passengers and the general public, as well as the design of airc ...
*
List of accidents and incidents involving commercial aircraft This list of accidents and incidents involving commercial aircraft includes notable events that have a corresponding Wikipedia article. Entries in this list involve passenger or cargo aircraft that are operating commercially and meet this list ...
{{Delta Air Lines Airliner accidents and incidents in Texas Aviation accidents and incidents in the United States in 1972 1972 in Texas Dallas–Fort Worth metroplex 9570 Accidents and incidents involving the McDonnell Douglas DC-9 May 1972 events in the United States