Southern Airways Flight 242

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Southern Airways Flight 242
Flight 242 debris field.jpg

Debris of the plane
Accident summary
Accident type failed emergency landing after double engine failure
place New Hope, Paulding County (Georgia) , United States
date April 4th 1977
Fatalities 63
Survivors 22nd
Fatalities on the ground 9
Aircraft
Aircraft type McDonnell Douglas DC-9-31
operator Southern Airways
Mark N1335U
Departure airport Northwest Alabama Regional Airport, Muscle Shoals
Stopover Huntsville-Madison County Airport
Destination airport Atlanta Municipal Airport
Passengers 81
crew 4th
Lists of aviation accidents

On April 4, 1977, a Douglas DC-9-31 crashed on Southern Airways Flight 242 after both engines failed while flying through a severe thunderstorm. Depending on the situation, the crew decided to make an emergency landing on a two-lane main thoroughfare ( Highway ) in Paulding County ( Georgia ), whereby the approaching machine first brushed several trees with its wings . The plane came off the highway when touching down and broke into several main pieces of debris, which hit a house and a gas station, among other things. In the accident, 62 of the 85 occupants were killed. In addition, eight people were killed on the ground and another was seriously injured. That person died of their injuries a month later, as did a passenger after two months, bringing the death toll to 72.

background

Captain Bill McKenzie and his first officer Lyman Keele had their service on the morning of the 4th of April in the near Muscle Shoals ( Alabama ) located Northwest Alabama Regional Airport competed and that day is already a common way Return on the route from Muscle Shoals Completed via Huntsville (Alabama) to Atlanta ( Georgia ) under normal weather conditions.

Before the second flight to Atlanta, the pilots in Muscle Shoals received current weather information from the responsible dispatcher at Southern Airways . His information on the weather situation was based on the information he had last obtained around 2:00 p.m. from the National Weather Service (NWS) and National Severe Storms Forecast Center (NSSFC). A SIGMET alert was issued for northern Georgia and western Alabama indicating isolated thunderstorms , some of which could be severe. The dispatcher also forwarded a tornado warning from the NSSFC to the pilots, which also applied to some of the districts in the state of Georgia that they would fly over on the second section of the route from Huntsville to Atlanta. The pilots did not receive current weather maps with the thunderstorms and tornadoes.

Flight history

The accident McDonnell Douglas DC-9 of Southern Airways at the Miami International Airport in 1977th

The Douglas DC-9 took off at 3:21 p.m. from Muscle Shoals for the Huntsville stage, where it made a scheduled stopover at 3:44 p.m. At this time, the dispatcher tried several times to obtain new information from the NWS weather service. He couldn't do this because the phone line was busy. In the meantime, the individual thunderstorm cells had combined to form a continuous weather front that, contrary to the earlier forecast, was approaching the border area between the states of Alabama and Georgia very quickly from the southeast. This multi-cell front moved forward at a speed of 55 knots (around 90 km / h) and was among the fastest since weather records began in the USA.

After a ten-minute stay in Huntsville, the machine took off at 3:54 p.m. for the onward flight to Atlanta without the flight crew having received any new information on the weather situation. The flight was carried out by the first officer (co-pilot), while the captain took on the tasks of “ pilot not flying ”. The departure control in Huntsville gave the crew immediately after starting a release to 17,000 feet (about 5.180 meters) to rise, and a distance to release VOR Rome (VOR Rome). A minute later, the air traffic controller pointed out a rain zone that was about five nautical miles (about nine kilometers) ahead in the direction of flight and which was one of the foothills of the weather front. This zone of moderate rain was also recorded by the aircraft's weather radar . The departure control over Huntsville turned the flight at 15:57 to the Area Control Center in Memphis ( Memphis Center ) and this just two minutes later to the Area Control Center in Atlanta ( Atlanta Center, Sector 39 ). The crew did not receive any new information about the weather situation from air traffic control in Atlanta, but did not ask for it. At 4:03 p.m. the flight was transferred to another air traffic controller ( Atlanta Center, Sector 40 ). At that time, the machine was about 35 miles (about 58 kilometers) west of the VOR Rome and about 20 miles (about 35 kilometers) west of the front. The captain initially decided to avoid the continuous storm front, which is now clearly visible on the weather radar, instead of flying through it. A few seconds later, however, the controlling co-pilot advised the master that the weather radar would indicate a “hole” in the front. The pilots discussed the possibility of a flight through for about a minute and continued the flight in the direction of the VOR Rome. At 4:06 p.m. the crew received a message from a TWA aircraft , the pilots of which stated that the weather north of VOR Rome would clear up. This information coincided with the display of the on-board weather radar, so that Flight 242 changed course to the left in a northerly direction. On this course the Douglas DC-9 flew into a zone with particularly strong thunderstorm activity. Subsequent evaluations by the NWS showed that at the time of the incident in Rome and the surrounding area the highest levels of precipitation in the country had been measured in the past three years.

When entering the storm front, the machine encountered severe turbulence. In addition, heavy rain and very heavy hail began. Because of the turbulence, the crew reduced the engine power. Shortly afterwards, the pilots received a request from air traffic control to descend to 14,000 feet (around 4,270 meters). For the descent they reduced the power of both engines again and unsuspectingly triggered a chain of events that led to the accident. Due to the absorption of the enormous amounts of rain and hail, the engine speed continued to drop and at 16:07 it briefly fell below the level required for on- board power generation , so that the power supply failed for 36 seconds. At 4:09 p.m., air traffic control instructed the crew to interrupt the descent and maintain an altitude of 15,000 feet (around 4,600 meters). The pilots, who were already just below this flight altitude, immediately reported that a cockpit window had broken due to hailstorms.

During the descent, the engines ran in idle thrust. When the pilots pushed the thrust levers forward in order to increase the engine power again and to go into the climb, the engine speed increased only slowly due to the resistance of the incident amounts of precipitation. As a result, the position of the thrust levers did not correspond to the actual speed of the engines. At the same time, the precipitates were pressed into the compressor and influenced the flow of the primary air flow . The flow in the compressor stages broke off, resulting in a stall (compressor stall) . Both engines overheated within 30 seconds. At the same time, an immense overpressure built up in the compressor, so that the blades of the sixth compressor row of the low-pressure compressor were bent forward and collided with those of the fifth compressor stage. The shovels in both rows were damaged and partially torn off. The chipped metal parts got into the high pressure compressor and caused further damage there. Between 16:09:36 and 16:10:05, the pilots reported the failure of both engines to air traffic control in quick succession. The air traffic controller suggested Dobbins Air Force Base in Marietta , 33 NM (about 61 kilometers) east-southeast of VOR Rome, as a possible alternative airport. When the crew asked for a radar vector for this military airport, they were asked to switch to the approach control frequency. Before the pilots could contact approach control, the power supply on board failed again at 16:10:56.

Approach to the road (dotted) as well as touchdown and rollout (solid line)

The aircraft then changed course to the left by approximately 180 degrees in a westerly direction. The reason for this remained unclear because the cockpit voice recorder was also affected by the power failure and was therefore not recording any calls at the time. The crew may have decided to leave the thunderstorm cell in the direction of entry in order to restart the engines outside the heavy rain zone. Due to the damage, however, this was impossible. The on-board power supply was restored by starting the auxiliary power unit (APU) at 16:13. The pilots then contacted approach control, from which they received the information that they were 20 miles (about 33 kilometers) west of Dobbins Air Force Base. The crew received instructions to turn right on an easterly course of 120 degrees. At the time, the machine was only 10 miles from another airfield, Cornelius Moore Airport in Polk County, Georgia . However, this place, which has a 1,220 meter (4,006 foot) long runway , was outside the control area of ​​air traffic control in Atlanta and was not known to the controller.

At 4:16 p.m., the machine was approximately 4,600 feet and 17 miles from Dobbins Air Force Base too far to glide . The crew asked the air traffic controller for a closer landing possibility and was given the name of Cartersville airfield , which was only designed for small aircraft and was about 10 miles (17 kilometers) north of the aircraft's position. Because this place could no longer be reached in gliding flight, the crew decided to land the machine on a two-lane highway ahead. On the approach, the Douglas DC-9 first grazed several trees with the left wing, then also with the right. The machine landed 570 feet past the point of first tree contact, offset from the center line on the highway. The outer area of ​​the left wing struck a pile of earth, whereupon the aircraft swerved to the left and deviated from the road. The machine collided with several traffic signs, crash barriers, five cars and a truck and then with other trees. Wreckage hit a gas station with an attached grocery store. The building burned out. The hull broke into five major sections. In addition, both wings and the entire tail section including the rudder and horizontal stabilizer were demolished. The debris was distributed over a length of 580 meters (1,900 feet) and a width of 90 meters (295 feet). The fuselage sections behind the wings caught fire as a result of the leaking kerosene . Of the 85 occupants of the aircraft, 62 were killed directly on impact or in fire, including both pilots. With the exception of one flight attendant , all 23 surviving occupants suffered serious injuries. In addition, eight people were killed on the ground and another seriously injured. This person and one passenger died later, so that the number of victims increased to 72. 1)

1) According to the ICAO specifications , only people who died within 30 days of an aircraft accident are statistically counted among the fatalities. In deviation from this, the total number including those who died later is stated in the info box (see above).

Accident factors

The following factors and errors contributed to the accident:

Missing weather information

During the short stopover in Huntsville, the pilots had not received any updated weather reports from the dispatcher of Southern Airways , although the weather service NWS had new information already 20 minutes before the scheduled departure time. In contrast to the earlier predictions, which were forwarded to the pilots before the start in Muscle Shoals, the announced individual thunderstorms had combined to form a multi-cell front that was approaching the region around Rome very quickly. The crew also received no information about the changed weather situation from air traffic control in Atlanta during the flight.

Pilot error

The decision of the pilots to dare to fly through the multi-cell front with the help of the weather radar was generally viewed as a mistake. It was known that the display of the weather radar could be disturbed by atmospheric influences. In addition, turbulence is not recorded by the weather radar. The investigators assumed that the “hole” discovered by the co-pilot did not actually exist in the front. At the time when the crew recognized the alleged "hole", the aircraft was flying through a rain zone with moderate strength. The surrounding precipitation probably led to a falsification of the radar image, which masked a zone of heavy precipitation behind. It remained unclear whether the pilots were influenced in their decision to fly into the front by the reports of two aircraft flying ahead. At around 4:06 p.m. the crew of a TWA aircraft stated that the weather north of VOR Rome would clear up. Earlier, at 4:03 p.m., the pilots of an Eastern aircraft had already communicated by radio when asked by air traffic control that a flight through the front would not pose a risk ( "It was not too comfortable but we didn't get into anything we would consider the least bit hazardous. " ).

technology

Ground tests and calculation models carried out by the NTSB showed that with a water absorption of more than 14 percent, the engine speed in idle thrust would have fallen below the level required for on-board power generation. This probably caused the first power failure on board. For the transition to the climb, the pilots increased the engine power by pushing the thrust levers far forward as usual. The engine speed increased as a result, but due to the slowing effect of the precipitation, it did not coincide with the position of the thrust levers. The insufficient amount of air sucked in led to the compressor pumping (compressor surge) and ultimately to a stall in the compressor (compressor stall). Neither was probably noticed by the pilots; Due to the arrangement of the stern engines and the hailstorm, acoustic perception was probably impossible. They left the thrust levers in the forward position, which caused both engines to overheat. At the same time, the engines continued to absorb enormous amounts of rain and hail. The evaporating precipitate caused an immense pressure increase in the compressor, which led to the bending of the sixth compressor stage and the partial tearing of the compressor blades.

Consequences

  • In cooperation with the engine manufacturer Pratt & Whitney , the aircraft manufacturer McDonnell Douglas recommended deactivating the automatic thrust control when flying through heavy precipitation zones and also not changing the engine power manually. If this is not possible depending on the situation, the thrust levers should only be pushed forward slowly or in stages, with the pilots having to monitor the engine speed.
  • The national aviation authority Federal Aviation Administration (FAA) established a standardized classification system for thunderstorm activities and prescribed a general avoidance of flights through dangerous weather zones. In addition, the FAA issued new framework conditions that led to an improved exchange of information between the national meteorological services, airlines and flight control centers.
  • Even before the accident, a development program to improve on-board weather radars had been initiated in August 1975. At that time, all installed radar systems had monochrome (one-color green) screens . These had a significantly lower resolution than the color screens used today. Today's models show differences in the density of precipitation using appropriate colors and allow pilots to more accurately assess the likely weather situation.

See also

Web links

Commons : Southern Airways flight 242 accident  - Collection of pictures, videos and audio files

Individual evidence

  1. ↑ accident report DC-9-31 N1335U , Aviation Safety Network (English), accessed on August 20, 2016th
  2. ^ Official accident report of the NTSB (in English) , accessed on June 27, 2016
  3. ^ NTSB, official investigation report, page 8, (in English) , accessed on August 9, 2016
  4. ↑ a b c NTSB, official investigation report, page 14, (in English) , accessed on August 9, 2016
  5. ^ NTSB, official investigation report, page 2, (in English) , accessed on August 9, 2016
  6. ^ NTSB, Official Investigation Report, pages 12 to 14, (in English) , accessed August 9, 2016
  7. ↑ a b NTSB, official investigation report, page 4, (in English) , accessed on August 9, 2016
  8. ↑ NTSB, official investigation report, page 31, (in English) , accessed on August 9, 2016
  9. ^ NTSB, official investigation report, pages 4 to 5, (in English) , accessed on August 9, 2016
  10. ^ NTSB, official investigation report, page 32, (in English) , accessed on August 9, 2016
  11. ↑ a b NTSB, official investigation report, page 5, (in English) , accessed on August 9, 2016
  12. ^ NTSB, Official Investigation Report, page 33, (in English) , accessed on August 9, 2016
  13. ^ NTSB, official investigation report, page 34, (in English) , accessed on August 9, 2016
  14. ↑ NTSB, official investigation report, page 6, (in English) , accessed on August 9, 2016
  15. ^ NTSB, official investigation report, page 8, (in English) , accessed on August 9, 2016
  16. ^ NTSB, official investigation report, page 17, (in English) , accessed on August 9, 2016
  17. ^ NTSB, official investigation report, pages 17 to 18, (in English) , accessed on August 9, 2016
  18. ↑ NTSB, official investigation report, page 7, (in English) , accessed on August 9, 2016
  19. ^ NTSB, official investigation report, page 21, (in English) , accessed on August 9, 2016
  20. ↑ NTSB, official investigation report, page 3, (in English) , accessed on August 9, 2016
  21. ↑ NTSB, official investigation report, page 19, (in English) , accessed on August 15, 2016
  22. ^ NTSB, official investigation report, pages 25 and 26, (in English) , accessed on August 15, 2016
  23. ^ NTSB, official investigation report, page 26, (in English) , accessed on August 15, 2016
  24. ↑ a b David Gero: Aviation disasters . Motorbuch Verlag, 1994, ISBN 3-613-01580-3 .

Coordinates: 33 ° 58 ′  N , 84 ° 47 ′  W