Mid Air Collisions

Brian Saunders
Human Factors
David Miller
June 18, 2011
Abstract

No pilot is immune from a mid air collision and it is one of the pilot’s worst nightmares. Although rare, mid air collisions are a tragic event of when two airplanes collide with each other during flight. Statically speaking, nearly all mid air collisions happen during daylight hours and in Visual flight rules (VFR) conditions and astonishing enough, the greater part of mid air collisions take place within five miles from the airport. The first recorded mid air accident occurred at an air show in the city of Milan, Italy on October 3, 1910. Even though it was a miracle that both pilots survived the accident, mid air collisions would continue to occur without this favorable of an outcome. By the nineteen fifties, and with the introduction of the new generation commercial airplanes, people started to travel more by air than by train; a spur of change was needed.
Between the years of nineteen fifty-six and nineteen fifty-eight, two high profile mid air collisions accidents occurred in uncontrolled air space. The accident between a United DC-7 and a TWA Constellation collided and crashed on 30 June 1956 over the Grand Canyon in Arizona killing all one hundred and twenty-eight passengers and crew. The second notable mid air collision was between a United Airlines Douglas DC-7 aircraft with forty-two passengers and two crew and a United States Air Force North American F-100 Super Sabre supersonic jet fighter aircraft carrying two crew members. They collided over Las Vegas and crashed in the desert killing all forty-nine individuals. These accidents brought a lot of attention to the general public on flying safety, uncontrolled airspace, and the lack of modernization of equipment of the air traffic controllers.
With these chains of events, this led to the increased funding to modernize air traffic controllers systems and hiring and training more air traffic controllers. Additionally, this led to the passing of the Federal Aviation Act of 1958 into law. This law dissolved the Civil Aeronautics Administration and creating the Federal Aviation Agency which gave the Federal Aviation Agency unprecedented and total authority over the control of American airspace, including military activity, and as procedures and air traffic controllers facilities were modernized, airborne collisions gradually subsided. But as the skies become more crowded the chances of such probable accidents will increase at a rate of two collisions per year. This became an actuality on November 12, 1996 when an older Saudi Arabian 747-100B jumbo jet airliner which was not equipped with a TCAS system was in route to Jeddah, Saudi Arabia collided with a Kazakhstan Airlines IL-76 freighter over New Delhi, India. This accident cost the lives of three hundred forty-nine people and remains the worst mid air collision to date.
There are several factors why mid air collisions take place. In the mid air collision over the Grand Canyon in nineteen fifty-six, the National Transportation Safety Board concluded that that the probable cause of this mid-air collision was that the pilots did not see each other in time to avoid the collision. Although the National Transportation Safety Board could not determine why the aircrew could not see each other, the investigators suggested it could have resulted from a combination of human factors such as Intervening clouds reducing time for visual separation, visual limitations due to cockpit visibility, and preoccupation with normal cockpit duties, preoccupation with matters unrelated to cockpit duties and physiological limits to human vision reducing the time opportunity to see and avoid the other aircraft. Furthermore, the likely hood for a mid-air collision is augmented by miscommunication, error in navigation, and deviations from flight plans.()
To aid in the prevention of mid air collisions, the Traffic Alert and Collision Avoidance System otherwise known as TCAS hardware and software and or other proximity warning devices were developed in the nineteen fifties and implemented in the mid nineteen seventies and provides pilots with electronic eyes for pilots giving them an enhanced view of nearby flight traffic. It wasn’t until nineteen eighty-one when the chief of the Federal Aviation Administration J. Lynn Helms committed the resources to the Federal Aviation Administration to develop an airborne collision system by nineteen eight-five. At this time and with help from the congressional legislation in nineteen eight-seven the Federal Aviation Administration mandated the installation of Traffic Alert and Collision Avoidance System II on all airliners by the end of nineteen ninety-three.(Genie). Its design was to enhance cockpit awareness of nearby aircraft and aid in the prevention of mid air collisions. It consists of hardware and software that are integrated into other systems in the cockpit and includes a display showing the relative positions and altitudes of aircraft up to thirty-five nautical miles from each other. For example, when aircraft comes within a certain range of each other, TCAS sounds an alarm and issues conflict advisor and prompts pilots to make evasive maneuvers through resolution instructions, acting as a backup to the ground air traffic control system’s separation processes. The Traffic Alert and Collision Avoidance Systems has proven to be an important safety tool in the aviation industry and has substantially reduce the steadily increasing threat of mid-air collisions from the past. Traffic Alert and Collision Avoidance System is now the world standard collision avoidance system for commercial aircraft.
In early aviation the term “see and avoid” was the only deterrence in preventing mid air collisions while flying in uncontrolled airspace, but as we moved to the jet age of the airline industry, aircraft began to travel faster and technology improved on mid air collision avoidance. Mid air collision avoidance software and hardware was developed. There are several types of Traffic Alert and Collision Avoidance Systems (TCAS) in the market, but I will focus on the three that are primarily used. The first one is TCAS one was the first generation of collision avoidance; it is mandated on all aircraft with ten to thirty seats and is used to accommodate the smaller planes that are used in general aviation and regional airlines. The next type of Traffic Alert and Collision Avoidance System is the TCAS two version seven. This version is the latest reversion of the Traffic Alert and Collision Avoidance System and is used in the United States, Japan, Australia, and most of Europe. It is a more advanced system than the TCAS one for which it analyzes the projected flight paths of approaching aircraft and issues an advisories to the aircrews. Traffic Alert and Collision Avoidance System two is required in all international aircraft, aircraft with more than thirty seats or weighing more than thirty-three thousands pounds. The last example I would like to highlight is the Portable Collision Avoidance System; this type of avoidance system was developed in nineteen ninety-nine and is generally used for flight schools, flying clubs, rented planes, or pilots who own their own aircraft. It provides the same similar functions as the Traffic Alert and Collision Avoidance Systems and has grown in popularity due to the fact it is portable and at a cost of five hundred to two thousand dollars, it is considerable less expensive than the Traffic Alert and Collision Avoidance System which costs between one hundred fifty thousand to two hundred thousand dollars.
When an aircraft is equipped with Traffic Alert and Collision Avoidance System it picks up and sends a signal to its aircrafts transponder receiver, these transponders receivers are miniature in size and serves as the same functions as the transponders used by air traffic controllers in controlling air traffic around airports. After the aircrafts transponder receives the signal it sends it to the cockpit and gives the aircrew vocalized alarm signals. There are two types of alarms signals the Traffic Alert and Collision Avoidance System provide sto the aircrew. The first one is traffic advisory; this advisory provides the aircrew with a spoken warning in the form of "Traffic, Traffic". This audio message is usually received when aircraft are within thirty-five nautical miles of each other. When this happens, the aircrew will not maneuver there aircraft in response to a traffic advisory, but will attempt to establish a visual contact, and be prepared to maneuver the aircraft if a resolution advisory occurs. The second alarm sent by the transponder can send to the aircrew a resolution advisory; this type of advisory is a more serious one. This advisory is an urgent threat prediction that traffic aircraft will enter the Traffic Alert and Collision Avoidance System collision airspace within approximately twenty to thirty seconds. When Traffic Alert and Collision Avoidance System issue a resolution advisory several things will happen, for example: a voice alert will sound, vertical guidance will be displayed, and symbogly will be displayed to the aircrew to make the necessary actions. Once the aircrew is notified of resolution advisory aircrews will respond without delay and maneuver as indicated by the Traffic Alert and Collision Avoidance System, unless it jeopardizes the safety of the airplane. Additionally, aircrew will always follow of resolution advisory alarm even if there is a conflict between the resolution advisory and an Air Traffic Control instruction to maneuver. Lastly, aircrew never maneuver in the opposite sense to an of resolution advisory, nor maintain a vertical rate in the opposite sense to a resolution advisory. Once the resolution advisory has been resolved or as permitted by workload by the aircrews, the aircrew will inform the appropriate air traffic controller of the deviation. Overall, Traffic Alert and Collision Avoidance System is a tool designed to prevent midair collisions between aircraft is used as a last resort.
As with any technology the Traffic Alert and Collision Avoidance System is not infallible. Pilots still need to be alert and have situational awareness when flying an airplane. Some problems associated with the Traffic Alert and Collision Avoidance System is that in order for the Traffic Alert and Collision Avoidance System to work it must be turned on and operating. In addition, it needs to be set up correctly. To further complicate the matter, smaller planes are not required to have a Traffic Alert and Collision Avoidance System whereas the larger aircraft are mandated by law. The commercial aviation industry feels that all aircraft operating in the United States should have a Traffic Alert and Collision Avoidance System built in and operating. But this can become very costly for the recreational pilots. Another concern with the Traffic Alert and Collision Avoidance System is that it doesn’t provide horizontal avoidance. Although it does call out voices to aircrew to perform vertical maneuvers for example, “CLIMB! CLIMB!” or DESEND! DESEND!” or “ADJUST VERTICAL SPEED:” it does not call out any horizontal messages. The aviation industry feel an improvement could be made to include voices like “BANK RIGHT AND DESEND!” or “BANK LEFT AND DESEND!” There is also was some confusion whether follow the instructions from the air traffic controller or the Traffic Alert and Collision Avoidance System resolution advisory. There are still some pilots that feel that the air traffic controllers will take care of them and others feel that the Traffic Alert and Collision Avoidance System was put into place to take care of them. But this wasn’t the case in this notable mid air collision over Germany on the fateful day on 1 July 2002 when a Tupolev Tu-154M passenger aircraft Flight 2937 flown by Bashkirian Airlines enroute to Barcelona collided with a DHL Boeing 757-23APF cargo aircraft over Uberlingen, Germany killing all seventy-one passengers and crew. At the conclusion of the investigation on 19 May 2004, the German Federal Bureau of Aircraft Accidents Investigation determined that the probable cause of the accident lay within the Swiss air traffic control system in charge and problems with the use of the collision warning system. The Boeing aircraft relied on the Traffic Alert and Collision Avoidance System resolution advisory and descended his aircraft and the Tupolev also descended by given guidance from the air traffic controller and eventually collided with each other. What makes this event more tragic is that the air traffic controller who was named as causal to accident was murdered seventeen months after the accident by an individual who lost his wife and two children in the collision. Another incident worth noting happened in Japan on 31 January 2001 when two JAL’ aircraft; an Boeing 747 and a Douglas DC-10 nearly collided due to the air traffic controller and Traffic Alert and Collision Avoidance System resolution advisory contradicting each other. As the Boeing 747 descended following the instructions of the resolution advisory, the Douglas DC-10 was told by the air traffic controller; who was tremendously busy at the time to also descend. The Boeing 747 pilots managed to avoid the accident by a narrow margin by adjusting the aircrafts pitch. Miraculously there were only injuries in this incident, it could have been worse. With both planes involved there were a total of six hundred and seventy-seven passengers and crew on board. This would have been by far the worst midair collision to date.
Although the Federal Aviation Administration states that when a situation where a conflict arises between Traffic Alert and Collision Avoidance System resolution advisory and air traffic controller, Traffic Alert and Collision Avoidance System resolution advisory must take priority. As mentioned above, this is not always the case in which things happen. Also worth mentioning, the two stated examples are classic examples of SHEL model liveware-liveware and liveware-software.