A traffic collision avoidance system or traffic alert and collision avoidance system (both abbreviated as TCAS, and pronounced tee-kas) is an aircraft collision avoidance system designed to reduce the incidence of mid-air collisions between aircraft.
 It monitors the airspace around an aircraft for other aircraft equipped with a corresponding active transponder, independent of air traffic control, and warns pilots of the presence of other transponder-equipped aircraft which may present a threat of mid-air collision (MAC).
 It is a type of airborne collision avoidance system mandated by the International Civil Aviation Organization to be fitted to all aircraft with a maximum take-off mass (MTOM) of over 5700 kg or authorized to carry more than 19 passengers.
 CFR 14, Ch I, part 135 requires that TCAS I is installed for aircraft with 10-30 passengers and TCAS II for aircraft with more than 30 passengers.
The 1965 Carmel mid-air collision occurred on December 4, 1965, when Eastern Air Lines Flight 853 (N6218C), a Lockheed Super Constellation en route from Boston Logan International Airport to Newark International Airport, collided in mid-air with Trans World Airlines Flight 42 (N748TW), a Boeing 707-131B en route from San Francisco International Airport to John F. Kennedy International Airport, over Carmel, New York, United States.
The 1993 Auckland mid-air collision was an aircraft accident in New Zealand.
 It occurred on 26 November 1993, when two aircraft operated by Airwork, under contract to the New Zealand Police, collided and crashed in central Auckland.
 The mid-air collision of the Aérospatiale TwinStar helicopter and Piper Archer aeroplane resulted in the deaths of all four occupants – a civilian Airwork pilot on each aircraft and two New Zealand Police officers on the helicopter.
 The accident occurred in daylight with excellent visibility, in uncontrolled airspace (class G), with both aircraft flying under visual flight rules.
 Both the helicopter and aeroplane were operated by Airwork (NZ), and working under contract to the New Zealand Police at the time of the accident.
The Charkhi Dadri mid-air collision occurred on 12 November 1996 over the village of Charkhi Dadri, to the west of New Delhi, India.
 The aircraft involved were a Saudi Arabian Airlines Boeing 747-100B en route from Delhi to Dhahran, Saudi Arabia, and a Kazakhstan Airlines Ilyushin Il-76 en route from Chimkent, Kazakhstan, to Delhi.
 The crash killed all 349 people on board both planes, making it the world's deadliest mid-air collision, the deadliest aviation accident to occur in India, and the third-deadliest aircraft accident in the history of aviation, behind only the Tenerife airport disaster and Japan Airlines Flight 123.
The 2009 Hudson River mid-air collision was a flight accident that occurred on August 8, 2009, at 11:53 a.m. (15:53 UTC).
 Nine people died when a tour helicopter and a small private airplane collided over the Hudson River near Frank Sinatra Park in Hoboken, New Jersey.
The 1948 Northwood mid-air collision took place on 4 July at 15:03 when a Douglas DC-6 of Scandinavian Airlines System (SAS) and an Avro York C.1 of the Royal Air Force (RAF) collided in mid-air over Northwood in London, UK.
 All thirty-nine people aboard both aircraft were killed.
 It was SAS's first fatal aviation accident and was at the time the deadliest civilian aviation accident in the UK.
 It is still the deadliest mid-air collision in British history.
As of January 2017, a total of 61 Boeing 747 aircraft, or just under 4% of the total number of 747s built, first flown commercially in 1970, have been involved in accidents and incidents resulting in a hull loss, meaning that the aircraft has either been destroyed or has been damaged beyond economical repair.
 Of the 61 Boeing 747 aircraft losses, 32 resulted in no loss of life; in one, a hostage was murdered; and in one, a terrorist died.
 Some of the aircraft that were declared damaged beyond economical repair were older 747s that sustained relatively minor damage.
 Had these planes been newer it would have been economically viable to repair them, although with the 747's increasing obsolescence this is becoming less common.
 747s have been involved in accidents resulting in the highest death toll of any aviation accident, the highest death toll of any single airplane accident and the highest death toll of a mid-air collision, although, as with most airliner accidents, the roots of causation in these incidents involved a confluence of multiple factors which rarely could be ascribed to flaws with the 747's design or its flying characteristics.
The 1963 Ankara mid-air collision occurred on Friday, 1 February, 1963 over Ankara, Turkey when Middle East Airlines Flight 265, a Vickers 754D Viscount completing the flight from Cyprus, came in for landing and collided in the air with a Turkish Air Force Douglas C-47A; after which both planes fell directly to the city below them.
 In total, 104 people died in the accident, including 87 on the ground.
On 29 September 1940, a mid-air collision occurred over Brocklesby, New South Wales, Australia.
 The accident was unusual in that the aircraft involved, two Avro Ansons of No. 2 Service Flying Training School RAAF, remained locked together after colliding, and then landed safely.
 The collision stopped the engines of the upper Anson, but those of the machine underneath continued to run, allowing the pair of aircraft to keep flying.
 Both navigators and the pilot of the lower Anson bailed out.
 The pilot of the upper Anson found that he was able to control the interlocked aircraft with his ailerons and flaps, and made an emergency landing in a nearby paddock.
 All four crewmen survived the incident, and the upper Anson was repaired and returned to flight service.
Middle East Airlines – Air Liban S.A.L. (Arabic: طيران الشرق الأوسط ـ الخطوط الجوية اللبنانية‎ ‎ "Ṭayyarān al-Sharq al-Awsaṭ - al-Khuṭūṭ al-jawiyyah al-lubnāniyyah"), more commonly known as Middle East Airlines (MEA) (Arabic: طيران الشرق الأوسط‎ ‎ "Ṭayyarān al-Sharq al-Awsaṭ"), is the national flag-carrier airline of Lebanon, with its head office in Beirut, near Beirut–Rafic Hariri International Airport.
 It operates scheduled international flights to Asia, Europe, the Middle East and Africa from its base at Rafic Hariri International Airport.

Question: The 1963 Ankara mid-air collision involved an airplane from a company with a head office in what city? 
Answer: Beirut