Question: Who hijacked a flight taking off in San Francisco using Boeing's only model of trijet aircraft?

Context paragraphs:
United Airlines Flight 93: United Airlines Flight 93 was a domestic scheduled passenger flight that was hijacked by four Al-Qaeda terrorists on board, as part of the September 11 attacks.  It crashed into a field in Somerset County, Pennsylvania, during an attempt by the passengers and crew to regain control.  All 44 people aboard were killed, including the four hijackers, but no one on the ground was injured.  The aircraft involved, a Boeing 757–222, was flying United Airlines' daily scheduled morning flight from Newark International Airport in New Jersey to San Francisco International Airport in California.

San Francisco Stock and Bond Exchange: The San Francisco Stock and Bond Exchange was a regional stock exchange based in San Francisco, California, United States.  Founded in 1882, in 1928 the exchange purchased and began using the name San Francisco Stock Exchange, while the old San Francisco Stock Exchange was renamed the San Francisco Mining Exchange.  The San Francisco Curb Exchange was absorbed by the San Francisco Stock Exchange in 1938.  In 1956 the San Francisco Stock Exchange merged with the Los Angeles Oil Exchange to create the Pacific Coast Stock Exchange.

Pan Am Flight 845: Pan Am Flight 845 was a Boeing 747-121, registration N747PA, operating as a scheduled international passenger flight between Los Angeles and Tokyo, with an intermediate stop at San Francisco International Airport (ICAO: KSFO).  On July 30, 1971, at 15:29 PDT, while taking off from San Francisco bound for Tokyo, the aircraft struck approach lighting system structures located past the end of the runway, seriously injuring two passengers and sustaining significant damage.  The crew continued the takeoff, flying out over the ocean and circling while dumping fuel, eventually returning for a landing in San Francisco.  After coming to a stop, the crew ordered an emergency evacuation, during which 27 passengers were injured while exiting the aircraft, with eight of them suffering serious back injuries. <ref name="APL84/85">

Pan Am Flight 7: Pan Am Flight 7, registration N90944, "Clipper Romance Of The Skies", was an around-the-world flight originating in San Francisco that flew westbound with several planned stops, ultimately scheduled to arrive in Philadelphia.  On the morning of November 8, 1957 the aircraft, a Boeing 377 Stratocruiser, departed San Francisco on its first leg to Honolulu, Territory of Hawaii at 11:51am PST.  Last contact with the aircraft consisted of a routine radio transmission between the pilot in command and a US Coast Guard cutter performing radar surveillance duty at Ocean Station November located at the approximate halfway point between the mainland and Oahu.  The flight never arrived in Hawaii.

Asiana Airlines Flight 214: Asiana Airlines Flight 214 was a scheduled transpacific passenger flight from Incheon International Airport near Seoul, South Korea, to San Francisco International Airport (SFO) in the United States.  On the morning of Saturday, July 6, 2013, the Boeing 777-200ER crashed on final approach into SFO.  Of the 307 people aboard, two passengers died at the crash scene, and a third died in a hospital several days later; all three of them were teenage Chinese girls.  Another 187 individuals were injured, 49 of them seriously.  Among the injured were four flight attendants who were thrown onto the runway while still strapped in their seats when the tail section broke off after striking the seawall short of the runway.  It was the first crash of a Boeing 777 that resulted in fatalities since that aircraft model entered into service in 1995.

United Airlines Flight 696: United Airlines Flight 696 was a flight from San Francisco International Airport in San Francisco, California, to Seattle, Washington, with 75 people in board.  After takeoff from San Francisco, Clay Thomas hijacked the Boeing 727, demanding the plane land in Oakland, California, and fuel up for a flight to Cuba.  The crew negotiated the release of all the passengers and cabin crew while on the ground in Oakland waiting for fuel.  Panicked by the sight of police vehicles, Thomas cut the fueling short and demanded an immediate departure to Cuba.  Once the plane was airborne, the pilot explained that the aircraft still did not have enough fuel to reach Cuba, and Thomas agreed to land in Denver, Colorado, for more fuel.  About 90 minutes after landing, the three members of the cockpit crew all jumped to safety from the open cockpit windows, all suffering injuries in the 18-foot (5.5-meter) jump.  Within five minutes of the escape and without hostages, Thomas meekly surrendered to the U.S. Federal Bureau of Investigation.  Thomas is currently incarcerated in a mental Institution in Colorado.

1990 Guangzhou Baiyun airport collisions: On 2 October 1990, a hijacked Boeing 737, operating Xiamen Airlines Flight 8301, collided with two other aircraft on the runways of the old Guangzhou Baiyun International Airport, while attempting to land.  The hijacked aircraft struck a parked China Southwest Airlines Boeing 707 first, inflicting only minor damage, but then collided with China Southern Airlines Flight 2812, a Boeing 757 waiting to take off, flipping onto its back.  A total of 128 people were killed, including seven of nine crew members and 75 of 93 passengers on Flight 8301 and 46 of 110 passengers on Flight 2812.

Boeing 727: The Boeing 727 is a midsized, narrow-body three-engined jet aircraft built by Boeing Commercial Airplanes from the early 1960s to 1984.  It can carry 149 to 189 passengers and later models can fly up to 2700 nmi nonstop.  Intended for short and medium-length flights, the 727 can use relatively short runways at smaller airports.  It has three Pratt & Whitney JT8D engines below the T-tail, one on each side of the rear fuselage with a center engine that connects through an S-duct to an inlet at the base of the fin.  The 727 is Boeing's only trijet aircraft.

1961 Holtaheia Vickers Viking crash: The 1961 Holtaheia Vickers Viking crash (Norwegian: "Holtaheia-ulykken" ) was a controlled flight into terrain incident on 9 August 1961 at Holta in Strand, Norway.  The Eagle Airways (later, British Eagle) Vickers 610 Viking 3B "Lord Rodney" was en route from London to Stavanger Airport, Sola on an AIR Tours charter flight taking a school group for a camping holiday.  The aircraft was making an instrument landing when it crashed 54 km north east of Stavanger.  The accident killed all 39 people on board.

Air Costa: Air Costa was an Indian regional airline headquartered in Vijayawada and based out of Chennai Airport.  It was owned by Indian business company LEPL Group.  The airline commenced operations as a regional airline in October 2013 using two Embraer E-170 aircraft with the first flight taking off from Chennai on 16 October 2013.  The airline got a permit for pan India operations in October 2016.  The airline focused on connectivity between tier II and tier III cities in the country and invested as of 2015.  Air Costa operated 32 daily flights to nine destinations from its focus cities Chennai and Vijayawada as of 2015.  The airline had a maintenance center in Chennai.  On 28 February 2017, it suspended operations until further notice.

Supporting paragraphs: United Airlines Flight 696 Boeing 727
Answer: Clay Thomas