Comet 4B: Originally developed for Capital Airlines as the 4A, the 4B featured greater capacity through a 2m longer fuselage, and a shorter wingspan; 18 were produced.

The aircraft that duly emerged was the DH106 Comet 4B, which was specifically for BEA operations. This variant can readily distinguished by its longer fuselage section (118 ft compared with 111 ft 6 in) and the lack of the wing pinion fuel tanks. 18 were built: 14 for BEA and 4 for Olympic Airways.

First flown in 1958 at Hatfield, the Comet 4 was a ‘stretched’ version of the Comet airliner, having higher all-up weight, with higher thrust engines and extra fuel to meet British Oversees Airways Corporation (BOAC) requirements for operating on the North Atlantic route.

Cyprus Airways Flight 284 was a de Havilland Comet that exploded during a flight to Nicosia International Airport on 12 October 1967 after a bomb was detonated in the cabin.

The 4B was the fastest Comet capable of up to 532 m.p.h. but optimum cruising speed was 520 m.p.h. at 23,500ft and 135,000lb giving a rate of fuel consumption of 11,500lb/hr.

The Comet 4 (including 4B/4C) was the most successful. 77 were built, twice as many as all the other series put together, and they flew a total of 1.7 million hours. It was in commercial service from October 1958 to November 1980, and XS-235 continued to fly for the MoD until 1997.

At 0258 hours at an estimated position 3fi041'N, 27O13'E, the aircraft passed a westbound BEA Comet which was flying at FL 280. Each aircraft saw the other; the Captain of the westbound aircraft has staked that flight conditions were clear and smooth.

The Comet 4 was a completely new aeroplane: one with over 50,000 hours of test and operational flying and a programme of scientific proving and ground testing which was unprecedented in aviation history, behind it – 80%, of which had been completed, with the Mk.3.

That deal fell through, but de Havilland went ahead and developed the "Comet 4B" for British European Airways (BEA), this variant being much the same as the Comet 4A except for a further stretched fuselage, with a maximum passenger capacity of 119 seats.

The aircraft involved was a de Havilland DH-106 Comet 4B, whose first flight took place on 8 June 1961. On 26 June 1961, the aircraft was delivered to British European Airways and went into operation with them with the aircraft registration G-ARJM.