best-selling commercial jetliner. The first of three former Japan Airlines Boeing 727-100 series was introduced on 13 April 1973. Among other modifications, the aircraft needed a full stall protection system fitted to meet British civil airworthiness requirements. Dan-Air's original eight Boeing 727-100s, which entered service between 1973 and 1978, differed from overseas-registered aircraft. Dan-Air's examples featured additional emergency doors each side of the rear fuselage as well as a stall-protection system known as a "stick pusher". The additional exits were needed for having the aircraft certificated for an increased maximum seating capacity of 150. This necessitated satisfying the British Civil Aviation Authority (CAA) requirement that all passengers could leave within 90 seconds using only half the available exits. Stall protection had been introduced in the light of experience with the stalling characteristics of both civil and military British T-tailed jet aircraft, including the loss of a Hawker Siddeley Trident on a test flight over Norfolk when it entered a deep stall. This stall-protection system consisted of a stick pusher, a "nudger" and an independent "shaker" for each pilot. When the aircraft was in danger of stalling it warned the pilots by shaking the control columns as well as correcting attitude and altitude, in an attempt to increase air speed and so avert an irrecoverable deep stall. It was estimated that installing stall-protection cost Dan-Air £100,000 per aircraft and up to £1 million for the entire fleet. As well as the Comets and 727s, Dan-Air mainly operated BAC One-Elevens and Hawker Siddeley 748s during its most successful period in the 1970s and 1980s. In May 1983, Dan-Air became the first to put the four-engined BAe 146 regional jetliner into commercial service. The aircraft types below formed part of Dan-Air's fleet at one point or another in the airline's 39-year history: Airbus A300 B4 Airspeed Ambassador Avro York BAC One-Eleven 200/300/400/500 series BAe 146-100/300 Boeing 707-320/320C Boeing 727-100/200 Advanced Boeing 737-200/200 Advanced/300/400 Bristol Freighter de Havilland Comet series 4/4B/4C de Havilland Dove de Havilland Heron Douglas DC-3 Douglas DC-4 Douglas DC-7 Handley Page Dart Herald Hawker Siddeley 748 series 1/2 Nord 262 Piper Apache Vickers Viscount series 700/800. Accidents and incidents Fatal accidents Throughout Dan-Air's 39 years, the airline suffered seven accidents involving the loss of aircraft and lives, three of which killed fare-paying passengers. These accidents were : 1958 Dan-Air Avro York crash: an Avro York crashed on 25 May 1958