It is the world's most-produced twinjet of its class. The original version featured a glazed-nose design and, like certain other Russian airliners (including its sister model the Tu-154), it can operate from unpaved airfields. A total of 854 Tu-134s were built of all versions (including test bed examples) with Aeroflot as the largest user; by 1995, the Tu-134 had carried 360 million passengers for that airline. Design curiosities of the Tu-134 included a sharp wing sweepback of 35 degrees, compared to 25–28 degrees in its counterparts. The engines on early production Tu-134s lacked thrust reversers, which made the aircraft one of the few airliners to use a brake parachute for landing. The majority of onboard electronics operated on direct current. Originally the aircraft had 56 seats in a single class configuration, or 50 seats in a two-class configuration. In 1968, Tupolev began work on an improved Tu-134 variant with a 72-seat capacity. The fuselage received a 2.1-meter (6 ft 11 in) plug for greater passenger capacity and an auxiliary power unit in the tail. As a result, the maximum range was reduced from 3,100 kilometers to 2,770 kilometers. The upgraded D-30 engines now featured thrust reversers, replacing the parachute. The first Tu-134A, converted from a production Tu-134, flew on 22 April 1969. The first airline flight was on 9 November 1970. An upgraded version, the Tu-134B began production in 1980, with the navigator position abandoned, and seating capacity increased to 96 seats. Efforts subsequently began to develop a Tu-134D with increased engine thrust, but the project was cancelled. For more details of development and variants, click here.