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The Aviation Traders ATL-98 Carvair is a retired air ferry conversion developed by Freddie Laker's Aviation Traders (Engineering) Limited (ATL). Based on the Douglas DC-4, it has a capacity of 22 passengers in a rear cabin, and five cars loaded in at the front. It is powered by four radial engines.

Design and development
Freddie Laker's idea to convert surplus examples of the Douglas DC-4 and its military counterpart the C-54 Skymaster to carry cars was a relatively inexpensive solution to develop a successor to the rapidly aging and increasingly inadequate Bristol 170 Freighter, the car ferry airlines' mainstay since the late 1940s.[1]

The Bristol Freighter's main drawback was its limited car payload: even the "long-nosed" Mark 32 was able to accommodate only three cars, in addition to 20 passengers. This made carrying cars by air a very risky business: if a booked car did not arrive for the flight, the one-third cut in payload made the flight unprofitable. This was made worse by the increasing average length of British cars during the 1950s: the average UK car in 1959 was 25 centimetres (9.8 in) longer than in 1950. The extreme seasonality of the car ferry business furthermore resulted in poor aircraft utilization outside peak periods. Moreover, repeated takeoffs and landings on short cross-Channel flights, in turbulent air at lower altitudes with tight turnarounds of as little as 20 minutes, made the aircraft prone to structural fatigue problems, necessitating rigorous and costly modification programmes, further increasing the type's operating costs on low-yield routes.[1]

When the major airlines replaced their obsolete piston airliners with new Boeing 707 and Douglas DC-8 jets on their prestige long-haul routes, the unit price of second-hand DC-4s dropped to as little as £50,000 (equivalent to £1 million today). The conversion of each of these airframes into car-passenger carriers cost about £80,000 (£1.6 million today). This was easily affordable by smaller airlines, such as the car ferry companies. Freddie Laker's cardboard model of a converted DC-4 featuring a door in the nose and a flight deck raised above the fuselage had shown that its payload was superior to the Bristol Freighter/Superfreighter. The aircraft conversion was designed to accommodate five average-sized British cars plus 25 passengers in the DC-4's longer and wider fuselage. British Air Ferries (BAF), for example, operated its Carvairs in a flexible configuration, either accommodating five cars and 22 passengers or two-three cars and 55 passengers, changeable from one configuration to the other in about 40 minutes.[2] In addition, the DC-4's lack of pressurisation was suitable for low-altitude cross-Channel flights, making the proposed structural conversion straightforward. The result was a new aircraft christened Carvair (derived from car-via-air). Source: Wikipedia