The Ligier JS27 was the Formula One car with which the Ligier team competed in the 1986 season.
The JS27 was a logical development of the previous year's JS25, with a lower fuel tank and revised aerodynamics. It was also lighter than its overweight predecessor, with the customer supply of Renault engines more effectively integrated into the overall package than before, although the specification of the engines was always slightly behind fellow-Renault users Lotus and was not developed through the course of the season.
Three JS27 chassis were built and ready to race for the first round of the championship in Brazil, and a further two were constructed during the course of the season: chassis 04 was introduced for the Belgian Grand Prix, whilst chassis 05 was ready in time for the race in Canada. Chassis 01 was written off due to the extensive front-end damage caused by Jacques Laffite's career-ending accident at the British Grand Prix.
The JS27 was initially driven by the French pairing of Ligier mainstay Laffite and René Arnoux. Both drivers were renowned as being fast and experienced, but their age and setup skills were cast into doubt before the start of the season. Arnoux, in particular, had missed all but the first race of the 1985 season after being sacked after the Brazilian Grand Prix by Ferrari, and at 42 years old, Laffite was the oldest driver on the grid.
The JS27 was instantly competitive, however, with numerous points finishes in the first half of the season, including two podium finishes from Laffite. At Detroit, both drivers were particularly fast, Laffite leading the race and eventually finishing third, whilst Arnoux looked on course for second place until he crashed. By the time of the British Grand Prix, Ligier were fourth in the Constructors' Championship: behind Williams, McLaren and Lotus, but ahead of Ferrari.
This race saw the team sustain a major setback, when Laffite was caught up in a first-lap pile-up and seriously injured his legs. The crash effectively ended his Formula One career, as he chose not to return once his injuries had healed. It also spelt the end for the Brands Hatch circuit in F1, and triggered new safety regulations for following years, the most obvious of which stipulated that a driver's feet had to be situated beind the car's front axle line for 1988.
Laffite's accident caused the Ligier team's morale to drop, and with a concurrent lack of development on the chassis, the JS27 was less competitive in the second half of the season. Arnoux and substitute driver Philippe Alliot could only score for points from the German Grand Prix onwards, but this was enough to secure fifth in the Constructors' Championship - the highest-placed team using Pirelli tyres.
The JS27 was one of the last truly competitive cars to be produced by the Ligier team; from 1987 the team would suffer a competitive slump that would last until the 1993 season. The JS27 was also the last Ligier chassis to lead a lap of a Grand Prix until Olivier Panis' victory in the 1996 Monaco Grand Prix, Ligier's last season in F1 before its takeover by Alain Prost.