(Reuters) - Boeing is moving into making aircraft seats to try to reduce costly delays to deliveries by plane manufacturers, forming a joint venture with car seating leader Adient .Adient Aerospace will develop and sell seats to airlines and leasing companies, both for installation on new airplanes and as retrofits on planes made by Boeing and rival manufacturers, the two companies said late on Tuesday.They cited forecasts suggesting the aircraft seating market would grow from $4.5 billion in 2017 to $6 billion by 2026.Adient's tie-up with Boeing is the industry's latest response to industrial problems in aircraft interiors, with congestion in cabin supplies contributing to late airplane deliveries in the past two years.These can cost airplane manufacturers $100,000 a day, said Vertical Research Partners analyst Rob Stallard, making the bottlenecks in aircraft seating a top industry priority."Both companies are investing in this joint venture because the seating supply chain has been a persistent challenge for customers and the industry. Boeing and Adient believe we can add value to the market," Adient's global communications director, Ulrich Andree, told Reuters.Adient, spun off from Johnson Controls in 2016, says it is the largest automotive seats maker, with a 34 percent share of a business dominated by five companies, and its 75,000 workers supply seats and interiors for 25 million vehicles a year.Traditionally, aircraft seat makers like B/E Aerospace and Zodiac Aerospace sell seats directly to airlines, a process that can involve multiple customized designs and regulatory approvals and lead in turn to industrial delays.France's Zodiac is in the process of being taken over by French engine maker Safran after a three-year factory crisis and a spate of profit warnings.The new venture deepens Boeing's involvement in the supply chain for cabin interiors after it introduced a new supplier of economy-class seats for its top-selling 737 series in late 2016: Huntington Beach, California-based LIFT by EnCore.That was seen as the first deal in which Boeing had agreed to buy seats from the supplier and offer them directly to airlines in an effort to reduce risk.But Adient Aerospace expects to follow the more traditional model of selling directly to airlines, Andree said, adding the company expects to start with a business seats program.The new venture reflects a shift by manufacturers like Boeing and Airbus towards greater vertical integration to reduce industrial risks and improve profit margins.Adient Aerospace's headquarters and initial factory will be based near Frankfurt and it will be 50.01 percent-owned by Adient. No financial details were released. The date for starting operations has not been decided, Andree said. (Reporting by Tim Hepher; Editing by Alexander Smith and Mark Potter)