(Reuters) - Spirit AeroSystems Holdings Inc was hit by troubles at top customer Boeing, driving the aircraft parts maker to report a 55% slump in quarterly revenue and a much bigger-than-expected loss on Tuesday. Spirit gets a big chunk of its revenue from Boeing Co, which was forced to cut back production due to the grounding of its 737 MAX jet and a slump in air travel due to the pandemic. The MAX was finally cleared late last year to fly after being grounded for nearly two years and Spirit hopes to benefit from a ramp-up in production at the planemaker. Shares of Spirit were down 3% in early morning trading as the company also reported a fall in fourth-quarter shipments to its other major customer, Airbus. “2020 was one of the most challenging years in aviation history. For Spirit, the 737 MAX grounding and the COVID-19 pandemic created a dual-crisis,” Spirit Chief Executive Officer Tom Gentile said. Spirit’s total deliveries of shipsets, or complete sets of parts, fell 48.9% to 231 units in the fourth quarter. Boeing 737 MAX deliveries fell to 19 shipsets from 153 a year earlier. Airbus last week forecast flat deliveries in 2021 as it braces for more coronavirus-induced uncertainty in the wake of an annual loss. Boeing has yet to set out detailed targets. Spirit posted a loss of $295.9 million, or $2.85 per share, in the quarter ended Dec. 31, compared with a profit of $67.7 million, or 65 cents per share, a year earlier. On an adjusted basis, the company lost $1.31 per share. Analysts had expected the company to report a loss of 85 cents per share, according to Refinitiv IBES data. Total revenue slumped 55.3% to $876.6 million.