GAS TURBINE ENGINE HYDRAULIC SYSTEM

A hydraulic system for a hydrogen fuelled gas turbine engine. The hydraulic system comprises a closed-loop hydraulic fluid conduit (232), a hydrogen-hydraulic fluid heat exchanger (230) configured to exchange heat between cryogenic hydrogen fuel and hydraulic fluid within the hydraulic fluid conduit (232), and a second fuel-hydraulic heat exchanger (518) configured to exchange heat between a second, non-hydrogen fuel and hydraulic fluid in the hydraulic fluid conduit (232).