A heat management system of a gas turbine engine for cooling oil and heating fuel, includes an oil circuit having parallel connected first and second branches. Each variable represents a different set of possible departure or arrival times for a particular market pair. The first tank part is disposed below the step member to support the step member. The recess and protrusion are sized and shaped for loose-fit longitudinal engagement of the protrusion within the recess when the track member is laid atop the track support.