Honeywell Aerospace supplies the systems that sit behind an aircraft's cockpit displays and under its wings: avionics, flight management and navigation software, propulsion engines for business jets, and the auxiliary power units that run an aircraft's systems on the ground. Customers span commercial airframers, business aviation and defence programmes. A large share of earnings comes from the aftermarket rather than from original equipment, because installed systems generate decades of spares, repairs and upgrades at better margins than the initial sale. That aftermarket base ties results to how many hours the global fleet flies as much as to new aircraft orders.