Hydraulic, Electrical, or Pneumatic: Which System Rules the Skies?
By Josh Eyre
For decades, commercial aircraft relied on a clear division. Pneumatic systems used hot bleed air from the engines for cabin pressurization, air conditioning, and anti-icing. Hydraulic systems provided the force needed to move large flight controls, while electrical systems powered avionics, lighting, and other onboard equipment. Each operated largely independently. On today’s newest aircraft, however, those boundaries have become increasingly blurred, or disappeared altogether.
Take the Boeing 787 Dreamliner, which fundamentally redefined aircraft architecture with its “more electric” design. Instead of relying on engine bleed air, the Dreamliner uses electrically driven cabin air compressors and an electrically heated wing anti-ice system. The more-electric architecture itself is estimated to reduce fuel consumption by around 3% by eliminating the need to extract bleed air from the engines, contributing to the aircraft’s overall efficiency gains. But this greater level of integration also introduces a new set of operational challenges:
Cascade Effects: On older aircraft, a fault in one system was often contained within that system. In more integrated architectures, however, an electrical fault can have knock-on effects across multiple aircraft systems, affecting functions such as environmental control and backup hydraulic or flight control systems.
Maintenance & Troubleshooting: Diagnosing faults in software-driven, integrated architectures requires engineers to understand electrical, mechanical, hydraulic, and software systems rather than treating each discipline in isolation.
Weight vs. Redundancy: Replacing extensive hydraulic plumbing with electrically powered systems can reduce weight and improve efficiency, but high-power electrical architectures also require sophisticated cooling systems, power distribution units, and multiple layers of redundancy to achieve the same levels of reliability.
The Airbus A350 takes a slightly different approach, adopting a hybrid architecture. Rather than eliminating hydraulics, it combines conventional hydraulic systems with electro-hydrostatic actuators (EHAs) on selected flight control surfaces. These self-contained units generate hydraulic pressure locally using electric motors when required, allowing critical control surfaces to remain operable even if the aircraft’s central hydraulic systems become unavailable. The result is improved redundancy while reducing the amount of hydraulic plumbing needed throughout the airframe.
Do you favor the traditional bleed-air and hydraulics-heavy philosophy of aircraft such as the Boeing 777, or the more-electric approach adopted by the Boeing 787 and Airbus A350? Which system integration trade-off surprises you most?
