The Airbus A350’s flight-control power architecture is a useful example of how modern airliners can combine conventional hydraulics with distributed electrically powered actuation. Airbus describes the underlying concept as “2H2E”: two segregated hydraulic systems supported by two segregated electrical systems. The architecture was first introduced by Airbus on the A380 and subsequently became part of the company’s design approach for the A350 and A400M. The purpose is not to make the aircraft “all electric” or to eliminate hydraulics. Instead, it changes how redundancy is created and how power is delivered to primary flight-control surfaces. [1]
On the A350, Airbus states that the aircraft uses two hydraulic circuits rather than the three-circuit architecture historically common on many large transport aircraft. Those circuits operate at a nominal 5,000 psi, or approximately 344.75 bar, according to Airbus aircraft-characteristics documentation. Airbus also identifies electro-hydrostatic actuators, or EHAs, and electric backup hydraulic actuators, or EBHAs, as technologies that enabled the removal of one conventional central hydraulic circuit. This article explains what that means technically, where the electrical part fits into an otherwise hydraulic control system, and why the distinction between central hydraulics and local hydraulic actuation matters. [2] [3]
From pilot command to surface movement
The A350 is a fly-by-wire aircraft. In a fly-by-wire system, the pilot’s control inputs are sensed electronically and processed by flight-control computers rather than being transmitted to the control surfaces through direct mechanical linkages. Airbus publicly describes the A350 flight deck as using fly-by-wire flight controls, while EASA’s type-certificate data sheet identifies the A350-941 and A350-1041 as certified large aeroplanes under the A350 type certificate. Fly-by-wire therefore describes the command and control logic; it does not, by itself, describe the source of physical power that moves a large aileron, elevator, spoiler or rudder against aerodynamic loads. [4] [5]
That distinction is fundamental. A computer can calculate the required surface deflection and issue an electrical command, but the actuator still has to generate force. On large airliners, hydraulic actuation has traditionally been attractive because pressurised fluid can transmit substantial power through relatively compact actuators. Airbus’s own explanation of the 2H2E concept notes that large-aircraft flight-control surfaces are typically moved by devices powered from central hydraulic systems. Its EHA concept changes the power path: electrical energy drives a local electro-hydraulic unit rather than relying solely on hydraulic pressure distributed from a central aircraft circuit. [1]
What “2H2E” actually means
Airbus defines 2H2E very specifically: “2H” represents two segregated hydraulic circuits and “2E” represents two segregated electrical systems. Airbus contrasts this with a conventional three-hydraulic-system, or “3H”, architecture. In a 3H arrangement, multiple independent hydraulic sources and distribution networks provide redundancy. In 2H2E, part of that redundancy is transferred to electrically supplied actuation. The important engineering point is diversity: the architecture does not simply duplicate the same energy path four times. It combines hydraulic and electrical power paths so that a loss affecting one type of distribution does not necessarily remove all capability to command the relevant control surfaces. [1]
Airbus says the concept was developed during the 1990s and first implemented on a large civil transport aircraft with the A380. The company subsequently adopted the concept on the A350. That history matters because the A350 implementation is not an isolated experiment; it belongs to an established Airbus architecture family. Nevertheless, component arrangements, control laws, actuator assignments and system details are aircraft-specific. Public descriptions of the 2H2E principle should therefore not be treated as substitutes for the A350 Aircraft Maintenance Manual, Flight Crew Operating Manual or approved system schematics. [1]
The A350’s two 5,000 psi hydraulic systems
Airbus aircraft-characteristics documentation identifies Green and Yellow hydraulic ground-service panels on the A350 and gives a nominal operating pressure of 344.75 bar, or 5,000 psi, for the A350-900; the same document gives approximately 344.74 bar for the A350-1000. Airbus’s maintenance-focused material describes the A350 as using a two-circuit, 5,000 psi hydraulic system. Those figures are important because the A350 did not compensate for removing a third central hydraulic circuit simply by making its two remaining systems copies of an older 3,000 psi layout. The higher nominal system pressure is part of the aircraft’s specific hydraulic architecture. [3] [2]
Pressure alone should not be interpreted as a complete measure of system capability. Hydraulic actuator force depends on pressure acting over piston area, while flow is required to move an actuator at the demanded rate. Aircraft design also has to account for pumps, reservoirs, filtration, heat, fluid condition, distribution, isolation and fault containment. Airbus’s public airport-and-maintenance document confirms the nominal pressure and service arrangements, but detailed flight-control performance and internal sizing remain matters for approved design data. It is therefore accurate to say that the A350 uses 5,000 psi nominal hydraulic pressure; it would be inappropriate to infer individual actuator forces from that figure without the corresponding certified component data. [3]
How an electro-hydrostatic actuator works
An electro-hydrostatic actuator combines electrical input power with local hydraulic power conversion. Airbus describes the EHA as a device that uses electrical energy to create the movement that would otherwise be produced using a central hydraulic supply. A useful way to understand the concept is to separate energy source from final actuation medium. The actuator still uses hydraulic pressure internally to move a piston, but the required hydraulic energy is generated locally by an electrically driven pump and self-contained hydraulic circuit rather than being continuously supplied from a central aircraft hydraulic network. [1]
Safran describes the same general EHA principle in its work on electrically powered landing-gear actuation: an electric motor-pump generates hydraulic power locally at the point of use. That Safran example concerns landing gear rather than the A350 primary flight controls, so it should not be read as a component description of the A350. It is nevertheless a manufacturer explanation of the electro-hydrostatic principle: retain hydraulic force generation at the actuator while replacing a long central hydraulic supply path with electrical distribution and local pressure generation. [6]
This architecture can be described as “power-by-wire” in a broad engineering sense, but that phrase should not be confused with the fly-by-wire command system. Fly-by-wire concerns how control demands are sensed, calculated and transmitted. Electro-hydrostatic actuation concerns how physical power reaches an actuator. On the A350, those concepts coexist: digital flight-control computers determine what the aircraft needs, while a mixture of conventional hydraulically powered servocontrols and electrically supported hydraulic actuators provides the force necessary to move the control surfaces. Airbus specifically identifies both EHA and EBHA technology in its A350 system description. [2]
EHA versus EBHA
Airbus distinguishes between Electro-Hydrostatic Actuators and Electric Backup Hydraulic Actuators in its A350 material. An EHA is fundamentally an electrically powered local hydraulic actuator. An EBHA adds an electrical backup capability to an actuator that can also operate from an aircraft hydraulic source. Public Airbus material does not expose every internal A350 actuator assignment, operating mode or control-surface mapping, and those details should be taken from approved aircraft documentation. The high-level distinction is nevertheless important: the architecture can combine actuators that are electrically self-powered with actuators that retain conventional hydraulic operation but have an electrically driven hydraulic backup mode. [2]
That mixed approach is one reason “the A350 has electric flight controls” is too imprecise. The aircraft certainly uses electronic command processing and electrically supported actuation, but it also retains central hydraulics. A more accurate description is that the A350 integrates conventional hydraulic power and distributed electrically powered hydraulic actuation within a redundant fly-by-wire flight-control system. Airbus’s 2H2E terminology captures that balance directly: two hydraulic systems and two electrical systems contribute to the power architecture. [1] [2]
Why electrical distribution changes redundancy
A central hydraulic circuit requires pumps, fluid, reservoirs, pipes or hoses, valves, filtration and distribution routes. If a design can replace part of that network with electrical cables feeding local actuators, it changes both the physical routing and the types of failure that must be considered. Airbus says its 2H2E architecture improves redundancy by using two electrical systems in place of one of the hydraulic systems found in a traditional 3H architecture. The company also states that EHA and EBHA technology allowed removal of one conventional hydraulic circuit on the A350. These are Airbus design claims and should be attributed to Airbus rather than treated as independent comparative testing. [1] [2]
The word “segregated” is especially important. Redundant systems only provide useful independence when common causes are controlled through design, routing, power-source separation, monitoring and protection. Airbus’s public 2H2E explanation explicitly describes the hydraulic and electrical systems as segregated. Certification of a large aeroplane also requires compliance with extensive airworthiness requirements, but the public type-certificate data sheet is not a detailed system-safety assessment. It confirms the certified A350 models and certification basis; it does not replace proprietary safety analyses that demonstrate the required behaviour under combinations of failures. [1] [5]
The maintenance argument — and how to read it carefully
Airbus promotes the A350’s simplified systems architecture as a maintenance advantage. The manufacturer states that a two-circuit hydraulic system means fewer parts, improved reliability, reduced leakage risk and lower weight compared with the conventional architecture used as its reference. Airbus also markets the A350 as capable of up to 25% lower airframe maintenance costs over 15 years compared with previous-generation aircraft. That 25% figure is a manufacturer claim, not an independently established universal result for every operator, route structure or maintenance programme, and it should be read in that context. [2]
There is nevertheless a straightforward engineering reason why architecture can affect maintenance workload: components that do not exist do not require the same inspections, fluid connections, seals, pipework support or replacement activity as components that do. That does not mean an EHA is maintenance-free. It contains electrical, mechanical and hydraulic elements of its own and remains subject to inspection, fault monitoring and approved maintenance requirements. Airbus Safety First material also emphasises that hydraulic-fluid condition matters because poor fluid quality can damage hydraulic components, including flight-control equipment; Airbus lists the A350 among aircraft for which hydraulic-fluid sampling and analysis are required at defined maintenance intervals. [7]
What happens when something fails?
The correct answer is not that the aircraft simply “switches from hydraulics to electrics.” Flight-control redundancy is distributed across multiple computers, power supplies, hydraulic sources, electrical sources, actuators and control surfaces. The response to a specific failure depends on exactly what has been lost and on the certified system logic. Airbus’s public 2H2E material explains the architectural principle — two hydraulic and two electrical systems providing diversified sources of actuation — but it does not publish a complete failure matrix for the A350. Any operational statement about which surfaces remain available after a particular combination of faults therefore belongs in approved Airbus flight-crew or maintenance documentation, not in a general educational article. [1]
Regulatory material shows why that caution matters. EASA has issued A350 airworthiness directives addressing flight-control components and modifications, including directives involving primary flight-control actuators and flight-control remote modules. Such directives are legally significant continued-airworthiness documents and may require inspections, replacements or modifications for defined aircraft populations. They should not be generalised into claims about the overall reliability of the A350 architecture. Their relevance here is narrower: they demonstrate that individual components within a highly redundant system remain subject to certification oversight and continued-airworthiness action throughout the aircraft’s service life. [8] [9]
Why the architecture is different from an “electric actuator”
An electro-hydrostatic actuator is not the same as a purely electromechanical actuator. In an EHA, an electric motor drives hydraulic pressure generation locally and that hydraulic pressure moves the actuator. In a purely electromechanical arrangement, an electric motor would drive the output through mechanical transmission without the intermediate hydraulic stage. The A350’s public Airbus documentation specifically refers to EHA and EBHA technology, so describing the relevant flight-control actuators as simply “electric motors moving the surfaces” removes an important part of the design. The system is more accurately understood as electrical energy feeding local hydraulic actuation. [1] [6]
This hybridisation is technically significant because it lets designers retain characteristics of hydraulic force production while altering the distribution network. Safran’s general EHA explanation says the technology retains hydraulic actuation while generating hydraulic power locally using an electric motor-pump. Airbus’s A350 material, meanwhile, identifies EHA/EBHA adoption as a factor allowing the third conventional hydraulic circuit to be removed. These two manufacturer sources describe the same broad engineering idea from different applications: electrical distribution can move energy to the vicinity of an actuator, where hydraulic power is then created or backed up locally. [6] [2]
How 2H2E fits the wider A350 electrical architecture
The A350 uses a modern electrical system with variable-frequency generation, which Airbus highlights alongside the aircraft’s simplified hydraulic architecture. That does not mean every traditionally hydraulic or pneumatic aircraft function has been electrified. The A350 remains a mixed-energy aircraft with hydraulic, electrical and pneumatic systems. For flight controls specifically, the important point is that electrical generation and distribution are not just avionics support services: through EHA and EBHA technology they also participate in providing physical control-surface actuation capability. [2]
The result is a design in which a pilot’s sidestick input begins as an electronic command, is processed within the fly-by-wire control system, and can ultimately be realised by actuators drawing power through different hydraulic or electrical paths. That is the conceptual value of 2H2E. It is not a marketing label for four identical systems, and it does not imply that the aircraft can disregard loss of power sources. It describes an architecture built around two segregated central hydraulic systems and two segregated electrical systems, with actuator technology designed to exploit both. [1]
The engineering significance
The A350’s flight-control architecture illustrates a broader trend in aircraft systems engineering: electrification does not necessarily mean replacing every hydraulic device with a mechanical electric motor. It can instead mean changing where power is generated and how it is distributed. With an EHA, high-capacity electrical distribution carries energy to a local motor-pump, while hydraulics remain inside the actuator. With an EBHA, electrical power can provide a backup hydraulic actuation path. Airbus says this combination enabled a two-circuit central hydraulic architecture on the A350 while preserving the redundancy required for a large fly-by-wire transport aircraft. [1] [2]
For readers, the most useful takeaway is therefore precise rather than dramatic. The A350 has not abandoned hydraulics. It uses two central hydraulic circuits operating at a nominal 5,000 psi and supplements the conventional hydraulic architecture with electrically powered or electrically backed electro-hydraulic actuators. Airbus identifies the overall redundancy concept as 2H2E. That combination is what allows the aircraft to distribute flight-control power through more than one energy domain while keeping the pilot interface fully fly-by-wire. [3] [1]
Verified Sources / References
- Airbus — Flight control system: more redundancy to enhance resilience.
- Airbus — Save up to 25% airframe maintenance costs with the A350. Maintenance-cost figures and comparative benefits in this source are Airbus manufacturer claims.
- Airbus — A350 Aircraft Characteristics: Airport and Maintenance Planning.
- Airbus — A350 Family.
- EASA — Type Certificate Data Sheets, including EASA.A.151 Airbus A350.
- Safran Landing Systems — electro-hydrostatic actuator principle.
- Airbus Safety First — Good quality hydraulic fluid for safe operations.
- EASA AD 2025-0152 — A350 primary flight-control actuators.
- EASA AD 2025-0008 — A350 flight-control remote module.
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