Hydraulic failure in aircraft is a loss of the fluid power network that moves flight-control surfaces, landing gear, brakes, and other hardware. Such a failure may be subtle, giving slow pressure decay and creeping control response, or it may be immediate, with a burst line leaving a control surface locked in one position.
When system A pressure is lost on a Boeing 737-800, pilots continue flight by selecting hydraulic system B and the standby package. They must crank the gear down by hand and accept the absence of autopilot, so the all-weather capability is no longer available. The same risk exists on other types: if all three hydraulic lines share one passage, as in the DC-10-10 where a single tail-bulkhead hole carries them, an engine-separation event can sever every line at once, illustrating how a single structural failure can translate into total hydraulic failure.
Expert behind this article
Jim Goodrich
Jim Goodrich is a pilot, aviation expert and founder of Tsunami Air.
What does it mean when a plane loses hydraulics?
Hydraulic system A loss reduces roll rate and speed brake effectiveness in flight. It disables flight spoilers (two on each wing) and ground spoilers, while loss of pressure disables the normal landing gear extension and retraction system. Manual gear extension becomes necessary, and the standby system remains unaffected. A total loss of aircraft hydraulics could necessitate the non-standard use of engine thrust to maintain aircraft control, and hydraulic failure may also result in loss of the autopilot or loss of some primary or secondary control surfaces.
During a hydraulic system failure, autopilot A disconnects, normal nose wheel steering is lost, and normal brakes cease to function. The flight crew therefore activates the alternate brakes and alternate nose wheel steering via the tiller. Lower half of the rudder rendered inoperative makes steering difficult and for ground operation the NNC directs using the tiller normally.
During a flight, engine 1 thrust reverser lost its normal hydraulic pressure, slowing thrust-reverser deployment. Yet, because the aircraft had triple redundant systems, damage to one meant flight controls still worked. Pressurised fluid normally transferred magnified force to actuators that moved control surfaces.
What causes hydraulic failure in aircraft?
The dominant source for hydraulic failure is contaminated fluid, solid particles, air, and water; these account for 80-90% of hydraulic failures. Air enters through aeration and cavitation, water enters through condensation, leaks, or poor servicing, and both enlarge clearance gaps, accelerate pump and valve wear, and erode seals until internal and external leaks appear. Slow leaks drain the reservoir, fast leaks from a ruptured line dump fluid in seconds, and either drop system pressure below the level needed to move flight-control actuators.
Pressure is lost when a pump fails, an actuator jams, or a valve sticks. Overheating thins the fluid, hardens O-rings, and cracks fittings, while cold weather stiffens seals and lowers material strength until they shear. Progressive fatigue in high-vibration zones lengthens internal cracks until passages open and fluid flows uncommanded. Manufacturing defects, overtightened joints, and poor maintenance that leave debris or incompatible chemicals in the lines act together cause failures.
Any loss of hydraulic fluid or pressure makes primary and secondary control surfaces inoperative, leaves flaps and slats extended, locks landing gear in the well, or takes the autopilot offline. The aircraft remains flyable, but approach speed rises and landing distance grows. The gear has to be lowered by gravity and wind pressure, nose-wheel steering and antiskid braking are lost, and the brake accumulator will allow only a limited number of brake applications. Leaked mist fills the cabin, obscures vision, and ignites on brakes that exceed 500°C (932°F), while an unchecked wheel-well fire weakens the wing structure.
What happens to an airplane after loss of hydraulics?
When there is a loss of hydraulics, backup systems engage instantly, emergency pumps pressurise the remaining fluid so the flight controls still work, and the aircraft's control and handling characteristics change markedly. Flaps remain in their current configuration, spoilers partially deploy, and wheel brakes revert to manual metering, forcing the crew to re-plan speeds, distances, and descent profiles. Pilots prioritise a controlled diversion and landing, knowing that damage to one means the flight controls still work but feel heavier, slower and less predictable. A malfunction becomes catastrophic if multiple circuits are breached. The case of United Airlines Flight 232 is well known: after loss of its engine caused uncommanded retraction of the outboard slats, those slats' asymmetric deployment produced a fatal roll and stall. Simultaneously, fragments severed all three hydraulic lines. Pilots were able to continue flying the aircraft with very limited control by varying engine thrust, yet the United Airlines DC-10 Flight 232 crash-landed at Sioux City Airport, illustrating that even triple or quadruple redundant systems are defeated by a single violent event.
How to fly a plane without hydraulics?
To fly a plane without hydraulics, you must utilize the manual reversion control system. Only small planes can fly without power actuation while larger jets need hydraulic pressure for every surface. Large jets and many turboprops therefore carry a standby hydraulic circuit, and the 737 has manual reversion in the event both primary systems are lost. Even after every actuator is silent, the pilot can still coax the airplane along. Phugoid instability mode requires careful use of the throttle; too much power drives a slow climb and dive cycle whereas too little lets the speed decay. An airplane can be flown with no aileron control as differential throttle or open-window drag will bank it. An open window or door deflects relative wind and induces a turn in that direction. An airplane can be flown with no rudder because differential thrust and slight bank substitute for the missing pedal. An airplane can be flown with no elevator, as long as the stabilizer trim motor still runs.
Has a plane ever landed without hydraulics?
Yes, a plane has landed without hydraulics. On 19 July 1989 United Airlines Flight 232, a McDonnell Douglas DC-10 that had departed Stapleton International Airport for O'Hare and Philadelphia, lost all three independent hydraulic systems when engine 3 disintegrated. With no flight controls, the crew kept the jet airborne for 32 minutes by differential power of the remaining two engines, then crash-landed at Sioux City, Iowa. 111 of 296 people aboard died, yet the event proved that a wide-body can be flown to touchdown after total hydraulic failure.
On 12 November 2001 an Airbus A300 DHL aircraft over Baghdad became the first jet airliner to land safely without any hydraulics, using only engine controls after a missile severed all fluid lines.
How long does it take to fix hydraulics on a plane?
Time needed to fix hydraulics is usually 2-4 hours, but the exact duration depends on several variables. If the task is limited to topping off hydraulic oil and replacing a few seals, the work will be finished closer to the two-hour mark. When the pump itself must be adjusted or repaired, and multiple seals are altered, the job moves toward the upper end of the range. Difficulty of cleaning and the complexity of the system exhaust also influence the schedule, yet crews rarely need more than a single maintenance window to return the aircraft to service.
The duration needed to remedy a hydraulic failure issue depends on the type and intensity of the malfunction: a little hole might be patched in a moment, yet a burst seam deep within the airframe can demand dismantling. Some hydraulic parts are hard to get to and their strategic arrangement for security means elimination of many boards or floorboards before entry is gained. Finding the exact origin of the trouble frequently wastes more hours than the true maintenance itself. A leading part breakdown, like a broken hydraulic valve, may linger if the substantial cause availability is not met. After any maintenance, a strict screening and sign-off process is required; the structure must be pressurized and functionally evaluated to ascertain it works within rigorous safety parameters.
