Hydraulic Failure

What hydraulics do in a helicopter

Most medium and large helicopters use hydraulic actuators between the pilot controls and the rotor swashplate. The actuators amplify pilot input — a small movement of cyclic produces a large, precisely-controlled movement of the swashplate without the pilot having to fight the air loads on the rotor blades.

Some smaller helicopters have no hydraulics at all (the Cabri G2 is a notable trainer with no hydraulic boost). Some have hydraulics only on cyclic, not on collective. Some have dual or triple redundant systems. The first thing to know about hydraulic failure in any aircraft is whether your aircraft even has hydraulics.

Recognition

Hydraulic failure announces itself through control feel:

• Controls suddenly feel stiff — much greater force needed for the same input.
• Forces increase with airspeed — at high cruise speeds, an unboosted control may take 30–50 lbs of cyclic force; in slow flight, it's manageable.
• Hydraulic warning light or pressure gauge indicates the failure — depending on aircraft, may precede or accompany the control-feel change.
• Possible noise from the hydraulic system if a leak or pump failure is the cause.

Procedure

The recovery is straightforward and gives you time:

• Reduce airspeed to reduce control forces. Each helicopter has a recommended "no hydraulics" airspeed in the POH — often around 60–70 KIAS — that balances control authority against control force.
• Land at the nearest suitable area. "Suitable" is more lenient than for engine failure; you can fly to a known airport or pad if it's within reasonable range. Don't push it — controls only get heavier as fatigue sets in.
• Plan a run-on landing. Avoid hover landings — the cyclic forces required to make small corrections in a hover can be exhausting and lead to over-control.
• Brief the passengers if time permits. The flight feel is going to be unusually firm, and they'll notice.

Aircraft variation

Hydraulic failure is one of the most aircraft-specific emergencies on the practical test. Examples:

• Robinson R44/R66 — single hydraulic system. POH procedure includes flying without hydraulics if the system fails or is intentionally turned off (some checklists include a hydraulic-off practice).
• Bell 206/407 — single dual-channel hydraulic system. Failure procedures and "no hydraulics" airspeed in POH.
• Eurocopter / Airbus singles — typically have a hydraulic test before flight; some have switchable hydraulics for training.
• Cabri G2 — no hydraulics at all. There's nothing to fail; controls always feel "heavy" relative to a hydraulically-boosted helicopter.
• Twin-engine helicopters — usually have dual or triple-redundant hydraulics; complete loss is a rare combined failure.

Some helicopters are flyable for hours without hydraulics; others are flyable for minutes before pilot fatigue becomes a factor. Know which kind yours is.

Training discipline

Hydraulics-off practice — where the system is intentionally disabled in flight to simulate failure — is a standard training maneuver in helicopters that allow it. The intent is to give pilots a feel for control forces and to practice the reduced-airspeed procedure before they encounter it for real.

Common errors during hydraulics-off practice:

• Over-controlling — large inputs with the heavier controls produce overshoots. Inputs need to be smaller and smoother than usual.
• Forgetting to reduce airspeed — the natural reaction to a control-feel problem is to firmly hold the controls; the actual fix is to slow down so the air loads decrease.
• Hover landings instead of run-ons — possible in some types but high-workload; the run-on is preferred for the actual emergency.

This is one of the easier emergencies to demonstrate, and the practical test in helicopters with hydraulics often includes a hydraulics-off pattern. Treat the training repetition seriously — it's the only way to feel control forces before you need to fly with them.