AS350 B3e course · Emergencies
Engine failure
Recognising it, and the seconds that follow
The essentials
When the engine fails, three things happen at once: the nose yaws right as torque disappears, rotor rpm starts to fall, and the horn sounds as it passes the low limit.
Rotor rpm decays fast — in seconds. The immediate response is to lower the collective to keep rpm and establish an autorotation, then fly to the best available landing area.
What else to do, and in what order, depends on height, speed and the RFM.
Why the nose goes right
With power on, the main rotor's torque pushes the nose left and you hold right pedal. When the engine stops, that torque vanishes — but your right pedal is still in. The nose swings right.
It's the opposite of the yaw in American types, and a converting pilot's instinct is wrong here. Left pedal straightens it.
What you see and hear
In principle, an engine failure shows as:
- a right yaw, and a change or loss of engine noise
- rotor rpm falling, and the low-rpm horn
- on the rpm indicator, the free-turbine needle falling away from the rotor needle as the freewheel lets go
- Ng, TOT and torque dropping on the VEMD or gauges
- then warnings that follow from the engine running down — engine oil pressure, the generator
The yaw and the sound usually arrive first. The lights confirm it.
Why rotor rpm falls so fast
In powered flight the blades carry enough pitch to need the engine's full output. When the drive stops, their drag is still there and nothing is replacing the energy — so the rotor slows, and the more pitch is in the blades, the faster it slows.
That's why a failure at high power — climbing, heavy, hovering — is the hardest case, and why every second of delay before the collective goes down costs rpm. The FAA handbook also notes a tendency for the nose to pitch down as the collective is lowered in cruise.
Source 1
What keeps working
The tail rotor is driven from the rotor side of the freewheel, so the main rotor keeps it turning and you keep yaw control. The hydraulic pump is driven from the main gearbox, so the controls stay boosted as long as the rotor turns.
The starter-generator is on the engine. As the gas generator runs down it drops off line and the battery takes over — expect the generator warning to join the others.
At height and speed
With height and speed, there's time: lower the collective, keep rpm in the green, set the autorotation airspeed the RFM gives, and turn towards a landing area. Then — if the RFM's procedure includes it and time allows — the checks and a restart decision.
At height, the first few seconds decide most of what follows.
Source 1
In the hover and low
In a low hover there's no time to autorotate: the aircraft settles on the stored energy in the rotor. Hold the heading against the right yaw, keep it level, and use the collective to cushion the touchdown.
Higher, with little speed, is the worst place — the shaded area of the height-velocity diagram. That's why time spent there is time to minimise.
After take-off
Just after take-off the aircraft is at high power, low speed and low height all at once: the yaw is strongest, rotor rpm decays fastest and there is little room to build speed.
The FAA handbook describes the take-off profile on the height-velocity diagram as the way through with least exposure to the shaded areas. Knowing where you would put the aircraft if the engine stopped — usually ahead, not behind — is decided before you lift.
Engine failure or governor failure?
A governor failing low droops rotor rpm much like an engine failure. The difference is in the engine indications: with a failed engine Ng, TOT and torque fall towards nothing; with a low-side governor failure the engine is still running, just not making the power asked of it.
The first move is the same — protect rotor rpm with the collective. The diagnosis decides what comes next, and the RFM treats them as different emergencies.
The restart question
Whether a restart is attempted, and when, is the RFM's call — and the pilot's judgement of the cause. An engine that stopped from fuel starvation is a different case from one that stopped with a bang, a fire warning or a chip light.
Low down, the answer is usually that there's no time: attention spent on a restart is attention taken from the landing.
Source 9
Why engines stop
Not every engine stoppage starts inside the engine. The FAA handbook names fuel — contamination or exhaustion — among the causes of forced autorotations, and notes that maintenance has often been a contributing factor. Engine control problems — FADEC, sensor or switching — can stop or upset a turbine too.
That's why fuel management and the walkaround are part of engine-failure prevention.
Across the variants
The aerodynamics of an engine failure are the same in every Astar. What differs is what surrounds it: the B2's Arriel 1D1 with its hydromechanical control, the B3's Arriel 2B or 2B1 and the B3e's Arriel 2D with FADEC — each with its own warnings and indications.
Power differs too, and with it the height-velocity diagram. Use the one in your aircraft's RFM, for its mass and conditions.
The engine fails in cruise. What is the immediate concern?
Rotor rpm decays in seconds. Lowering the collective keeps it.
Which way does the nose yaw at engine failure in the Astar?
Right. Torque disappears while your right pedal is still in.
Where is an engine failure hardest to survive?
Too little height and too little speed to set up an autorotation — the shaded area.
After an engine failure, are the flight controls still hydraulically boosted?
The pump runs off the gearbox, so boost remains while the rotor turns. The generator, on the engine, does not.
Rotor rpm is drooping. Ng and TOT are steady at a normal value. What is more likely?
A failed engine shows Ng, TOT and torque falling away. Steady engine readings point elsewhere.
Sources
- Helicopter Flying Handbook (FAA-H-8083-21B) · FAA · Chapter 11, Helicopter Emergencies and Hazards
- Clockwise-rotating helicopter differences · Helicopter Ground
- Aviation Investigation Report A08A0007 (AS 350 BA C-FHHH, power-recovery autorotation, Mount Pearl) · Transportation Safety Board of Canada · Summary, History of the flight, Analysis, footnote 2
- Helicopter Flying Handbook (FAA-H-8083-21B) · FAA · Chapter 4, Helicopter Components, Sections, and Systems
- Aviation Investigation Report A04A0050 (AS350 B3) · Transportation Safety Board of Canada
- AS-350 Hydraulic System (investigation docket document) · NTSB
- Helicopter Flying Handbook (FAA-H-8083-21B) · FAA · Chapter 7, Helicopter Performance
- AS350B3 rolls — engine controls · Aerossurance
- Helicopter Flying Handbook (FAA-H-8083-21B) · FAA · Chapter 5, Rotorcraft Flight Manual
- Type-Certificate Data Sheet E.073, Arriel 1 series engines · EASA · Issue 05, 20 February 2025
Educational only. Not approved training material, and never a substitute for the Rotorcraft Flight Manual, an instructor, or your operator's procedures. Figures marked as manufacturer data or test results are not limitations. This content is a draft and has not yet been reviewed by an instructor.