AS350 B3e course · Emergencies
Electrical failures
Generator off, battery on, clock running
The essentials
A generator failure leaves the battery carrying the aircraft. It lasts a limited time, so the RFM's procedure sheds loads and sets how soon to land.
A battery temperature warning, where fitted, means a battery that may be heading for thermal runaway.
Know before you need it what still works on battery alone — and what the engine control depends on.
How it presents
A generator caution is the usual first sign, with the electrical readings showing the battery discharging. Sometimes the first sign is subtler: lights dimming at night, a radio fading, equipment dropping off one by one.
A generator also stops when the engine does — the starter-generator is on the engine — so the caution may be part of a larger picture. Look at what else is happening before treating it on its own.
Source 1
Time on the battery
How long a battery lasts depends on its capacity, age, temperature and the load. A cold morning, an old battery and every light and radio switched on shorten it dramatically.
Load shedding isn't optional tidying-up: it's what makes the battery last until you land.
Source 1
What still works
Before an electrical failure is a good time to learn which instruments, radios and lights stay on the battery bus, and which go. Night and poor visibility make that list much more important.
The RFM's systems section and the electrical emergency procedures have the details for your aircraft.
When the screens go
On aircraft with the VEMD, the engine and system readings are on electronic screens. In a total electrical failure they go dark with everything else, and so may the warning panel and the horn.
What you have left is what doesn't need aircraft power. Find out before you need it which indications on your aircraft are independent — and practise reading the aircraft by sound and feel.
The engine control's power
An engine needs no electricity to keep turning — but its control might. A hydromechanical control, like the B2's, meters fuel mechanically. A FADEC is a computer, and the question is what powers it when the aircraft's bus is gone.
The answer for your engine is in the RFM's systems description. Know it before you are low, slow and dark with a generator light on.
Battery temperature
A nickel-cadmium battery can enter thermal runaway: heat lowers its resistance, so it draws more charging current, which makes more heat. Left alone, it can end in smoke, fire or a ruptured cell.
The warning, where fitted, catches it early; the response is about breaking the cycle, as the RFM directs. Battery chemistry varies between aircraft and modifications — know which yours has.
Source 2
Night and cloud
An electrical failure in daylight VFR is an inconvenience with a deadline. At night, or in poor visibility, the same failure takes away the instrument lighting, the landing light and the radio you would use to ask for help.
That is the case to plan for: what you would see by, and where you would land, if the panel went dark now.
The generator fails. What's the main consequence?
The battery takes over. Shedding loads extends its time.
Why does a total electrical failure matter so much on a VEMD-equipped aircraft?
The screens go dark with the rest. Know which indications are independent.
What is the danger behind a battery temperature warning?
A battery in runaway gets hotter as it charges, and can end in smoke or fire.
Sources
- Helicopter Flying Handbook (FAA-H-8083-21B) · FAA · Chapter 4, Helicopter Components, Sections, and Systems
- Aviation Maintenance Technician Handbook — Airframe (FAA-H-8083-31B) · FAA · Chapter 9, Aircraft Electrical System, pp. 9-20–9-21 (NiCd batteries, thermal runaway)
- Helicopter Flying Handbook (FAA-H-8083-21B) · FAA · Chapter 5, Rotorcraft Flight Manual
- Aviation Investigation Report A04A0050 (AS350 B3) · Transportation Safety Board of Canada
- Arriel 2D — Airbus H125 engine · Safran Helicopter Engines
- Type-Certificate Data Sheet E.073, Arriel 1 series engines · EASA · Issue 05, 20 February 2025
- Helicopter Flying Handbook (FAA-H-8083-21B) · FAA · Chapter 12, Night Operations
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.