AS350 B3e course · Emergencies
Chips, oil pressure and temperature
What the transmission and engine are telling you
The essentials
Chip detectors in the engine and gearboxes catch metal particles in the oil. Oil pressure and temperature warnings watch the lubrication itself.
A gearbox or engine that has lost its oil pressure has limited time. A chip light can be the first sign of a part starting to fail — or a harmless flake.
The RFM sets the urgency for each. Your job is to recognise it, confirm it, and land as soon as the book says.
Separate systems, separate warnings
The engine and the main gearbox each have their own oil system, with their own pressure and temperature indications and chip detection. The tail gearbox carries its own oil, and on many types its own chip detector.
Knowing which light belongs to which box is the first step of diagnosis: an engine oil problem threatens the engine, a gearbox oil problem threatens the rotor. The captions vary between variants; learn yours.
What a chip detector detects
A chip detector is a magnet in the oil. When metal particles bridge its contacts, it completes a circuit and lights a caution. It can't tell a small flake from the start of a bearing failure.
What happens next — other symptoms, the RFM's procedure — decides how seriously to take it. Maintenance will examine what it caught.
Source 1
Why main-gearbox oil matters most
The main gearbox carries the whole rotor and drives the tail rotor. Without oil its gears and bearings overheat, wear and can seize.
Autorotation does not help with that: the freewheel sits between the engine and the gearbox, so it frees the rotor from a failed engine but not from a failed gearbox. A seized gearbox stops the rotor and the tail rotor together. That's why loss of gearbox oil pressure sits near the top of the urgency scale.
Engine oil
Low engine oil pressure, especially with rising oil temperature, means the engine's bearings are losing lubrication. The likely end is an engine failure — so the case is handled with an autorotation in mind.
That changes how you choose where to go: towards somewhere you could land without power, and with height in hand while you get there.
The tail gearbox
The tail gearbox is small and out of sight, and on many light helicopters has no pressure indication — so a chip light may be the only warning it gives. Check what yours has. A new vibration felt in the pedals, or a change in yaw control, is a second indication worth taking very seriously.
Its oil level is a walkaround item for that reason.
Pressure and temperature together
Low oil pressure with rising temperature is a real loss of lubrication. Low pressure with normal temperature might be a sensor. A chip light with rising temperature or a new noise or vibration is more serious than a chip light alone.
Look for the second indication — then act on the more cautious reading.
"It's always a false alarm"
Sensors and wiring do fail, and many chip lights turn out to be fuzz. That experience builds the most dangerous belief in this chapter: that the next one will be too.
The RFM's urgency is set for the case where it isn't. A false alarm costs a landing and an inspection. Ignoring a real one can cost a gearbox in flight.
Source 1
After the landing
What the chip detector caught, and the oil's condition, tell maintenance whether it was fuzz or the start of a failure. That is their call, not the pilot's.
Continuing the flight because the light went out, or because nothing else happened, is deciding without the evidence.
Source 1
A chip light comes on and the oil temperature is rising. How does that compare to a chip light alone?
A second symptom makes a real failure much more likely.
What does a chip detector tell you?
Metal in the oil — not how much or why.
Why can't autorotation save you from a seized main gearbox?
The gearbox is downstream of the freewheel. If it seizes, the rotor and tail rotor stop with it.
Engine oil pressure is falling and its temperature rising. What should you plan for?
An engine losing lubrication is likely to fail. Plan the route and height for an autorotation.
Sources
- Helicopter Flying Handbook (FAA-H-8083-21B) · FAA · Chapter 4, Helicopter Components, Sections, and Systems
- Helicopter Flying Handbook (FAA-H-8083-21B) · FAA · Chapter 5, Rotorcraft Flight Manual
- Helicopter Flying Handbook (FAA-H-8083-21B) · FAA · Chapter 12, Night Operations
- Helicopter Flying Handbook (FAA-H-8083-21B) · FAA · Chapter 11, Helicopter Emergencies and Hazards
- Helicopter Flying Handbook (FAA-H-8083-21B) · FAA · Chapter 8, Ground Procedures and Flight Preparations
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.