Aircraft Engine Systems: Fire Protection, Hydraulic, and Environmental Systems

What method is used to discharge an HRD bottle in a turbine engine installation?

An electrically ignited powder charge blows a knife through the seal on the bottle and discharges the contents.

Which type of fire detection system operates on the rate of temperature rise?

The thermocouple system.

What is indicated if the yellow blow-out plug of the fire extinguisher system on the side of an engine nacelle is blown out?

The built-in fire extinguishing system has been discharged by normal operation.

What is indicated if the red blow-out plug of the fire extinguisher system on the side of an engine nacelle is blown out?

The built-in fire extinguishing system has been discharged by a high temperature condition.

How is a pressure-type continuous-element fire detector system checked for operation?

Low-voltage alternating current is sent through the sheath of the detector element, heating the diaphragm switch.

What is used to flush a hydraulic system that uses Skydrol hydraulic fluid?

Trichlorethylene.

What is used to flush a hydraulic system that uses mineral base hydraulic fluid?

Naphtha, varsol, or Stoddard solvent.

Where can you find the type of hydraulic fluid that is required for a particular aircraft?

In the maintenance manual for the aircraft or on a placard on the system reservoir.

What is used to remove phosphate-ester base hydraulic fluid from aircraft tires?

Soap and water.

What must be done to the lines that are disconnected when servicing an aircraft hydraulic system?

They must be capped with the correct fluid line cap or plug.

What are two ways aircraft hydraulic reservoirs may be pressurized?

By an aspirator in the fluid return line or by bleed air from one of the engine compressors.

Why do some hydraulic pressure gauges have a snubber installed between them and the hydraulic pump?

The snubber keeps the gauge from fluctuating.

Can a thermal switch-type fire detection system indicate a general overheat condition?

No, this is a spot-type fire detection system and cannot indicate an overheat condition.

Can a thermocouple-type fire detection system indicate a general overheat condition?

No, this is a rate-of-temperature-rise-type system and cannot indicate a general overheat condition.

How is a thermocouple-type fire detection system checked for operation?

Current is sent through the heater in the thermal test unit, heating the thermocouple.

Does a break in a continuous-loop fire detection system keep the system from detecting a fire?

No, the unit will show a fault when tested but will still warn of a fire.

Does the pressure-type continuous-element fire detector system detect a general overheat condition?

Yes, a high temperature on a small portion of the sensor will cause it to warn of a fire.

What are the two most commonly used fire extinguishing agents for engine fires?

Carbon dioxide and Halogenated hydrocarbon, such as Halon 1301.

What extinguishing agent is used in the high-rate discharge fire extinguishing systems installed in most turbojet engine installations?

Halon 1301.

What happens when the pilot pulls the fire-pull T-handle in the flight deck of a jet transport airplane?

The bottle discharge switch is uncovered and armed, fuel is shut off to the engine, and hydraulic fluid is shut off to the pump.

How can a mechanic determine the state of charge of the HRD bottles of fire extinguishing agent?

By using a pressure gauge on the bottle.

What are the two main gases that make up our atmosphere?

Nitrogen and oxygen.

Why are the cabins of most turbine-powered aircraft pressurized?

To provide supplemental oxygen for occupants at high altitudes.

Where does the pressurizing air come from on most turbine-powered aircraft?

From air bled from one of the engine compressors.

How is cabin pressure controlled in a pressurized aircraft?

By modulating the outflow valve with a pressure controller.

What is meant by the constant differential mode of cabin pressurization?

It maintains cabin pressure a constant amount above outside air pressure after reaching the maximum allowed.

What is the function of the cabin outflow valve on a pressurized aircraft?

To maintain the correct amount of pressure inside the cabin.

What is the function of the cabin pressure safety valve on a pressurized aircraft?

To prevent cabin pressure from exceeding the maximum allowable differential pressure.

Why must pressurized aircraft have a negative pressure relief valve?

To prevent the cabin from being under lower pressure than the outside.

What keeps the cabin of a pressurized aircraft from being pressurized when on the ground?

A squat switch on the landing gear holds the safety valve open.

Where does the warm air come from that is used to heat the cabin of a large jet transport aircraft?

Warm engine compressor bleed air.

Where does the warm air come from that is used to heat the cabin of most small single-engine reciprocating-engine-powered aircraft?

From a shroud around the engine muffler.

What are the two basic types of hydraulic fluid used in modern aircraft?

Mineral base fluid and phosphate ester base fluid.

What kind of filter is a micronic filter?

A filter with a special paper element.

Does the main hydraulic pump take its fluid from the bottom of the reservoir or from a standpipe?

It normally takes its fluid from a standpipe.

Why are some hydraulic reservoirs pressurized?

To ensure fluid is supplied to the pumps at high altitudes.

What is a double-action pump?

A pump that delivers fluid with the movement of the handle in both directions.

Why do most engine-driven hydraulic pumps have a shear section in their drive couplings?

To prevent further damage if the pump seizes.

What does an unloading valve do in a hydraulic system?

It controls system pressure by redirecting fluid back to the reservoir.

What is the purpose of an accumulator in an aircraft hydraulic system?

To hold pressure on the hydraulic fluid in the system.

What is the purpose of an orifice check valve in an aircraft hydraulic system?

To allow full flow of fluid in one direction and restrict flow in the opposite direction.

Where are line-disconnect fittings normally located in an aircraft hydraulic system?

In the lines connecting the engine-driven pump to the hydraulic system.

What is meant by a single-action hydraulic actuating cylinder?

A cylinder that uses hydraulic fluid to move the piston in one direction, returning by a spring.

What is the source of the compressed air used in a medium-pressure pneumatic system on a turbine-engine powered aircraft?

Normally bled from one of the stages of the engine compressor.

What kind of device is used to control the speed of movement of the piston in a pneumatic actuator?

A variable orifice.

Why do most high-pressure pneumatic systems include a moisture separator?

To remove water before it can freeze and block the system.

What is the difference between an open-center selector valve and a closed-center selector valve?

Open-center valves allow fluid flow through their center when not actuated; closed-center valves trap fluid in lines.

What are the three ways supplemental oxygen can be carried in an aircraft?

Gas, Liquid, Solid

What kind of gaseous oxygen must be used to service an aircraft oxygen system?

Only aviators breathing oxygen

What is used to check an oxygen system for leaks?

A special leak-detector liquid that is a form of non-oily soap.

What is a continuous-flow oxygen system?

An oxygen system that continuously flows a metered amount of oxygen into the mask.

What is a pressure-demand oxygen system?

An oxygen system that flows oxygen to the mask only when the wearer of the mask inhales.

What identification must be stamped on an oxygen bottle that is carried in an aircraft?

Date of manufacture, all hydrostatic tests, DOT 3... serial number

Does a thermocouple fire detection system warn the pilot of a general overheat condition?

No, it operates on the rate of temperature rise, and it identifies only a fire.

Does a thermal switch fire detection warn the pilot of a general overheat condition?

No, it only actuates when there is a fire

What type of fire extinguisher agent is best for both cabin fires and engine fires?

Halon 1301

What is a major disadvantage of "CB" fire extinguishing agent for extinguishing aircraft fires?

It is corrosive to aluminum and magnesium

Why is carbon tetrachloride not recommended as a fire extinguishing agent?

Produces phosgene, a deadly gas, when it is exposed to flames

What is used as a fire extinguishing agent in most of the high-rate discharge systems installed in aircraft?

One of the halogenated hydrocarbons, such as Halon 1301, pressurized with nitrogen.

What happens when the Fire-Pull T-handle is pulled in a jet transport aircraft?

It basically cuts off fuel and hydraulics that are in the aircraft so it doesn't potentially contribute to the worsening of the fire.

What releases the fire extinguishing agent in a high-rate discharge bottle?

An electrically ignited powder charge blows a knife through a seal in the HRD bottle

What three types of fire extinguishers are recommended for extinguishing cabin fires in an aircraft?

Water, Halon 1301, and carbon dioxide

How does a carbon monoxide detector warn the occupant of an aircraft of an excess of carbon monoxide?

The detector crystals in the indicator change color

What are two types of smoke detectors that are used in an aircraft?

Photoelectric and visual smoke detectors

Where are smoke detectors normally located in an aircraft?

Baggage and cargo areas

What type of fire extinguisher is recommended for extinguishing a brake fire?

A dry powder type extinguisher.

How is a CO2 fire extinguisher checked for the amount of charge it contains?

By its weight

How can you determine whether or not a built-in fire extinguishing system has been discharged?

By checking the blowout plugs on the outside of the aircraft near the extinguisher agent bottles

What precaution must you observe when checking the electrical squib of an HRD fire extinguisher bottle for electrical continuity?

It only takes a small amount of current to ignite it, therefore make sure it is grounded

What is indicated if the red disk in a built-in fire extinguishing system is blown out?

The agent bottle has been discharged because of an overheat condition

What is indicated if the yellow disk in a built-in fire extinguishing system is blown out?

Somebody intentionally activated it.