AME - Aircraft Maintenance Engineer Hydraulic and Pneumatic Systems Questions and Answers — Questions and Answers
Question 1: An AME is troubleshooting an aircraft hydraulic system and observes that the system pressure fluctuates rapidly and excessively when a component is operated. The pump is known to be in good condition. What is the most likely cause of this issue?
- The system filter is completely clogged.
- The hydraulic fluid is contaminated with water.
- The accumulator has lost its nitrogen pre-charge. (Correct answer)
- The system relief valve is stuck in the open position.
Correct answer: The accumulator has lost its nitrogen pre-charge.
The primary function of an accumulator is to dampen pressure surges and supplement pump flow. If the nitrogen pre-charge is lost, the accumulator's diaphragm or piston has no gaseous 'cushion' to absorb pressure spikes from pump operation and component actuation, leading to rapid and excessive pressure fluctuations.
Question 2: Which of the following is a critical safety and maintenance consideration when working with phosphate ester-based hydraulic fluids such as Skydrol?
- It is highly compatible with natural rubber seals and most standard paints.
- It is an excellent paint remover and is harmful to many traditional aircraft finishes and plastics. (Correct answer)
- It is non-toxic and requires no special personal protective equipment.
- It has a low flash point, making it more flammable than mineral-based fluids.
Correct answer: It is an excellent paint remover and is harmful to many traditional aircraft finishes and plastics.
Phosphate ester-based hydraulic fluids like Skydrol are known for their excellent fire resistance but are also powerful solvents. They are incompatible with many materials, including most standard paints, plastics, and natural rubber seals, which they can soften and destroy. Proper PPE, including gloves and goggles, is required as the fluid is irritating to human tissue.
Question 3: What is the primary operational characteristic of a constant-delivery hydraulic pump, such as a gear-type pump?
- It varies its output flow based on system pressure demand.
- It requires no system pressure regulator as it self-regulates.
- It delivers a fixed volume of fluid per revolution, regardless of system pressure. (Correct answer)
- It can only operate effectively at low RPMs.
Correct answer: It delivers a fixed volume of fluid per revolution, regardless of system pressure.
A constant-delivery (or constant-displacement) pump moves a fixed amount of fluid for each rotation of the pump's shaft. Because it is always attempting to move this fluid, the system must incorporate a pressure regulator or relief valve to divert excess flow and prevent over-pressurization when there is low demand.
Question 4: An AME is tasked with replacing a component in the aircraft's high-pressure pneumatic system. Before loosening any fittings on the component, what is the most critical safety step that must be performed?
- Verify the component's part number matches the maintenance manual.
- Ensure the aircraft's electrical and hydraulic systems are depowered.
- Don appropriate personal protective equipment (PPE).
- Confirm that the specific pneumatic system has been fully depressurized by checking the pressure gauge. (Correct answer)
Correct answer: Confirm that the specific pneumatic system has been fully depressurized by checking the pressure gauge.
High-pressure pneumatic systems store a tremendous amount of energy. Attempting to disconnect a fitting before fully bleeding off the pressure can result in an explosive release of gas, turning components into dangerous projectiles. Verifying a zero-pressure reading on the system gauge is the most critical safety action to prevent serious injury.
Question 5: In a typical large transport aircraft, which component is primarily responsible for regulating the pressure and temperature of engine bleed air before it is distributed to various pneumatic systems?
- The pneumatic system check valve.
- The APU load compressor.
- The Pressure Regulating and Shutoff Valve (PRSOV). (Correct answer)
- The cabin outflow valve.
Correct answer: The Pressure Regulating and Shutoff Valve (PRSOV).
The Pressure Regulating and Shutoff Valve (PRSOV), often called a Bleed Air Valve, is the primary component that modulates the flow of hot, high-pressure air from the engine's compressor section. It regulates the downstream pressure and often incorporates a heat exchanger or precooler to reduce the air to a usable temperature for systems like air conditioning and wing anti-ice.
Question 6: Which of the following is considered the primary cause of wear and malfunction in the majority of aircraft hydraulic systems?
- Fluid viscosity breakdown due to high temperatures.
- Particulate contamination in the fluid. (Correct answer)
- Entrained air causing cavitation.
- Chemical breakdown from exposure to UV light.
Correct answer: Particulate contamination in the fluid.
Particulate contamination is widely recognized as the leading cause of hydraulic system problems, accounting for a vast majority of failures. Tiny particles of metal, rubber, and dirt act as an abrasive, causing scoring and wear on the precision-machined surfaces of pumps, valves, and actuators, which leads to internal leakage, reduced efficiency, and eventual component failure.
AME - Aircraft Maintenance Engineer Hydraulic and Pneumatic Systems Questions and Answers
An AME is troubleshooting an aircraft hydraulic system and observes that the system pressure fluctuates rapidly and excessively when a component is operated.
The pump is known to be in good condition.
What is the most likely cause of this issue?