Engine Instrumentation Questions and Answers

Answer: C

Correct answer: Only three

Three of the pairs are sound. Falling oil pressure with rising oil temperature is the classic signature of a loss of quantity, since less oil carries the same heat. Rising vibration over successive flights indicates a developing rotor imbalance. Rising exhaust temperature at a constant thrust setting shows deteriorating engine condition, the engine working harder for the same output.

The fourth is wrong, and inverts a serviceability check. A manifold pressure gauge should read ambient with the engine stopped, because it measures absolute pressure. That reading confirms the gauge is working rather than indicating a failure.

Answer: D

Correct answer: Only three

The first three pairs give the right reason for monitoring each parameter. Cylinder head temperature is watched for detonation and thermal damage; oil pressure for bearing survival; and fuel used for range and endurance planning.

The fourth misassigns engine pressure ratio, which is a thrust-setting parameter derived from the pressure rise across the engine and says nothing about the oil system. Oil condition is monitored by oil pressure, oil temperature and quantity. Three of the four are therefore correctly matched.

Answer: A

Correct answer: Cabin differential pressure

Cabin differential pressure is an airframe and air conditioning parameter: it is the difference between cabin and ambient pressure, monitored for structural and physiological reasons, and it says nothing about how the engine is performing.

The other three are engine performance parameters. Engine pressure ratio and rotor speed are thrust-setting parameters, and exhaust gas temperature reports the thermal condition of the turbine. Bleed air taken from the engine supplies the pressurisation system, but that connection makes cabin pressure a consumer of engine air, not a measure of engine performance.

Answer: B

Correct answer: Oil pressure

Pressure is not a temperature, so no thermocouple measures it. Oil pressure is sensed by a transducer - a diaphragm or bourdon element with a strain gauge or capacitive pickoff - which converts displacement into an electrical signal.

The other three are all temperatures, and all are thermocouple applications in a typical installation: exhaust gas and turbine gas temperature on turbines, and cylinder head temperature on piston engines. The thermocouple suits them because it is self-generating, rugged and good at the high temperatures where a resistance element would struggle.

Answer: C

Correct answer: Oil temperature

Oil temperature is a health parameter. It reports the condition of the lubrication system and is watched alongside oil pressure and quantity, but nothing about it tells the crew how much thrust or power the engine is producing.

The other three are all thrust or power setting parameters, each chosen because the quantity a pilot actually wants - thrust - cannot be measured directly. Engine pressure ratio and fan rotor speed serve that purpose on turbofans, and torque does so on a turboprop, where power follows as \( P = T\omega \).

Answer: D

Correct answer: The serial number of the engine

Instrument markings encode operating information: the ranges and limits a pilot must act on at a glance, in green, yellow and red. A serial number is administrative data belonging to the aircraft records and the engine data plate, and it changes nothing about how the instrument is to be read.

The other three are precisely what the colour code exists to convey - the normal operating range, a caution range for limited periods, and a limit not to be exceeded. The value of the code is that it is read without interpretation, which arbitrary numbers on the dial would defeat.

Answer: A

Correct answer: They remove the need for engine limits

Limits come from the engine's own mechanical and thermal tolerances, not from how its parameters are displayed. Changing the instrumentation changes nothing about what the turbine or the bearings can withstand.

The other three are genuine reasons for remote indication. Keeping fuel and oil out of the cockpit removes a leak and fire hazard behind the panel; avoiding long capillary lines removes both lag and a breakage risk; and an electrical signal can be recorded for trend monitoring and processed for display, which a mechanical linkage cannot.

Answer: B

Fuel is burning but the rotor is not accelerating, so the energy goes into heating rather than into speed. Cutting the fuel stops the temperature rise before the limit is reached, which is why the two indications are watched together.

Answer: C

Correct answer: A loss of oil quantity from a leak

The two indications move together in a way that points to quantity. Less oil in the system means the pump can no longer maintain pressure, and the same heat rejected into a smaller mass of oil raises its temperature.

A faulty transducer or thermocouple would explain one indication but not both, and two independent sensors failing in a consistent direction at once is most unlikely. A blocked fuel filter would show in fuel pressure or flow, not in the oil system. The correct reading is that the oil is going somewhere, and the response is to reduce power and divert before the film is lost.

Answer: D

Correct answer: A blocked or iced engine pressure ratio probe

Rotor speed, fuel flow and exhaust gas temperature are independent of the EPR sensing system, and all three agree with each other in saying the engine is producing less than the target setting suggests. When one indication disagrees with three that concur, suspect that indication.

A blocked or iced pressure probe corrupts the ratio and lets the crew set less thrust than intended - a serious matter on take-off, where the shortfall may not be apparent until the acceleration is visibly poor. It is why probe heating is required and why the secondary parameters are cross-checked against the setting.