Engine Instrumentation Questions and Answers

Answer: A

Correct answer: Both A and R are true, and R is the correct explanation of A

Both are true and the reason gives the principal motive. A direct reading gauge brings the fluid itself forward through a pipe, so a fractured line puts hot oil or fuel behind the instrument panel, directly in front of the crew.

Remote indication leaves the sensor at the engine and carries only an electrical signal, removing that hazard entirely. Two further gains follow: no long capillary to introduce lag or to break, and a signal that can be recorded for trend monitoring and processed for display alongside other parameters.

Answer: B

Correct answer: 1 and 2 only

The first two are correct. Engine pressure ratio is turbine discharge over compressor inlet pressure, and it is used to set thrust because thrust itself cannot be measured in flight.

The third is false, and dangerously so. Both pressure probes are exposed to the airstream and both can ice; a blocked probe corrupts the ratio without any flag, so the instrument reads the target value while the engine produces something else. Probe heating exists for that reason, and the setting is cross-checked against rotor speed, fuel flow and exhaust temperature.

Answer: C

Correct answer: 1 and 2 only

The first two describe thermocouple practice correctly. The Seebeck output depends on the difference between the hot and cold junctions, and cold junction compensation adds the reference temperature back in so that the display reads the absolute temperature of the hot junction.

The third is false. The combustor outlet is too hot for a probe to survive there, so turbine inlet temperature is inferred from a measurement further downstream - at the exhaust or between turbine stages - using a relationship established during engine development.

Answer: D

Correct answer: 1 and 2 only

The first two state the colour code correctly: green is the normal continuous range and yellow a caution range acceptable for limited periods.

The third misstates red, and reverses the very distinction the code exists to draw. A red radial line marks a limit that must not be exceeded at all - it carries no time allowance whatever. Brief use is what yellow permits; red permits none. An exceedance of a red limit is recorded and reported for maintenance action rather than simply noted.

Answer: A

Correct answer: 1 and 2 only

The first two are sound. Falling pressure with rising temperature is the classic loss-of-quantity signature: less oil cannot sustain the pressure, and the same heat rejected into a smaller mass raises its temperature. And a single faulty probe would normally move one indication alone, which is why two consistent indications point to a real fault rather than an instrument one.

The third is false. Oil temperature rises for other reasons - a blocked cooler, a hot day, high power - so it cannot diagnose a leak by itself. It is the combination that identifies the cause.

Answer: B

Correct answer: A-1, B-2, C-3, D-4

Each instrument reports a different quantity. A tachometer indicates rotor speed as a percentage of a chosen datum rather than in rpm, so that one scale and one set of limits serve engines of different absolute speeds.

Engine pressure ratio is turbine discharge over compressor inlet pressure. A torquemeter measures shaft torque, which with governed rpm gives power on a turboprop. A manifold pressure gauge reads absolute pressure in the induction manifold - absolute, which is why it indicates ambient with the engine stopped rather than zero.

Answer: C

The colour convention is common across the instrument panel, which is what lets a scale be read at a glance without recalling the numbers. The white arc is the one marking specific to airspeed rather than to engine parameters.

Answer: D

Correct answer: A-1, B-2, C-3, D-4

Each symptom points to its own system. Falling oil pressure with rising oil temperature indicates a loss of oil quantity, since less oil sustains neither the pressure nor the heat load.

Rising exhaust temperature at a fixed thrust setting shows the gas path deteriorating, the engine working harder for the same output. Vibration rising over successive flights indicates a developing imbalance in the rotating assembly. And a target pressure ratio achieved while every other parameter reads low points to the indication itself - a blocked EPR probe, the one case where the instrument rather than the engine is at fault.

Answer: A

Two of the four measure temperature by quite different means, and only the thermocouple generates its own voltage. That self-generating property is why it needs no excitation supply and survives a loss of electrical power.

Answer: B

Correct answer: Cabin differential pressure

Cabin differential pressure is the difference between cabin and ambient pressure, monitored for structural and physiological reasons. It belongs to the pressurisation system and says nothing about how the engine is running.

Fuel flow, rotor speed and exhaust gas temperature are all engine parameters, reporting consumption, speed and thermal condition respectively. Engine bleed air does feed the pressurisation system, but that makes the cabin a consumer of engine air rather than a measure of engine performance - a connection easily mistaken for a relationship.