Operation of Systems practice questions

Answer: A) Air data: airspeed, altitude, angle of attack; inertial reference: attitude, heading, position

An ADIRU's air data part supplies airspeed, altitude and angle of attack. Its inertial reference part supplies attitude, heading and position. Both feed the displays, autopilot and flight controls.

• ACorrect. The air data reference part supplies parameters such as airspeed, altitude and angle of attack. The inertial reference part supplies attitude, heading and position to the displays, autopilot and flight controls.
• BIncorrect. The functions are swapped. Attitude and position come from the inertial reference part, and airspeed and angle of attack come from the air data part.
• CIncorrect. Radio altitude comes from the radio altimeter and glideslope deviation comes from the ILS receiver. Neither comes from the inertial reference function.
• DIncorrect. Inertial reference is self-contained: it gets attitude and position from its own sensors, not from ground-based radio fixes.

Answer: A) Hot start, usually from an overly rich fuel/air mixture; cut off fuel to the engine immediately

A hot start is a start with normal rotation in which EGT exceeds its limit, usually because the fuel/air mixture is too rich. The crew must cut off fuel immediately. A hung start (stalled acceleration) and a wet start (no light-off) are different abnormal starts.

• ACorrect. FAA guidance defines a hot start as a start with normal engine rotation in which exhaust temperature exceeds prescribed limits, usually caused by an excessively rich mixture. Fuel must be shut off at once to avoid turbine damage.
• BIncorrect. In a hung start the engine lights off but stops accelerating below idle RPM. Here the rotation is normal and the problem is excessive EGT, so this is a hot start, not a hung start.
• CIncorrect. A wet (no light-off) start means fuel flows but does not ignite, so EGT does not rise. A rapid EGT rise means combustion is occurring and the temperature limit is being approached.
• DIncorrect. A start where EGT is heading past the AFM limit is abnormal. Continuing risks damage to turbine blades and other hot-section parts, so the start must be aborted.

Answer: C) Low-pressure spool

• AIncorrect. It's the low-pressure spool.
• BIncorrect. That's N2.
• CCorrect. Including the fan.
• DIncorrect. It's the low-pressure spool.

Answer: A) Anti-ice keeps ice from forming; deice removes ice that has already built up

Anti-ice systems keep ice from forming, so they are normally turned on before or when entering icing. Deice systems remove ice that has already built up. The difference is purpose, not where the system is used or what powers it.

• ACorrect. Anti-ice systems, such as heated bleed-air leading edges or freezing-point depressant fluid, keep ice from forming on the surface. Deice systems, such as pneumatic boots, break off ice after it has built up.
• BIncorrect. This reverses the definitions. Prevention is anti-icing; removing ice that has already formed is deicing.
• CIncorrect. The difference is purpose, not energy source. Hot bleed air is a common way to anti-ice wing leading edges, and pneumatic boots deice mechanically, without heat.
• DIncorrect. Both ideas apply on the ground and in flight. Ground crews deice and anti-ice with fluids, and in-flight anti-ice systems protect engine inlets and wings during the flight.

Answer: D) About 10,000 feet

• AIncorrect. The warning is standard.
• BIncorrect. That's too low.
• CIncorrect. That's too high to wait.
• DCorrect. Crews then don oxygen and act.

Answer: C) Moves hydraulic power between systems

• AIncorrect. That's a fuel transfer system.
• BIncorrect. That's a TRU.
• CCorrect. It provides backup pressure.
• DIncorrect. That's the pressurization system.

Answer: B) Combining navigation sensor data with performance calculations to guide lateral and vertical paths

An FMS combines inputs from several navigation sensors with performance functions to provide lateral and vertical guidance to the displays and autopilot. Engine control, TCAS and TAWS are separate systems.

• AIncorrect. Engine-level fuel metering and ignition control are done by the engine fuel control or FADEC. The FMS may send thrust targets for performance management, but it does not control the engine directly.
• BCorrect. An FMS is an integrated suite of sensors, receivers and computers with a navigation database. It takes inputs such as GPS, DME, VOR and IRU and provides RNAV and performance guidance, including lateral and vertical paths, to the displays and the autoflight system.
• CIncorrect. This describes the traffic alert and collision avoidance system (TCAS), which is separate from the FMS.
• DIncorrect. This describes the terrain awareness and warning system (TAWS/EGPWS), not the FMS.

Answer: A) Transformer-rectifier unit (TRU)

A transformer-rectifier unit steps AC voltage down and rectifies it to DC, which is how a jet with AC generators powers its DC buses. An inverter does the reverse.

• ACorrect. A TRU first steps the AC voltage down with a transformer, then rectifies it to DC to feed the DC buses. If the TRUs fail, the airplane can lose DC power except for the battery.
• BIncorrect. A static inverter works in the opposite direction. It converts DC, usually from the battery, into AC so that essential AC instruments keep working when the generators are lost.
• CIncorrect. A CSD keeps the generator turning at a constant speed so the AC output stays at a constant frequency. It produces no DC.
• DIncorrect. A bus tie breaker connects or isolates electrical buses so that one source can power another bus. It does not convert AC to DC.

Answer: B) Prevent deploying reversers in flight or at unsafe times

• AIncorrect. They limit reverser use.
• BCorrect. Air/ground logic is used.
• CIncorrect. That's prevented.
• DIncorrect. They control reverser deployment.

Answer: A) To let one system fail while critical functions such as the flight controls stay powered

Multiple independent hydraulic systems provide redundancy, so critical functions such as the flight controls stay powered after one system fails. The systems are deliberately isolated from each other.

• ACorrect. FAA system-safety guidance gives two or more hydraulic systems as an example of redundancy, meaning more than one independent way to perform a function, so that function continues after a failure.
• BIncorrect. The systems are kept separate and independent. Their pump outputs are not combined in series to raise actuator pressure.
• CIncorrect. Redundant systems are deliberately isolated so that one leak or failure does not drain or disable the others. Free transfer of fluid would defeat that purpose.
• DIncorrect. Transport airplanes still need an emergency means of extending the landing gear if any single hydraulic, electric or equivalent energy source fails.