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Module 14 - Part 2 > Chapter 2 - Full Authority Digital Engine Control (FADEC) > Flashcards

Chapter 2 - Full Authority Digital Engine Control (FADEC) Flashcards

1
Q

What does a FADEC monitor and control in order to achieve the required thrust?

A
  • Engine pressure ratio
  • N1 low pressure compressor or fan speed
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2
Q

How are FADECs interconnected?

A

By a Cross-Channel Data Link (CCDL)

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3
Q

What properties does the ADC feed to the FADEC?

A
  • Altitude
  • Mach number
  • Airspeed
  • TAT
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4
Q

How can the FADEC provide maximum efficiency in the compressor?

A

By changing the air flow geometry by adjusting variable inlet guide vanes and variable geometry vanes within the first few stages of the compressor

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5
Q

What provides the feedback in a FADEC closed loop system?

A

Engine speed or EPR

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6
Q

How else can a FADEC control compressor and/or turbine efficiency?

A

Automatic adjustment of blade clearance

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7
Q

What is usually across the contacts of discrete signals?

A

10 kΩ resistor

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8
Q

When will the Permanent Magnet Alternator (PMA) take over supply to the FADEC from the essential bus?

A

At 50% N2 and above

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9
Q

Describe the PMA?

A
  • Driven by the accessory drive gearbox
  • Four separate windings
  • Two 3 phase and two single phase
  • 3 phase power to channel A and channel B
  • Single phase windings feed the redundant exciters in the ignition system
  • One phase of the 3 phase supply is used to derive a secondary N2 signal
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10
Q

What is the purpose of the current limited excitation voltage fed to the discrete signals?

A

Allow the FADEC to detect open and short circuit failure conditions in the aircraft engine wiring

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11
Q

What is engine transient rate limiting?

A

Acceleration and deceleration limits which restrict the rate of change of commanded fuel flow

Prevents surge on acceleration or blowout on deceleration

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12
Q

What is controlled in CVG scheduling?

A

The IGVs and the first 5 stages of CVG

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13
Q

What is the maximum allowable temperature of the ITT?

A

1690°F or 921°C

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14
Q

At what values will engine protection shut down occur?

A

N1 exceeds 105% (approx 9135 RPM) or N2 exceeds 105.5% (approx 16750 RPM) for overspeed

N2 is less than 54% (approx 8500 RPM)

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15
Q

What are the cockpit discrete inputs?

A
  • Thrust ratings
  • Thrust mode selector panel
  • Engine start/stop
  • Ignition on/off
  • Anti-ice on/off
  • FADEC reset
  • Alternate FADEC select
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16
Q

What are the aircraft discrete inputs?

A
  • Air/ground (WOW)
  • Landing gear down
  • Thrust reverser deployed
  • Thrust reverser stowed
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17
Q

What are the engine sensor inputs?

A
  • N1 primary fan speed
  • N1 secondary fan speed
  • N2 HP rotor speed
  • P2.5 compressor inlet pressure
  • T2.5 compressor inlet temperature
  • ITT
  • P0 ambient static air pressure
  • Compressor variable geometry position feedback
18
Q

At the stated speeds, what is required for the engine protection and shutdown?

A

Both FADECs to agree

19
Q

For ground starts, which exciter is used?

A

Selected alternatively for consecutive ground starts

20
Q

What is the primary supply for the ignition system?

A

Single phase winding in the PMA which provides 20-40 VAC at all N2 speeds above 10%

21
Q

How often do the ignition capacitors discharge?

A

Four to seven times per second

22
Q

Why would the ignition switch be selected to ON?

A

As a safety precaution when flame out is possible

23
Q

What position is the exciter relay in to provide a spark?

A

De-energised

24
Q

What are the four thrust rating modes?

A

Maximum take-off - T/O-1 - 100% N1
Maximum continuous - CON - 86% N1
Maximum climb - CLB - 76% N1
Maximum cruise - CRZ - 70% N1

25
Q

Which thrust rating modes are inhibited on the ground?

A

CON, CLB and CRZ

26
Q

What height of pressure altitude is applicable to CON, CLB and CRZ?

A

CON - 300 ft, landing gear not locked down
CLB & CRZ - 500 ft, landing gear not locked down, both engines operating

1700 ft for all above the take-off altitude, both engines operating for CLB & CRZ

27
Q

Why does the FADEC use the REF TO TEMP setting?

A

In place of the TAT supplied by the ADC to compute the corrected fan speed during take-off

28
Q

What is the purpose of TAKE-OFF DATA STORE?

A

Used to calculate N1 target during take-off

29
Q

Under what conditions will the RESET/ALTN switch not change to the alternate FADEC?

A

If the selected FADEC is not capable of controlling the engine

30
Q

What happens if there is indication of an inadvertent thrust reverser deployment?

A

The engine thrust is reduced to IDLE

31
Q

What provides the position feedback signal to the FADEC from the main metering valve?

A

Linear variable inductance transducer (LVIT)

32
Q

How is the main metering valve (servo valve) biased?

A

Closed

33
Q

What does the pressure raising valve (PRV) ensure?

A

By spring loading, a minimum gear pump pressure at low engine speeds

34
Q

When is the Latching Shut Off Valve (LSOV) START solenoid energised, thus allowing the opening of the PRV?

A

At 23% N2

35
Q

What determines the angle of the inlet guide vanes and the first five variable geometry compressor vanes?

A

Fuel pressure fed to the actuator from the CVG control valve, operated by a torque motor under FADEC control

36
Q

Within the FADEC computer, what will signal a lane change is necessary if a fault is detected?

A

Passing demand and engine feedback through a comparator unit

37
Q

What does ‘engine steady state’ limiting mean?

A

Fuel flow is limited to prevent overspeed of the LP and HP rotors

There is also an HP underspeed logic to prevent fuel flow being reduced to a value which would result in an N2 underspeed

38
Q

When would both exciters in the ignition systems operate?

A

For in-flight restarts

39
Q

Why is a tri-lane potentiometer used in the throttle lever circuit?

A

In case of failure

If one potentiometer fails, the other two will still send valid information to the ‘majority wins’ circuit in the computer

40
Q

In the Lane Controller system, what receives the input signal from the throttle lever?

A

Full Authority Fuel Controller (FAFC)

Module 14 - Part 2 (3 decks)

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