AGK Engines - Control & Operation

Question 1

Normal Start Sequence

Answer 1

Start selected

Ignition commences

Air start valve opens (N2 rotation)

Fuel delivery (minimum)

Light up occurs (EGT Rise)
~Increase fuel flow to increase N2]

N1 begins to rotate

Self-sustaining speed

Starter circuit disconnects (air start valve closes)

Fuel flow increases to accelerate engine

Stable ground idle

-Once at stable ground idle, they’ll be a notice difference in speeds of the spools
~N2 spins faster than N1

Question 2

Types of starter motor?

Answer 2

Two types of starter motor, both connected to the accessory gearbox

Air (pneumatic starter)

Electric (Starter/Generator)

Question 3

Air (pneumatic starter) - starter motor

Answer 3

Driven by compressed air and controlled by an air start valve
~Air supplied from external source, cross bleep or APU
~Incorporates an overrun clutch to prevent damage from failing to disconnect

HP spool rotates first to initiate starting

Question 4

Electric (Starter/Generator) - starter motor

Answer 4

Used on More Electric Aircraft (MEA) such as B787
~During the start sequence AC electric spins the motor, turning the accessory gearbox
~Once at ground idle, the system flips to generator mode

HP spool rotates first to initiate starting

Question 5

Start malfunctions, engine may suffer the following…

Answer 5

Dry Start

Hung Start

Hot Start

Wet Start

Question 6

Dry Start characteristics

Answer 6

Low and stagnating RPM

No EGT rise

No fuel flow

~Maybe due to malfunction of the HPSOV

Question 7

Hung Start characteristics

Answer 7

Low and stagnating RPM

High EGT

Low fuel flow

Maybe the result of:
~Compressor stall
~Low bleed pressure
~Engine failing to reach self-sustaining speed
~Early disconnection of the starter motor

Question 8

Hot Start

Answer 8

Normal increase In RPM

Rapid and excessive EGT rise

Normal fuel flow

Possible following a previous failed start attempt

Question 9

Wet Start

Answer 9

Low and stagnating RPM

No EGT rise

Some indicated fuel flow

A dry run (blow through) should be carried out before attempting a restart

Question 10

Multi-spool engine start

Answer 10

Ground idle
~ N1 - 20-25%
~ N2 - 50-60%

Flight idle is a higher idle setting allowing the engine to respond to any speed increase quicker

Question 11

Airborne Relight

Answer 11

Same requirements as ground start

Starter motor not required as the engine will be windmilling

A manual start may be used to better control operation of the start valve and igniters

Altitude ans Airspeed considerations must be taken into account
~Usually below 25,000ft and 250kts
~Known as the relight envelope

Question 12

Thrust indications

Answer 12

Max t/o: maximum allowed; usually time limited

Max continuous: Maximum thrust than can be used continuously

Go Around: thrust value close to , but less than, maximum thrust

Max climb: used for routine, all engine climbs

Question 13

EPR and thrust indications

Answer 13

Engine Pressure ratio (EPR)

Accurate method to indicate pressure thrust

Compares the pressure rise in the exhaust with static pressure in the intake

If a sensor becomes unavailable (iced up) the engine will revert to N1 Thrust setting

Question 14

N1 and Thrust indications

Answer 14

N1 Thrust Setting

Thrust set by percentage of Fan RPM

FADEC will rotate N2 to a desired value in order to provide an N1 rotation and given Thrust setting

Question 15

Turbo-prop Torque Indications

Answer 15

Percentage of maximum - Torque

usually measured using soil pressure or a electronic Wheatstone bridge

In t/o or high power conditions, percentage may exceed 100% for a limited time

Question 16

De-rate and Flex thrust

Answer 16

To maximise engine life and reduce costs, reduce thrust is available via FMC
~Engines will provide thrust in a worst case scenario
~Under all other conditions, especially cold and sea level environments the engine will perform better than required
~Under these conditions the crew can legally plan a reduced power t/o

Two methods available:
-De-rating
-Flexible (Flex) thrust.

Question 17

De-rating

Answer 17

Reduces the thrust available from maximum value

Has the effect of imposing a lower thrust limit on the engine
~The Vmcg and Vmca speeds will change and are available through the performance manual

DISADVANTAGE- full thrust not available should it be required

Question 18

Flex Thrust

Answer 18

Another alternative to reducing engine thrust on t/o
Common method - use assumed temp

As max thrust decreases, air temp increases (eng can be fooled into producing less thrust)

Using assumed temp for which this would be produced (at full thrust) is interned into FMC as OAT for the day (e.g 67°C)
~ENetring OAT of 67°C will reduce then thrust by a given amount

BENEFIT- if full thrust is required, thrust levers can be set to TO/GA to disregard the flex configuration

As full thrust is available, Vmcg and Vmcd must be calculated based on full thrust used (worse case scenario)

Question 19

Thrust in flight - high/low by-pass

Answer 19

High
~Reduced thrust is more pronounced as there’s a lower RAM effect in the by-pass duct
~Fuel consumption ∝ temp = more fuel efficient in cruise
~thrust can be reduced (less drag)
~fuel flow reduction

Question 20

Engine seizure

Answer 20

Is when one or both spools stop rotating
~e.g. due to lack of lubrication, deformation of engine component or failure of compressor/turbine blade

Detected by vibrations, rapid rundown of spool(s),
Increase in EGT or engine internal temperature
Adverse yaw from asymmetric effects

As vibration increases, as a precaution - shut down engine