Starting System

Question 1

Hung Start

Answer 1

N2 speed stabilising at a lower than normal rpm and a subsequent increase in EGT.

Question 2

When should igniter activation occur?

Answer 2

Before fuel is introduced into the combustion chamber

Question 3

What is delivered by the air turbine starter motor?

Answer 3

High speed, high pressure bleed air, rotating a turbine at a high speed, low torque.

Question 4

Sources of Air

Answer 4

EXT PWR

APU

Crossfeed from running engine.

Question 5

Start Sequence

Answer 5

1. IGN and Starter Circuit Motor ON. HP Spool begins to rotate (N2)
2. LP Compressor (N1) begins to rotate.
3. Pilot opens HP cock (Fuel Valve) at a Set N2.
4. Fuel ignites, EGT rises, Fuel flow increases.
5. Self sustaining speed, typically 30-40% reached, starter motor and IGN cancelled due to speed sensor.
6. Gas Temperature rapidly rises as engine accelerates. EGT reaches a maximum
7. EGT reduces and stabilises as N2 and N1 reach idle. 55-60% and 25% respectively.

Question 6

Wet Start

Answer 6

Engine doesn’t light up within specified period.

EGT doesn’t rise.

Stagnation of RPM and Low Fuel Flow.

Causes:

Faulty high energy ignition unit or igniter plug.

Run a dry crank, and blow out existing vapour. Should see white fumes.

Question 7

Hot Start

Answer 7

EGT exceeds maximum value.

Could be caused by tailwind, low air pressure in manifold, or a failure to vent.