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Pilot's Handbook of Aeronautical Knowledge
Aircraft Systems
Ignition System

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Pilot's Handbook of Aeronautical Knowledge



Table of Contents

Chapter 1, Introduction To Flying
Chapter 2, Aircraft Structure
Chapter 3, Principles of Flight
Chapter 4, Aerodynamics of Flight
Chapter 5, Flight Controls
Chapter 6, Aircraft Systems
Chapter 7, Flight Instruments
Chapter 8, Flight Manuals and Other Documents
Chapter 9, Weight and Balance
Chapter 10, Aircraft Performance
Chapter 11, Weather Theory
Chapter 12, Aviation Weather Services
Chapter 13, Airport Operation
Chapter 14, Airspace
Chapter 15, Navigation
Chapter 16, Aeromedical Factors
Chapter 17, Aeronautical Decision Making




Although an automatic waste gate system is less likely
to experience an overboost condition, it can still occur. If
takeoff power is applied while the engine oil temperature is
below its normal operating range, the cold oil may not .ow
out of the waste gate actuator quickly enough to prevent an
overboost. To help prevent overboosting, advance the throttle
cautiously to prevent exceeding the maximum manifold
pressure limits.

A pilot flying an aircraft with a turbocharger should be aware
of system limitations. For example, a turbocharger turbine
and impeller can operate at rotational speeds in excess of
80,000 rpm while at extremely high temperatures. To achieve
high rotational speed, the bearings within the system must be
constantly supplied with engine oil to reduce the frictional
forces and high temperature. To obtain adequate lubrication,
the oil temperature should be in the normal operating range
before high throttle settings are applied. In addition, allow
the turbocharger to cool and the turbine to slow down before
shutting the engine down. Otherwise, the oil remaining in
the bearing housing will boil, causing hard carbon deposits
to form on the bearings and shaft. These deposits rapidly
deteriorate the turbocharger's efficiency and service life. For
further limitations, refer to the AFM/POH.

High Altitude Performance
As an aircraft equipped with a turbocharging system climbs,
the waste gate is gradually closed to maintain the maximum
allowable manifold pressure. At some point, the waste gate
will be fully closed and further increases in altitude will
cause the manifold pressure to decrease. This is the critical
altitude, which is established by the aircraft or engine
manufacturer. When evaluating the performance of the
turbocharging system, be aware that if the manifold pressure
begins decreasing before the specified critical altitude, the
engine and turbocharging system should be inspected by
a qualified aviation maintenance technician to verify the
system's proper operation.

Ignition System

In a spark ignition engine the ignition system provides a
spark that ignites the fuel/air mixture in the cylinders and is
made up of magnetos, spark plugs, high-tension leads, and
the ignition switch. [Figure 6-16]

A magneto uses a permanent magnet to generate an electrical
current completely independent of the aircraft's electrical
system. The magneto generates sufficiently high voltage
to jump a spark across the spark plug gap in each cylinder.
The system begins to .re when the starter is engaged and the
crankshaft begins to turn. It continues to operate whenever
the crankshaft is rotating.

Most standard certificated aircraft incorporate a dual ignition
system with two individual magnetos, separate sets of wires,
and spark plugs to increase reliability of the ignition system.
Each magneto operates independently to .re one of the two
spark plugs in each cylinder. The .ring of two spark plugs
improves combustion of the fuel/air mixture and results in
a slightly higher power output. If one of the magnetos fails,
the other is unaffected. The engine will continue to operate
normally, although a slight decrease in engine power can be
expected. The same is true if one of the two spark plugs in
a cylinder fails.

The operation of the magneto is controlled in the flight deck
by the ignition switch. The switch has five positions:
1. OFF
2. R (right)
3. L (left)

With RIGHT or LEFT selected, only the associated magneto
is activated. The system operates on both magnetos with
BOTH selected.