Therefore, in planning for each
flight, remember that general aviation engine instruments are not
precision laboratory types, so cross-check, and give yourself an
extra margin for safety.
More aircraft are being fitted
with digital readouts. Some digital equipment can automatically
monitor the engine functions and will sound an alarm if anything
goes outside preset limits. Digital instruments can be harder and slower to read than
the traditional analogue type as the brain must take additional
steps before interpreting them. An instrument reading of whatever type
is only as good as its sender unit.
The instruments of all aircraft
operate within a 'normal' range and the operator rapidly becomes
adjusted to seeing these. The pilot should be vigilant that engine
functions remain within these ranges. An abnormal indication showing
on any instrument is immediate cause for concern.
it is prudent
to land as
possible as it
Aircraft are usually also fitted
with a low voltage warning light which is placed in a prominent
position. If a problem arises with the charging circuit, it will
begin to flicker and then show red. The light may quite normally
flicker or show dull red at very low RPM.
cylinder temperature gauge (CHT)
Most engines are fitted with a CHT
on one cylinder only. Every engine design has a cylinder that runs
slightly hotter than the rest. If the temperature climbs towards the
red line it may indicate a serious problem.
exhaust gas temperature gauge (EGT)
The EGT is the primary instrument
to help the regulation of the fuel/air mixture. The red cursor
indicates temperature never exceed.
This is the primary indicator that
all is well with the engine. A cold engine will always show a very
high oil pressure. Once hot, the pressure should remain in the green
arc under normal RPMs. A low pressure may indicate a serious problem
with the oil pump or engine bearings. The acceptable ranges of
pressure are stated in the aircraft operating manual. The oil
pressure will diminish if the engine becomes overheated as the
viscosity of the oil becomes too thin and begins to break down.
The oil temperature gauge is also
very a important device for monitoring the wellbeing of the engine.
High power should not be used until the temperature has climbed into
the operating range as damage can occur to the engine. If the
temperature climbs into the red sector, it indicates that a serious
problem may have developed.
This is usually a very instrument
situated at the lower left of the panel. In monitors the condition
of the vacuum system which is driven from the engine. The vacuum
system drives the gyros for the attitude indicator and direction
This instrument measures (usually
in US gallons/hours) the fuel flow to the engine. This instrument
illustrated above also combines the manifold pressure gauge.
The manifold pressure is used on complex aircraft and monitors the
power setting of the engine.
Notorious for their unreliability
are aircraft fuel gauges. Calculate fuel used and if possible never
fly unless you can actually see the fuel through the filler cap!
Aircraft instruments come in a
profusion of designs and combinations but all fulfil the same common
purpose; to give as much notice to the pilot as possible that
something is going wrong.