TEXTRON LYCOMING OPERATOR'S MANUAL
0-360 and
ASSOCIATED MODELS
SECTION
3
e. A proper magneto
check is important. A magneto
preflight test is
useful to determine that both magnetos are functioning properly and
that no spark
plug is misfiring.
Additional factors,
other than
the igni-
tion system,
affect magneto drop-off. They
are load-power output, pro-
peller pitch, and mixture
strength. The important thing
is that the engine
runs
smoothly because magneto drop-off
is affected by the variables
listed
above. Make
the magneto
check in accordance
with the
following
procedures:
(1) Fixed Wing Aircraft.
(Controllable pitch propeller). With propeller in minimum pitch angle,
set the engine to produce
50 - 65% power as indicated
by manifold
pressure gage. At these settings,
the ignition system and
spark plugs
must work harder
because of the greater pressure
within the
cylinders.
Under these conditions,
ignition problems, if they
exist,
will occur. Magneto
checks at low power settings
will only indicate
fuel / air distribution quality.
(Fixed pitch propeller). Aircraft that are equipped with fixed pitch pro-
pellers, or not equipped with manifold pressure gage, may check
magneto drop-off with engine
operating at approximately
1800 RPM
(2000 RPM maximum).
Switch from both
magnetos to one and note
drop-off; return to both
until engine regains speed and switch to the other magneto and note
drop-off. Magneto drop-off at 2000 RPM should not exceed 200 RPM
on
either magneto; but under some
conditions; i.e., field elevations,
temperature and
carburetor characteristics,
a drop in excess of 200
RPM (plus 25 RPM) may be experienced. If engine speed stabilizes
and if the engine continues
to operate smoothly,
the ignition system
is operating satisfactorily.
(2) Helicopter.
Raise collective
pitch stick to obtain
15 inches manifold pressure
at
2000 RPM.
Switch from both magnetos to one and note drop-off; return to both
until engine regains speed and switch to the other magneto and note
drop-off. Drop-off should not exceed 200 RPM. Drop-off between
magnetos should not exceed 50 RPM. A smooth drop-off past nor-
mal is usually a sign of a too lean or too rich mixture.
f. Do not operate on a single magneto for too long a period; a few seconds
is usually sufficient to check drop-off and to minimize plug fouling.
Revised July, 1989
3-5
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