Learjet 60 - N2 Indicators

Pilot's Manual

Learjet 60
The
frequency of the output
signal
represents the speed of the rotating
N7 group . One sensor provides output
signals
to the N7 indicator, and
channel A
of the
FADEC while
the other sensor provides output
signals
to
channel B
of the
FADEC
and the opposite engine's
FADEC
(used
for
APR
and
engine synchronizer) .
When electrical power is not available
to the instrument, the pointer and N7 bug
will
go to the lowest possible
position and the
digital
display
will
be blank . Upon
initial
power-up,
the indicator
will
conduct a self test .
During
the self test, the
digital
dis-
play segments
will illuminate
and indicate "188 .8" .
Failure
of the self
test is indicated by three dashes
in
the
digital
display and no pointer
movement . Electrical power
for
the indicators is 28 VDC supplied
through the
2-amp L
and
R
N7 circuit breakers on the pilot's and copi-
lot's circuit breaker panels respectively
. In
the event of a
normal
electri-
cal system failure, the N7 indicators are powered by the emergency
power system
. Refer
to
Airplane Flight
Manual
for
instrument
limit
markings
.
N2 INDICATORS
An
N2 indicator
for
each
engine
is installed on the center instrument
panel
.
Each indicator utilizes both a four-place
digital
display and a
cir-
cular scale with
pointer
to indicate N2
. The
circular scale is marked
from
0% to 110%
in
5%
RPM
increments .
The digital
display uses
light-
ed segments to show the turbine speed to the nearest tenth of a percent .
Each
engine
is equipped with two induction-type speed sensors
in-
stalled on the
right
side of the accessory gearbox
. The
gearshaft teeth
on the centrifugal
impeller (within
the accessory gearbox) rotate adja-
cent to the stationary speed sensors . As the gearshaft turns, its teeth
cause the frequency output of the speed sensors to change proportion-
ally .
Since the accessory gearbox is driven by the N2 spool, the frequen-
cy of the output
signal
represents the speed of the rotating N2 group .
One sensor provides output
signals
to the N2 indicator, and channel A
of the
FADEC while
the other sensor provides output
signals
to
channel
B
of the
FADEC
and the opposite engine's
FADEC
(used
for APR
and
engine synchronizer) .
When electrical power is not available to the
in-
strument, the pointer
will
go to the lowest possible position and the
digital
display
will
be blank . Upon
initial
power-up, the indicator
will
conduct a self test .
During
the self test, the
digital
display segments
will
illuminate
and indicate "188 .8" .
Failure
of the self test is indicated by
three dashes
in
the
digital
display and no pointer movement . Electrical
power
for
the indicators is 28 VDC supplied through the
2-amp L
and
R
N2 circuit breakers on the pilot's and copilot's circuit breaker panels
respectively
. Refer
to
Airplane Flight
Manual
for
instrument
limit
markings
.
2-14 PM-123
Change 5