surfaces should be accomplished carefully
to prevent propeller erosion from reversed
airflow and, in dusty conditions, to prevent
obscuring the operator's vision.
The propeller blade angle may be reversed to
shorten landing roll. To reverse, propeller levers must
be positioned at HIGH RPM (full forward), and the
power levers are lifted up to pass over an IDLE detent,
then pulled aft into REVERSE setting. Power levers
must be pulled back through normal idle speed range
before being positioned in REVERSE. One yellow
caution light, placarded REV NOT READY, on the
caution/advisory annunciator panel, Figure 2-17, alerts
the pilot not to reverse the propellers. This light
illuminates only when the landing gear handle is down,
and if propeller levers are not at HIGH RPM (full
forward). This circuit is protected by a 5-ampere
circuit breaker, placarded LANDING GEAR RELAY C
D1 and LANDING GEAR CONTROL D2 T , located
on the overhead circuit breaker panel.
2-58. PROPELLER TACHOMETERS.
a. Propeller Speed Indicator (N2) C D . Two
tachometers on the instrument panel register propeller
speed in hundreds of RPM, Figure 2-26. Each
indicator is slaved to a tachometer generator unit
attached to the corresponding engine.
b. Propeller Speed Indicator (N2) T . Two
digital/bar graph propeller tachometers located on the
center of the instrument panel display the measured
N2 concurrently in a 1 alphabetic, 3½ numeric
character digital display and a 38-segment bar graph
The indicator has a digital range of 0 to 2500
RPM while displaying current N2 and 0 to 4000 while
displaying exceedence N2. The bar graph display has
a range of 0 to 2500 RPM.
The digital display will contain dashes (----) when
the measured N2 is greater than 2500 RPM. When
displaying exceedence N2 values the actual measured
value, not "----", will be displayed up to 4000 RPM.
The dashes will be prefixed with an "F" if an
EEPROM failure has been detected and with and "E" if
an event has been stored and played back.
The indicator performs BIT on the LCD display,
ROM (program memory), RAM (volatile data memory),
and EEPROM (Non-volatile data memory), and input
signal. The display BIT shall consist of displaying all
active LCD segments for three seconds on power up.
If the ROM or RAM fails BIT the indicator display will
be blank. If the input signal fails BIT the indicator will
prefix the digital display with "F".
BIT failures are not stored in EEPROM. Failures
detected shall therefore not affect the display after
power is cycled unless the failure is encountered
Each exceedence event will consist of two 16-bit
words. One word will contain the peak RPM
measured during the event and the other word
contains the event duration in seconds.
A maximum of 50 events can be recorded. If
more than 50 events are recorded, only 50 will be
stored. As new events are recorded, the oldest events
will be discarded.
The indicator will prefix the digital display with an
"E" when an event is being or has been recorded and
not played back.
The indicator will start recording an event
immediately when the indicator has measured RPM
greater than 2200 or when the indicator has measured
RPM exceeds 2081. The flashing will cease and
digital display will be prefixed with an "E" when the
indicator begins recording an exceedence. The
indicator will end exceedence recording and store the
event when the measured RPM drops to 2080 or
The even display takes precedence over normal
digital display. The bar graph will continue to display
current N2 data. To activate the event display press
the EXCEEDENCE DISPLAY switch for 0.2 seconds
or longer. The most recent event will be displayed
first. Each event display contains the following cycle:
(1) The event number will be displayed for
(2) The event peak RPM will be displayed for
(3) The event duration in seconds will be
displayed for 2 seconds.
All three data items displayed during playback
will be prefixed with a "P" unless an EEPROM BIT
failure has been detected in which case the display will
be prefixed with an "F".
The event display will be terminated after all of
the recorded events have been displayed. Once the
playback sequence has been performed the "E"