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be displayed in amber. AHRS reversion is de-
scribed later in this chapter.
INITIALIZATION
The AHRS systems require approximately
two (2) minutes to initialize on the ground
following application of power to the DC elec-
trical system (essential busses). During this
time each AHRS performs a self-test and is
brought into alignment with true local verti-
cal and magnetic heading. The initialization
of each AHRS is complete when the red ATT
FAIL and red HDG TEST flags clear on the
corresponding ADI and HSI/MFD.
During initialization the airplane must remain
stationary. Wind gusts, passenger loading, en-
gine start or other preflight operations will
normally not hinder AHRS alignment. If the
initialization requires more than 2 minutes, the
AHRS may have detected excessive motion.
If the PFDs/MFD displays are ON (avionics
master switches - On), AHRS alignment may
be monitored by observing the HSI heading
move from 115° to 0°. Alignment may be com-
pleted by the time the avionics master switches
are turned on (display units powered-up) dur-
ing the normal checklist sequence.
If an alignment is unsatisfactory, initialization
may be restarted by cycling primary and sec-
ondary power to that AHRS. Momentarily
turning airplane main batteries off and back
on will restart initialization for both AHRS's.
To reinitialize a single AHRS, pull and reset
the appropriate AHRS circuit breakers.
Airborne initialization may be attempted by
pulling and resetting the primary and sec-
ondary power source circuit breakers for the
affected AHRS. The airplane must be main-
tained in wings-level unaccelerated flight dur-
i n g t h e r e - a l i g n m e n t p r o c e s s . I n f l i g h t
alignment time is normally 20 seconds.
AHRS POWER SOURCE
Each AHRS has a primary and a secondary DC
electrical power source (Figure 16-24). The
No.1 (left) AHRS receives primary power
from the left essential bus and secondary or
backup power from the right essential bus.
The No.2 (right) AHRS receives primary
power from the right essential bus and sec-
ondary power from the left essential bus.
Should either essential bus fail in flight, power
to both AHRS's is uninterrupted. Separate cir-
cuit breakers for each system, primary and
secondary, are provided in the INSTRU-
MENT/INDICATIONS group on the pilot and
copilot circuit breaker panels. The AHRS #l
PRI and #2 SEC circuit breakers are located
on the pilot's side, and the AHRS #2 PRI and
#l SEC circuit breakers are located on the
copilot's side.
AHRS REVERSION
Failure of an AHRS is apparent when the on-
side horizon and pitch lines are removed from
the ADI, the brown half of the ADI is removed
(sphere turns entirely blue) and a red ATT
FAIL annunciator appears in the upper center
of the ADI. Also, the heading compass rose
freezes at the existing heading and is accom-
panied by a HDG FAIL annunciator on the
HSI above the fixed airplane symbol.
If either AHRS fails inflight, the AHRS re-
version switch on the airplane system reversion
panel allows the pilot to select the remaining
AHRS to supply attitude and heading infor-
mation to both pilot displays. The three posi-
tion switch is labeled "1 - AHRS NORM - 2"
(Figure 16-24). For any switch position other
than NORM, an amber attitude source annun-
ciator (ATT1 or ATT2) will appear above and
to the left of the ADIs on both PFD displays
(Figure 16-32), and a corresponding heading
source annunciator will appear above the com-
pass lubber line on the PFD HSIs (MAG1 or
MAG2) and MFD map.
If AHRS #1 fails, attitude information will be
lost to the weather radar for antenna stabi-
L E A R J E T 4 5
P I L O T T R A I N I N G M A N U A L
16-35
FOR TRAINING PURPOSES ONLY
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