Electrical System Malfunctions
T-45C TS, ADV & IUT ENG-03
II. Undervoltage condition 1.8.1.3.4.1
Fig 3: Undervoltage
A. Indications
Condition Failure
1.
MASTER ALERT flashes
2.
Caution and warning tones sound
3.
GENERATOR warning light illuminates
4.
AC INV caution light illuminates -- aircraft 165456
and lower before AFC 199 incorporated
5.
C AUG caution light illuminates
6.
F PRES caution light illuminates
NOTE: There is a 30-sec delay in the illumination of
the F PRES caution light after the loss of the
Generator Bus.
B. Verifications: BATTERY VOLTS meter reads 25 VDC or
less
C. Effects on flight and safety: With the generator no
longer on line, the nonessential AC buses have
automatically shed and electrical power is limited to
battery power voltage available. Functional equipment
on the essential buses are limited to required operational
voltage and may fail at any time even though battery
voltage is still indicated on the voltmeter.
NOTE: A failure of the undervoltage sensing unit itself will
remove the ability of the electrical system to detect a low voltage
condition on the generator bus; therefore the GENERATOR
warning light will not illuminate if the generator voltage drops
below 25 VDC. The first indication of an undervoltage sensing
unit failure would be to have observed voltage of less than 25
VDC without the GENERATOR warning light being illuminated.
When this happens the nonessential AC load is retained,
thereby depleting the battery voltage at a faster rate. Once the
battery voltage is below approximately 21.5 VDC the inverters
will start to fail. While the voltage is between 21.5 and 24 volts,
it would be best to secure the generator to shed the
nonessential AC load which will extend the battery life.
Change 4 (9-98)
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