In the integrated flight systems accessory unit (ifsau). When
AC power is not available, a 5 minute time delay keeps the DC
power relay energized, and the right ADIRU operates on DC
power. After 5 minutes continuous operation on DC power, the
time delay circuit deenergizes the relay and DC power to the
right ADIRU is removed. This feature allows the airplane battery
to drain at a slower rate.
ADIRS - NO COOLING AND ON DC WARNING
General
The integrated flight systems accessory unit (IFSAU) contains a
circuit which causes the ground crew call horn to tell
maintenance personnel of unsafe ADIRU operation. This
occurs when the airplane is on the ground and the ADIRUs
are on dc power or when the equipment cooling system fails.
ADIRU DC Power Operation
The ADIRUs send 28v dc to the AND logic circuit in the IFSAU.
When an ADIRU senses that it is on dc power, it sends an ON
DC discrete to the IFSAU. The discrete goes through a 20
second delay to the AND gate logic. After twenty seconds of dc
operation, the AND gate supplies power to the crew call horn
relay. The relay energizes when the air/gnd relay is in the gnd
position. The energized crew call relay closes the relay switch,
and 28v dc power causes the horn to operate.
Equipment Cooling Failure
Two equipment cooling sensors monitor the cooling air flow to
the ADIRUs. A low flow relay in the sensor will close when the
cooling air flow fails. The closed relay lets 28v dc go to the
IFSAU. The 28v dc discrete goes through a 20 second delay to
the AND gate logic. After twenty seconds, the AND gate
supplies power to the crew call horn relay. The relay energizes
when the air/gnd relay is in the gnd position. The energized
crew call horn relay closes the relay switch, and 28v dc power
causes the horn to operate.
ADIRS - CONTROL AND WARNING
General
These are the units that interface to supply control and warning
data to the pilots:
* ISDU
* MSU
* IRS master caution unit.
ISDU Interface
The ISDU supplies both ADIRUs with test discretes, heading
data, and present position data. The ADIRUs supply IR data and
fault data to the ISDU.
MSU Interface
The MSU supplies mode discretes to the ADIRUs. The ADIRUs
supply align and fail discretes to the MSU. The MSU also
receives an ON DC discrete from the ADIRUs. The ON DC
discrete goes through the IRS master caution unit.
IRS Master Caution Unit Interface
The IRS master caution unit receives fail and ON DC discretes
from the ADIRUs. The IRS master caution unit supplies discrete
outputs to the MSU and to the master caution lights and
annunciators.
ADIRS - SYSTEM INPUTS
General
Each ADIRU receives inputs from these on-side components:
* AOA sensor
* Pitot ADM
* Static ADM.
The AOA sensor gives angle of attack information to the ADIRU.
The ADIRU uses angle of attack to modify pitot and static
values.
The pitot ADM gives the ADIRU total air pressure information.
This is used to calculate airspeed and mach number.
The static ADM gives the ADIRU static air pressure information.
This is used to calculate altitude and airspeed.
These components supply data to both ADIRUs:
* TAT probe
* DEU 1 and DEU 2
* Window and pitot heat module
* Inertial system display unit (ISDU)
* FMC 1 and FMC 2.
The TAT probe gives total air temperature to the ADIRUs. The
ADIRUs use TAT to modify altitude and airspeed calculations.
DEU 1 and DEU 2 give barometric correction to the ADIRUs. The
ADIRUs use barometric correction to calculate corrected
barometric altitude.
The window and pitot heat module sends a discrete signal to
the ADIRUs when anti ice heat is on. The ADIRUs modify the