B737NG IRS Q's [Archive]

Ka8 Flyer

18th Aug 2007, 16:12

Hi folks,

according to the manual, the IRS on the B737 NG has two electrical power sources:
the switched hot battery bus and the AC Stby Bus (IRS1) / Xfer Bus 2 (IRS2).

1) The right IRS will switch off 5 minutes if its AC power source fails. Will it also switch off if the left IRS is inop or not turned on?

2) Can you perform an IRS alignment using only the Switched Hot Battery Bus? If its possible, what will happen to IRS 2 after 5 minutes? Will it just stop alignment and turn off?

Thanks!

Mark

IFixPlanes

18th Aug 2007, 19:05

http://img254.imageshack.us/img254/36/adirspowervw4.th.jpg (http://img254.imageshack.us/my.php?image=adirspowervw4.jpg) http://img254.imageshack.us/img254/1529/adirspower2br3.th.jpg (http://img254.imageshack.us/my.php?image=adirspower2br3.jpg)

Out of the books...
ADIRS - POWER
The ADIRU operates with 115v ac or 28v dc. 115v ac is the normal power source.
Each ADIRU has a separate ac and dc power source. The left ADIRU gets power from these buses:
- 115v ac stby bus
- 28v dc sw hot battery bus.
The right ADIRU gets power from these buses:
- 115v ac xfr bus 2
- 28v dc sw hot battery bus.

AC Reference Voltage
The 28v ac stby bus supplies a servo reference voltage to the left ADIRU and to the left angle of attack (AOA) sensor. The 28v ac xfr bus 2 supplies servo
reference voltage to the right ADIRU and to the right AOA sensor.

Integrated Flight Systems Accessory Unit
The integrated flight systems accessory unit (IFSAU) gets ac power from the 115v ac xfr bus 2. DC power comes from the 28v dc sw hot bat bus. The IFSAU uses these inputs to control power going to the right ADIRU and to supply power to the crew call horn when the ADIRUs operate with dc power on the ground.

Air Data Modules
The left ADIRU supplies 13.5v dc to the left pitot ADM and to the left static ADM. The right ADIRU supplies 13.5v dc to the right ADMs.

Inertial System Display Unit
The inertial system display unit (ISDU) gets 28v dc from the left and the right ADIRU.

IRS Master Caution Unit
The IRS master caution unit gets power from the 28v dc bat bus.

ADIRS - DC POWER OPERATION
General
The ADlRUs operates with AC or DC power. AC power is the norrnal power source. lf the AC power source is not available, DC power from the airplane
battery will supply power to the ADIRUs.

Left ADlRU DC Operation
When AC power is not available, the left ADIRU will operate on DC power from the 28v dc sw hot battery bus. The left ADIRU will continue to operate on DC
power until the battery power is less than 18v dc.

Right ADlRU DC Operation
DC power to the right ADIRU goes through a time delay circuit in the integrated flight systems accessory unit (lFSAU). 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 ADlRU is removed. This feature allows the airplane battery to drain at a slower rate.