STANDBY INSTRUMENTS D/O
ISIS
DESCRIPTION
The back of ISIS is equipped with two pressure connectors:
- one is connected to the standby pitot probe for total pressure
acquisition,
- the other one is connected to the combined standby static probes for
static pressure acquisition.
The ISIS indicator contains the following subassemblies:
- one pressure module,
- one inertial module,
- one computation module,
- one display module and,
- one interface module.
The pressure module is connected to the total and static pressure
connectors. Each pressure line is connected to a pressure sensor in
the pressure module. The inertial module is composed of three
gyrometers (gyrolaser) measuring angular speeds and two specific
linear accelerometers (pitch + roll). The computation module includes
a Central Processing Unit (CPU), which calculate the operational
parameters (attitude, altitude and airspeed), and a graphic card, which
receives the data from the CPU and sent it to the display module. The
display module is fitted on the front face of ISIS. It is of the Liquid
Crystal Display (LCD) type. The front face is also fitted with several
knobs for operation purposes. The interface module is composed of:
- a filtering board linked to an electrical connector at the back of ISIS,
- the 28V DC power supply unit,
- the interface board which links the pressure, inertial, computation
and display modules.
POWER SUPPLY
ISIS is supplied with 28V DC from the ESSential BUS bar. In case
of loss of this bus bar, the HOT BUS bar automatically takes over,
provided the Computed Air Speed (CAS) is greater than 50 kts. In
case of a power supply cut-off less than 50 ms, there is no effect on
the display.
OPERATION
When ISIS is energized, a delay of 90 seconds is necessary for
initialization. ISIS computes and displays own air and inertial
parameters. When the airspeed data is not valid, the CAS information
is provided as a back-up by Air Data/Inertial Reference Unit (ADIRU)
1 or ADIRU 3 regarding the ATT/HDG selector switch position. The
ADIRU also provides a Ground Speed (GS) information for
flight/ground condition, as a back-up. A BAROmetric selector knob
enables the display and adjustment of the standard barometric pressure
in hPa. When the Landing System P/BSW, located on the upper right
part of the indicator, is pushed, the G/S and LOC scales come into
view. The BUGS P/BSW allows to display the BUGS page. This page
is used to program characteristic speeds and altitudes displayed on
the related speed and altitude scales. The (-) P/B is used to get access
to the next bug and the (+) P/B to return to the previous bug. Air and
inertial parameters are processed by the computation module using
data from the pressure and inertial modules. The pressure module
sends the total and static pressure data while the inertial module sends
accelerations and angular rates data. Once computed, the parameters
are sent to the display module for indication to the crew. The LS data
is sent by the Multi-Mode Receiver (MMR) 1. Air Data/Inertial
Reference System (ADIRS) parameters computed by ISIS are sent to
the Flight Data Interface and Management Unit (FDIMU). The ISIS
can operate from 0 to 600 kts without deterioration of airspeed data.
It can operate from -2.500 to 55.000 ft and up to 40.000 ft/min without
deterioration of altimeter data. For the horizon data, the ISIS can
operate from -180 to +180 deg without deterioration.
