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characteristics are defined for each display system and programmed into the
EGPWC as part of the configuration software.
(b) Cockpit annunciations can vary somewhat aircraft to aircraft or operator to
operator. In addition, several system options are defined by the installation
configuration. One of these is EGPWS lamp format. For MK V EGPWS, two
formats are provided: Lamp Format 1 and Lamp Format 2.
For Training Purpose Only Printed:May 2005
B757-200Aircraft Recur rent Training Manual - 13 -
B. SYSTEM MAINTENANCE
(1) MAINTENANCE PHILOSOPHY
(a) The EGPWS is an “on-condition” only maintenance system. No scheduled
maintenance is required. This is accomplished by both continuous Built-In-Test
(BIT) and event initiated test functions. Event initiated test refers to both power-up
tests and manually activated Self-Tests. Results of these functions are indicated by
system status indicators and messages so that the systems functionality can be
assessed.
(b) Detected faults are indicated to the flight crew during normal flight operations by
system status annunciators or flight display messages in the cockpit (i.e., GPWS
INOP or FAIL, W/S INOP or FAIL, TERR INOP or NOT AVAILABLE). On the
ground, system status indications are expanded to direct fault isolation to the fault
source whether internal or external to the EGPWC. Several levels of reporting are
provided by the EGPWS Self-Test, and multiple means are provided to access the
information. The intent is to provide information that will encourage the line
mechanic to correct the real problem through clear fault messages and minimal
effort.
(2) SYSTEM OPERATION DURING AN INOP CONDITION
(a) EGPWS continued airworthiness is predicated on system status indications. An
indication of TERR INOP (only) or NOT AVAILABLE (only) is likely to indicate a
loss of necessary GPS data for performing Terrain Alerting and Display functions,
but has no effect on basic GPWS (Modes 1-7) functions. Additionally, a GPWS
INOP (only) indicates a loss of basic GPWS functions, but this could be limited to
say Mode 4 only because of a loss of necessary data required for that mode alone.
In any case, the EGPWS will provide alerting based on the current capability of the
EGPWC and its inputs.
C. BITE AND TEST
(1) BIT DESCRIPTION
(a) The EGPWC contains an extensive BIT capability. The BIT functions provide high
confidence that the Warning Computer and interface signal sources are operating
properly, and that the EGPWS will perform its intended function. Detected failures
are indicated via GPWS INOP, Windshear INOP, and Terrain INOP/NA
annunciations and on the ARINC 429 bus output. Failures detected during flight
are saved in the flight history and are enunciated during Level 4 of the cockpit
Self-Test. BIT status is also available through the RS-232 port by use of a PC or
terminal. If the EGPWC detects an internal Warning Computer fault, it will turn on
all the INOP lights. If the EGPWC detects an external input fault, it may or may not
turn on the INOP light(s) depending on the input fault, the type of installation, and
whether the aircraft is airborne or on the ground.
(b) The EGPWC BIT performs three types of functions: Operation Monitoring,
Operation Tests, and Restricted Tests.
(c) Operation Monitoring consists of software checks that are performed as part of the
normal Warning Computer processing. Operation Monitoring includes checks of
data values and program flow control variables used for the warning computations
to ensure they are within expected ranges. The statuses of various EGPWC
hardware subsystems are continuously verified including core processor checks,
voice generator circuitry checks, and ARINC 429 wrap-around tests. Operation
Monitoring also includes extensive testing of the input signals to ensure the
EGPWC is using proper data for its calculations.
For Training Purpose Only Printed:May 2005
B757-200Aircraft Recur rent Training Manual - 14 -
(d) Operation Tests run during normal operation without disrupting the EGPWC
warning calculations or annunciations. Operations Tests include CPU instruction set
tests, A/D tolerance tests, ROM check-sum verification tests, and
nondestructive RAM tests. Operation Tests are scheduled by the operating system
to be performed between the routines required for normal operation.
(e) Restricted Tests destroy data or take an excessive amount of time to complete
and cannot be run during normal system operation. These tests are usually run
during system power up or during a cockpit initiated Self-Test. These tests
primarily consist of more thorough hardware checks that would disrupt normal
　
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