Shuttle Reference Manual Space Shuttle Orbiter Systems Caution and Warning System

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The primary caution and warning system is designed to warn the crew of conditions that may adversely affect orbiter operations. The system consists of hardware and electronics that provide the crew with both visual and aural cues when a system exceeds predefined operating limits. The primary system's visual cues consist of four master alarm lights, a 40-light array on panel F7 and a 120-light array on panel R13. The aural cue is sent to the communications system for distribution to flight crew headsets or speaker boxes.

The C/W system interfaces with the auxiliary power units, data processing system, environmental control and life support system, electrical power system, flight control system, guidance and navigation, hydraulics, main propulsion system, reaction control system, orbital maneuvering system and payloads. The audio alarms are classified as emergency (class 1), C/W (class 2) and alert (class 3).

The emergency alarms consist of a siren (activated by the smoke detection system) and a klaxon (activated by the delta pressure/delta time sensor that recognizes a rapid loss of cabin pressure), and they are annunciated by hardware. The siren's frequency varies from 666 to 1,470 hertz and returns at a five-second-per-cycle rate. The klaxon is a 2,500-hertz signal with an on/off cycle of 2.1 milliseconds on and 1.6 milliseconds off, mixed with a 270-hertz signal with a cycle of 215 milliseconds on and 70 milliseconds off.

The class 2 alarm is activated by the primary (hardware) system, the backup (software) system or both. The C/W tone is an alternating 375 hertz and 1,000 hertz at 2.5 hertz. The alternating C/W alarm tone is generated when the hardware system detects an out-of-limit condition on any of the 120 parameters it monitors or when the software (backup) system detects a parameter that is out of limits.

Both guidance, navigation and control and systems management software sense out-of-limit conditions. These software systems also serve some less critical parameters and annunciate the systems management alert tone. The SM alert tone is a steady tone of 512 hertz of predefined duration generated in the C/W electronics when activated by inputs from the onboard computers.

Visual cues for the flight crew consist of four red master alarm push button light indicators on panels F2, F4, A7 and M052J; the 40-light (red or yellow) C/W light array on panel F7; the 120 parameter status lights on panel R13; the blue SM alert light on panel F7; the red backup C/W light on panel F7; fault messages on cathode ray tubes; and status characters on CRTs.

Inputs enter the C/W logic circuitry from the onboard computers through multiplexers/demultiplexers to activate alarm tones and the backup C/W alarm. Some of these are used to turn the backup C/W light on panel F7 on and off. One additional signal resets the master alarm lights and tones.

The primary C/W system has three modes of operation: ascent, normal and acknowledge. These modes are controlled by the caution/warning asc , norm, ack switch on panel C3. The normal mode is discussed first.

One hundred twenty inputs are received by the primary C/W system directly from transducers through signal conditioners or from the flight forward MDMs and are fed into a multiplexing system. Of these 120 inputs, 95 come directly from transducers, five are from input/output processors, 18 are provided through MDM software and two are spares. These inputs can be either analog or bilevel. The analog signals are zero to 5 volts dc; the discretes are either zero, 5, or 28 volts dc. All of these inputs are designed to provide upper or lower limit detection. If the parameter has exceeded its limits, it will turn on the C/W tone, light the appropriate C/W light on panel F7, illuminate the four red master alarm push button light indicators and store the parameter in memory. The C/W tone can be silenced and the master alarm red light extinguished by depressing any one of the master alarm push button light indicators; however, the C/W light on panel F7 will remain illuminated until the out-of-tolerance condition is corrected. Any one of the master alarm push button light indicators will reset all tones, including the systems management tone.

The C/W ascent mode is the same as the normal mode, except that the commander's red master alarm push button light indicator will not be illuminated.

The C/W acknowledge mode is also the same as the normal mode, except that the 40 annunciator lights on panel F7 will not be illuminated unless one of the red master alarm push button light indicators on panel F2 for the commander or panel F4 for the pilot is depressed.

Each of the 120 status C/W red parameter lights on panel R13 receives an input from a specific parameter. A primary C/W parameter matrix cue card identifies the 120 input channels and correlates them to the panel F7 C/W annunciator light matrix. If an out-of-limit condition exists on a specific parameter that is set on panel R13, it illuminates the corresponding light on panel F7. If the caution/warning param status switch on panel R13 is held in the tripped position when an out-of-limit parameter light on panel F7 is illuminated, the corresponding light on panel R13 will also be illuminated.

The three caution/warning parameter select thumbwheels on panel R13 provide signals to the C/W electronics unit and define the specific parameter for enabling and inhibiting the parameter and setting and reading the parameter's limits.

The caution/warning limit set switch grouping on panel R13 is used to change limits or to read a parameter's limits. The three value thumbwheels provide the signals to the C/W unit, defining the voltage value setting of a parameter's upper or lower limit, X.XX.

The caution/warning limit set limit upper switch on panel R13 provides a signal to the C/W electronics unit, which modes the electronics to set or read the upper limit of a parameter specified by the settings on the value thumbwheels for that parameter; and the caution/warning limit func switch is cycled to set or read the upper limit of that parameter. The caution/warning limit lower switch on panel R13 functions in the same manner as the limit upper switch, except for the lower limit for a parameter.

The caution/warning limit set func set switch position on panel R13 provides a signal to the C/W electronics unit, which sets the value specified by the limit set value thumbwheels into the parameter as specified by the parameter select thumbwheels and limit set limit switch. The limit set func read switch position on panel R13 provides a signal to the C/W electronics unit, which illuminates the lights under the status limit volts X.XX columns on panel R13, that correspond to the voltage parameter limit specified by the parameter select thumbwheels and the limit set limit switch. The value read corresponds to the parameter's full-scale range on a scale of zero to 5 volts dc. The limit sec func switch center position disables the set and read functions.

The caution/warning param enable switch position on panel R13 provides a signal to the C/W electronics unit to enable the parameter indicated on the parameter select thumbwheels, which allows the parameter to trigger the primary C/W alarm when out of limits. The inhibited position operates the same as enable , except it inhibits the parameter from triggering the primary C/W alarm. The center position of the switch disables the enable and inhibit functions.

The caution/warning param status tripped switch position on panel R13 provides a signal to the C/W electronics unit, which illuminates the C/W status lights on panel R13 that correspond to the parameters that are presently out of limits, including those that are inhibited. The inhibited position illuminates those C/W lights on panel R13 that have been inhibited. The center position disables the tripped and inhibited functions.

The caution/warning memory read switch position on panel R13 provides a signal to the C/W electronics unit, which illuminates the C/W status lights on panel R13 that correspond to the parameters that have been out of limits since the last positioning of this switch or the caution/warning memory switch on panel C3 to clear . The clear position on panel R13 or panel C3 provides a signal to the C/W electronics unit that clears from the memory any parameters that are presently within limits, but any parameters that are out of limits during this action remain in memory. The center position of the switch on panel R13 or panel C3 disables the clear and read functions.

The caution/warning tone volume A switch on panel R13, when adjusted clockwise, increases the system A siren, klaxon, C/W, and SM tone generator output signals to the audio central control unit. The B switch functions the same as the A switch for system B tone generators.

The caution/warning lamp test switch on panel R13, when positioned to left, provides a signal to the C/W electronics unit, which illuminates the left five columns of the C/W status matrix lights on panel R13. The right position functions the same as the left, except for the right five columns of lights.

The backup C/W system is part of the systems management fault detection and annunciation, GN&C; and backup flight system software programs. All backup C/W alarms are class 2. Only the 69 backup C/W alarms that are produced by FDA have limits that can be changed and displayed in engineering units accessed through the SM table maintenance specialist function display (SPEC 60). The remaining backup C/W alarms that are produced by the guidance and navigation program are accessed through general-purpose computer read/write procedures. A backup C/W out-of-tolerance condition will trigger a master alarm light, illuminate the red backup C/W alarm light on panel F7, and display a message on the fault message line and fault summary page on the SM CRT.

The SM alert program is another portion of the SM program and operates like the backup C/W system. It is designed to inform the flight crew of a situation leading up to a C/W or one that may require additional procedures. When an SM alert parameter exceeds its limits, the blue SM alert light on panel F7 is illuminated, a discrete is sent to the primary C/W system to turn on the SM tone, and the software displays a fault message on the fault message line and fault summary page on the SM CRT.

Annunciator lights provide visual indications of the status of the vehicle and payload systems. The annunciator lights are classified as emergency, warning, caution and advisory. Emergency and warning annunciators are red; cautions are yellow; and advisory may be white (status), green (normal configuration), yellow (alternate configuration) or blue (special applications).

Annunciator lighting is provided by incandescent lamps that illuminate the lens area of the annunciators. Most annunciators are driven by an annunciator control assembly that controls the illumination of the lights during a normal or test input and the brightness level. The C/W status lights and GPC status lights have separate electronic units for lighting control.

There are three different lens configurations for push button indicator and indicator lights. One configuration has illuminated nomenclature in the appropriate color on an opaque black background, and the nomenclature cannot be seen until it is illuminated. Another configuration has non-illuminated white nomenclature on an opaque black background and a bar that illuminates in the appropriate color; this nomenclature is always visible. The third configuration has a bar that is illuminated on an opaque black background and no nomenclature on the lens, but the nomenclature is available as part of the panel.

The forward flight deck annunciator bus select ACA 1 and ACA 2/3 switches on panel O6 provide electrical power to enable the corresponding ACAs. ACA 1 is enabled by positioning bus select ACA 1 to either the MN A or MN B position, and thus the annunciator lights associated with ACA 1. Bus select ACA 1 also provides electrical power to the annunciator light intensity bright , var switch on panel O6 and the low, med rotary switch on panel O6, controlling the intensity of the annunciator light associated with ACA 1. ACAs 2 and 3 are enabled by positioning the bus select ACA 2/3 switch to either the MN B or MN C position, and thus the annunciator lights associated with ACAs 2 and 3. Bus select ACA 2/3 also provides electrical power to the annunciator light intensity bright , var switch on panel O6 and the low, med rotary control on panel O6, thus controlling the intensity of the annunciator light associated with ACAs 2 and 3. The off position of the bus select ACA 1 switch removes power from ACA 1, disabling the annunciator lights associated with it. The off position of the bus select ACA 2/3 switch removes power from ACAs 2 and 3, disabling the annunciator lights associated with them.

The annunciator intensity switch on panel O6 positioned to bright bypasses the intensity low , med rotary control on panel O6. The annunciator intensity switch positioned to var permits the intensity low, med rotary control to control annunciator light intensity.

The annunciator lamp test switches on panel O6 or panel O8 positioned to left apply power to the ACA 1, 2 and 3 annunciator lamp test circuits, illuminating annunciator lights on panels F2, F6, L1, O1 and M029J; the 20 C/W lights on panel F7; and the SM alert on panel F7. Positioning the lamp test switches to right applies power to the ACA 1, 2 and 3 annunciator lamp test circuits, illuminating the annunciator lights on panels C3, F4, F8 and M052J; the 20 C/W lights on panel F7; and the main engine lights.

The aft flight deck annunciator bus select switch on panel A6 provides electrical power to enable ACAs 4 and 5. ACAs 4 and 5 are enabled by positioning bus select to either the MN B or MN C position, and thus the annunciator lights associated with ACAs 4 and 5. The bus select switch also provides electrical power to the annunciator light intensity bright, var switch on panel A6 and the low , med rotary control on panel A6, thus controlling annunciator light intensity associated with ACAs 4 and 5. The off position of the bus select switch removes power from ACAs 4 and 5, disabling the annunciator lights associated with them.

The annunciator intensity switch on panel A6, when positioned to bright, bypasses the intensity low, med rotary control on panel A6. Positioned to var, it permits the intensity low , med rotary control to vary annunciator light intensity.

The annunciator lamp test switch on panel A6, when positioned to left, applies power to the ACA 4 and 5 annunciator lamp test circuits, illuminating the annunciator lights on panels A2 and A6 and columns 0 through 4 on panel R13. Positioning the switch to right applies power to the ACA 4 and 5 annunciator lamp test circuits, illuminating the annunciator lights on panel A7 and columns 5 through 9 on panel R13.