C-17A Aircraft Warning and Caution Computer System (WCC)
The WCC is housed in a 3/4 ATR Short chassis with a 10-card capacity. System interface connections are made through three dual insert connectors. The WCC module complement consists of: Discrete Multiplex modules, 1553 module, Memory module, CPU module, and a Power Supply module. The WCC weights approximately 18.5 pounds, dissipates 34 watts (typical) and operates from 28 Vdc input power.
Both WCCs contain dual MIL-STD-1553B bus transmitters/receivers to provide connections via dual redundant 1553 busses to their associated equipment. In addition, each WCC accepts up to 385 input discrete signals connected in parallel to both WCCs. The WCCs also provide 15 parallel-connected, discrete lamp driver outputs for the warning and caution annunciators.
One WCC acts as the 1553 bus controller (BC) while the other functions as a remote terminal (RT). Both WCCs receive the same discrete and 1553 bus inputs and compute the same messages. Only the WCC that is designated as the BC transmits to the WAP and other annunciators. The other WCC is in "hot standby." In the event of a detected failure in the BC, a hand-over, take-over is made and the standby WCC takes over as BC. Cross connected, hard wired "health status" discrete signals accomplish the seamless switch over.
Built-in-Test (BIT) circuits are incorporated in each WCC to provide in-aircraft detection and annunciation. Periodic BIT is used to detect functional degradation or component failures. Failure data is logged in NOVRAM for later readout by maintenance personnel.
The WCC is housed in a 3/4 ATR Short chassis with a 10-card capacity. System interface connections are made through three dual insert connectors. The WCC module complement consists of: Discrete Multiplex modules, 1553 module, Memory module, CPU module, and a Power Supply module. The WCC weights approximately 18.5 pounds, dissipates 34 watts (typical) and operates from 28 Vdc input power.
The WCC is capable of processing a maximum of 420 input discretes. It is currently configured to accept a maximum of 385 input discretes.
The primary WCC is the MIL-STD-1553B bus controller while the backup WCC functions as the backup bus controller and is configured as a remote terminal on the 1553 bus. The two WCCs continuously perform periodic Built-in-Test (BIT) in the background mode, and via dedicated, hard-wired, cross-connected health monitor discrete lines, each WCC continuously informs the other WCC about its 'health'. While the primary WCC controls the 1553 bus, the backup WCC, configured as an RT, continuously updates itself in order to maintain the same configuration and data as the primary WCC. All of the input discretes are connected in parallel to both WCCs. Likewise, all output discretes are connected in parallel and can be driven from either WCC. In the event that the Bus Controller WCC detects an internal fault, it will signify the failure via its health discrete. The backup WCC will detect the Bus Controller failure and it will automatically take over and change its configuration from an RT to become the Bus Controller. This hand-over, take-over is transparent to operation of the Warning and Caution System, except for the failure annunciation posted on the overhead Warning Panel.
The Warning and Caution Computer accepts discrete vehicle (aircraft) data and data from the 1553B bus connecting specialized peripheral LRUs. The WACS contains dual redundant MIL-STD-1553B bus communication ports and can function as the bus controller or a Remote Terminal (RT). The WACS processes signals from all sources and manipulates the inputs via a Boolean logic to provide warning messages on the Warning Panel or by lighting annunciator lamps. The WACS computers are dual redundant, connected in parallel, and feature automatic switchover in the event of a failure.
CPU Type(s):
PACE 1750A
CPU Speed:
1 Mips (6 MIPS possible)
Size: (inches)
7.6 high by 7.5 wide by 12.6 deep
Weight:
18.5 pounds
MTBF:
20,611 Hours
Power Requirements:
28 Vdc, 34 Watts
Interfaces:
Dual Channel MIL-STD-1553B (Bus Controller), over 300 A/C Input Discretes, 15 Output Discretes