B. APU Fault Data The Built-in Test Equipment (BITE) is a function incorporated in the ECB, which detects, localize and memorize failures. It ensures the detection and display (via CFDS) of failures related to the ECB, ECB interface circuirity, the APU systems and the APU itself. The BITE operation is automatically but can also intiated manually. Additionally the ECB records the failure history of the APU-system in its nonvolatile memory for further processing.
 4. Power Supply____________ (Ref. 49-61-00)
 5. Interface_________
 A. Aircraft Digital Interface The ECB communicates to the aircraft via three seperate LOW SPEED ARINC 429 buses.
 (1)
 ARINC 429 Input from the CFDS The ECB uses this bus to receive specified data from the CFDS with applicable ARINC lables.

 (2)
 ARINC 429 Output to the CFDS
 The ECB uses this bus to transmit data to the

 -CFDS
 -SDAC
 -AIDS.

 (3)
 ARINC 429 Input from the ECS The ECB uses this bus to receive specific data from the ECS.

 B. APU-System Interface
 (Ref. 49-61-00)

 6.
 Component Description

_____________________
 (Ref. 49-61-00)

 7.
 Operation/Control and Indication:

_________________________________ The ECB 59KD operates in various states dependant on operating characteristics of the engines and signals from the aircraft. A given state can contain several modes of operation. The states are as follows:
 -POWER-UP,
 -WATCH,
 -START PREPARATION,
 -STARTING,
 -RUN,
 -COOLDOWN,
 -
SHUTDOWN.

 A.
 POWER-UP State The ECB enters this state when power is initially applied or when power is re-applied after an interruption in excess of the specified limits. The power up state lasts 3 seconds +/- 0.3 secs. The ECB is capable of recognizing and recording the momentary occurence (150msec) of a start, or emergency stop signal. These signals could be issued by the aircraft shortly after power-up or at any time during power-up. When the ECB receives and validates a start signal within 100 msecs, the start in progress output is energised. The start in progress output also applies to the watch state. When an emergency stop signal is received, the ECB closes the air intake and then deactivates the aircraft relay output.

 B.
 WATCH State After completion of the POWER-UP state the ECB enters the watch state. The ECB is still capable of recognizing and recording the occurence of start-, or emergency stop signals.

 C.
 START PREPARATION State When the start command is received, speed is less or equal to 7% and there are no prohibitive conditions the ECB will enter the START PREPARATION state. In case the speed is greater than 7% the start is inhibited until speed is equal to or less than 7%, at which time the ECB enters the START PREPARATION state automatically without a new start command.

 D.
 STARTING State The starting state requires the ECB to operate the APU by conducting the start sequence. The receipt of a stop signal anytime during the STARTING state leads to a shutdown without a cooldown period. The starting state is comnpleted and goes to run state 2 seconds after reaching 95% speed.

 E.
 RUN State After completion of the start sequence activities of the STARTING state, the system enters the RUN state. In the RUN state the closed-loop steady-state speed-control is implemented and the APU system is ready for loading (Ready to Load condition).

 F.
 COOLDOWN State In the RUN state, receipt of a stop command will put the APU into a COOLDOWN state. The cooldown time is up to a maximum of 120 seconds.

 G.
 SHUTDOWN State At any point during the START PREPARATION, STARTING, RUN or COOLDOWN states an APU shutdown may take place due to system faults or a stop command. The serverity of faults and how to they result in APU shutdown is shown in Table 1. The ECB software recognizes the removal of the stop command or cycling of the master switch and the receipt of a start command during the shutdown state. When this occurs the ECB will not close the air intake, conduct the built in tests of the ROM checksum, speed injection, discrete and analog outputs and restart the APU when the speed drops below or equal to 7%.

 (1) Description of Table 1 / Table 2 A fixed Fault Code Number (FCN) is allocated to each detectable fault. Each FCN (with some exceptions) is linked to a LRU ID. Both, the FCN and the LRU ID, are shown in the LAST LEG REPORT, PREVIOUS FLIGHT REPORT etc. . In many occasions two or more FCNs are linked to the same LRU ID. This happens when different FCNs (faults) are in conjunction with the same Line Replaceable Unit (LRU).
　
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