【原】虚假货舱加热故障（在发动机关车时）

【事件描述】

在发动机关车时，在FWS和CMS报告如下虚假指示：

• Cargo Heat Fault
• FMC 231 TAV Moving Fault

• 这些虚假指示仅发生在安装前和后货舱加热控制器（可选）的飞机上：

• P/N 23948-01AA.

• FIN 10HC

【技术背景/分析】

在发动机关车时，货舱加热控制器（CHC：Cargo Heat Controller）执行配平空气活门（TAV： Trim Air Valve）的飞后检查。

两个TAV将执行测试：

1. TAV将由马达驱动完全打开和关闭，CHC检查TAV是否可以完全打开和闭合。这是通过计算打开和关闭的马达步数来完成的。在通过设置的限位电门完全闭合指示前，马达步数必须在一定范围内（公差包含在CHC软件中）。

2. TAV将与测试的那个相同的方式打开。TAV的CHC输出驱动器关闭是由电门关闭的；CHC软件检查TAV是否能关闭是通过安装在TAV上的弹簧。弹簧完全关闭位置与测试的那个相同的限位开关进行检查。

如果在TAV测试期间，CHC的电源中断一次或多次，持续5ms-25ms，CHC的微处理器仍通电 (transparency time requirement)，但TAV的输出与电源断开。在活门的电源恢复之前，弹簧力导致向关闭位置移动几度。这种部分弹簧力闭合会导致开启或关闭时的步数不匹配，并因TAV运动不一致而导致货舱加热故障。

【解决方案/建议】

在这种虚假故障触发的情况下没有操作后果。

如果在发动机关车时发生这种事件，则可以通过C/B重置CHC约2秒钟来清除故障。

CHC将在通电后执行相同的测试，如果指示的根本原因是发动机关车时的电源中断，则通电后的测试将不会导致故障。

如果实际故障处于激活状态，则该测试也会指示该故障。

【参考】

REF.ISI21.43.00007

(Issue date:17-APR-2024)

DESCRIPTION

During engine shutdown, spurious indications at FWS and CMS were reported as follows:

• Cargo Heat Fault

• FMC 231 TAV Moving Fault

These spurious indications only occur for FWD and AFT installation of the Cargo Heat Controller (optional):

• P/N 23948-01AA.

• FIN 10HC

TECHNICAL BACKGROUND/ANALYSIS

The CHC performs a post-flight check of the trim air valve (TAV) at engine shutdown.

Two TAV tests are performed:

1. TAV will be completely opened and closed by the motor driver and the CHC checks if the TAV can be completely opened and closed. This is done by counting of the motor steps for opening and closing. The number of steps have to be in a certain range (tolerance is included in the CHC SW) before the fully closed indication by a limit switch is set.

2. TAV will be opened in the same way as for test one. The CHC output driver for the TAV is switched off and the CHC SW checks if the TAV could be closed by the spring installed in the TAV. The spring closure fully closed position is checked by the same limit switch as for test one.

If during the TAV test one the power supply to the CHC is interrupted once or several times for 5ms - 25ms, the microprocessor of the CHC is still supplied by power (transparency time requirement) but the output to the TAV is disconnected from power.

The force of the spring causes a movement of several degrees to the close position before the power to the valve returns.

This partially spring force closing causes a mismatch in step counting for opening or closing and leads to the cargo heat fault because of the TAV movement discrepancy.

SOLUTION / RECOMMENDATION

There is no operational consequence in case of such spurious fault triggering.

The fault can be cleared via a reset of CHC by push/pull of the C/B for about 2 seconds if such an event occurs at engine shutdown.

The CHC will perform the same test after this power-up and if the root cause of the indication was the power interrupt at engine shutdown, the test after power-up will result in no fault.

If a real fault is active, it will also be indicated by this test.