有时候我们会发现机长或观察员的ACP面板上发射键只能在VHF 1位，也只能接收VHF 1的信号；副驾驶的ACP面板上发射键只能在VHF 2位，同样也只能接收VHF 2的信号。这就是ACP面板的应急工作方式，是通过其上ALT/NORM电门进行控制。以下是AMM PART 1 的23-51-00内相关内容，有兴趣就仔细研读一下吧。

ALT-NORM Switch：
You use the ALT-NORM switch to select either normal or emergency operation of the flight interphone system. Each station operates independently.

When you select NORM, the flight interphone system operates as usual.
When you select ALT, the flight interphone system operates in the emergency mode. The only ACP control that operates is the R/T position of the PTT switch. The hand-mic does not operate.
When you select ALT on the captain or observer ACP, you hear receiver audio from the VHF-1 transceiver at the headphone and headset jacks. When you key the MIC, the audio and PTT
signals go to the VHF-1 transceiver.
When you select ALT on the first officer ACP, you hear receiver audio from the VHF-2 transceiver at the headphone and headset jacks. When you key the MIC, the audio and PTT signals go to the VHF-2 transceiver.

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