I apologize if this has been asked before but I couldn't find an answer. Tutorial #2 states that in RL you should notify ground crew before you start engine and APU fire test. I was wondering about that statement and starting my 737 from cold & dark I noticed that radios won't work if you only have battery power supply (starting APU without ground power) therefore you can't activate FLT switch on ACP. So how do you notify the guys on the ground you're gonna test fire system if you don't have your radios on? My only guess would be using service interphone system. The FCOM vol. 2 states:

 

The service interphone system provides intercommunication between the flight deck, Flight Attendants, and ground personnel. /.../ Anyone who picks up a handset/microphone is automatically connected to the system.

You don't use radios to talk to the ground crew. You can use service interphone, or simply walk out and tell them.

When I worked for the airlines, the flight crew would ring the "ground call" bell if they needed to talk to us. They never warned us when they did the apu fire tests. It was an unspoken rule that, if the fire bell rang more than 15 seconds, whoever was closest would hit the extinguisher button. Obviously, common sense plays a role in such things. If the aircraft has been sitting all night, and the apu fire bell goes off, obviously the flight crew is performing their preflight. Now if the aircraft is on a short turn, has the apu running, and the bell goes off, we would pay a little more attention. The flight crew would probably be quicker in taking care of any issue as they would be within an arms reach of the extinguisher controls whereas we would have to go into the main gear bay to get to it.

 

I do remember when I was working a turn on a 757-300, and they performed an "extended" apu fire test (about 25 seconds.) I had my finger on the button when they concluded the test (On the 757, the extinguisher controls are on the nose gear...along with a bright flashing red light and a pretty loud horn.) Needless to say, I'm happy that I didn't push the button.