Emergency Switch Question

[Stinson]

I've combed the POH for clues and so far- none. What exactly does the red Emergency Switch do? And what level of emergency necessitates the need to break the wire seal and flip it?

I have a Diamond Star DA-40, IFR certified.

Any insight is appreciated!

[Rich]

It causes the Attitude Indicator and the floodlight to be powered by the emergency battery pack. Generally it's for electrical system failure at night or in IMC. Other things could cause it, but basically the expected sequence is:

1. Alternator failure - you're instruments, lights, avionics, etc. are on battery alone. So you go to essentail bus and possibly trim load from there.
2. Battery runs down (depending on variables, could be anything from 5 minutes to an hour for this to happen). If you're night or IMC, you pop this switch and you now have ~30 minutes to get out of the situation.

[Stinson]

So, use it after Ess Bus runs out of power?

[Rich]

So, use it after Ess Bus runs out of power?

That's the basic way to think of it. I could see battery failure alone getting you to need it.

[Stinson]

Thanks!!

[Lance Murray]

Think of it this way. If you are down to a single power source (battery) you use the essential avionics switch for load shedding. When the battery is close to failing you activate the emergency power switch to have cabin lighting and attitude indicator functionality for the rest of your life or until exiting IMC.

[Chromer]

The batteries for the emergency switch have to be changed every so many years, even if the switch is never activated. Depending on the year of your plane the battery pack is located in a different spot, same general area. On the older Diamonds the battery pack is located on the right side lower panel under the transponder, to get to the pack you have to remove the upper dash panel and then one bolt (far right side)holds the pack in place. Once this bolt is out the pack will drop down to the floor so make sure you hold it in place. Undo the wire and remove the pack to have the batteries replaced. The batteries for these are standard AA, 28 of them, when they are replaced make sure you check the voltage before reinstalling pack in the plane to make sure they are all installed properly. The newer packs are attached to the back of the dash panel, I haven't seen these but they look like they might be a sealed pack.

[Rich]

Even better, for those of us with the older ones, those batteries are essentially free. You have to change them out after 2 years, but they still have years of life in them for other stuff one inevitably has that needs AA batteries 

[skypriority]

Emergency switch ON is also the very first step in the “Electric Fire / Smoke in Flight” emergency checklist. This allows for AI and flood light function when the master switch is turned off in step 3. (Step 2 is to unlatch the canopy as needed.)

[Lance Murray]

As said above for the older packs make sure the voltage is checked. One of my springs were corroded and caused voltage issues.