To avoid failing this part of the test, Appareo recommends using ground mode before takeoff and after landing. Normal operation on the ground is when your transponder is in ALT mode, the transponder display will show Ground (GND) mode indicating that you’re on the ground but you’re still in ALT mode. (Note: GND only displays once you have acquired a GPS position.)
Before takeoff: Once you’ve started the airplane, press SBY to put Stratus ESG into Standby mode. Once the lat/long fields have populated on the display, press ON or ALT once to transition into Ground mode. (Note: Do not press ALT twice or you will be prompted to override Ground mode and place the transponder in ALT mode.)
When you begin taxiing, do not taxi at a speed faster than 15 knots for more than 10 seconds or the transponder will return to ALT mode. Once you’re airborne, Stratus ESG will automatically transition into ALT mode. (Stratus ESG only switches from Ground mode to ALT once airborne, but you have to have ALT selected before taxing.)
After landing: Clear the runway and stop for 10-15 seconds. Stratus ESG will transition back into Ground mode. Again, do not taxi at a speed faster than 15 knots for more than 10 seconds or the transponder will return to ALT mode.
The table below describes each transponder mode. These modes will automatically transition for various phases of flight. Unless otherwise instructed, no action is needed.
When powered on, Stratus ES/ESG will be restored to the same mode that it was in when it was powered off (ALT, ON, or SBY).
| Mode | Key | Description |
| Off | PWR | Stratus ES/ESG is powered off. |
| Standby | SBY | Stratus ES/ESG is powered on and does not send responses to any ATC interrogations. |
| Altitude | ALT | Stratus ES/ESG is powered on and responds to all Mode A/C/S interrogations. Altitude is reported. |
| Ground (GND) | Auto-detected | Stratus ES/ESG is powered on and is on the ground.* Altitude is not reported. |
| On | ON | Stratus ES/ESG is powered on and responds to all Mode A/C/S interrogations, but altitude reporting is suppressed. |
*If Ground mode is detected while you’re in the air, press ALT or ON to override Ground mode and enter into Altitude or On mode. This disables automatic Ground mode.
To re-enable automatic Ground mode, press SBY. You will enter into Standby mode and clear the Ground mode override. Then, press ALT or ON to return to Altitude or On mode (with automatic Ground mode enabled).