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The spektrum documentaion and Youtube videos only show 3 modes for configuring AS3X / SAFE. This means that where we want the safety for one of those Modes to be OFF we are then down to 2 Modes. The following creates another Mode(s) that utilises the Heading function to keep a squirrely model dead straight on its take off run. 

This is How To Set up 4 Modes, both on the Tx and Rx, so that Mode 4 can be used for holding the rudder straight down the runway.

I used a NX8+ Tx and a AR630 Rx to set this up.

The following assumes you have done a Rx Forward Programming > Factory Reset and run through the usual Forward Programming setup routine such as Orientation, assigning a gain knob etc.

This table is a summary what we are going to setup for each of the 4 flight modes:-

On the NX8+ configure a Flight Mode Matrix to merge two physical switches into one output channel with 4 distinct values per the above table

Follow these steps on the NX8+:-

Step 1: Configure the Transmitter Flight Mode Matrix

1. Press the roller to open the menu, go to System Setup, and select Flight Mode Setup.
2. Change Switch 1 to your primary 3-position switch (e.g., Switch B).
3. Change Switch 2 to your override 2-position switch (e.g., Switch A).
4. Scroll down to Next. You will see a grid mapping the switch combinations to FM 1, FM 2, FM 3, etc.
5. Assign them so flipping Switch A acts as an override or shifts you into a 4th mode. For example:
   • Switch A Pos 0: Switch B gives you FM 1, FM 2, FM 3
   • Switch A Pos 1: Overrides everything to FM 4

You will probably find that SWA Pos 1 duplicates some of the Pos 0 Modes. We don’t want this. To ensure that SWA Pos 1 only activates FM4 then adjust all 3 Modes to FM4 on the right of the screen Like this:-

Step 2: Route Flight Modes to a Channel

Now we need to send these 4 transmitter modes out on a single servo channel (e.g., Aux 6).

1. In System Setup, go to Channel Assign.
2. Click Next to go to the Channel Input Config screen.
3. Find an open channel, like Aux 6, click it, and change its input to FMode.
4. Make sure SWA and SWB are not assigned to any other channel. If they are then change their Input value to Inh.
5. Back out to the main Model screen, roll over to the Monitor screen, and flip the Flight Mode switches. You should see the Aux 6 bar move between 4 positions as you click through your 4 modes. Note that FM4 takes the channel to +125. This is ok and what the Rx is expecting.

Step 3: Map the Receiver in Forward Programming

With the transmitter switched on:-

1. Power on the receiver. Go to the NX8+ main menu and select Forward Programming.
2. Go to Gyro Settings > F-Mode Setup.
3. Select FM Channel and assign it to the channel you just used (e.g., Aux 6).
4. Cycle through your physical switches on the NX8+. Look closely at the Forward Programming screen. You will see it track Flight Mode 1, 2, 3, and 4.
5. From there go back into AS3X Settings and SAFE Settings to assign your Off, AS3X+, Self-Level, and Heading Hold attributes to each of those 4 active states per the above table.
6. For Mode 4, to activate the Heading Hold menu, AS3X must be set to Act in F-Mode Setup. Set SAFE to Inh.

In the Heading menu set YAW to 40%. There will be a warning message. Ignore it.

At The Runway

1. Taxi out in your preferred taxi mode (e.g, Mode 1: OFF).
2. Line up in to wind on the runway and let the plane come to a complete stop.
3. Flip to Mode 4. (The receiver instantly captures the heading with the model pointing right down the runway).
4. Advance the throttle smoothly. Do not touch the rudder stick. The Heading Hold will fight any engine torque or crosswind and keep the nose straight.
5. Apply gentle manual elevator to raise the tail, build speed, and rotate into the air. The rudder lock is maintained until either a) the stick is moved or b) another Mode is selected. Moving another control surface e.g. Elevator will not release the Rudder lock.
6. As soon as the model is airbourne, flip SWA back to Pos 0. SWB will now be in control. 
7. Good practice is to have preset SWB to your preferred airbourne flying Mode before taking off e.g. Mode 2 AS3X. This will save fumbling around and be a relaxed transition out of Mode 4.

Author: Mark Bennett

Date: October 2026