Interesting, there is a boolean for if the player is falling (i.e. in the air).
Or, even neater, somewhere after the player presses the dash key, use a ‘Switch on Movement Mode’ to modify the logic for each mode.
Then I’d instantly switch the character movement mode to flying. Have the flying movement mode set up as suits U with regard to gravity, acceleration, top speed etc. (run on a timeline or timer in the same way U did the for the walking movement mode).
If U set the walking/flying modes’ acceleration very high, the boost will seem instant.
U could use “Launch Character” too, and to stop just apply a counter force when Ur dash time is up (see the ‘anti skid’ snippet above and apply the counter force in the negative direction.
I don’t have the editor in front of me right now, but I’m fairly sure there is a ‘Cancel Movement’. or ‘Cancel All Velocity’ node U could apply once to zero all velocity right before U begin the launch or dash acceleration.