Also, if you #1 power tray is full I do not believe new power icons will automatically populate any other open trays.
If you only have 1 tray, click on the ' + ' icon at the top, right of your tray. That will open a 2nd tray above the 1st. You can keep opening more trays that way.
You can locate all of your powers by clicking on 'Power' in the tool bar above you powers tray. Flight will be in a group in the right column of powers, scroll down to see it, then click and drag to you power tray.