Centered Path is the second upgrade of Path 3 for the Monkey Ace in BTD6. It adds a new targeting option "Centered Path" that sends the Monkey Ace along a circular path along the center of the map. It doesn't matter where the Monkey Ace landing pad is for a Monkey Ace set to Centered Path; they will all loop around the same path, albeit different parts of the loop depending on timing at which the player changes the loop setting.
It costs $255 on Easy, $300 on Medium, $325 on Hard, and $360 on Impoppable.
Besides just being an extra flight option, this upgrade is substantially useful on maps such as Park Path or Pat's Pond, although it is exceptionally more useful on the former due to how much more map coverage is utilized.
This upgrade is one of many upgrades spelled in American English. What makes this fact interesting is that Ninja Kiwi is a New Zealand company, despite primarily using British English, especially when "-re" words are normally spelled as "-re" in New Zealand instead of the American "-er" (e.g. "meter" for "metre", or in this case, "center" for "centre").
The name of the upgrade icon for Centered Path is "FlightOrdersUpgradeIcon.png". It was likely that the upgrade name "Flight Orders" was scrapped in favor of the current name.