Practical Use of TO TO Waypoints

[MoppleTheWhale42]

Hi,

to my understanding the difference between FROM TO and TO TO waypoints is the information I get in the CDU Nav/Attributes page: In case of TO TO the CDU provides the course between the two waypoints (not the course between the current location of the airplane and the next waypoint).

So far, so good. But, what is the practical use of TO TO waypoints? I cannot figure out when to use TO TO waypoints.

Thank you & kind reagrds

Mopple

[MirabelleBenou]

I'm quite interrested in the answer also

[jaylw314]

A hypothetical example might be an instruction to stay west of the line between waypoint 4 and waypoint 5 (for deconfliction or politics, perhaps).  If want to be in MISSION mode instead of FLT PLN mode for whatever reason, you can change the attribute of waypoint 5 to be TO-TO.  Now you can just turn the CRS to vaguely the correct heading, and if you keep the needle on the right, you are guaranteed by the GPS database to be west of that line.  OTOH, dialing in the expected course on the CRS while in TO-FROM mode requires you to be precise with the dial, and it doesn't take into account any compass or instrument errors.  Even if you can dial in the precision of the CRS needle to within 1 degree, that's a mile of error if the waypoints are 60 miles apart.

If you REALLY need GPS precision between two waypoints, TO-TO is the way to go.  Of course, in most cases, FLT PLN would be the easier answer, but it amounts to the same thing

 

Edited December 17, 2023 by jaylw314

[ASAP]

On 12/17/2023 at 5:13 AM, MoppleTheWhale42 said:

So far, so good. But, what is the practical use of TO TO waypoints? I cannot figure out when to use TO TO waypoints.

If you want to fly an exact ground track without deviating off the "black line" you can use TO TO waypoints. In practice though they are not often used. My understanding is that the setting is generally left to FROM-TO in most cases.

Edited December 18, 2023 by ASAP