ruralsub123 -- A little more info would be helpful.
-- As a 5/1 AUX, you earn leave only while working the AUX. Probably just extra $ when filling in on the releif day.
"does my manager assign me as the primary of both routes"?
-- If you are referring to the Matrix, you can only be primary on one route. ( #5 on the Matrix check list - a relief carrier can only hold one primanry position -- which would be filling in for your regular carrier )
"Then after 90 days I fill out a form 50 changing to leave earning status?
-- Going with your regular rural carrier will be out for an extended period of time. You essentially become the regular for that route. Manglement will have to figure out how to cover your AUX.
-- Page 50 of the current contract: When an RCA....is working the route...where the carrier is on extended leave, the employee is entitled to work at least the evaluated hours of the assigned route and then may be replaced to avoid payment of overtime or additional overtime. ( stop by your AUX once in a while to ensure it is being kept up to date )
-- You won't be filling out any Form 50 after 90 days of filling in for your regular. The District office does that ( or used to -- anyone?? ). Sounds as if your PM does not know what a Form 50 is -- scary!