15 C.F.R. § 998.54

Professional mariners serving in a position aboard a NOAA ship to which they have been temporarily promoted pursuant to 5 CFR 335.102(f) shall be paid the difference between their temporary and permanent rates of pay for leave accrued while serving in the temporary promotion position unless:

(a) The professional mariner uses the leave before returning to their permanent position; or

(b) The professional mariner is permanently promoted to the higher position without further competition.