I know that priests of any Church sui iuris can concelebrate at each other’s respective liturgies, but in order for a priest to celebrate a particular rite, he must have the appropriate faculties. How does this work for deacons? Can a Ukrainian Greek Catholic deacon fulfill the role of the deacon in a TLM solemn mass? Can a Latin deacon fulfill the role of a deacon at a Byzantine divine liturgy? Or would appropriate faculties be required as in the case of a priest celebrating the liturgy.
There is a Roman Catholic deacon who regularly serves at the Ruthenian parish I attend. I don’t know if there’s a matter of actual granting of faculties involved, but I believe the permission of the bishops is required.
Initially St. John Cantius applied for Latin as well as Byzantine expression, which I believe included their deacons. They had to abandon that effort due to jurisdiction. If only a single bishop were involved, it would probably have been no problem.
Deacon Ed, a member of this forum who has not been active since last year, is a bi-ritual deacon. (But you probably know that.) I don’t know if any of his old posts would have the information you are looking for.
If it’s something that happens only once, or on rare occasions, no permission is needed, but if it happens regularly, then he needs to have faculties.
Latin Catholic deacons may assist or preside and eastern Catholic deacons may assist but not preside. It is possible for a deacon to assist in the liturgy of another ritual church.
For the 1962 Extraordinary Form, deacons can serve as Deacon or Sub-deacon for Solemn Mass.
Presiding by a Latin Deacon: Sunday rite in the absence of a priest, weddings, funerals, exposition, blessings, exorcisms, presentation of the Creed and Lord’s Prayer, Liturgy of the Hours (Divine Praises).
Per the CCEO the eastern deacon cannot baptize ordinarily, may not witness marriages, and may not do funeral rites. ( The deacon in the Byzantine tradition does acts only as a layman in the Divine Praises.) Also, unlike the Latin deacon, the oriental deacon is forbidden to assume public offices that require the use of civil power (CCEO canon 383), and he needs more permission to perform certain specific worldly occupations than the Latin deacon.