FAA
This is a compilation of what I could find relevant to the question. Feel free to come up with corrections if I missed anything (I'm an EASA FCL guy)
Co-pilot Landing Currency:
- Part 61: 3 takeoff/landings in previous 12 months (61.55)
- Part 135: no requirements other than those in part 61 (above)
- Part 121: 3 takeoff/landings in previous 90 days (121.439)
Co-pilot Instrument Currency:
- Part 61: no requirements for SIC
- Part 135: 135.245 requires that SIC's must meet part 61 PIC instrument currency requirements in 61.57(c) (see below)
- Part 121: recurrent flight training every 12 months, including at least 1 ILS approach to minimums
Following is the list of relevant FARs :
§ 61.55 Second-in-command qualifications
(b) Except as provided in paragraph (d) of this section, no person may serve as a second in
command of an aircraft type certificated for more than one required
pilot flight crewmember or in operations requiring a second in command
unless that person has within the previous 12 calendar months:
(2)
Except as provided in paragraph (e) of this section, performed and
logged pilot time in the type of aircraft or in a flight simulator
that represents the type of aircraft for which second-in-command
privileges are requested, which includes --
(i) Three takeoffs and
three landings to a full stop as the sole manipulator of the flight
controls;
(d) This section does not apply to a person who is:[...operating part
121,125,135...]
(e) The holder of a commercial or airline transport
pilot certificate with the appropriate category and class rating is
not required to meet the requirements of paragraph (b)(2) of this
section, provided the pilot: [... is not carrying paying
passengers...]
§ 61.57 Recent flight experience: Pilot in command.
(a) General experience.
(1) Except as provided in paragraph (e) of this section, no person may
act as a pilot in command of an aircraft carrying passengers or of an
aircraft certificated for more than one pilot flight crewmember unless
that person has made at least three takeoffs and three landings within
the preceding 90 days, [...]
(c) Instrument experience.
Except as provided in paragraph (e) of this section, no person may act
as pilot in command under IFR or in weather conditions less than the
minimums prescribed for VFR, unless within the preceding 6 calendar
months, that person has: [...6 approaches, holdings, intercepting
&tracking course...]
§ 135.245 Second in command qualifications
(a) [...] no certificate holder may use any person, nor may any person
serve, as second in command of an aircraft unless that person holds at
least a commercial pilot certificate with appropriate category and
class ratings and an instrument rating. For flight under IFR, that
person must meet the recent instrument experience requirements of part
61 of this chapter.
This is an excerpt from an FAA Legal Interpretation concerning 135.245:
Next, unlike a PIC, an SIC's qualification to operate an aircraft
under IFR in part 135 service is not dependent on compliance with §
135.297. Rather, § 135.245 sets the qualifications for pilots serving as SIC in part 135 operations. It states that a pilot must meet the
instrument experience requirements of part 61 to serve as SIC in
flight under IFR. Section 61.57(c) sets out the recent instrument
flight experience requirements which include, among other things, six
instrument approaches within the previous six months. See Legal
Interpretation to Gerald Naekel, from Donald P. Byrne, Assistant Chief
Counsel Regulations and Enforcement Division (June 18, 1991) (noting
that although the section title refers to pilots in command, the
instrument recency requirements of that section apply to SICs).
§ 135.247 Pilot qualifications: Recent experience.
(a) No certificate holder may use any person, nor may any person
serve, as pilot in command of an aircraft carrying passengers unless,
within the preceding 90 days, that person has—
(1) Made three takeoffs and three landings as the sole manipulator of
the flight controls in an aircraft of the same category and class and,
if a type rating is required, of the same type in which that person is
to serve; or [...]
§ Part 121.433 Training required
(c)Recurrent training. (1) No certificate holder may use any person
nor may any person serve as a required crewmember on an airplane
unless, within the preceding 12 calendar months -- (i) For flight
crewmembers, he has satisfactorily completed recurrent ground and
flight training for that airplane and crewmember position and a flight
check as applicable;
§ Part 121.439 Pilot qualifications: Recent experience.
(a) No certificate holder may use any person nor may any person serve
as a required pilot flight crewmember, unless within the preceding 90
days, that person has made at least three takeoffs and landings in the
type airplane in which that person is to serve.
EASA
FCL is very clear about it: PIC and co-pilot both need to be landing current. If holding an IR rating then specific night currency is not required. No instrument currency is required as long as the IR is valid.
FCL.060 Recent experience
(b) Aeroplanes, helicopters, powered-lift, airships and sailplanes. A
pilot shall not operate an aircraft in commercial air transport or
carrying passengers:
(1) as PIC or co-pilot unless he/she has carried out, in the preceding
90 days, at least 3 take-offs, approaches and landings in an aircraft
of the same type or class or an FFS representing that type or class.
The 3 take-offs and landings shall be performed in either multi-pilot
or single-pilot operations, depending on the privileges held by the
pilot; and
(2) as PIC at night unless he/she:
(i) has carried out in the preceding 90 days at least 1 take-off,
approach and landing at night as a pilot flying in an aircraft of the
same type or class or an FFS representing that type or class; or
(ii) holds an IR;