As a First Officer at Gulf Air the limitations on;
- operating as Pilot Flying in Low Vis conditions (take-off/approach/landing)?
Unless the Captain is incapacitated or is a TRI or TRE, any takeoff or landing with a cloud base below 500' AGL and/or Vis less than 1500m is Captain only takeoff/landing.
- calling for and executing a Rejected Take-off?
Captain only.
- landing/take-off in adverse weather conditions, eg. x-wind/contaminated
runways/wind shear/etc?
Unless the Captain is incapacitated or is a TRI or TRE, surface Cross-wind component shall not exceed 15 knots. Runway shall not be contaminated. There is no published restriction on FO's conducting approaches where windshear has been reported.
- challenging/demanding approaches like circling approaches/Cat C airfields?
Our previous edition of the Operations Manual had a restriction on FO's conducting takeoffs and landings at Cat C airfields. This verbage is now absent, with the exception of one airfield briefing (Kathmandu) where the Captain must conduct the takeoff or landing (unless, incapacitated, of course). Having said that I expect that most Captains still apply the previous interpretation.
- taxiing the aircraft?
No, unless Captain is incapacitated.
- signing the Tech log?
Not the Tech Log, but the First Officer signs the Aircraft Cabin Log.