Interesting--UA can check through to G3, but G3 can't to UA:
Results from ExpertFlyer.com
Code:
Interline Agreements:
Flying G3
E-Ticket Interline Agreements
AF AR DL IB KL QR
Paper Ticket and Baggage Interline Agreements
MAY ISSUE TICKETS INCLUDING
AF AR AT DL EQ H2 IB KL NH QR UX 2K 7I
MAY CHECK BAGGAGE TO
AA AF AR AT CA CI DL EQ EY H2 IB KL NH QR
UX 2K
ETA: well, if you search KVS, you get a different answer:
[KVS Availability Tool 7.4.2 - Reference: Interline Agreements [IET]: G3]
Code:
ELECTRONIC INTERLINE CARRIER AGREEMENTS-G3
INTERLINE CARRIER CODES
AA - AC - AF - AM - AR - AV - AZ - BA - CA - CI
CM - CU - DE - DL - DT - EK - EQ - ET - EY - HR
H2 - IB - JL - KE - KL - LH - LR - LX - LY - MU
NH - OA - PY - QF - QR - SA - SQ - SU - S4 - TA
TG - TK - TP - TX - T0 - UA - UN - US - UX - VR
YO - 7I