“Sent to airline” means China Post has given the parcel to airline company. It does NOT necessarily mean the parcel has been on plane.
The ‘sent to airline’ status will stuck for long time until the parcel arrives an airport which has scanning service. This might take 2 to 4 weeks in regular season and 4 to 6 weeks in holiday season. Normally the parcel should have arrived destination country when new status shows up.
If over 30 days (or 45 days in rush season) after “sent to airline” and you still do not receive the parcel, then you should be cautious. The parcel might be lost or seriously delayed somewhere outside China. You should open a dispute to claim your money back from seller. check the post How to claim refund for lost parcel?