What actually happens to your bag between check-in and the plane?

Rather more than most passengers imagine, and understanding the chain explains why bags go missing where they do.

The journey:

Check-in. A bag tag is printed carrying a ten-digit licence plate number and a barcode encoding the flight, destination and routing. This number, not your name, is what the system tracks.

Injection into the baggage system, where the bag joins a network of conveyors.

Screening. Every hold bag is screened, typically by multi-view X-ray or CT, which builds a three-dimensional image. Bags that cannot be cleared automatically go to progressively higher levels of inspection, ending with manual search — which is why a bag occasionally contains a notice that it was opened.

Sortation. Automated scanners read the barcode at multiple points and divert the bag toward the correct make-up area. Bags whose tags cannot be read — damaged, obscured, or badly attached — go to a manual encoding station, and this is a common failure point.

Loading. Bags are loaded into containers (ULDs) on wide-body aircraft, or loose into the hold on smaller ones, and positioned according to a load plan that controls the aircraft's weight and balance.

Reconciliation. Under security rules, hold baggage must generally be matched to a boarded passenger. If you check a bag and do not board, it must be found and removed — which is a genuine cause of departure delays.

Transfers are where most mishandling happens. A bag connecting between flights must be unloaded, re-sorted and reloaded within the connection time, and tight connections are the single largest cause of bags arriving separately.

Practical implications: remove old tags, which confuse scanners; put contact details inside the bag as well as outside; photograph the bag and keep the tag receipt; and allow generous connection time for checked luggage.