But passengers will not be able to use miles accrued through a code-share flight until sometime in the first three months of next year.

In particular, Swissair said, the airlines could operate many more code-share flights.

With the introduction of airline alliances and code-share flights, frequent-flyer programs are often extended to allow benefits to be used across partner airlines.

The carriers also said they would limit the number of code-share flights under the alliance to 650 per two-carrier combination in the first year.

More code-share flights are planned, the airlines said.

Please use my experience to warn other travellers to be sharp-eyed about possible code-share flights and the challenges they can present.

The code-share flights are sold on a reciprocal basis and operated under the relevant airline's own flight number.

Lufthansa sells more than 15,000 code-share flights a week as its own, through agreements with 36 other airlines.

In many cases, travelers can accrue and redeem miles on code-share flights.

Spotting a code-share flight online is relatively easy.