I am travelling with Turkish Airlines, from Berlin to Istanbul, and I am allowed 30kg of luggage or check-in. However, in the booking it doesn't mention the number of luggage items that I am allowed. I tried calling the sales office but they put me on hold multiple times and the calls then randomly ended.
Therefore, I am curious if anyone knows any more about this situation?
Airlines generally use one of two models for checked baggage allowances - either a "piece" model or a "weight" model. Some airlines will use the same model for all flights, whilst others will use one model for some flights, and the other for other flights.
Under a "piece" model you are limited to a set number of pieces of checked baggage. Each piece will have a maximum weight, but the weight of one piece will not impact your allowance for any other piece. If your allowance was 2 pieces, each up to 23kg and one piece was 10kg, then the other piece would still be limited to 23kg.
With a piece model, excess baggage charges generally apply if you want to check more bags that your limit, OR if any of the bags are over the allowed per-bag weight.
Under a "weight" model, your allowance is based on the total weight of all of your bags - with no general limit to the number of bags that can be checked. In your example you have a 30kg limit, which would allow you to check a single bag weighing 30kg, OR one bag weighting 10kg and another weighing 20kg, OR three bags weighting 10kg each.
With a weight model, excess baggage charges generally only apply if your total weight is over the allowed weight.
Specifically for Turkish airlines, the use both "piece" and "weight" models depending on the region of the flight. You can find details of the regions for the piece model and the regions for the weight model on their website. An easier way to check is instead to use the baggage calculator available on their website which will tell you the exact model and limitations for a specific flight.
As you've stated, Berlin to Istanbul uses the "weight" model and allows 30kg of weight for Economy passengers, so you will be allowed have multiple bags, up to a total weight of 30kg.
(Note that the links to the TK website above include "traveling-with-pets" in the URL itself, however this appears to be an error as these links have nothing to do with traveling with pets. Anyone that's used the TK website in the past will know that issues like this are not uncommon!)
Good idea is to check with the airline. I could not find precise info on the website of Turkish Airlines, but they say that in case of code sharing the luggage allowance is determined by the company operating the flight. Therefore, in other terms you need to understand whether the flight will be operated by Turkish Airlines themselves or by one of their partners like Lufthansa. Airlines often combine both "piece" and "weight" models, meaning that the passenger is allowed to take luggage of certain maximum weight packed in a given number of pieces or less. See, for example, luggage allowances at Swiss.
