Added:
You may look at:
Business Class - airberlin.com
To find a list of Lounges that you can use with an AB BP and QF/Oneworld Status.
Never had an issue with my QF-Status.
Just my Experiences:
TXL: You can use the BA or the AF Lounge. Both are landside in the central area. BA is slightly better. Views are the same (AF is one floor above BA).
Remember to leave the lounges in time, as you have to clear security before the flight.
The AF Lounge can be used if you depart late. The BA lounge closes after the last BA flight has left. So for my usual sleeper flight back home I have no choice (better than nothing). My clear choice goes to the BA Lounge.
HAM: Airport Lounge is very convenient just after security control.
NUE: Unmanned Entrance - you have to get a Lounge Code at the Checkin or Ticket-Desk.
MUC: Bad Lounge Situation. AB flies from T1A, but there is no lounge in T1A.
You can use the Airport (Atlantic) Lounge (T1A) and the BA Galleries Lounge (T1B).
There are two connecting corridors in the whole T1: One for Schengen and one for Non-Schengen.
Both Lounges are in Non-Schengen. The only place where you can get from Schengen to Non-Schengen and vice versa is at T1C!
So the most convenient way: Clear Security at T1C. Do not forget to ask if the "Transfer Passport Control" in T1C is open.
Use the Lounge. The go upstairs show your passport and walk to T1A. No extra security needed.
If you find yourself in T1A and want to use the Lounge just go upstairs to the Connecting Corridor and walk to T1C. Use the Passport Control there and go downstairs into the Lounge. If the "Transfer Passport Control" is open, you can do that in under 10 Minutes walking.
I rate the BA Lounge in T1C much better, but they have sometimes quite rude Lounge dragons. I had quite an unpleasant experience - the dragon was rude and I was only let in after I insisted that she called the supervisor.
The way to the Lounge is easy. Just enter T1B, tell the BP and Passport Control that you want to use the Lounge.
Then you have two options, which are both not good:
Long way without security Check: Go to T1C --> Transfer Passport Control -> Go back to T1A
Shorter Distance with security Check: Go landside (Follow the Exit Signts) --> Clear Passport Control --> Walk landside to T1A --> Clear Security again.
But to be fair: If you are flying with the dark side in T2 and have a remote gate the walking distance can be worse than with the Oneworld T1 Layout.
VIE: Very convenient Airport Lounges (One Schengen and one Non-Schengen).
DUS: Airport Lounge (the former BA Terrace).