What are the "panels" on the wingtips of the Panavia Tornado? I am wondering about the purpose of the panel marked with the number 156 in this picture:


The same black panel can be seen on the wingtips here:


And also here:


What purpose does this panel serve? It could be just a construction technique, but in that case why would they cut a hole in the larger panel just to cover it up with the smaller black one?
From another cutaway drawing:


  
    57: Wing tip antenna
  




Found here, but the original source is unknown.