In my book they give some German sentences with the respective English translations, this is to explain the use of als and wenn, but that is not what is bothering me. I am not sure why they are using the German Perfekt, in what seems to require the Präteritum.
Als ich am Bahnhof angekommen bin, haben meine Freunde auf mich gewartet = When I arrived to the station, my friends waited for me
Wenn (Jedes Mal) sie sich getroffen haben, waren sie glücklich vs. When they met, they were happy
Wenn (Jedes Mal) er nach Amerika geflogen ist, haben ihn seine Freunde am Flughafen abgeholt = When (Every time) he travelled to America , his friends checked him up at the airport
In order to have those English sentences, I would have expected the German sentences to be:
Als ich am Bahnhof ankam, warteten meine Freunde auf mich = When I arrived to the station, my friends waited for me
Wenn (Jedes Mal) sie sich trafen, waren sie glücklich = When they met, they were happy
Wenn (Jedes Mal) er nach Amerika flog, holten ihn seine Freunde am Flughafen ab = When (Every time) he travelled to America , his friends picked him up at the airport
If I had been given only the German sentences, I would have thought they were incorrect, because they translate to bad English.