The "Entfernungspauschale" basically "commuting deduction" is 0,30€ per km distance from work, the airport. BOTH WAYS! This is ONLY the case for aircrews, unless it's one way. The maximum deduction you can get is 4700€ per year and you can either chose to get it in form of (1.) a tax return or (2.) in form of a "Freibetrag" basically a monthly tax exemption.
In case of (1.) you will need to maintain a "Fahrtenbuch". Basically a logbook (including gas receipts) of EVERY ride you make. No matter if private or work related.
No Fahrtenbuch needed for (1), just a roster. There are companies that automatically work through your roster and give you a listing of km and tax deductible expenses (for being away from home) depending on which country you flew to. Not connected, but i use easydutyplan.de for that service.