A row has started over whether a Eurowings flight was cancelled because the pilot was too scared to fly to Turkey.
Passengers were left stranded in Stuttgart on Saturday 22 July when flight 4U2904 from Stuttgart to Ankara was cancelled.
Eurowings issued a statement in the early hours on Sunday morning, saying: "Flight 4U2904 was annulled because one of the pilots called in sick.
"Because this happened at short notice, it was unfortunately not possible to activate a replacement pilot for this flight."
It is the first cancellation by the airline along that route this month following 55 successful flights, but passengers who had hoped to board the plane questioned the company statement.
According to Deutsche Welle, the brother of one of the passengers said that staff from Eurowings had said the flight was cancelled because the pilot was "afraid" of the ongoing diplomatic row between Berlin and Ankara.
Another passenger said a similar thing to the broadcaster ARD.
One activist wrote on the Eurowings Facebook page saying: ""It's high time to recognise that these measures are aimed not just at Turkey (which is bad enough) but Turkish people in the EU.
"Rise up and boycott companies like this."
Pilots who work for Lufthansa, Eurowings' parent company, are allowed to declare themselves "unfit to fly," if they feel they are unable to correctly discharge their duties.
Germany changed their travel advice for those hoping to visit Turkey last week following the jailing of journalists and human rights activists.
The foreign ministry in Germany summoned the Turkish ambassador after several activists were arrested including the citizen, Peter Steudtner.
Foreign Ministry spokesman Martin Schäfer said: "The Turkish government needs to immediately and directly hear the German government's outrage and incomprehension as well as its crystal-clear expectations in the case of Peter Steudtner and, this time, without diplomatic niceties."