The 230-page plan contained not only instructions on what to do in case of a natural disaster and air accidents, but also provided detailed information on how to act during a terrorist attack, bomb threat and hostage situation, Deutsche Welle wrote.
Moreover, the document contained details about where passengers should gather in case of an emergency.
The secret plan was developed for the airport's stuff only, but has been publicly available for over five months.
Airport representatives have yet to comment on the issue. However, a number of German journalists found the incident shocking. Taking into account the recent bombings at the airport in Brussels and the fact that the Cologne/Bonn airport is viewed as a possible target of Daesh terrorists, the situation is extremely shocking, express.de wrote.