Germany is one of Europe’s worst enforcers of air safety rules, trailing only Greece in failing to comply with basic requirements to protect passengers, according to a confidential report by Europe’s top aviation watchdog.

German regulators failed to uphold or enforce European Union air safety rules in more than 15 sensitive areas, according to the report, dated March 7 and reviewed by The Wall Street Journal. The country—Europe’s biggest economy and home to some of the continent’s most-traveled air hubs, including Frankfurt...