A China Eastern Airlines flight from the Anhui city of Anqing to Shanghai was delayed for nearly two hours on Tuesday after workers found evidence which suggested that one of the passengers had attempted to throw coins into the plane’s engine.

That evidence was two coins, one found near the edge of an engine and the other discovered on the ground nearby.

Afterward, police checked over surveillance tape and were unable to find any sign of coin throwing. Later, an officer boarded the plane and asked if anyone had tried to chuck coins into the plane’s engine, promising that if they spoke up they would not be punished. However, no one replied.

Twice before, elderly Chinese travelers have been caught throwing coins in a plane’s engine in a bid to earn some good luck towards having a safe flight.

In the first incident, an 80-year-old woman chucked 1.7 yuan into the engine of a China Southern Airline’s plane at Shanghai’s Pudong airport, causing a five-hour delay and a million yuan in damages. Despite this, the woman was not charged with any crime due to her old age.