How does 1.6 million euros worth of gold bars go missing on a plane?

According to news.com.au, Air France says it has filed a complaint after gold bars worth about 1.6 million euros ($A2.2 million) were stolen from a plane bound for Zurich from Paris.

"We hope the investigations will allow us to quickly determine the sequence of events and identify those responsible," a spokesman said.

The gold bars, weighing about 50kg, were placed inside the plane at Paris's Charles-de-Gaulle airport last Thursday by employees of the US security firm Brink's.

It is as yet unclear how the theft happened, but an airport source said the robbers had ‘probably made use of airport accomplices’.

This kind of shipment takes place every day, and Brink's employees always stay on the tarmac until the plane takes off.