Flybe said the pilot had experience of flying a number of different passenger planes
A pilot with 30 years' experience told passengers on a flight to Paris that he was returning to the UK because he was not qualified to land in foggy weather.
Flybe flight BE1431 from Cardiff was approaching Charles De Gaulle airport on Tuesday when the captain made the announcement over the tannoy.
A Flybe spokeswoman said there had been dense fog in Paris and the company stood by the pilot's decision "100%".
The 62 passengers were put on the next flight to Paris or offered a refund.
The Flybe pilot concerned has 30 years' commercial aviation experience flying a number of different passenger aircraft types, said the Flybe spokeswoman.
"He has relatively recently transferred his 'type-rating' from a Bombardier Q300 to a Bombardier Q400 and has not yet completed the requisite low-visibility training to complete a landing in conditions such as the dense fog experienced in Paris Charles de Gaulle," she said.
"The captain therefore quite correctly turned the aircraft around and returned to Cardiff, a decision which the company stands by 100%.
"Aviation is the most highly regulated form of public transport in the United Kingdom. As a result, technical situations like these arise where a pilot with 30 years experience correctly abides by regulatory rules.
"At no point was passenger safety compromised."
Flybe added that when the pilot took off from Cardiff, the weather at Paris Charles De Gaulle was clear.
Ronan Boyle, from Ballycastle in Northern Ireland, said he was a passenger on the flight, heading for a conference on rural retailing.
He said: "Everyone was totally shocked when he said he couldn't land in the fog, it caused a bit of a panic as we never knew what was going on and thought it was a little unusual. A lot of people feared for the worst."
The Civil Aviation Authority described the incident as "quite unusual but probably not unheard of".
"I guess he thought when he initially took off that conditions would be suitable for him to land," said a spokesman.
"There are different classifications of aircraft and when an aircraft is updated, pilots who have flown an older version have to completely retrain.
"There can be significant differences in terms of how an aircraft is operated.
"Different climatic conditions like fog require a certain level of skill and he probably didn't have the level of training required for this particular aircraft."