A row's broken out after it looked like Prince William used an RAF helicopter to land at his girlfriend's house, and to go to a party with his brother.
The Ministry of Defence has said the trips were all part of an official training exercise.
But some people are angry as they think it's a waste of money and not a proper use of military equipment.
The prince touched the Chinook helicopter down in a field belonging to his girlfriend's parents in Berkshire.
He was in the field for about 20 seconds, but no-one got on or off the helicopter.
It's also been revealed that on the day he graduated, he flew from an airbase to London where he picked up his brother Harry, and they then flew to the Isle of Wight.
Officials say this was because he has to fly over water as part of his training, but it also looks like William and Harry were there for a party thrown by one of their friends that weekend.
In a statement, the officials said pilots often practise landing in fields and small spaces to prepare them for flying in war zones.
But other flying experts have said these landings was a waste of expensive training, especially when military equipment is needed for the British forces fighting in Iraq and Afghanistan.
The Prince has won his 'wings'
Prince William won his 'wings', making him qualified to fly military planes, on April 11, after four months training with the Royal Air Force (RAF).
William's time with the RAF and Navy are to help prepare him to become head of the armed forces, if he becomes king.