Marie Claire has reported in the past that Prince William's use of helicopters as a means of transportation, especially with his wife Kate Middleton and their three children, has infuriated the queen. While many royals, including the queen herself, were away on their annual summer vacation, the five Cambridges (and their puppy Aura) left Kensington Palace on Monday and boarded a helicopter for their vacation. According to one royal expert, this was in defiance of the queen's orders, and William and Kate will likely be summoned to speak to Her Majesty the Queen about their decision once the Cambridges return from their vacation.

Neal Schon quotes an earlier report in the Daily Mail, claiming that the Queen "spoke to William quite strongly about the matter and urged him to give up helicopter flights altogether" for safety reasons, the Express reports.

"Prince William and Princess Catherine appear to have defied orders from the queen," Sean says. 'This week they were seen boarding a helicopter in the back area of Kensington Palace and enjoying a short vacation. The Queen was concerned about this. For safety reasons, it is a royal rule that they travel in separate planes. Apparently, the Queen had spoken firmly to William about this. However, this is the only time it must have slipped Prince William's mind. When Prince William and Princess Catherine return from their short vacation, they will be summoned to Windsor to explain the cause of their actions."

According to the Express, some reports claim that William did, in fact, ask his grandmother for permission before boarding the plane. The royal protocol of not allowing members of the royal family, especially the two heirs, to fly together, as Prince William and his eldest son, Prince George, do, makes sense for the obvious reason of protecting the future of the monarchy. While this rule can currently be overridden to some extent with the Queen's permission, just three years after George turns 12, he will no longer be able to fly with his father without exception (and without Her Majesty's permission).

"To protect the heir to the throne, the rule is that no more than two heirs to the throne can travel on the same plane," the Express reported. If a plane carrying more than one heir to the throne were to crash, the future of the monarchy would quickly become unstable. George is now treated like the rest of the royal family and can travel with his family with the Queen's permission, but at age 12 he must fly separately from his father. William is not allowed to travel with Prince Charles, and the Prince of Wales is also restricted from traveling with his mother."

The Queen's permission to travel with the Prince of Wales is also restricted.

Although plane crashes are thankfully less common today, the Queen's husband, Prince Philip, lost his sister, Princess Cecile, in a plane crash in 1937. The Queen's uncle, Prince George, Duke of Kent, died in a plane crash in 1942, and the Queen's cousin, Prince William, Duke of Gloucester, died while competing in an air show in 1972.