Prince William is a very experienced helicopter pilot, but his frequent trips between Kensington Palace in London and his home at Anmer Hall in Norfolk by this mode of transport cause no end of concern for his grandmother, Queen Elizabeth.

William often takes the stick and flies himself, his wife Kate, and their children, Prince George, Princess Charlotte, and Prince Louis, the 115-mile distance between their two residences. The Sun on Sunday, via PEOPLE, reported that this habit has made Her Majesty the Queen "very worried" and "sleepless at night" with fear.

It has long been understood that heirs to the throne do not fly together due to unspeakable events that could result in tragedy, but the rule has been relaxed in the Cambridge family so that the family of five can spend more time together, "The Daily Mail" The Daily Mail reported.

The Queen has told her courtiers that she wants William to stop flying by himself, especially in bad weather, as helicopters are not the safest means of transport, the Sun on Sunday reported.

"It keeps the Queen awake at night and she is understandably very worried.

The article continued." She knows William is a competent pilot, but thinks it is not worth the risk to keep all five of them flying together, and she can't imagine what would happen. It would cause a constitutional crisis.

After his father, Prince Charles, William is second in line to the throne; his children George, Charlotte, and Louis are third, fourth, and fifth, respectively.

William is an accomplished pilot, completing his Royal Air Force training in 2010 and then serving as a search and rescue pilot for a number of years, often flying in severe weather conditions. He later also served as an ambulance pilot. William is often in charge of flying the family helicopter, but sometimes another pilot and crew fly it.

According to the Mirror, Her Majesty the Queen is still haunted by the 1967 helicopter accident in Newbury, Berkshire, which killed Air Commodore John Blount, the captain of Queen's Flight, and three others. No royal family members were on board this accident.

"It has completely put her off," a source told the Daily Mail. 'So she is very worried about William and his family.'

As a result of the 1967 crash, the Queen reportedly only uses helicopters when she has no other choice, especially hates winter, and will not board after dark. According to the Daily Mail, Her Majesty the Queen reportedly had "numerous conversations" with William and asked him to stop,

fearing that the accident would threaten his claim to the British throne.

"The Queen is worried that William, no matter how good a pilot he is, bad weather or an accident could strike at any moment," the Daily Mail reported." She thinks the future is bright with them at the helm after Charles, but if something happens to him and his family, it is hard to think about."

The Cambridges are reportedly looking for a home in Windsor to reduce the need for regular helicopter trips. Buckingham Palace "does not comment on private conversations" about this matter, according to PEOPLE magazine.