There has been an unprecedented increase in turbulence involving aircraft in Australia.
The Australian Transport Safety Bureau said turbulence doubled over the three-month period between October to December 2013, compared to the previous three months, significantly above the five year historical average.
Turbulence is the leading cause of in-flight injuries and an increase directly affects the safety of cabin passengers.
But the ATSB could not speculate as to why it was happening, according to Dr Stuart Godley head of the ATSB's Aviation Research Team.
"During the last five years there has been an increase in reporting, particularly from cabin crew, about an increase in turbulence, but we don't know why this is occurring," he said.
"Because they are weather-related, these events are cyclical.
"We're used to seeing more of them in summer, but this increase is unprecedented."
Turbulence is caused by the irregular movement of air and often cannot be seen.
When air masses with different speeds, direction or temperatures meet each other, turbulence is likely to occur.
While turbulence is normal and occurs frequently, it can be dangerous - especially for passengers not wearing seatbelts or carrying unsecured items.
That was the case for one passenger in November 2013 who sustained a serious head injury from a laptop computer that fell from an overhead locker during a turbulent flight to Sydney.
Another passenger was injured after being struck by an iPad.
Godley said passengers not wearing seatbelts are more likely to be seriously injured when turbulence hits.
"Serious head injuries can be sustained when a person hits the overhead panel where luggage is stored because they did not wear a seatbelt," he said.
"Cabin crew have had legs broken from walking around the cabin when turbulence hit," he said.
Clear air turbulence (CAT) can pose a great amount of danger as it cannot be detected and hit any time, which is exactly what happened when cabin crew were commencing a meal service during a flight from Cairns to Tokyo in 1996.
Passengers, crew and meal trolleys hit the ceiling of the aircraft and landed heavily, seriously injuring passengers who were not belted up.
Bone fractures, lacerations, neck and back strains, dislocated shoulders and shattered teeth were reported.
Four were admitted to hospital.
While nothing that extreme has been reported during the recent bout of increased turbulence, Goddard warns passengers to keep their seatbelts on in the off-chance it should happen.
Some areas of Australia are more prone to turbulence and Sydney has been a common spot for it to occur over the last summer, Goddard said.
"122 incidences of turbulence were recorded, 35 of which occurred on flights in to and out of Sydney, which seems to be a hotspot for turbulence," he said.
"Brisbane and the Gold Coast is another area which experiences a high amount."
- Sydney Morning Herald