Traveller's Checks: Things that go bump in the flight

It was after the fifth successive roller coaster flight last spring that I wondered if I was developing a fear of flying. After years of happily hopping on planes I was unnerved by the unrelenting turbulence I was now experiencing on every flight. But there was a connection: the five flights were within the tropics, the zone within 23.5 degrees north and south of the equator.

It was after the fifth successive roller coaster flight last spring that I wondered if I was developing a fear of flying. After years of happily hopping on planes I was unnerved by the unrelenting turbulence I was now experiencing on every flight. But there was a connection: the five flights were within the tropics, the zone within 23.5 degrees north and south of the equator.

Simply put, turbulence is a lack of smoothness in the air immediately around the aircraft. In the northern hemisphere we tend to encounter turbulence related to the jet stream when flying to the United States. In the tropics turbulence tends to be much more widespread and aircraft frequently encounter convection turbulence, caused by the immense heat generated in tropical zones.

The main culprit is a mass of air called the inter-tropical convergence, an area of thundery showers, moving north and south of the equator, where warm air collides with the north-east trade winds. The convergence extends pretty much worldwide so is difficult to avoid for those heading north south from the UK to South Africa or to Singapore and Australia. In addition, from April to August the monsoon thunderstorms hit Asia, while flights in the region can also expect to encounter the easterly jet stream, which heads from India to the Arabian peninsula and is associated with clear-air turbulence, which aircraft radar cannot spot. As if that were not enough, hot rising ground air can make the few thousand feet around take-off and landing a bumpy affair.

"Turbulence is usually associated with huge cumulonimbus clouds that in the tropics can climb up to 45,000ft," said Nick Ricketts, aviation forecaster for the Meteorological Office. Yet aircraft routinely avoid the worst areas, he added. "Within these clouds it can get extremely turbulent. Thunderstorms can be picked up on the aircraft radar and pilots will always fly around or over them but it can still get quite bumpy."

It is extremely unlikely that turbulence would endanger modern aircraft and there has been no recorded incident of a plane being brought down by bad weather since the 1960s. "It would be wrong to say it's impossible because it has happened before when we knew less about meteorological conditions than we do today," said Captain Paul Douglas, flight technical and training general manager for British Airways. "The opportunity for thunderstorms to become much taller is greater in the tropics but this also means they are more easily defined. We just wouldn't fly our passengers through a thunderstorm. The feeling of turbulence can be exaggerated in comparison with what is going on outside. It can be an irritant, like driving over cobblestones, but it is innocuous.

"In 20 years of flying I've never had an experience where I thought turbulence was potentially perilous. New aircraft are deliberately flown through this kind of weather in testing and they come out the other end without any bother."