ALMOST EVERY airline flight these days, at least over the USA, seems to entail an encounter with turbulence. This is usually akin to driving over cobblestones or, sometimes, potholes, but occasionally it is like driving off a cliff.

On 19 July, an American Airlines Airbus A300 hit clear-air turbulence en route from Miami to San Juan, Puerto Rico, injuring at least 26 passengers and crew. It was the latest in a series of encounters which has the US Federal Aviation Administration and National Transportation Safety Board (NTSB) reviewing past incidents.

Turbulence has not been viewed as a serious problem. Although it is a significant cause of airline injuries, it seldom kills passengers. NTSB records list 25 clear-air turbulence incidents between 1989 and 1994, an average of about four a year. The worst year was 1989, with 56 injuries, eight of them serious, in five incidents. Between 1990 and 1994, there were only 27 injuries caused by turbulence, but two fatalities, the NTSB says.

According to Flight International calculations there have been at least seven turbulence incidents involving US airlines already this year, and at least 50 passengers and crew have been injured, some seriously. This was enough to prompt the FAA, in early July to remind passengers to wear seat belts at all times.

New rules on seat-belt use are likely to emerge from the FAA and NTSB reviews, but technology may, in the end, be called upon to provide a more reliable solution. So far there are few signs of a major effort to develop a sensor able to locate difficult-to-detect clear-air turbulence - a phenomenon, which may yet prove to be what wind shear once was - an underestimated threat to airline safety.

Source: Flight International