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Turbulence could be making a more serious comeback in air travel

Crikey, 10 October 2017
One of the worst things about flying before the jet age began on a large scale in the late ’50s was turbulence, and resulting air sickness. But there are warnings, as well as some statistical claims, that things are getting rougher than before, despite the apparent smoothness of jet travel that has long been taken for granted by generations of air travellers. This week’s “return to your seat and buckle up” contribution to the genre comes from America’s ABC. It is based on an article in Geophysical Research Letters journal, and as is often the case, the general news story has a high tease-to-factual-content ratio that makes it less than useful to those of us who want to know what it is really about and how it might affect them.

The article is an analysis as to how increased upper atmosphere turbulence attributable to climate change is potentially lifting the risk of clear-air turbulence, or CAT. CAT first came to the attention of air travellers after the shift to faster, higher flying jets, which operated where the propeller-driven aircraft of old couldn’t venture.

The days of a Lockheed Electra or Vickers Viscount being full of passengers chundering into airsick bags while bouncing around for more than an hour below the clouds between Sydney and Melbourne were replaced by the velvet-like ride of higher-reaching 727s.

However, at infrequent intervals, the “CAT’s claws” (as headline writers liked to describe them) would strike with zero warning, far above the usual bumpy flight levels, at around 26,000 feet. CAT can strike with enough violence to punch unrestrained passenger heads through ceiling panels, and break arms and legs. The “attack” was often over in seconds, but the results could be devastating, and the certification strength and resilience of airframe components had to be raised in later designs to levels where the risk of severe structural damage was much less likely.

But these events continue to happen, and according to the study, with rising frequency. And they come with do-not-exceed rules that mean compulsory component inspections and repairs or replacements when the load or gust data recorded during a flight crosses the limits imposed by regulations.

Recent generations of regular flyers have only withstood these events with less damage to themselves by taking to heart the advice to keep seat belts loosely fastened even when the warning sign is off.

CAT is not like other, more common forms of in-flight turbulence that can be detected or predicted by on-board sensors and ameliorated by the active gust-alleviation systems of the latest Airbuses and Boeings, using rapid changes to ailerons, elevators and rudders.

Fast and frequent systems-driven adjustments to these control surfaces soften, confine or even eliminate the up, down and sideways jerkiness that can sometimes intrude on a flight. But if this study is correct, global warming means that the CAT’s claws will become much more of a problem, not just because more people are flying more often, but because of the pent-up heat energy destabilising the higher flight levels their jets are using.

Turbulence could be making a more serious comeback in air travel

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