Turbulence: Not Just An Airline Problem
In August 2021, the NTSB adopted a safety research report titled “Preventing Turbulence-Related Injuries in Air Carrier Operations Conducted Under Title 14 Code of Federal Regulations Part 121.” The reason they focused only on airline turbulence events was that the percentage of turbulence-related accidents was very high for airlines and very low for Part 135 and general aviation operations.
Turbulence encounters are the most-common defining event for airline accidents. From 2009-18, turbulence accounted for 111 out of 295 accidents, or 37.6%. The corresponding figures for Part 135 accidents were seven out of 443, or 1.6%, and for general aviation 79 out of 13,297, or 0.6%.
Does this mean turbulence is not a hazard for corporate, business or general aviation? Hardly. We all fly in the same sky with the same weather. There are worthwhile lessons in the report for business and GA aircraft even though they have fewer people aboard and fewer people walking around when turbulence strikes.
First, the rate of turbulence-related accidents hasn’t improved since 1989. Despite 31 NTSB recommendations on the subject since 1978, the picture hasn’t changed. The rate fluctuates around an average figure of about 0.05 accidents per 100,000 flight hours.
Next, of the five common types of turbulence--convective, clear air, mountain wave, surface feature and wake vortex--convective and clear air accounted for the most accidents--over 86%. Furthermore, convective turbulence accidents are twice as common as clear air accidents.
About 30% of all turbulence-related accidents happened during descent between 10,000 and 20,000 ft.
Only 53% of the crews involved in turbulence accidents were aware of the risk of turbulence, based on preflight briefings, weather reports, ATC reports, seeing weather on the radar, or experiencing light turbulence or chop. Almost half of the crews either didn’t comment or were caught by surprise.
A common problem for all pilots and operators is getting timely and accurate information about the location, altitude and severity of turbulence. Airline pilots have dispatchers to consult about turbulence, but airlines still have turbulence accidents.
Up high, pilots help each other out with ride reports to Center controllers. In descents and approaches, however, mutual aid is more difficult. Controllers get busy, frequencies get congested, and bumpy cumulus clouds rise and roll across the sky at rapid rates. Figuring out the best way in and out of busy airports while avoiding turbulence is sometimes as much a matter of luck as skill.
One interesting tool the National Weather Service added in the early 2000s is the graphical turbulence guidance (GTG) forecast. It provides forecasts of clear air and mountain wave turbulence from the surface to FL500 for up to 18 hr. in advance. It is good for preflight planning and is also easy for cabin crew and passengers to use. However, it isn’t much help for convective turbulence in and around airports.
A companion product to GTG called graphical turbulence guidance nowcast (GTGN) is under development and it holds promise. It combines short-term GTG forecasts with pilot reports (PIREPs), eddy dissipation rate (EDR) data and NexGen radar turbulence detection to produce a turbulence estimate every 15 min. It could be the tool that finally enables pilots to avoid the worst turbulence over short ranges during descents and approaches. Even if the turbulence is unavoidable, it may give pilots enough warning to alert the cabin.
The FAA’s office of Weather Technology in the Cockpit (WTIC) is also working on using ADS-B data--primarily vertical rate information--to measure, categorize and rebroadcast turbulence awareness information to pilots.
Of the NTSB’s 13 findings in its turbulence report, the first is probably the most important. “Wearing a seat belt reduces the risk of serious injury for all aircraft occupants during turbulence-related accidents in Title 14 Code of Federal Regulations Part 121 air-carrier operations.”
Only one out of 123 injured passengers and flight attendants in the study was wearing a seat belt when the turbulence struck.
Since wearing a seat belt seems to be the obvious solution to virtually all turbulence-related accidents, we must ask why the victims weren’t wearing them. That’s a topic for another column.