Most of the 245 stall warnings reported in Australian regular public transport (commercial airlines) from 2008 through 2012 were associated with turbulence, gusty winds or wind shear; occurred along with stick shaker activation; and lasted less than two seconds, the Australian Transport Safety Bureau (ATSB) says (Figure 1).1
An ATSB report issued in late 2013 said that none of the stall warnings resulted in an actual stall or loss of control, and none led to serious injuries to passengers or crewmembers, although some minor injuries were reported during stall warnings that occurred in severe turbulence or with temporary control anomalies.
Australian law requires that stall warning events be reported to the ATSB, enabling the agency to analyze the circumstances associated with the events.
The report says that about 70 percent of stall warnings reported to the ATSB in the five-year period were actual warnings of an approaching stall; the remainder were false stall warnings caused by system problems.
Stall warnings, and stick-shaker activations, were reported in a range of phases of flight and aircraft configurations. Excluding the false stall warnings, 55 percent of the actual warnings occurred in visual meteorological conditions, including all stall warnings that occurred during initial climb, typically while the crew was retracting flaps or other high-lift devices, the report said (Figure 2). Of the 45 percent of stall warnings reported in instrument meteorological conditions, about three-quarters occurred during the climb, cruise, maneuver and descent phases, usually during wind shear–related turbulence or while maneuvering around rain or clouds. The other one-quarter occurred during approach and landing.
Of the 169 actual stall warnings, 81 percent occurred along with a flight disturbance such as turbulence, wind shear, a gust or a change in wind direction (Figure 3). Of these, 65 percent involved either a Boeing 747 or 767, the report said.
- ATSB. Stall Warnings in High Capacity Aircraft: The Australian Context, 2008 to 2012, Aviation Research Report AR-2012-172. Nov. 1, 2013.