Safety Recommendation
The Australian Transport Safety Bureau recommends that the Civil
Aviation Safety Authority in conjunction with the Bureau of
Meteorology and Airservices Australia develop a standard scale of
thunderstorm intensity for use within the aviation industry.
The following response dated 13 April 2004 was received from the
Bureau of Meteorology:
In some countries a single scale of thunderstorm intensity is used
in severe weather warnings to the general public. There is no
agreement currently, however, that it is appropriate to use such a
scale in aviation forecasts and warnings.
There is good reason for the reluctance to introduce such a scale.
Among of the most significant hazards for aviation associated with
thunderstorms are microbursts. There is, however, no correlation
between microburst intensity and the intensity of the thunderstorm
with which it is associated. An intense microburst may develop from
a weak storm and there may only be a weak down draft from an
intense thunderstorm. Ascribing an intensity scale to a
thunderstorm would not only not convey any useful information to
the aviation community, but could even be counterproductive in the
sense that it could lead pilots to believe that there is less
danger in flying into a thunderstorm that has a low intensity than
one with a high intensity, when this is not the case.
It should be noted also that existing aviation forecasts, the
Terminal Aerodrome Forecasts and Trend Type Forecasts, already
allow for a description of the expected severity of the individual
elements of a thunderstorm - the strength of wind gusts, the
intensity of rain, the presence of hail etc, and the associated
reductions in cloud ceiling and visibility.
The Bureau would not support the introduction of a standard scale
of thunderstorm intensity for aviation purposes, but will
investigate options for providing additional information to pilots
and controllers that might serve to highlight the potential hazards
of particular meteorological phenomena. The Bureau has significant
skills in the area of severe thunderstorm warnings and will work
with Airservices (Australia) to determine the best way of
communicating the nature of the potential meteorological threats
associated with thunderstorms to pilots and controllers.
