April 3, 2012
Depending upon the threat level, the acoustic warning varies the
bleeper frequency.
Information about Warnings
If there are several fixed or moving objects within radio range, the
device uses a mathematical algorithm to determine that which
poses the most immediate threat, and issues a warning about this
threat and none other. The pilot is unable to acknowledge the
warning. However, in spite of a warning having been given for a
single object it remains possible that several, or other objects
simultaneously represent a major threat, or in effect are together
more dangerous than the object for which the warning was issued.
If the device simultaneously detects a threat from a moving object
and a fixed object, then a warning is issued for that which
represents the earliest threat of collision.
On the basis of calculation the device indicates the direction taken
by the most dangerous object, and its current location. The device
does not indicate where the closest proximity may occur, nor what
avoiding action is required. Whether and what avoiding action
should be taken is the sole responsibility of the pilot, whose
correct response must be based upon his own observation of the
local airspace. In particular, he must observe the avoidance rules
of the air, and ensure that the avoidance action does not endanger
any other airspace users. Depending upon the flight phase, the
device uses different forecast processes, movement models and
warning calculations to provide the pilot with the best possible
support without distraction. For example, sensitivity is reduced
when a sailplane is thermalling. These models and processes are
optimised, but always represent a compromise. As seen by the
pilot, these models will issue 'unnecessary' warnings; in other
words the device may give a warning in situations where there is
no subjective danger. It is also possible that the device will not
give warning of the most serious threat, or gives no warning at all.
Warnings are given at very short notice, normally up to 20
seconds prior to the closest calculated proximity. The intensity of
the warning indicates the threat level (calculated collision time)
but not the geometric distance. The device only issues a warning if
it calculates and predicts a considerable threat of collision. It is
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