ENSTROM 480/480B RFM SUPPLEMENT
7-1
Report No. 28-AC-042
Feb 24/11
CHAPTER 7. HELICOPTER AND SYSTEMS
DESCRIPTION AND OPERATION
7-1. General
1. The PDS warns the pilot by means of audio and visual
warnings whenever a powered transmission line is detected.
It accomplishes this by sensing the electric field that is
emitted from active power lines. The electric field around a
power line is a direct effect of the voltage on the power line.
The field strength is a function of the voltage on the line,
the distance from the line, and objects (trees, buildings,
etc.) in the vicinity of the line. The electric field is detected
by measuring the voltage differential between the aircraft
skin and the PDS antenna. This voltage differential is
affected by the electric field strength, electric field
distortions around the aircraft, temperature, and humidity.
Static electrical build up on the aircraft will cause
distortions of the electric field and reduce the system
sensitivity.
Thus, the ability of the PDS to detect a power line
depends on the voltage on the line, the surrounding terrain
and obstructions, the distance from the line, temperature,
humidity, and static electricity on the aircraft.
To maximize the effectiveness of the system, pilots
should observe the following:
a. The PDS will not work on un-energized lines. It will
not detect guy wires or power lines that are not
currently carrying electricity.
b. The warning distance is proportional to the voltage
being carried in the line. The warning distance will be
smaller for lower voltage lines.
c. If the pilot is flying in an area where power lines can
be expected, such as low altitude, he should slow
down to increase the time he has to react to a
warning.
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