An HDD Rig Master relies on a clear signal from his steering sonde to control the orientation of the HDD drill head. However, signal loss may occur due to electromagnetic interference, for example emitted by existing power cables in the vicinity of the bore path. As a result, temporarily loss of orientation may occur leading to a uncontrolled drift in the bore path as this example shows.

The Reduct survey crew followed the recommended standard operational procedure and mapped the pipe four times (so-called FBBF method). When compared to the as-planned profile, the measurement results reveal that the as-built profile deviates up to 4.5m (15ft) from the planned profile in the horizontal plane XY and approximately 1.5m (5ft) in the vertical plane Z (depth).