Wire and powerline hazards in low flying

Wire strikes cause a significant share of low-flying accidents, many over level terrain, in good weather, at very low altitude (TC AIM AIR 2.4.3).

Visibility:

• Hydro towers are easy to see; wires between them are not: without background contrast the eye misses them.
• Wires and towers camouflage against ground terrain, especially in poor visibility.
• May only stand out once below their height, silhouetted against sky (TP 1102 Ex.21).

Marking vs real risk:

• Structures 500 ft AGL and higher must carry high-intensity strobe lighting if assessed as hazards.
• Most aircraft collisions with man-made structures happen below 300 ft AGL: marked threshold sits well above real risk.

Wire types:

• Only safe way past a shield wire: cross at a tower, never mid-span (safe altitude, maximum clearance).

Crossing technique near any powerline:

• Follow a line on its right-hand side. Watch for other crossing lines and guy cables. Sometimes only one side is safe to fly.
• Expect radio and electrical interference.
• Before operational low flying: overflight and map check.
• Leave an out: cross at 45° to the line.
• Always fly above the height of the support structures.

Transmission lines (over 69 kV; TC AIM AIR 2.4.4):

• Cross valleys, rivers, roads, straits.
• May or may not be marked, depending on height and local traffic.
• Markers usually on highest (shield) line, sometimes a lower conductor.
• Marker flags presence of an obstacle, not its height.

Trap: treating a visible tower as the whole hazard; the wire kills and is the part unseen.

Practice