There are at least 2,381 operational oil and gas pipelines distributed across 162 countries. The combined length of these pipelines is more than 1.18 million km (730,000 miles). The United States has the largest number of operational gas pipelines in the world. Across the US there are more than 210 pipeline systems, totaling over 490,850 km (305,000 miles) of interstate and intrastate pipelines.
To inspect and maintain that infrastructure aircraft are routinely utilized to survey natural gas transmission pipelines for leaks or damage. Airborne sensors detect methane or hydrocarbon plumes around a pipeline indicating a leak. GPS and on-board mapping software record the plume’s location and intensity for reporting and repair.
There are generally two types of sensors used; those that sample the air as the aircraft moves through a plume, and those that sense a plume at a standoff distance using FLIR or laser spectrometry. The standoff sensors have become more popular recently as their underlying technologies have seen rapid advances.
All sensors require the aircraft to fly as low as possible over the pipeline to improve their readings. Helicopters can fly lower more safely than airplanes, but are more expensive to operate. Ideally, neither would be used as large unmanned aerial vehicles can host existing aircraft sensors, and fly much lower without endangering a pilot.