Pilot
Pilot turns up in 2 fields: boilers, mining. Here is what it means to the people in each one.
Pilot in boilers
A small flame that lights the main burner and is often used to prove ignition before main fuel flows.
Standing pilots burn all the time and are proven by a thermocouple or thermopile; intermittent pilots light on each call for heat and stay on through the cycle; interrupted pilots shut off once main flame is proven. On commercial burners, the pilot must be proven by the scanner during pilot trial for ignition before the main valves are allowed to open.
"Pilot's lazy and yellow, the orifice is probably half plugged, pull it and clean it."
Pilot in mining
A small preliminary tunnel or heading driven before a larger excavation.
A small-diameter tunnel or bore driven ahead of the main excavation profile. Miners and engineers use it to explore ground conditions, establish ventilation, or provide a void to blast into when expanding to the full tunnel diameter. It reduces the risk of unexpected ground failures in the main heading by exposing faults and water inflows early.
"We'll drive a pilot through the fault zone first to bleed off any trapped water before widening to full face."