Which of the following is NOT a type of aircraft commonly used in aerial firefighting?

Commercial airliners are not commonly used in aerial firefighting primarily because they are designed for passenger transport rather than firefighting operations. Their size, configuration, and purpose don't lend themselves to the specific requirements of deploying fire retardants or water effectively.

In contrast, helicopters are versatile and can maneuver into tight spaces to deliver water or retardants directly onto fire locations. Drones are increasingly being utilized for reconnaissance and monitoring, providing valuable data that can help coordinate firefighting efforts. Tankers, often modified aircraft, are built specifically for carrying large quantities of water or fire retardants, making them ideal for covering wide areas of wildfires. Thus, the operational roles and designs of helicopters, drones, and tankers align with the needs of aerial firefighting, while commercial airliners remain focused on civilian transportation.