Each type of instruction — primary, advanced, instrument, CFI, CFII, aerobatic — brought its own challenges and rewards, but there was one type of instruction I enjoyed most of all — instructing in gliders. This was truly the essence of flying. While the cockpit was incredibly simple, the flying itself was always challenging. In a power aircraft, as long as we didn't run out of gas there was no doubt we would return easily and safely to the airport. In a glider, I not only had to keep an eye on the student and how the lesson was progressing, but I also had to keep track of where we were and ensure we could make it back to the airport. This required constant awareness of altitude, wind direction and speed, and distance to the airport. Some days there would be enough lift that we could gain some altitude between maneuvers. Other times, it was a short 20-minute flight as we descended inexorably toward the ground.