I recently came across commercial pilots volunteering to work overtime, but I’m unclear on the details. Is this something that usually happens when pilots are frequently on reserve shifts?
There’s really no pilot “overtime” per se. What most airlines do offer is a variety of “premium” pay for picking up open trips on your days off.
For Reserve pilots that usually means you’ll be paid for the trip above your monthly guarantee (regardless of how many hours you fly). For lineholders that usually means the trip will be paid anywhere from 150-200% of your regular pay.
There are limits to how much you can fly. As long as you are still legal under flight time and rest rules, you’re allowed to pick up additional flying on your off days. The pay incentive is one reason people do it. Depending on the companies work rules, you may even get the day off awarded later in the month plus the extra add pay. It’s a good deal for a flexible pilot as well as for scheduling needs.
There is not only monthly and yearly limits on how much you may actually fly, there is also Part 117 rules that must follow for rest periods etc. At my airline, being on reserve I can’t pick trips up freely because of duty times etc., but as a line holder if there was open time and it didn’t interfere with Part 117, the option is there.