They use an iPad from 2017, which is not too old. I think it depends on the type of charger they use.
@RoDude1230 check your charging adapter and how many watts it can provide. If it says 12W (the charging brick that came with your iPad) or higher, then you’re good. If you’re using a small charging brick, like a 5W charging adapter, then that’s why your iPad runs out of battery during your flight since 5W is not enough power to charge your iPad when you’re running a graphic intensive app like Infinite Flight. I use an iPad Pro 2017, and I use a 12W charger that came with my iPad to charge my iPad when I do my flights.
When you’re doing long flights, lower the graphics in the settings, lower the brightness, and set the time to ‘Night’. This will allow your iPad to not use as much power to fuel the high graphics and will allow your iPad to charge.
If you update your iPad to iPadOS 15, the latest version, you can set Low Power Mode for your iPad, just like you can set Low Power Mode on iPhone. You can ask Siri to turn on Low Power Mode, or add that option in the Control Center.