Fuel miniumums
Previous poster.
Not a rule of thumb, but a CARDINAL rule. If a commercial aircraft lands with less than 30 minutes worth of fuel, then the flight crew has not done their job properly. Having to declare a fuel emergency (valid MAYDAY) means there have been errors made along the way, CRITICAL errors. With provisions, we are operating with 30 minutes, alternate, and 3% on domestic and overseas routes. This means that little has to change before serious consideration must be made of landing prior to destination. It is a critical part of the pilots' job to monitor the fuel remaining and determine if the destination can be achieved with adequate (and legal... two different things) reserves.
"Pushing it" is not an option nor is permitting dispatch to run roughshod over the crew.