“I’m going to ask for 380 and another shortcut,” says Greg, sitting to my right and pointing to the CJ3’s MFD, which shows an arrival time of 16:19 Zulu. We are about three-quarters of the way down the East Coast en route from White Plains, New York, to Boca Raton, Florida, and we have a numbers problem. Greg thinks a 16:00Z arrival will solve our problem, but I don’t see how we can manage that. He reasons that descending from Flight Level 450 to 380 will improve our groundspeed because our true airspeed (and fuel burn) is greater at the lower altitude.
We descend and beg for a more direct routing. Soon our arrival time is showing 16:10. Our numbers problem is actually a duty hours and flight hours problem. We know we can fly only 10 hours per 24-hour period in the Part 135 environment. There are some exceptions, but this is complicated enough as it is, so I’ll try to keep it simple. We also know we can fly only if we have had 10 hours of consecutive rest in the preceding 24. This means that what we did yesterday affects what we can do today. For instance, if we flew six hours yesterday between 6 a.m. and noon local time, we can do only four more hours today before noon. If we leave at 10 local, we can fly eight hours. If we don’t fly until noon, we can fly a full 10 hours (as long as we meet all the other rest requirements), as our previous 24 hours is “clean” (this is the so-called “look-back” period). This curious requirement makes for some interesting situations.
