How much rest does the crew need before they can depart again?

Crew members are required to have a 10-hour rest period within each 24-hour cycle. The maximum duty day is 14 hours and must be followed by a 10-hour rest period at their hotel.

When scheduling a flight, operators usually account for 12 hours of rest instead of 10. This extra two hours allows the crew time to get to their hotel, rest for the required time, and return to the airport.

What does ‘max crew duty’ mean?

Max crew duty is the maximum amount of time that a pilot can be on duty, or be working, within 24 hours. The max crew duty is 14 hours out of a 24-hour day. Part 135 regulations also require crew members to work only a set number of hours in consecutive days.

Here are the limits to the number of hours crew members and pilots can operate:

Pilots conduct a pre-flight inspection and fuel up two hours before flight. After the flight, they need another hour for their post-flight routines on the plane. If there’s a fuel stop, this might take one hour. This leaves up to 10 hours to fly, which is the maximum permitted in 24 hours. This is sometimes referred to as the 24/10 rule.

If a pilot goes over the max crew duty, they can get infractions on their record or even lose their license. If a client is running late and a crew is nearing their max crew duty, they may have to change the flight plans. For example, let’s say a round-trip is set to take 10 hours, and the client is running three hours late. This means the crew would exceed their max crew duty if they were to complete the flight, so a fresh crew would be needed.

Having said that, there is something referred to as ‘Captain’s discretion’ allowing the Captain to extend the shift by up to three hours. Any more than that, and the aircraft would have to land. This decision rests with the Captain only – not the passengers, and not the airline or operator.

Captain’s discretion should not be taken lightly, because pilot fatigue is a very serious threat. FAA regulations on flight hours have been carefully thought-out to avoid fatigue, which reduces the chance of human errors being made. Working an extra hour or two may not seem like it would have a major impact but, over time, this can increase the risk of long-term fatigue. That’s why there are rules not just on the hours worked in one day, but also over a month and year.

Are some flights so long they require two crews?

Some longer flights will require two separate crews, but this varies from one country to another. In the United States, pilots can fly up to 10 hours, or 11 hours if there’s a third crew member on board.

If the flight is longer than this, two sets of crew will be needed. There will need to be an area for one crew to rest while the other work, usually the enclosed rear cabin.

That said, most aircraft can't travel that far nonstop. The typical maximum range of an ultra-long-range aircraft is 13 hours; with a second set of crew, you can enjoy an extra three hours without stopping for fuel.

If you have a long flight but you’d prefer to only have one crew on board, you can plan a fuel stop so that the old crew could get off and the new crew could get on while refueling. For example, let’s say the refueling is planned for Iceland. The second crew can fly there in advance, giving them time to rest. Your plane then stops to refuel in Iceland and collects the new crew. With the fresh crew on board, you can then fly for another 10 hours. This could work on a flight from the US to Australia, for instance.