Duty time is what is left after mandatory rest. Further,
there are limits on flight hours and some exceptions for
number of crew in the cockpit and weather delays.

§ 121.471 Flight time limitations and rest requirements:
All flight crewmembers.
(a) No certificate holder conducting domestic operations may
schedule any flight crewmember and no flight crewmember may
accept an assignment for flight time in scheduled air
transportation or in other commercial flying if that
crewmember's total flight time in all commercial flying will
exceed-

(1) 1,000 hours in any calendar year;

(2) 100 hours in any calendar month;

(3) 30 hours in any 7 consecutive days;

(4) 8 hours between required rest periods.

(b) Except as provided in paragraph (c) of this section, no
certificate holder conducting domestic operations may
schedule a flight crewmember and no flight crewmember may
accept an assignment for flight time during the 24
consecutive hours preceding the scheduled completion of any
flight segment without a scheduled rest period during that
24 hours of at least the following:

(1) 9 consecutive hours of rest for less than 8 hours of
scheduled flight time.

(2) 10 consecutive hours of rest for 8 or more but less than
9 hours of scheduled flight time.

(3) 11 consecutive hours of rest for 9 or more hours of
scheduled flight time.

(c) A certificate holder may schedule a flight crewmember
for less than the rest required in paragraph (b) of this
section or may reduce a scheduled rest under the following
conditions:

(1) A rest required under paragraph (b)(1) of this section
may be scheduled for or reduced to a minimum of 8 hours if
the flight crewmember is given a rest period of at least 10
hours that must begin no later than 24 hours after the
commencement of the reduced rest period.

(2) A rest required under paragraph (b)(2) of this section
may be scheduled for or reduced to a minimum of 8 hours if
the flight crewmember is given a rest period of at least 11
hours that must begin no later than 24 hours after the
commencement of the reduced rest period.

(3) A rest required under paragraph (b)(3) of this section
may be scheduled for or reduced to a minimum of 9 hours if
the flight crewmember is given a rest period of at least 12
hours that must begin no later than 24 hours after the
commencement of the reduced rest period.

(4) No certificate holder may assign, nor may any flight
crewmember perform any flight time with the certificate
holder unless the flight crewmember has had at least the
minimum rest required under this paragraph.

(d) Each certificate holder conducting domestic operations
shall relieve each flight crewmember engaged in scheduled
air transportation from all further duty for at least 24
consecutive hours during any 7 consecutive days.

(e) No certificate holder conducting domestic operations may
assign any flight crewmember and no flight crewmember may
accept assignment to any duty with the air carrier during
any required rest period.

(f) Time spent in transportation, not local in character,
that a certificate holder requires of a flight crewmember
and provides to transport the crewmember to an airport at
which he is to serve on a flight as a crewmember, or from an
airport at which he was relieved from duty to return to his
home station, is not considered part of a rest period.

(g) A flight crewmember is not considered to be scheduled
for flight time in excess of flight time limitations if the
flights to which he is assigned are scheduled and normally
terminate within the limitations, but due to circumstances
beyond the control of the certificate holder (such as
adverse weather conditions), are not at the time of
departure expected to reach their destination within the
scheduled time.

[Doc. No. 23634, 50 FR 29319, July 18, 1985, as amended by
Amdt. 121-253, 61 FR 2612, Jan. 26

"john smith" wrote in message
...
| In article ,
| "RST Engineering" wrote:
|
| Jim, I haven't looked up the part 121 rules since I left
the airlines, but
| as I recall, the "duty time" is defined as flight time.
No limit on how
| long a crewmember can sit idling on the ground. Last I
looked it was 8
| hours a 24 hour day, 40 hours in a 7 day week, 100 hours
in any 30 day
| period ("month") and 1000 hours in a calendar year.
Perhaps that has
| changed.
|
| As I was recently told, the crew clock doesn't start until
the first
| engine is started.