ON FADEC engines, it is when they are turned off. FADEC will limit N1 and N2 for given flight phases. But as stated, the full thrust rating would only be available at static sea-level. Most FADEC controlled engines will set a limit for the thrust for flight phases based on pressure , temperature, AND velocity:
From a FADEC manual for the CFM56-7
Each N1 is calculated according to the following flight
conditions :
- Temperature : the thrust delivered depends on
outside air temperature (OAT). By design, the
engine provides a constant thrust up to a predetermined
OAT value, known as “corner point”,
after which the thrust decreases proportionally to
maintain a constant EGT value.
- Pressure : with an increase in altitude, thrust will
decrease when operating at a constant RPM due
to the reduction in air density, which reduces the
mass flow and fuel flow requirements.
- Mach : when mach number increases, the velocity of
the mass of air entering the engine changes,
decreasing thrust. To determine the fan speed, the
EEC calculates M0 from the static pressure, the
total pressure and the TAT values.
- Bleed : ECS bleed and anti-ice bleed are taken into
account in order to maintain the same EGT level
with and without bleeds.