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2.4. Maximum Structural Zero Fuel Weight (MZFW)
Bending moments, which apply at the wing root, are maximum when the quantity of fuel in the wings is minimum (see Figure B8). During flight, the quantity of fuel located in the wings, mWF, decreases. As a consequence, it is necessary to limit the weight when there is no fuel in the tanks. This limit value is called Maximum Zero Fuel Weight (MZFW).
Therefore, the limitation is defined by:
actual ZFW ≤ MZFW
The takeoff fuel is the sum of the trip fuel and the fuel reserves. Consequently:
actual TOW ≤ MZFW + Takeoff Fuel
2.5. Maximum Structural Taxi Weight (MTW)
The Maximum Taxi Weight (MTW) is limited by the stresses on shock absorbers and potential bending of landing gear during turns on the ground. Nevertheless, the MTW is generally not a limiting factor and it is defined from the MTOW, so that:
3. MINIMUM STRUCTURAL WEIGHT
The minimum weight is the lowest weight selected by the applicant at which compliance with each structural loading condition and each applicable flight requirement of JAR/FAR Part 25 is shown.
Usually, the gusts and turbulence loads are among the criteria considered to determine that minimum structural weight.
4. ENVIRONMENTAL ENVELOPE
“JAR/FAR 25.1527 The extremes of the ambient air temperature and operating altitude for which operation is allowed, as limited by flight, structural, powerplant, functional, or equipment characteristics, must be established.”
The result of this determination is the so-called environmental envelope, which features the pressure altitude and temperature limits. Inside this envelope, the aircraft’s performance has been established and the aircraft systems have met certification requirements.
The following Figure (B9) is an example of an A320 environmental envelope, published in the Flight Crew Operating Manual (FCOM).
5. ENGINE LIMITATIONS
5.1. Thrust Setting and EGT Limitations
The main cause of engine limitations is due to the Exhaust Gas Temperature (EGT) limit (Figure B10).
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The TakeOff (TOGA) thrust represents the maximum thrust available for takeoff. It is certified for a maximum time of 10 minutes, in case of engine failure at takeoff, or 5 minutes with all engines operative.
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The Go Around (TOGA) thrust is the maximum thrust available for go-around. The time limits are the same as for takeoff.
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The Maximum Continuous Thrust (MCT) is the maximum thrust that can be used unlimitedly in flight. It must be selected in case of engine failure, when TOGA thrust is no longer allowed due to time limitation.
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