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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 

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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). 

- 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. 

- The Go Around (TOGA) thrust is the maximum thrust available for go-around. The time limits are the same as for takeoff. 

- 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. 

- The Climb (CL) thrust represents the maximum thrust available during the climb phase to the cruise flight level. Note that the maximum climb thrust is greater than the maximum cruise thrust available during the cruise phase. 

5.2. Takeoff Thrust Limitations 

Figure B11 shows the influence of pressure altitude and outside air temperature on the maximum takeoff thrust, for a given engine type. 

At a given pressure altitude, temperature has no influence on engine takeoff thrust, below the so-called reference temperature (Tref) or flat rating temperature. Above this reference temperature, engine thrust is limited by the Exhaust Gas Temperature (EGT). The consequence is that the available thrust decreases as the temperature increases. 

On the other hand, at a given temperature, any increase in the pressure altitude leads to decreasing the available takeoff thrust. 

C. TAKEOFF 

1. INTRODUCTION 

The possibility of engine failure during takeoff should always be considered, and the crew must be provided with the appropriate means of deciding on the safest procedure in the event of such a failure. 

Figure C1: Takeoff Profile

During the takeoff phase, the pilot must achieve the sufficient speed and angle of attack conditions to balance the aircraft’s lift and weight forces. 

At the end of the ground acceleration phase, the pilot pulls the stick to start the rotation. During this phase, acceleration is maintained and the angle of attack is increased in order to achieve a higher lift. The ground reactions progressively decrease until lift off. 

As mentioned above, the performance determination must take into account the possibility of an engine failure during the ground acceleration phase. For FAR/JAR certified aircraft, failure of the most critical engine must be considered. 

“JAR/FAR 1.1 : 'Critical Engine' means the engine whose failure would most adversely affect the performance or handling qualities of an aircraft”, i.e. an outer engine on a four engine aircraft.