4.2.4. Loss of Gradient during a Turn 

During a turn, an aircraft is not only subjected to its weight (W), but also to a horizontal acceleration force (Fa). The resulting force is called “apparent weight” (Wa), and its magnitude is equal to the load factor times the weight (nz.W). 

Considering the above Figure C18, the load factor (nz) can be expressed versus the bank angle (Φ) as follows: 

1 n= z cosφ 

So, as soon as the aircraft is banked, the load factor becomes greater than one. This induces a loss of climb gradient, as the climb angle can be expressed as follows (refer to the “Climb” chapter) : 

Thrust 1

γ 

% =. 

nz .Weight L/D 

“AMC OPS 1.495 (c)(4) The Aeroplane Flight Manual generally provides a climb gradient decrement for a 15° bank turn. For bank angles of less than 15°, a proportionate amount should be applied, unless the manufacturer or Aeroplane Flight Manual has provided other data.” 

The loss of gradient versus the bank angle is provided in the Airbus Flight Manual (AFM), as well as in the Airbus Performance Program Manual (PPM) as shown in Figure C19. 

On airbus fly-by-wire aircraft, the autopilot limits the bank angle at takeoff with one engine inoperative to 15°. Some Engine Out Standard Instrument Departures (EOSID) require a turn to be performed with a bank angle of 20° or more. When a turn with more than a 15° bank angle must be carried out, the aircraft must be manually flown. 

4.2.5. Takeoff Flight Path with Obstacles 

Once the obstacles are taken into account, the maximum takeoff weight at brake release must be calculated so that the net flight path clears the most penalizing obstacle with a vertical margin of 35 feet (or 50 feet when the bank angle is greater than 15°). 

Obstacle A (Figure C20), imposes a minimum Net second segment gradient and, therefore, a minimum Gross second segment gradient. This results in a takeoff weight limitation. 

Obstacle B helps determine the minimum acceleration height. This height must be between 400 feet and the maximum acceleration height (10 minutes at TOGA). The minimum acceleration height ensures a vertical clearance of 35 feet (or 50 feet) between the net flight path and the obstacle. 

The net acceleration segment is longer than the gross one, as the end of both segments is assumed to be reached after the same flight time. 

4.2.6. Takeoff Funnel 

The takeoff funnel represents an area surrounding the takeoff flight path, within which all obstacles must be cleared, assuming they are all projected on the intended track. The contours of this area, also called departure sector, differ between the JAR and the FAR regulations, and will be dealt with separately in the following section. 

“JAR-OPS 1.495 

(a) An operator shall ensure that the net take-off flight path clears all obstacles […] by a horizontal distance of at least 90 m plus 0.125 x D, where D is the horizontal distance the aeroplane has traveled from the end of the take-off distance available or the end of the take-off distance if a turn is scheduled before the end of the take-off distance available. For aeroplanes with a wingspan of less than 60 m a horizontal obstacle clearance of half the aeroplane wingspan plus 60 m plus 0.125 x D may be used.” 

The semi-width at the start of the departure sector is a function of the aircraft’s wingspan. The following Table (C9) provides the values for each aircraft type: 

Table C9: JAR-OPS Semi-Width at the Start of the Departure Sector 

“JAR-OPS 1.495 (d) For those cases where the intended flight path does not require track changes of more than 15°, an operator need not consider those obstacles which have a lateral distance greater than: 

. 300 m, if the pilot is able to maintain the required navigational accuracy through the obstacle accountability area, or 

. 600 m, for flights under all other conditions.” 

“JAR-OPS 1.495 

(e) For those cases where the intended flight path does require track changes of more than 15°, an operator need not consider those obstacles which have a lateral distance greater than: 

. 600 m, if the pilot is able to maintain the required navigational accuracy through the obstacle accountability area, or 

. 900 m for flights under all other conditions.” 

The Required Navigational Accuracy is defined in AMC-OPS 1.495. It can either be obtained via navigation aids, or by using external references in case of Visual Course guidance (VMC day flights).