3. WEIGHTS3. WEIGHTS

Performance JAR 25Performance JAR 25

WEIGHTSWEIGHTS

Takeoff weights

MTOW

RLW

SSLW & FSLW

OLTOW

Weight limited by Vmbe or Vmaxtire

Runway Bearing Capacity

TAKEOFF WEIGHTSTAKEOFF WEIGHTS

Remember that the ATOW must be equal or lower than the lowest of:

OTOW

MZFW + Takeoff Fuel

OLW + Trip fuel

TAKEOFF WEIGHTSTAKEOFF WEIGHTS

The OTOW is given by the lower of:

MTOW

Runway Limited Weight (RLW)

Segment Limited Weight (SSLW, FSLW)

Obstacle Limited Takeoff Weight (OLTOW)

Weight limited by Vmbe or Vmaxtire

SSLWSSLW

The Second Segment Limited Weight (SSLW) or Climb Limited Takeoff weight is determined by the climb requirements just after takeoff assuming one engine inoperative.

The second segment begins with the landing gear retracted and ends at level-off altitude (at least 400 ft).

CONFIGURATION CLIMB REQUIREMENTS

Takeoff thrust set 2 engines: 2.4%

Takeoff flap 3 engines: 2.7%

Gear up 4 engines: 3.0%

V2 speed

SSLWSSLW

Some factors that affect SSLW are DA, engine bleed and flaps.

Low flap settings will decrease RLW and increase SSLW, and vice versa. The optimum flap setting will be a compromise between the two.

Using the “improved climb performance” procedure (V2 + 10 climb) will increase the SSLW, paying the price of a RLW reduction.

Flap

OTOW

RLW

SSLW

Optimum flap

OLTOWOLTOW

The Obstacle Limited Takeoff Weight (OLTOW) is determined by the obstacle clearance (35 ft) within the departure sector.

OLTOWOLTOW

Factors that affect OLTOW are:

Distance to obstacles

Wind

Density altitude

Engine bleed (A/C, anti-ice…)

Flap setting

RUNWAY BEARING CAPACITYRUNWAY BEARING CAPACITY

The runway strength may be not enough to bear the weight of a heavy aeroplane. Depending on the mass, number of tyres, pressure of tyres, etc, two classifications have been established:

ACN: Aircraft Classification Number. It represents the load that the aircraft puts onto the runway and taxiways.

PCN: Pavement Classification Number. It must be equal or higher than the ACN to permit operation of the aircraft.

PCN CODEPCN CODE

1. PCN number 5. Pavement evaluation method

2. Type of pavement T = technical evaluation

R = Rigid U = By experience

F = Flexible

3. Pavement subgrade category EXAMPLES:

A = High 25 / F / B / X / T

B = Medium 59 / R / A / W / T

C = Low

D = Ultra – low

4. Maximum tyre pressure authorised

W = High, no limit

X = Medium (max. 217 psi)

Y = Low (max 145 psi)

Z = Very low (max 73 psi)