Airfield Performance AnalysisAirfield Performance Analysis

The weight at which an The weight at which an aircraft can take-off or land aircraft can take-off or land

at any particular airfield at any particular airfield might be constrained by might be constrained by

airfield physical layout, the airfield physical layout, the aircraft design, runway aircraft design, runway

loading limitation, loading limitation, environmental constrains or environmental constrains or

ambient conditions ambient conditions

Airfield Performance AnalysisAirfield Performance AnalysisRunway: A number of important Runway: A number of important

definitions exist for runway lengths, and definitions exist for runway lengths, and we must distinguish between those we must distinguish between those distances which are designated as distances which are designated as

“available” and which are “required” for a “available” and which are “required” for a specific take-off. specific take-off.

-Take-off Distance (TOD) required to -Take-off Distance (TOD) required to enable the aircraft to start its roll from enable the aircraft to start its roll from

brake-release, pass through the required brake-release, pass through the required speed, lift and clear an altitude of 35 feet speed, lift and clear an altitude of 35 feet

at the end of the runwayat the end of the runway

Airfield Performance AnalysisAirfield Performance Analysis-Acceleration & Stop Distance (ASD) -Acceleration & Stop Distance (ASD)

required which, for a given weight, is the required which, for a given weight, is the distance necessary to ensure that the distance necessary to ensure that the

aircraft can come to stand safely on the aircraft can come to stand safely on the runway if the take-off is abortedrunway if the take-off is aborted

-Finally, the Take-Off Run (TOR) is the -Finally, the Take-Off Run (TOR) is the distance from brake-release point up to a distance from brake-release point up to a point halfway between lift-off to the 35 point halfway between lift-off to the 35

feet point. feet point.

The Take-off weight of the aircraft must The Take-off weight of the aircraft must be such as the TOD, ASD & TOR required be such as the TOD, ASD & TOR required

must be equivalent to the TOD, ASD & must be equivalent to the TOD, ASD & TOR availableTOR available

Airfield Performance AnalysisAirfield Performance AnalysisObstacles: An aircraft take off from a Obstacles: An aircraft take off from a

runway it is likely, at some stage, to pass runway it is likely, at some stage, to pass over obstacles in the flight path. These over obstacles in the flight path. These obstacles, whether they be building or obstacles, whether they be building or

mountains, may impinge upon the mountains, may impinge upon the allowable take-off weight which is allowable take-off weight which is

calculated according to the ambient calculated according to the ambient conditions. If obstacles are present the conditions. If obstacles are present the

runway length must be artificially runway length must be artificially reduced in order to ensure that aircraft’s reduced in order to ensure that aircraft’s

weight is such that a better climb weight is such that a better climb performance can be achieved to clear the performance can be achieved to clear the

obstaclesobstacles

Airfield Performance AnalysisAirfield Performance AnalysisAmbient conditions: The efficiency of an Ambient conditions: The efficiency of an aircraft & its engines is a function of the aircraft & its engines is a function of the density of the air. The less dense the air, density of the air. The less dense the air, the less efficient the aircraft. Air density the less efficient the aircraft. Air density decreases as altitude and temperature decreases as altitude and temperature increase, so at hot or high airfield an increase, so at hot or high airfield an

aircraft needs longer distance to take-off. aircraft needs longer distance to take-off.

Some of the classic “problem” airfield are Some of the classic “problem” airfield are in Mexico, Madrid, Nairobi, Johannesburg, in Mexico, Madrid, Nairobi, Johannesburg, Addis Ababa, Harare, Sa’naa, Quito & La Addis Ababa, Harare, Sa’naa, Quito & La

PazPaz

Airfield Performance AnalysisAirfield Performance AnalysisWet & Dry conditions: Standing water on a Wet & Dry conditions: Standing water on a

runway will obviously impede the progress of an runway will obviously impede the progress of an aircraft across the surface. Energy that could aircraft across the surface. Energy that could have been used to accelerate the aircraft is have been used to accelerate the aircraft is

dissipated and braking distance expand. The dissipated and braking distance expand. The practical effect is that the required runway practical effect is that the required runway

distances are increased distances are increased

wind: A head wind reduces the acceleration wind: A head wind reduces the acceleration distance required because the aircraft can take-distance required because the aircraft can take-

off at a lower ground speed. A tailwind has off at a lower ground speed. A tailwind has opposite effect and acceleration distance is opposite effect and acceleration distance is

increased. A pilot must take into consideration the increased. A pilot must take into consideration the effect of the wind component for a real take-off effect of the wind component for a real take-off

case. case.

Airfield Performance AnalysisAirfield Performance AnalysisRunway Loading: There are several methods used Runway Loading: There are several methods used to assess runway loading but most common is the to assess runway loading but most common is the

ACN/PCN method, which has been adopted by ACN/PCN method, which has been adopted by ICAO & their member nations. A runway is ICAO & their member nations. A runway is

assigned a Pavement Classification Number (PCN) assigned a Pavement Classification Number (PCN) that describes the bearing strength of a that describes the bearing strength of a

pavement for unrestricted operations. An aircraft pavement for unrestricted operations. An aircraft has an Aircraft Classification Number (ACN) that has an Aircraft Classification Number (ACN) that expresses the relative impact of an aircraft on a expresses the relative impact of an aircraft on a

pavement of a specified standard subgrade.pavement of a specified standard subgrade.

In order for an aircraft to be allowed to use a In order for an aircraft to be allowed to use a runway, its ACN should be less than the runway’s runway, its ACN should be less than the runway’s

PCNPCN

Airfield Characteristics That Airfield Characteristics That Affect TakeoffAffect Takeoff

Airport elevationAirport elevationAirport temperatureAirport temperature Obstacles

Stopway/clearway

Wind

Slope

Length

Plus many others

En-Route Performance AnalysisEn-Route Performance Analysis

We need to undertake, in En-We need to undertake, in En-Route Performance Analysis, a Route Performance Analysis, a simulation of performance on simulation of performance on

the network in order to the network in order to measure two principal measure two principal

parameters: the amount of parameters: the amount of payload that can be carried, payload that can be carried,

and the amount of fuel burnedand the amount of fuel burned

En-Route Performance AnalysisEn-Route Performance Analysis

Temperatures: it influences engine performance & Temperatures: it influences engine performance & therefore the rate of climb of the aircraft. More therefore the rate of climb of the aircraft. More

energy must be expended by Engines in order to energy must be expended by Engines in order to lift the aircraft to higher altitude in a condition lift the aircraft to higher altitude in a condition

where Temperature higher than ISA (International where Temperature higher than ISA (International Standard Atmosphere). At sea level, ISA is Standard Atmosphere). At sea level, ISA is

equivalent to 15 degree Celsius. equivalent to 15 degree Celsius.

Winds: it has dramatic effect on aircraft en-route Winds: it has dramatic effect on aircraft en-route performance. In the case of a headwind, the air performance. In the case of a headwind, the air

distance becomes greater than the ground distance becomes greater than the ground distance and more fuel is consumed, and in the distance and more fuel is consumed, and in the case of tailwind the opposite is true. For each case of tailwind the opposite is true. For each

performance calculation we need to determine performance calculation we need to determine the Equivalent Still-Air Distance (ESAD) for the the Equivalent Still-Air Distance (ESAD) for the

mission mission

En-Route Performance AnalysisEn-Route Performance AnalysisFlight & Block time: The block time Flight & Block time: The block time

describes the time taken between “block describes the time taken between “block off” and “block on” – in other words, off” and “block on” – in other words,

engine star-up, ground maneuvers or taxi engine star-up, ground maneuvers or taxi time are included. The flight time time are included. The flight time

incorporates the mission time from start incorporates the mission time from start of take-off run to the landing of the of take-off run to the landing of the

aircraft. The distinction is important as aircraft. The distinction is important as one economic calculation, maintenance one economic calculation, maintenance cost, is based upon flight times whereas cost, is based upon flight times whereas the others are based on block time. the others are based on block time.

Typical Mission ProfileTypical Mission ProfileThere must be fuel on board for all There must be fuel on board for all segmentssegments

Taxi out Taxi in

Takeoff

Climb

Step cruise

Approach and land

Descent

Block time and fuel

Mission

Flight time and fuel

Distance

Most flights reach their destinations as planned. However….

En-Route Performance AnalysisEn-Route Performance Analysis

Reserve Policies: The Reserve Policies: The purpose of a reserve policy purpose of a reserve policy is, naturally, to ensure that is, naturally, to ensure that aircraft is carrying enough aircraft is carrying enough

fuel to reach another fuel to reach another airfield in the event of the airfield in the event of the destination airfield being destination airfield being

unavailable. unavailable.

Percent Flight

Time or Fuel

Missedapproach

Climb

Approach and land

Descent

Reserve

Contingency

Cruise

Flight to alternate

Hold

Typical Reserve ProfileTypical Reserve ProfileThere must be fuel on board for all segmentsThere must be fuel on board for all segments

Typical Reserve ProfileTypical Reserve ProfileThere must be fuel on board for all segmentsThere must be fuel on board for all segments

…there is always a chance of bad weather at the destination, enroute thunderstorms, unexpected headwinds, or runway intrusions.

En-Route Performance AnalysisEn-Route Performance AnalysisSelection of alternatives: Diverting to alternative Selection of alternatives: Diverting to alternative

airfield usually occurs owing to poor weather condition, airfield usually occurs owing to poor weather condition, but may also be due to an obstruction on the runway. but may also be due to an obstruction on the runway. The longer the distance from the intended destination The longer the distance from the intended destination to the alternative, the higher becomes the amount of to the alternative, the higher becomes the amount of fuel to be loaded at departure. A long alternate means fuel to be loaded at departure. A long alternate means that fuel burn is increased, as the aircraft must burn that fuel burn is increased, as the aircraft must burn

fuel to carry fuel. fuel to carry fuel.

Fuel requirement for a typical flight profile: Fuel requirement for a typical flight profile: Segment or stage fuel- the fuel burnt during climb, Segment or stage fuel- the fuel burnt during climb,

cruise and descentcruise and descentTrip fuel- Fuel brunt during take-off, climb, cruise, Trip fuel- Fuel brunt during take-off, climb, cruise,

descent and approach.descent and approach.Block fuel- Fuel burnt during trip, taxi-out and taxi-inBlock fuel- Fuel burnt during trip, taxi-out and taxi-in

Total fuel loaded- Fuel burnt (Block Fuel) + allowance+ Total fuel loaded- Fuel burnt (Block Fuel) + allowance+ diversion diversion

(allowance is usually 5% of the trip fuel)(allowance is usually 5% of the trip fuel)

En-Route Performance AnalysisEn-Route Performance AnalysisTankering :There are some airfield where Tankering :There are some airfield where

either fuel supplies are unreliable or there either fuel supplies are unreliable or there is no fuel supply available at all e.g. is no fuel supply available at all e.g.

Lhasa. Sufficient fuel has to be uplifted at Lhasa. Sufficient fuel has to be uplifted at the departure point to return from the the departure point to return from the

destination. Carrying fuel for an onward destination. Carrying fuel for an onward stage obviously imposes some penalties – stage obviously imposes some penalties – structural limitation & payload. There is structural limitation & payload. There is

an economic balance to be struck an economic balance to be struck between the price difference of fuel between the price difference of fuel

between the origin and destination, the between the origin and destination, the value of the payload surrendered, and value of the payload surrendered, and

the cost of fuel burned to carry additional the cost of fuel burned to carry additional fuel. fuel.

The Magic of Flight….The Magic of Flight….