Aircraft performance

1. Airfield Performance AnalysisAirfield Performance Analysis
The weight at which anThe weight at which an
aircraft can take-off or landaircraft can take-off or land
at any particular airfieldat any particular airfield
might be constrained bymight be constrained by
airfield physical layout, theairfield physical layout, the
aircraft design, runwayaircraft design, runway
loading limitation,loading limitation,
environmental constrains orenvironmental constrains or
ambient conditionsambient conditions

2. Airfield Performance AnalysisAirfield Performance Analysis
Runway: A number of importantRunway: A number of important
definitions exist for runway lengths, anddefinitions exist for runway lengths, and
we must distinguish between thosewe must distinguish between those
distances which are designated asdistances 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 fromenable the aircraft to start its roll from
brake-release, pass through the requiredbrake-release, pass through the required
speed, lift and clear an altitude of 35 feetspeed, lift and clear an altitude of 35 feet
at the end of the runwayat the end of the runway

3. Airfield Performance AnalysisAirfield Performance Analysis
-Acceleration & Stop Distance (ASD)-Acceleration & Stop Distance (ASD)
required which, for a given weight, is therequired which, for a given weight, is the
distance necessary to ensure that thedistance necessary to ensure that the
aircraft can come to stand safely on theaircraft 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 adistance from brake-release point up to a
point halfway between lift-off to the 35point halfway between lift-off to the 35
feet point.feet point.
The Take-off weight of the aircraft mustThe Take-off weight of the aircraft must
be such as the TOD, ASD & TOR requiredbe such as the TOD, ASD & TOR required
must be equivalent to the TOD, ASD &must be equivalent to the TOD, ASD &
TOR availableTOR available

4. Airfield Performance AnalysisAirfield Performance Analysis
Obstacles: An aircraft take off from aObstacles: An aircraft take off from a
runway it is likely, at some stage, to passrunway it is likely, at some stage, to pass
over obstacles in the flight path. Theseover obstacles in the flight path. These
obstacles, whether they be building orobstacles, whether they be building or
mountains, may impinge upon themountains, may impinge upon the
allowable take-off weight which isallowable take-off weight which is
calculated according to the ambientcalculated according to the ambient
conditions. If obstacles are present theconditions. If obstacles are present the
runway length must be artificiallyrunway length must be artificially
reduced in order to ensure that aircraft’sreduced in order to ensure that aircraft’s
weight is such that a better climbweight is such that a better climb
performance can be achieved to clear theperformance can be achieved to clear the
obstaclesobstacles

5. Airfield Performance AnalysisAirfield Performance Analysis
Ambient conditions: The efficiency of anAmbient conditions: The efficiency of an
aircraft & its engines is a function of theaircraft & 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 densitythe less efficient the aircraft. Air density
decreases as altitude and temperaturedecreases as altitude and temperature
increase, so at hot or high airfield anincrease, 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 areSome of the classic “problem” airfield are
in Mexico, Madrid, Nairobi, Johannesburg,in Mexico, Madrid, Nairobi, Johannesburg,
Addis Ababa, Harare, Sa’naa, Quito & LaAddis Ababa, Harare, Sa’naa, Quito & La
PazPaz

6. Airfield Performance AnalysisAirfield Performance Analysis
Wet & Dry conditions: Standing water on aWet & Dry conditions: Standing water on a
runway will obviously impede the progress of anrunway will obviously impede the progress of an
aircraft across the surface. Energy that couldaircraft across the surface. Energy that could
have been used to accelerate the aircraft ishave been used to accelerate the aircraft is
dissipated and braking distance expand. Thedissipated and braking distance expand. The
practical effect is that the required runwaypractical effect is that the required runway
distances are increaseddistances are increased
wind: A head wind reduces the accelerationwind: 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 hasoff at a lower ground speed. A tailwind has
opposite effect and acceleration distance isopposite effect and acceleration distance is
increased. A pilot must take into considerationincreased. A pilot must take into consideration
the effect of the wind component for a real take-the effect of the wind component for a real take-
off case.off case.

7. Airfield Performance AnalysisAirfield Performance Analysis
Runway Loading: There are several methods usedRunway Loading: There are several methods used
to assess runway loading but most common is theto assess runway loading but most common is the
ACN/PCN method, which has been adopted byACN/PCN method, which has been adopted by
ICAO & their member nations. A runway isICAO & their member nations. A runway is
assigned a Pavement Classification Number (PCN)assigned a Pavement Classification Number (PCN)
that describes the bearing strength of athat describes the bearing strength of a
pavement for unrestricted operations. An aircraftpavement for unrestricted operations. An aircraft
has an Aircraft Classification Number (ACN) thathas an Aircraft Classification Number (ACN) that
expresses the relative impact of an aircraft on aexpresses 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 aIn order for an aircraft to be allowed to use a
runway, its ACN should be less than the runway’srunway, its ACN should be less than the runway’s
PCNPCN

8. Airfield Characteristics ThatAirfield Characteristics That
Affect TakeoffAffect Takeoff
AirportAirport
elevationelevation
AirportAirport
temperaturetemperature
Obstacles
Stopway/clearway
Wind
Slope
Length
Plus many others

9. En-Route Performance AnalysisEn-Route Performance Analysis
We need to undertake, in En-We need to undertake, in En-
Route Performance Analysis, aRoute Performance Analysis, a
simulation of performance onsimulation of performance on
the network in order tothe network in order to
measure two principalmeasure two principal
parameters: the amount ofparameters: the amount of
payload that can be carried,payload that can be carried,
and the amount of fuel burnedand the amount of fuel burned

10. 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. Moretherefore the rate of climb of the aircraft. More
energy must be expended by Engines in order toenergy must be expended by Engines in order to
lift the aircraft to higher altitude in a conditionlift the aircraft to higher altitude in a condition
where Temperature higher than ISA (Internationalwhere Temperature higher than ISA (International
Standard Atmosphere). At sea level, ISA isStandard Atmosphere). At sea level, ISA is
equivalent to 15 degree Celsius.equivalent to 15 degree Celsius.
Winds: it has dramatic effect on aircraft en-routeWinds: it has dramatic effect on aircraft en-route
performance. In the case of a headwind, the airperformance. In the case of a headwind, the air
distance becomes greater than the grounddistance becomes greater than the ground
distance and more fuel is consumed, and in thedistance and more fuel is consumed, and in the
case of tailwind the opposite is true. For eachcase of tailwind the opposite is true. For each
performance calculation we need to determineperformance calculation we need to determine
the Equivalent Still-Air Distance (ESAD) for thethe Equivalent Still-Air Distance (ESAD) for the
missionmission

11. En-Route Performance AnalysisEn-Route Performance Analysis
Flight & Block time: The block timeFlight & Block time: The block time
describes the time taken between “blockdescribes 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 taxiengine star-up, ground maneuvers or taxi
time are included. The flight timetime are included. The flight time
incorporates the mission time from startincorporates the mission time from start
of take-off run to the landing of theof take-off run to the landing of the
aircraft. The distinction is important asaircraft. The distinction is important as
one economic calculation, maintenanceone economic calculation, maintenance
cost, is based upon flight times whereascost, is based upon flight times whereas
the others are based on block time.the others are based on block time.

12. Typical Mission ProfileTypical Mission Profile
There must be fuel on board for allThere 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….

13. En-Route Performance AnalysisEn-Route Performance Analysis
Reserve Policies: TheReserve Policies: The
purpose of a reserve policypurpose of a reserve policy
is, naturally, to ensure thatis, naturally, to ensure that
aircraft is carrying enoughaircraft is carrying enough
fuel to reach anotherfuel to reach another
airfield in the event of theairfield in the event of the
destination airfield beingdestination airfield being
unavailable.unavailable.

14. Percent
Flight
Time or
Fuel
Missed
approach
Climb
Approach and land
Descent
Reserve
Contingency
Cruise
Flight to alternate
Hold
Typical Reserve ProfileTypical Reserve Profile
There 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.

15. En-Route Performance AnalysisEn-Route Performance Analysis
Selection of alternatives: Diverting to alternativeSelection 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 destinationThe longer the distance from the intended destination
to the alternative, the higher becomes the amount ofto the alternative, the higher becomes the amount of
fuel to be loaded at departure. A long alternate meansfuel to be loaded at departure. A long alternate means
that fuel burn is increased, as the aircraft must burnthat 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 descent
Trip 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) +Total fuel loaded- Fuel burnt (Block Fuel) +
allowance+ diversionallowance+ diversion
(allowance is usually 5% of the trip fuel)(allowance is usually 5% of the trip fuel)

16. En-Route Performance AnalysisEn-Route Performance Analysis
Tankering :There are some airfield whereTankering :There are some airfield where
either fuel supplies are unreliable or thereeither 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 atLhasa. Sufficient fuel has to be uplifted at
the departure point to return from thethe departure point to return from the
destination. Carrying fuel for an onwarddestination. Carrying fuel for an onward
stage obviously imposes some penalties –stage obviously imposes some penalties –
structural limitation & payload. There isstructural limitation & payload. There is
an economic balance to be struckan economic balance to be struck
between the price difference of fuelbetween the price difference of fuel
between the origin and destination, thebetween the origin and destination, the
value of the payload surrendered, andvalue of the payload surrendered, and
the cost of fuel burned to carry additionalthe cost of fuel burned to carry additional
fuel.fuel.

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