aircraft operating characteristics

“Aircraft Operating Characteristics”

Chapter 4 - Airport OperationsAshford,N. et.al.

INSTITUTO TECNOLÓGICO DE AERONÁUTICADIVISÃO DE ENGENHARIA DE INFRA-ESTRUTURA AERONÁUTICA

DEPARTAMENTO DE TRANSPORTES

José Alexandre T.G.Fregnani

21/03/2007

IT 204 Análise Operacional e Gerencial de Aeroportos

AO4 - Aircraft Operating Characteristics

Index

1. General Considerations

2. Departure Performance

3. Approach Performance

4. Operations in inclement weather

5. New Large Aircraft

1/24GENERAL / DEPARTURE / APPROACH / INCLEMENT WEATHER / NLA


General Considerations : Characteristics

•The function of the design and operation of runways and their approaches must

allow safe transition between flight and ground maneuvering.

• Aircraft operations close do the ground :

�Low speeds (80 to 150Kt).

�Extremes of lift and control envelopes.

�Expose the aircraft to risk of contact with ground.

• Aircraft Performance must match carefully with airport´s

infrastructure:

�Ground Maneuvering.

�Capability to climb and descent over obstacles.



General Considerations : Aircraft Performance

• Aircraft Performance has a huge impact on airline economics.

• Reductions of payload

( indireclty weight)

indicate large reductions

in potential profit.


• At a given speed drag is a function of lift and therefore weight.

• Weight is the principal variable for Field lengh and Climb capability (WAT and

Obstacle clearance).

THRUST - T

DRAG -D

LIFT -L

WEIGHT - W

W•cos

γ

W•se

nγ

θγ

dt

dv

g

1

W

DTgradient climb ) (γtan •−

−==

•Aircraft performance is primarly a function between the excees of thrust to drag and excess of lift to weight.

LIFT – L

THRUST - T

WEIGHT - W

DRAG – D

L

D=

W

T


General Considerations : Aircraft Performance

Therefore weight is the most important factor for both Performance and Economics !



General Considerations : Matching Infrastructure

• Operators will not use airfields

where significant reduction of

payload is required or are not

adequate for the aircraft size.

• There is an economic limit to

the airport operator´s ability to:

Extend Field Lengh and Protect Obstacle Clearance Surfaces.

Principles in matching aircraft to the infrastructure:

1. Demonstrated Performance of the aircraft;

2. Use of Net Performance;

3. Assesment of Probability of failure (safety assesment);

4. Regulation of operations (JAR-OPS1/FAR 121) and performance (JAR/FAR 25).



General Considerations : Takeoff Field Lenght Required

All Engines

distance

Acel-Go

distance

Acel-Stop

distance

• All Worldwide takeoff

Regulations are based on

FAR25 or JAR 25.

• Takeoff distance

demonstration is based

on OEI or AEO

configurations.

• 1 sec. from Vef to V1.

• Takeoff Field Lenght

Required is the maximum

of:• 1.15 x All Eng.Distance

• Acel-Go distance.

• Acel-Stop distance.



General Considerations : Takeoff Field Lenght information


• Runway dimensions Information may be found in AIP (Aeronautical

Information Publication) and NOTAM (Notice to Airman).

• When limited by climb capability (WAT or Obstacle), the excess of ASDA

may be used to increase energy and improve climb gradient. Higher takeoff

speeds are expected (V1.VR andV2).

→ this is called IMPROVED CLIMB or OPTIMUM V2 technique.



General Considerations : Risk Analysis

• Risk of na accident per flight is acceptable, cathegorized and quantified.

• Under and Overshoot analysys (Monk 1981).

• RESA of 1000 ft beyond

runway strip would contain

half of the under/overshoot

accidents.

• Better to Go-Around !!!


General Considerations : Risk Analysis

• It is possible to construct protected

airspace surfaces to limit the probability

of aircraft outside them to the remote

risk category (10-7).


•Safety requirements and economical

operations may not go in the same

direction(Ex: OEI perf. x minimum Fuel

Climb).

• More severe operational limitations are

set once the risk increases.


Departure Performance : Takeoff facts

• Takeoff performance is based on on screen height of 50 ft over threshold,

in case of Acel-GO condition.

• 2 seconds added for pilot´s reaction time between V1 and initial braking

action.

• JAR 25 requires wet runway performance accountability for all aircraft

models. This states 15 ft screen height (Acel-GO) , V1set 4 secs earlier and

one thrust reverser credit is allowed (Acel-STOP).

• Until 1998 the FAA did not require wet runway accountability, but it is now

required for airplanes certified post FAR 25 Amendment 25-92.

• Takeoff Overrun incidents :

• Related to pilot´s training and V1 concept (see slide 11).

• Moving the Airport Operator for provision of RESA (Runway Excursion Safety Area) in addition to strip and prepared stopway.

.


• Analysis of all Jet Transport overrun incidents/accidents statistics between

1950 and 1997.

• Results:

� In more than 75% of the events, aircraft were able to fly with all

engines operating.

� Most of overruns occurred above 80 KIAS, with high energy and

therefore difficulty on braking for complete stopping.

�Less than 25% of the incidents were related to OEI or Fire.

• Actions:

� V1 seen as an action speed ( the decision must be made before).

� FirstPilot´s action to braking the aircraft must occur at V1.

� Only reject takeoff above 80 kt in case of OEI, Fire or Aircraft broken.

� Pilot´s training: V1 callout made 5kt earlier.

� Change in regulations : FAR/JAR 25.



Departure Performance : Takeoff Safety Training Aid ( Boeing,1998)


Departure Performance : Takeoff Climb Gradients


• One Engine Inoperative Climb requirements (FAR 121 and 135 aircraft):

Gross Climb Gradient Required

Climb

Segment

1st 2nd 4th

2 ENG 0.0% 2.4% 1.2%

3 ENG 0.3% 2.7% 1.5%

4 ENG 0.5% 3.0% 1.7%

• All engines Climb:

� Gross gradient

reduced by 3.2%.

� JAR requires

minimum of:

�5.2% (2nd)

�4.1% (4th)

�CON thrust

• Light aircraft (general aviation) :“See and avoid obstacles below clound base”


Departure Performance : Special Takeoff Procedures


• “Get them high early” technique (ATA).

� Derivative from

recommended ICAO

NAP procedure.

� Close monitoring of

pitch angle with V2+10.

� Thrust reduction at

1500ft AGL.

• “Full Clean-up” technique (ATA):� Maintain Takeoff thrust until flaps retracted.

� Fuel economy (159kg B737) but reduction on engine´s life.


Departure Performance : Takeoff Limitations


• Other economic or environmental

considerations : noise, emissions,etc..

• Any margin between

the MTOW and Actual

Takeoff Weight may be

used for Fuel Tankering

or;



Approach Performance : Landing factors

• FIELD LENGTH LIMITS (FAR 121.195 and JAR-OPS-1.515.):

ACTUAL LANDING DISTANCEdemonstrated in flight test as follows:

� V/S < 6 ft/sec at 3 deg glide slope.

� Zero slope, smooth, DRY, hard

surface runway.

� Manual Wheel braking.

� Other braking devices: auto

spoilers deployment.

� All data reduced to ISA

Temperature.

� Vref at 50 ft over threshold.

� Vref = 1.23Vs1g

� No reverse thrust credit.

Approach Performance : Landing characteristics



• Correct conditions at the threshold are important to

provide the predicted landing performance.

• Stabilized Approach Concept is necessary:

� Correct height (52ft for a glide path of 3 deg).

� Correct Speed : Vref.

� Adequate rate of descent: from 500 to 1000

ft/min.

� Adequate thrust.

� On glide path.

• Ground aids must be satisfactory to provide adequate

performance : PAPI and VASIS systems for visual.

• Full precision approach (ILS CAT I/II and III) are the

best aid to accurate flying. Autoland and Head Up

Display guidance may be used.

Decision Height(DH) and Runway Visual

Ranges (RVR) for Precision Approaches.

CAT DH (ft) RVR (m)

I 200 800

II 100 400

IIIa N/A 200

IIIb N/A 50

Approach Performance : Missed Approach performance



In Cruise Configuration

Required a Positive Net

Gradient at 1500ft AGL

with OEI.


Approach Performance : Obstacle Clearance


• Approach path must maintain

obstacle clearance on expected

flight path.

• ICAO Doc. 8168 defines how to

design approach procedures,

defining MDA/MDH and DA/DH.

• ICAO Annex 14 defines airport

protection areas.


Approach Performance : Special Approaches

• Reductions on noise/ fuel are obtained

avoiding unecessary drag on delaying

flaps and gear selection as much as

possible. (Lufthansa : B737 / 200 kg).

• Two Segment Approaches.

• “High and Fast” , unconfottable for

pilots (R/D higher than1000 ft/min on

final approach).

• NASA CDA (Continuous Descent

Approach) : tailored arrivals.pdf

• Constant Mach/IAS

• Decel at 15000 ft to Initial

Approach speed.

• Continuous descent down to FAF.



Inclement Weather


• Inclement weather conditions have direct impact on runway capacity, due to the

increased occupancy time. Runway Capacity reduction is function of:

� Wake turbulence (vortex systems).

� IFR Operations.

� Autoland (requires extended flare).

� Increasing braking distances on wet,contaminated and slippery runways and

thus decreasing values of high speed exits (15 kt on slippery / 40 kt on dry rwy)

• Author suggests the design of exit locations based on poor landing performance.

• Croswind Effect : limitations on Flight Manuals depending on runway conditions (10

kt limitation is usually set for WET runways). Critical for STOL aircraft.

• Performance dificulties may arise with standing water, snow, slush or ice.

� Large reductions on V1 and payloads are expected.


Inclement Weather : Braking friction


• Airport authorities report the friction characteristics of the runways using friction

measuring devices (skidometer, mu-meter, friction tester, etc…)

•These reported friction characteristics, however, do not represent the actual

aircraft braking friction, as many variables like aircraft weight, speed, braking

mechanism, tire and undercarriage characteristics are not considered on its

determination.

Reported Braking Action

Reported Friction Coefficient(ICAO)

Good (wet runway) 0.40 and above

Medium to good 0.39 to 0.36

Medium 0.35 to 0.30

Medium to poor 0.29 to 0.26

Poor ( wet ice) 0.25 and below

• The measured characteristics are

reported by the airport authorities as

"Reported Braking Action“.

• “GOOD” means no directional

difficulties ( as in a WET runway)


Inclement Weather :Windshear


• Windshear is defined as a rapid and strong

variation of wind speed/direction in a given

altitude within a short distance.

• Most of the times is associated to variable

winds near surfaces due to thunderstorm cells

(called Microbursts).

• Strong variable gusts may invert tail to

headwinds almost immediately, leading the

aircraft to AOA variation near to stall.

• Low Level anemometers system may me

installed at periphery of airport area, in order to

provide warning alerts to pilots.

• Windshear scape guidance on aircraft´s F/D.


New Large Aircraft


• In recent years there have been considerable

discussion concerning the introduction of

aircraft capable to carry 800 to 1000 PAX.

• A380 operational in 2Q/2007 and B747-8 in

1Q/2009 are real examples. Larger dimensions

and weights than current heavy aircraft are

expected.

• Some problems are evident to Airport

Infrastructure and capability:

� Vortex systems : runway ocupancy time

extended due to larger separations.

� Increased taxiways, runways, aprons

lateral separations;

� Cleaning and servicing.

� Loading passengers and cargo.


New Large Aircraft : Are the airports prepared ?



THANK YOU !THANK YOU !THANK YOU !THANK YOU !

José Alexandre T. Guerreiro [email protected]

[email protected]

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