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AP4ATCO - Factors Affecting Aircraft Performance During Final Approach and Landing
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28. Factors affecting aircraft performance during final approach and landing
a) article description Factors affecting performance during final approach and landing (final approach speed, landing distance). Engine failure during approach and landing.
b) source (IANS) 6.5 6.9 1.2 (examples)
c) additional sources
d) SKYbrary sources: FAA Airplane Flying Handbook (FAA-H-8083-3A) – chapter FAA Pilot’s Handbook of Aeronautical Knowledge (FAA-H-8083-25A) – chapter 10 FSF ALAR Briefing Note 8.1 - Runway Excursions And Runway Overruns FSF ALAR Briefing Note 8.2 - The Final Approach Speed FSF ALAR Briefing Note 8.3 - Landing Distances FSF ALAR Briefing Note 8.4 - Braking Devices FSF ALAR Briefing Note 8.7 - Crosswind Landings Airbus - Landing Techniques - Crosswind Landings Landing on Contaminated Runways Tailwind Operations Landing Distances
FACTORS AFFECTING AIRCRAFT PERFORMANCE DURING FINAL APPROACH
When an aircraft is established on the final approach track in the vicinity of the destination aerodrome, it is considered to be in the final approach phase of its flight. During the final approach, the flaps are progressively lowered as the aircraft is slowed to landing speed. The spoilers are "armed", i.e. they are put in a state whereby they will be automatically deployed fully on touchdown. They can also be deployed manually by the pilot if desired. In addition, the undercarriage is also lowered at about 5 NM from touchdown. Both flaps and undercarriage produce drag and will require the addition of power.
Following the final approach the aircraft will start the landing phase. It begins from certain height above the runway until a complete stop by the aircraft. It comprises of an airborne segment, touchdown and a ground roll. Once on the ground the thrust reverser and spoilers will be deployed and wheel breaking will be applied in order to stop the aircraft more efficiently and use less landing distance.
Certain elements have a direct and significant impact on landing roll distance. Some of them may be the effect of unstabilized approach. The effect is likely to either disrupt traffic flow on the runway or even lead to accident / incident.
These element are:
- deviation from normal (published) descent gradient - deviation from calculated final approach speed - tailwind or crosswind component on approach and during flare / roll - runway contamination / water on the runway
Factors affecting the speed on final approach
The speed on final approach (in reference to the ground) is a factor with a large influence on the landing distance required. Because of that, an aircraft would normally land into the wind, and with as low airspeed as possible. Taking both items into consideration, the ground speed on final approach will be affected by the following factors:
As aircraft mass increases, more lift is required to balance the weight. The minimum speed at which the required lift can be achieved will be higher when the aircraft has a greater mass. Thus the airspeed on final approach depends on aircraft mass, that is, an aircraft is expected to fly with higher airspeed on final approach when its mass is greater (minimum speed increases with aircraft mass).
During final approach the flaps are progressively lowered and the drag is increased. When the undercarriage is lowered the drag is increased even further.
It is possible to reduce the airspeed while maintaining the same rate of descent. This allows a steep final approach with a relatively low speed. The advantage of this factor is used to the maximum possible extend and upon landing the configuration will be with landing flaps (maximum).
Air density (aerodrome elevation)
The landing speed (VREF) will be an IAS appropriate to the mass, but the true air speed upon landing (used to determine the ground speed) depends on the air density (aerodrome elevation and temperature). So, the higher the aerodrome elevation the higher the true airspeed for a given landing speed (IAS). The speed on final approach increases with aerodrome elevation.
The aircraft ground speed on final approach is derived from the true airspeed corrected for the wind. Therefore, in headwind conditions the aircraft ground speed on final approach is reduced; while it is increased in tailwind conditions.
For the calculation of the landing distance required it is allowed to use 50% of the headwind component and 150% of the tailwind component.
Sudden changes in wind’s direction and speed will affect the ground speed of the aircraft as well. In addition, the safety margin must be increased and therefore the aircraft would normally fly at slightly higher speed on final approach if it is known that such conditions prevail in a given situation.
FACTORS AFFECTING AIRCRAFT PERFORMANCE DURING LANDING
Factors affecting the landing distance
Before commencing an approach, the crew will check and confirm that the required landing distance is less than the landing distance available. When determining the landing distance required, following factors are considered:
Landing speed and technique
The distance required for landing is proportional to the square of the aircraft’s ground speed on landing. Thus increased landing speed will give a significantly increased landing distance requirement. For rough calculations the below values are a good reference:
Condition Effect on landing distance
Excess airspeed On dry runway 300 feet (90 meters) per 10 knots On wet runway 500 feet (150 meters) per 10 knots Extended flare (floating) 2500 feet (760 meters) per 10 knots
Delayed touchdown (at normal speed) 230 feet (70 meters) per second Excessive height over threshold
(at normal speed) 200 feet (60 meters) per 10 feet above normal over-threshold height
One may easily calculate that a plane which normally needs 4000 feet (1210 meters) of landing roll by executing an approach 10 knots too fast, for a wet runway and flying over the threshold 20 feet too high will need 4900 feet (about 1500 meters). That is 25 % more !
If during the landing the pilot will delay touchdown or perform an extended flare the required landing distance may almost double !
Beside the landing speed, aircraft mass affects the deceleration and the required brake drag as well. Increased mass reduces the deceleration for a given deceleration force and therefore increases the landing distance (inertia). In the same time, increased mass increases the brake drag available (greater pressure on the ground) and this decreases the landing distance.
However, the net effect is that the landing distance required will increase with increasing mass, but to a lesser degree than the increase of takeoff distance with increasing mass. Aircraft configuration
Several runway overrun events have been caused by ground spoilers not being armed while the aircraft were being operated with thrust reversers inoperative. Failure to arm the spoilers will result in a typical landing distance factor of 1,3 (or 1,4 if combined with inoperative thrust reversers) where 1,0 is the factor with spoilers armed.
Delay in lowering the nose landing gear to the runway maintains lift, resulting in less load on the main landing gear and, hence, less braking capability. This also delays the nosewheel spin-up signal, which is required for optimum operation of the anti-skid system on some aircraft.
Low density (high temperature, low pressure or high aerodrome elevation) will give an increase in the required landing distance due to the decrease of the engine reverse thrust and higher landing speed.
The wind affects the deceleration force during the landing roll. A headwind component adds to the deceleration force and therefore increases the breaking efficiency; while a tailwind component for the same reason reduces the breaking efficiency.
Different methods for calculations of final approach in respect to wind conditions are used:
- half of the steady head wind component plus the entire gust value (limited to a maximum value – usually 20 knots) is added
- one-third of the ATC reported average wind velocity or the gust velocity (whichever is higher), limited to a maximum value (usually 15 knots)
- or a graphical assessment based on the ATC reported wind velocity and angle, limited to maximum value (usually 15 knots)
Usually no wind corrections are applied for tailwind.
For more information about operations with tailwind wind component refer to SKYbrary’s article: Tailwind Operations
If the runway is sloping, the weight component along the runway will add to or subtract from the deceleration force. A downhill slope will increase the landing distance required and an uphill slope will reduce the landing distance.
For example, a 1 percent downhill slope increaes landing distance by 10 percent.
The brake drag depends on the runway coefficient of friction, and this depends on the runway surface and the conditions. A hard dry surface gives the highest coefficient of friction, while a wet surface or grass gives a lesser coefficient. Ice or snow on the runway or runways on which hydroplaning occurs will give a very small coefficient of friction.
The following values are typical for landing distance factors, compared to dry runway (factor 1.0):
- wet runway : 1,3-1,4 - compacted snow covered runway: 1,6-1,7 - standing water or slush contaminated runway: 2,0-2,3 - icy runway: 3,5-4,5
Also please note that there is a direct relationship between runway conditions and maximum allowed crosswind component. Refer to the table:
For more information about contaminated runways landings please refer to SKYbrary’s article: Landing on Contaminated Runways
ATC actions affecting final approach and landing
Some unfortunately common ATC mistakes and practices may lead to situations where final approach speed and landing distances are affected (which also may concide with unstabilized approache occurrence):
- improper speed control - high speed requests on final approach path (especially below 2000 feet above aerodrome level) or lack of high speed restrictions below flight level 100
- delayed descent clearances
- no available precision approach at night or in poor weather conditions
- late runway or approach type change
- vectoring to runways with significant tailwind component
- vectoring into short final distances
- vectoring which require the crews to intercept glidepath from above
- lack of or wrong informations about distance to touchdown
- lack of information about preceding traffic (concerns mainly wake turbulence category and distance to “heavy” category traffic)
Summary and landing distances of most popular aricraft types Flight Safety Foundation (FSF) Approach-and-landing Accident Reduction (ALAR) Briefing Note 8.3 — Landing Distances contains the following diagram which shows the approximate effects of various factors on landing distance:
LANDING DISTANCE – POPULAR AIRCRAFT TYPES
The table below presents landing distances for most popular aircraft types. Values are based on Eurocontrol’s Aircraft Performance Database. All aircraft types names are hyperlinked to the database (for reference to more specific data).
The following values of landing distances dataare declared based on maximum landing mass in ISA conditions, with no wind, on dry runway with no slope:
AIRCRAFT TYPE ICAO DESIGNATOR LANDING DISTANCE
LANDING DISTANCE OVER 2000 METERS
Ilyushin 86/87 IL86 2200 F16 Fighting Falcon F16 2130 Tupolev 154 T154 2100 Thunderbolt A-10 A10 2100 Beech Super King Air B350 2010 Boeing 707-300 B703 2000
LANDING DISTANCE 1500-2000 METERS
Cessna 650 Citation 7 C650 1920 Gulfstream 4 GLF4 1900 Fokker 100 F100 1800 McDonnell Douglas MD81 MD80 1800 Gulfstream 5 GLF5 1700 Airbus A340-500 A345 1600 Embraer 145 E145 1600 Falcon 900 F900 1600 Boeing 737-400 B734 1532 Antonov 124 Ruslan A124 1500 Galaxy C5 C5 1500 Eurofighter EUFI 1500
LANDING DISTANCE 1000-1500 METERS
Fokker 70 F70 1490 Learjet 35 LJ35 1478 Boeing 737-800 B738 1440 Learjet 60 LJ60 1430 Airbus A300-600 A306 1400 Bae-146-200 B462 1400 Airbus A380-800 A388 1350 Canadair Regional Jet RJ-700 CRJ7 1350 Falcon 50 FA50 1300 Airbus A310 A310 1274 Cessna 525 Citation CJ1 C525 1235 Embraer 135 E135 1200 Airbus A319 A319 1200 Ilyushin 96 IL96 1200 Globemaster C17 C17 1200 Avro Regional Jet RJ85 RJ85 1200 Cessna 550 Citation C550 1200 Falcom 10/100 FA10 1164 Fokker 27 F27 1128 McDonnell Douglas MD87 MD87 1100 Saab 2000 SB20 1100 Saab 340 SF34 1100 ATR 72-200 AT72 1100 ATR 42-500 AT45 1100 Boeing 757-200 B752 1040 Embraer 170 E170 1000 Boeing 767-200 B762 1000 Transall C160 C160 1000
LANDING DISTANCE BELOW 1000 METERS
Airbus A321 A321 930 Douglas DC10 DC10 915 Falcon 2000 F2TH 915 Hawker 1000 H25C 900 Boeing 777-200 B772 900 Cessna 750 Citation 10 C750 900 Airbus A330-200 A332 889 McDonnell Douglas MD11 MD11 884 Dash 8 Q400 DH8D 838 Dornier 328 D328 825 Antonov 26 AN26 820 Airbus A320 A320 810 Boeing 747-300 B743 800 Cessna 421 Golden Eagle C421 800 Beech 1900 B190 750 Cessna 310 C310 750 Learjet 45 LJ45 700 Hercules C130 C130 700 Starlifter C141 C141 630 Boeing 747-400 B744 610 Fokker 50 F50 600 Dornier 228 D228 550 DHC-6 Twin Otter DHC6 546 Boeing 747-200 B742 500 ATP ATP 500 Socata TBM700 TBM7 450 Pilatus PC12 PC12 450 Piper 46 Malibu PA46 400 Piper 34 Seneca PA34 300 Cessna 172 C172 200 Socata Tobago TOBA 160
1. [Question type: multiple choice, based on AirQuestions FACT-LN/151]
Q: For calculation of the landing distance required the pilot is allowed to use
A1: 50% of the reported tailwind and 150% of the reported headwind A2: 50% of the reported headwind and 150% of the reported tailwind A3: 50 % of the reported tailwind, headwind has no effect on landing distance
Correct answers: A2
2. [Question type: multiple choice, based on AirQuestions FACT-LN/137]
Q: Which factor is the most significant for the length of runway required for landing ? A1: temperature A2: ground speed on final approach A3: aircraf’t mass A4: IAS during final approach
Correct answers: A2
3. [Question type: multiple choice]
Q: Some ATC mistakes and practices may lead to situations where landing distance is affected A1: high speed requests on final approach path or lack of high speed restrictions below flight level 100 A2: late runway or approach type change A3: vectoring into short final distances A4: vectoring which require the crews to intercept glidepath from above A5: all above
Correct answers: A5
29. Other factors affecting aircraft performance