Crosswind landing
A crosswind landing with an airplane is a landing in a crosswind . Because landings without any crosswinds are the exception, in flying practice one speaks of a crosswind landing only when there is a stronger crosswind of approx. 10 to 25 knots (kt, approx. 18 to 46 km / h).
Crosswind landings place increased demands on the skill and attention of the pilot, who must take into account and compensate for the lateral drift caused by the wind during the approach in order to achieve a precise touchdown on the runway . There are different techniques for doing this.
Every aircraft manufacturer sets limits for crosswind landings for its aircraft. These are usually staggered according to the condition of the runways, but the stability of the landing gear also plays a role. The manufacturer also recommends a certain technique for crosswind landing with its aircraft.
Three common landing techniques in crosswinds are:
- the crosswind landing with a hanging wing ( sideslip );
- the crosswind landing with a lead angle , also called crabbing ;
- a combination of lead angle and hanging wing.
Basics
Airplanes are constructed in such a way that when they move around the yaw axis (vertical axis or vertical axis) they tend to return to their old position, which is why their longitudinal axis or direction of flight is difficult to change to the right or left. Aircraft have a high yaw stability due to their design.
Aircraft tend to turn into the wind because of the large surface fin . In cross winds, the aircraft will turn away from the runway direction so that the bow is directed against the wind.
Cross wind
The crosswind can be broken down vectorially into a headwind component coming from the front in the runway direction and a crosswind component (precisely 90 ° laterally, i.e. at right angles to the runway). The pilot has the appropriate diagrams, navigation computers and rules of thumb for this .
Only the crosswind component is decisive for the crosswind landing. It is calculated from the (ground) wind speed multiplied by the sine of the wind angle to the runway. Example: A crosswind of 40 kt with an angle of incidence of 60 ° to the landing direction has a (90 °) crosswind component of approx. 35 kt .
There are several ways to determine the wind direction on the ground before landing. The windsock is probably the oldest device through which wind information is available to the pilot. The wind direction can be determined quite easily, while the wind strength can only be roughly estimated from the degree of filling of the windsock. At controlled airfields, the wind is also measured by a weather station and displayed in the control tower , averaged over the last 2 minutes. The air traffic controller makes this information available to the pilots for take-off and landing without being asked. At larger airports, this wind information is also recorded on a recorded message, the so-called ATIS . This allows pilots to find out about the weather conditions at the airfield without first having to fly over the landing area or having to ask questions about important radio frequencies.
Example of a usual wind information in English-speaking air traffic: Wind 290, 13 knots gusting 30 knots, varying between 260 and 310 degrees (wind from 290 °, 13 knots in gusts of up to 30 knots, turning between 260 and 310 degrees)
Landing direction
The pilot selects the landing direction so that the landing can be carried out against the wind direction. This enables the lowest possible airspeed over the ground and thus a short landing taxi distance. In the early years of aviation, the runway was often a more or less circular meadow on which the pilot could land in any direction, depending on the wind direction. The pilot previously flew low over the windsock at the airfield in order to recognize the wind direction. The motto was: "If you look into the mouth of the windsock, something is wrong", because then you landed with a tail wind. The planes had large wings for their weight, which allowed them to be flown slowly and required only a short landing distance.
With the advent of paved runways, on which heavy aircraft could touch down at high landing speeds, pilots were tied to two fixed landing directions. With the prevailing westerly winds in Germany, the runways are still preferably oriented in an east-west direction - RWY 09/27. In the worst case, the wind blows at right angles to the runway and thus creates a significant crosswind component.
Lead angle
In order to compensate for the drift to the side, a slip angle (also called lead angle or windward angle ) is flown in cross winds . A course ("heading") is flown that prevents drifting from the centerline. This is done by turning the aircraft nose (the aircraft longitudinal axis) into the wind.
The size of the required lead angle depends on the size ratio of crosswinds to airspeed. The lead angle can be determined graphically using a wind triangle . In flying practice, it is mostly flown. For example, with a crosswind of 50 kt and a flight speed of 100 kt, an aircraft needs a lead angle of 30 ° in order to fly a desired course over the ground. Whereas, for example, with a cross wind of 50 kt and a flight speed of 250 kt, a significantly smaller lead angle (11.5 °) is required.
In the course of the landing approach, the airspeed is gradually reduced from cruising speed to 1.3 times the stall speed. As a result, the influence of the crosswind on the lead angle increases relative to the flight speed, which is why the lead angle has to become larger and larger for compensation. The aircraft nose must therefore be turned a little further into the wind in order to maintain the course over the ground. Furthermore, with decreasing altitude, due to the influence of ground friction, there is a tendency that the wind strength also decreases, which in turn may require a change in the lead angle. In practice, however, the effect of the decreasing airspeed usually predominates.
Wind vane effect
With constant wind strength and direction, a flying aircraft moves in a homogeneous air mass, which moves in the wind direction with respect to the ground.
Amplifies the wind, however, he first pushes the rudder at the stern in Leerichtung because it opposes him the greatest attack surface and relatively far from the center of gravity is removed the aircraft. Airplanes therefore show a tendency to turn the tail out of the wind and thus the nose into the wind when the crosswind is refreshing.
Landing techniques in cross winds
Crosswind landing with hanging wing
One possible landing technique in crosswinds is landing with the wing hanging down (side-gliding method or sideslip approach).
The first part of the approach is flown with a lead angle, as in cross-country flights in cross winds. In the last part of the approach, in the short final approach, however, the flight attitude is changed to with a hanging wing and opposite rudder and the lead angle is given up.
The wing facing the wind (windward wing) is "left hanging" by moving the ailerons to the side from which the wind is coming. For example, when there is a cross wind from the right, aileron is given to the right. As a result, the upper side of the fuselage of the aircraft turns into the wind, the aircraft has a “list”. So that the nose of the aircraft does not gradually turn into the wind due to the aileron deflection, the rudder must be used to counter-steer, in the example to the left. With the help of the rudder, the aircraft nose is steered exactly in the direction of movement of the aircraft.
With this method, the rudder and ailerons are deflected against each other. This condition is called "crossed oars" in pilot jargon. Due to the crossed oars, there is a side glide . That is why this method is also called the sideslip method.
The aircraft's bank angle is kept as stable as possible after the appropriate value has been “flown”. On the other hand, the alignment of the aircraft nose has to be corrected continuously with the rudder.
The aircraft is flown until touchdown - with the wing hanging, oars crossed and aligned with the runway. As a result of the inclined position of the aircraft, the main landing gear facing the wind touches down first, preventing it from drifting downwind.
The required cross slope increases with the relative proportion of the crosswind component. Therefore, the higher the crosswind and the slower the aircraft flies, the greater the bank angle - and thus the risk of the wing or engine touching the ground when touching down.
The advantage of this approach method is that the longitudinal axis of the aircraft is already aligned with the center of the runway during the approach and no more rotations are required before touchdown.
Crosswind landing with a lead angle
The second method of crosswind landing is landing with a lead angle without a hanging wing. It is also known as the pushing method or crabbed approach ( de-crab method or de-crab in the flare ), since the aircraft is approached with a pushing angle (= lead angle) until shortly before (approx. 1–2 s) touchdown . The term "crab" refers to the crabs walking sideways. Commercial aircraft are mostly landed using this method, as it offers increased passenger comfort and the distance between the engines and the runway is greater than with the landing technology discussed above.
When approaching with a lead angle to the right, on the final approach, while the aircraft moves along the extended runway centerline, the pilot sees the runway further to the left than normal.
On wet or contaminated runways, the lead angle is maintained until touchdown so as not to destabilize the short final approach by additional maneuvering. This makes it easier for the aircraft to touch down precisely at the targeted landing point. On dry runways, the lead angle is given up shortly before touchdown to protect the landing gear and tires. To do this, the pilot steps into the rudder on the side facing away from the wind, the nose aligns in the direction of the orbit. That is what gave this landing method the name kick-out method . At the same time, the ailerons must be turned to the opposite side facing the wind to prevent the wing from lifting on the windward side and to keep both wings horizontal.
Depending on the type of aircraft, in particular the size and weight of the aircraft begins this aligning the aircraft longitudinal axis of the runway center line before the flare (flare) .
Combination of lead angle and sideslip
If only the sideslip method is used, it will eventually reach its physical limit due to the wing geometry. The landing method with a lead angle also reaches its physical limit at some point due to the stress on the tires and the chassis. The combination of both methods allows a compromise, a smaller bank angle and a smaller lead angle. With this mixed technique of lead angle and sideslip (English crab & slip ) you can land safely even in much stronger cross winds.
Crosswind landing with autopilot
Typical autopilots for light aircraft can also fly a lead angle during approach, and two-axis autopilots can also fly during an approach on the glide path of an instrument landing system or an RNAV / GPS approach. Only autopilots ( autoflight system ) with Autoland mode ( automatic landing mode; short: Autoland; automatic landing ) are permitted for fully automatic landings. Such autopilots have so far only been available for commercial aircraft. To do this, the aircraft must be equipped with appropriately certified autopilots. The maximum crosswind components are significantly reduced for automatic landings. The Autoland mode is mainly selected for very poor visibility, but not for strong cross winds.
Example for Maximum Crosswind Component for Autolanding with the autopilot:
-
Boeing 737 NG - Automatic landing (dual channel CAT2 or CAT3 approach):
- Cross wind max. 20 kt
- Headwind max. 25 kt
- Tail wind max. 10 kt
- If only one autopilot is switched on (single channel autopilot), it can only be used above 158 ft above ground (measured with a radar altimeter) (Minimum Use Height, MUH)
- Boeing 757 - 15 kt
- Boeing 747-200 - The Autoland function maintains the lead angle up to a few meters before touchdown. When the main landing gear has reached a height of 2 ft (approx. 61 cm) above the ground, the aircraft's longitudinal axis begins to align with the runway axis using the rudder.
Cross wind landings of individual types of aircraft
Boeing B-52
Only on the Boeing B-52 can the main landing gear for crosswind landings be turned up to 20 ° to both sides (bogie) in order to be able to compensate for crosswinds during take-off and landing. In this way, the aircraft can land and take off with a lead angle without the pilot having to correct it at the last moment. Despite the lead angle, the aircraft then rolls straight (= parallel to the runway) over the tires.
Boeing 737
For the Boeing 737 the Maximum Demonstrated Crosswind ( see below ) for dry or damp runways according to the manual is 35 kt or 36 kt for the B737 NG. The maximum tailwind for landing is 10 kt.
The Boeing 737 has additional special shock absorbers on both main landing gears, which allow the main landing gears to turn slightly sideways if they are loaded by a side impact. Therefore, when taxiing a B737, it can sometimes be observed that the aircraft rolls with a slightly twisted longitudinal axis.
At Southwest Airlines , B737 NGs originally purchased without these special shock absorbers were later even retrofitted with them to improve their landing properties in crosswinds.
Boeing 747
In principle, the Boeing 747 , like any other aircraft, can be landed with both techniques (hanging wing or lead angle). However, the landing with hanging surfaces (wing low approach) is very limited with the 747. Due to the low wing level and the engines 1 and 4 mounted far out, the maximum permitted bank angle is limited to 8 ° during touchdown in order not to run into the risk of a pod strike (the engine nacelle touches the ground).
While twin-engine jets in particular fly with a lead angle, but align themselves parallel to the runway before they float out and from then on compensate for the crosswind with a hanging wing, the 747 is flown with a lead angle until immediately before touchdown when there is a strong crosswind component with a lead angle Runway aligned.
As a destination point (Engl. Aim point ), a point further selected somewhat Luv (into the wind) from the runway center line. During the float, the aircraft is aligned to the runway center line by means of the rudder. At the same time, the aileron is moved to the opposite side to keep the wings horizontal. The inertia of the relatively heavy B747 prevents a large part of the lateral drift for the few seconds remaining until touchdown.
Since the B747 cannot let the wing hang down far, its main landing gear is specially reinforced and designed so that it can withstand pushing landings with a deviation of up to 40 ° from the aircraft's longitudinal axis. The main landing gear of the B747 cannot be rotated in flight. Only when rolling, the two center main gear rotate with when the nose gear is controlled. However, due to the rigid arrangement and the offset of the landing gear groups, the 747 has to be aligned extremely precisely because it tends to keep in lane.
Boeing 757
The limit of the Boeing 757 for crosswind landings is 40 kt. The maximum demonstrated crosswind , without gusts, is 30 kt.
Airbus A380
The Airbus A380 demonstrated six crosswind landings and five crosswind starts at 40 kt (74 km / h) cross winds with gusts of up to 56 kt (104 km / h) for its type approval in Keflavik on November 10, 2005 . This value was considerably higher than would have been required for its type approval.
Light aircraft
Each manufacturer describes the Maximum Demonstrated Crosswind somewhat differently in their manuals . Most light aircraft often cannot withstand lateral shear forces on the landing gear, which is why the pilot must carefully set them down without pushing them.
- Cessna 150 - Maximum Demonstrated Crosswind: Landing 15 kt, Takeoff 20 kt
- Cessna 172 - Maximum Demonstrated Crosswind: 15 kt. If there is a strong crosswind, the flaps should be in the lowest possible position (depending on the length of the runway). If the approach is to fly with a flap position of more than 20 °, the pilot can feel a certain oscillation of the elevator (at normal approach speed) with the sideslip with full rudder deflection . However, this does not affect control of the aircraft. The best control in crosswind landing is with the "hanging wing" method. However, other crosswind techniques can also be used to land. After touching down with the nose landing gear, keep the direction and only brake lightly now and then. Crosswind landings were demonstrated at 15 kt.
- The Cessna 195 has a trailing main landing gear. It was not specifically designed for landings with strong crosswinds. The chassis construction should only protect against light lateral loads on the chassis leading to a rollover on the ground. Later models of the C-195 had a special crosswind gear , which allowed the passive rotation of the landing gear by lateral landing forces. The fluttering of the following landing gear was dampened by a spiral spring, which also centered the landing gear. The landing gear could only turn outwards, while the inward rotation (towards the aircraft fuselage) was mechanically limited. Photo: Cessna C-195 at the moment of touchdown with the left main landing gear
- Columbia 400 - Maximum Demonstrated Crosswind: 23 kt
- Piper PA-28 - Maximum Demonstrated Crosswind: 17 kt. For crosswind landings, the approach speed should be slightly higher than the normal approach speed. If possible, the flaps should only be extended to 0 ° to 25 °.
- Piper PA-44 - Maximum Demonstrated Crosswind (for landings): 17 kt. For crosswind landings, the approach speed should be slightly higher than the normal approach speed. The flaps should only be extended to 0 ° to 25 ° and should be retracted immediately after touching down. The approach should be made with a lead angle into the wind until the pilot is ready to float out. Only then is the windward wing suspended so that the lead angle can be given up without drifting to the side. At the same time, the rudder aligns the landing gear with the runway. Long side slips should be avoided when the fuel gauge is low.
- The ERCO Ercoupe from Engineering and Research Corporation (ERCO) (built 1940-1970) had no rudder pedals. The Ercoupe was steered exclusively with the control horn. The ailerons and rudders were connected to each other by cables so that the aileron and rudder could not move in opposite directions. Therefore, the sideslip method for crosswind landings is prohibited here and only the pushing method must be used.
Tail-wheel planes
The most common accidents in tailwheel aircraft occur during crosswind landings, followed by crosswind take-offs and taxiing in crosswinds. Tail-wheel aircraft are designed in such a way that the wind vane effect is much more pronounced, which is why they are much more susceptible to cross winds than aircraft with nose landing gear. But that doesn't make tail wheel planes harder to fly or more dangerous. However, they are less tolerant of pilot errors. In addition to correctly assessing his flying skills, the pilot must also know and observe the limits of his aircraft. Tail-wheel planes are more restricted than nose-wheel planes in crosswinds.
The approach is usually with a hanging windward wing and opposite rudder in order to stay aligned with the runway, even when floating out and rolling out. But also the approach technique with lead angle and “kick straight at the last moment” is possible with tail-wheel planes, but requires a lot of skill when straightening, because tail-wheel planes tend to break away to the side.
The actual landing can also be carried out as a three-point landing in cross winds . Due to the hanging surface, in this case it is actually a two-point landing on the main landing gear facing the wind and the tail wheel. After touching down on these two points, the aircraft rolls down until the leeward main landing gear touches down last. In very gusty winds, the tail is landed on the main landing gear with the stern hanging low ( tail-low wheel landing ).
In strong side wind, the so-called wheel landing is preferably carried out (engl. Wheel landing ), in which the aircraft at a shallow angle on the (windward) main landing gear touches first, while the rear end initially remains in the air. The advantage here is the significantly higher touchdown speed compared to the three-point landing, which makes the crosswind less of a burden (but also extends the required landing distance). After touchdown, the rudder is pushed forward to keep the stern up as long as possible while it is coasting. If the tail sinks too early, it can easily happen that the aircraft takes off again briefly due to the suddenly increased angle of attack and is then uncontrollably exposed to the crosswind - a frequent cause of accidents. As long as the tail is in the air, the aircraft will slip sideways, so landing on the wheel requires the pilot to be extremely concentrated.
When coasting under crosswind conditions, tail-wheel planes tend to roll over (ground loops). It is therefore essential that you touch down without drift or lead angle.
Shoulder and high wing aircraft
High- wing and shoulder- wing planes , such as the BAe 146 , the De Havilland DHC-8 or the Antonow An-24 , can land with a hanging wing because of the greater ground clearance. However, high-wing and shoulder-wing planes often have long and filigree main landing gears when they are retracted into the wings or engine nacelles. These main landing gears then hardly tolerate any lateral shear loads from landings with a lead angle.
Safety aspects of crosswind landing
Strong crosswinds entail increased dangers, as the pilot is more challenged in the final phase of approach and landing. Crosswind landings require a lot of physical work from the pilot. He has to make quick and large steering inputs and the landing is often less "controlled". Hard landings and ground contact with wing tips or engine nacelles are much more common. Crosswind was a factor in over a third of landing accidents.
The quality criterion for a crosswind landing is not whether it was softer or harder or whether the aircraft shook a lot during the approach phase. The main criterion is the certainty that it does not drift to the side when touching down, that it is exactly aligned with the runway and that, as with any normal landing, it also maintains the approach speed, touches down at the touchdown point on the center line in order to have reserves to the right and left. As for normal landings, a stabilized approach is the mandatory requirement that must be met before a landing. If a stable state is not reached during the approach up to the decision height, then you have to take off. For safety reasons, the same also and especially applies to crosswind landing.
Even after landing, when taxiing, 8% of accidents occurred, especially in crosswinds and a wet runway.
Despite the clearance from air traffic control, it is ultimately the decision and then the responsibility of the pilot on which runway to land. If the crosswind is too strong, he should definitely consider applying for landing clearance again for another runway with more favorable wind conditions. The clearance to land, as the name suggests, is only a permit, but not an instruction from air traffic control that the pilot must comply with.
The pilot will also include waiting for an improvement in wind conditions as an option in his planning. He may need to fill up with more reserve fuel than is normally required before departure .
During the approach and landing briefing , the crosswind and the planned landing technique must also be discussed.
Another security option in marginal side wind landing, the Next fly to a destination alternate (engl. Alternate airport ), better match on the landing direction and wind direction.
Landing incidents and accidents come first in the accident statistics. Although landings appear to be bad or good only at the last moment, the result is usually decisively influenced much earlier - by operating and training manuals, training methods and the decision-making processes in the flight preparation phase as well as during the flight.
Crosswind landings on runways with reduced braking effect represent an increased risk of accidents. The Netherlands National Aerospace Laboratory (NLR) found that landings with more than 15 kt crosswinds increase the accident frequency significantly.
Another study has shown that the risk of accidents increases sharply when landing in a crosswind of over 20 kt. 33% of landing accidents are caused by strong crosswinds, tailwinds or wind shear .
A sufficient safety cushion must therefore be available for the pilot and the aircraft in crosswind landings. The airline must therefore set appropriate, safe "operational maximum crosswind landing limits" (Maximum Crosswind Demonstrated - see below ) for the pilot and aircraft.
Just as important as the wind speed of the crosswind is the constant and therefore predictable wind speed and direction from which the crosswind is blowing. Gusty winds from variable directions make a crosswind landing much more dangerous. The pilots also tend to excessive steering deflections in strong gusts of wind. The workload of controlling the rudders may become too great for the pilot.
Safety training for crosswind landings
In July 2008, the airfield EDHF "Hungry Wolf" in Itzehoe of Europe's first simulator for crosswind landings of single engine airplanes installed. The moment before touching down on the runway is stretched in time. So it is possible to consciously and repeatedly practice different aspects of crosswind landing with variably adjustable parameters.
Accidents in crosswind landings
On December 24, 1997, a Boeing 757 from Transavia Airlines, a charter flight from Las Palmas, landed at Schiphol Airport (Netherlands) in a strong, gusty cross wind, 30 kt with gusts of up to 45 kt from 220 ° - variable 200 ° to 260 ° , on runway 19R in pushing position. The nose landing gear broke away. The aircraft skidded 3000 m over the runway and came to a stop next to the runway. Only three passengers were slightly injured. The captain was the pilot flying . The approach took place with the autopilot, which was switched off 100 ft above ground, 8–10 seconds before touchdown. The pilot was then unable to correctly align the aircraft with the runway. The Transavia Airlines Operations Manual did not set any clear limits for crosswind landings. If the pilot had switched off the autopilot earlier, he would have had more time to correctly align the aircraft with the runway.
On March 1, 2008, a Lufthansa Airbus A320 from Munich (flight LH 044) touched the ground with the tip of the left wing during a crosswind landing at Hamburg Airport in Hamburg-Fuhlsbüttel. Although hurricane Emma generated gusts of up to 55 knots and runway 33 was more favorable to the wind, the crew decided to land on runway 23, as this has complete electronic landing aids. It was approached with a large lead angle (although precisely this large angle to the runway was often depicted as dangerous by the press, that was completely correct from a flying perspective). Shortly before touchdown, the A320 was hit by a particularly strong gust, rolled to the left on a steep bank and touched the ground with the tip of the left wing. The crew got the aircraft under control again, took off and then landed safely on runway 33. Nobody was injured, the winglet on the left wing tip of the aircraft was damaged. The decision of the crew to land on runway 23 was discussed extensively in the media; However, many experts do not see this as a wrong decision, since gusts on the landing approach are unpredictable. After investigations by the aviation authority, it turned out that the machine also contributed to the accident. The on-board computer interpreted the brief touchdown of the left main landing gear as a landing and partially blocked the rudder deflections or reduced the maximum possible aileron deflections by half. Since this behavior was not known to the pilots and is not mentioned in the operating manuals, the situation was overcome with great difficulty. As a consequence, the Federal Aviation Office asked Airbus to revise the flight control software and the operating manuals. After several days of repairing the winglet, the machine was returned to regular service.
Maximum Demonstrated Crosswind
For the type certification of an aircraft, proof of crosswind landing at Maximum Demonstrated Crosswind is required.
The maximum demonstrated crosswind is listed in the flight manual in the chapter Operational Limitations . Often the Maximum Demonstrated Crosswind is also only abbreviated as demonstrated crosswind - German: demonstrated crosswind. The terms Maximum Demonstrated Crosswind Velocity or Maximum Demonstrated Crosswind Component are also used. On the other hand, the German translation, maximal demonstrated cross wind, is not in use .
At this wind speed, a very experienced test pilot from the aircraft manufacturer demonstrated a safe and clean crosswind landing as part of the type certification of the aircraft type . A test pilot who has flown heavy crosswind landings very often and has brought his landing technique to the highest perfection can of course master higher wind speeds in a crosswind landing than an average commercial pilot.
Therefore, airlines often set their own, stricter limits for crosswind landings for the everyday use of their average experienced airline pilots.
In the JAR 25237 stipulates that be demonstrated for a type certificate need that safe landings and takeoffs at:
- a) at least 20 kt crosswind (precisely: a 90 ° crosswind component of the wind speed) or
- b) a fifth of the stalling speed in the landing configuration (engl. reference stall speed V SRO ) are possible.
Of the values a) or b), the greater value applies, but it does not have to be greater than 25 kt.
For some aircraft types, the Maximum Demonstrated Crosswind is not listed in the Operational Limitations chapter . Then JAR 25.237 - variant b) applies, that is, the “Maximum Demonstrated Crosswind” is then a fifth of the stall speed in landing configuration ( reference stall speed V SRO ). A very rough rule of thumb is always: The “Maximum Demonstrated Crosswind” is 20-25 kt.
The aircraft manufacturer specifies upper limits for the wind speed of the crosswind component - Recommended Maximum Crosswind (German: Recommended Maximum Crosswind ). It is given separately for dry, damp and wet webs. But not for standing water on the track, ice, snow or slush. These limits are determined on the one hand for dry runways on the basis of tests ( Maximum Demonstrated Crosswind ) and on the other hand for humid and wet runways on the basis of simulations ( maximum computed crosswind ). The manufacturer only needs to prove the Maximum Demonstrated Crosswind on a dry runway.
The Maximum Demonstrated Crosswind does not necessarily have to be the permitted limit. It's just the speed at which the manufacturer demonstrated a crosswind landing. For type approval, it is sufficient for the manufacturer to have his test pilots demonstrate safe crosswind landings within the approval requirements. It doesn't have to risk a crash to demonstrate landings in even more extreme crosswinds. Unless the aircraft is to be demonstrated as being particularly suitable for crosswind landings. But then many pilots will also go to this limit, there will be more accidents with this type of aircraft and the manufacturer will not be happy about this negative advertising. The manufacturer remains on the safe side if he does not go to the physical limits with his Maximum Demonstrated Crosswind and still leaves a reserve.
The Maximum Demonstrated Crosswind is limited, among other things, by the effectiveness and area of the rudder. If it is kicked to the side as far as it will go, i.e. it has a full deflection, it can only compensate for a crosswind up to a certain wind strength. If the crosswind goes beyond this, the aircraft drifts to the side despite full rudder deflection. The rudder deflection is used both for landing with a lead angle with alignment at the last moment, as well as for crosswind landing with the wing hanging and the rudder stepped in the opposite direction. The limits for the crosswind component in crosswind landings usually do not result from the limited strength of the main landing gear, but from the limited steering capacity of the rudder. If a pilot lands at crosswind speeds beyond the Maximum Demonstrated Crosswind , the aircraft will drift sideways over the runway despite full rudder deflection. But if the pilot accepts the pushing landing, which he can then no longer "kick away" at the last moment, then an accident-free landing is still possible with a sufficiently stable landing gear. In the event of an accident, however, there could be problems with the air traffic control and the aircraft insurer due to the operating limits being exceeded.
The limits for crosswind landings specified by the manufacturer in the aircraft manual can also result from the landing gear or the airframe. The manufacturer also publishes its recommended landing technique for crosswind landings.
Often pilots set their own personal limit for crosswind landings before taking off their flight or are given a limit by their airline. This self-limitation depends on the total number of flight hours, his experience from previous crosswind landings, the time since the last crosswind landing (real or in the simulator), the total experience of both pilots. Some airlines have different limits for the captain and first mate, but these do not necessarily have to be based on real skill levels.
According to the flight manuals of most aircraft, crosswind landings of a maximum of 25 to 28 kt crosswinds are permitted ( Maximum Allowable Crosswind ).
Runway restrictions
The ICAO recommends a limit of 15 kt crosswinds for night landings on runways that are subject to noise abatement runways .
Night landings are restricted at Schiphol Airport :
- on dry runway - to max. 25 kt cross wind,
- on dry to wet runway - to max. 15 kt cross wind,
- on a wet runway - to max. 5 kt cross wind.
Crosswind landings with seaplanes
Since the floats of seaplanes have a much larger side surface, even a landing with a small lead angle can cause a large lateral force and capsize the aircraft when it touches down, since the floats are not designed for such large lateral forces. They practically sink under water and create a very high drag. It is therefore not possible to slide sideways, as with wheels on a fixed runway. When touching down with a lead angle, the downwind swimmer (facing away from the wind) is pushed deeper into the water because of the wind force acting from the side.
Due to the wind, the wind vane effect and sliding on the water surface, the pilot can lose control of the direction of movement of his aircraft and overturn with the aircraft. When the leeward swimmer sinks under the water, the leeward wing tip touches the water at high speed, "digs itself into the water" and the aircraft overturns. Therefore, the approach is not with a lead angle, but with a hanging wing. What makes things more difficult is the wave movement, which can simulate a drift that does not even exist, because unlike a fixed runway, the water surface does not stand still. The waves seem to move for the pilot and create the optical impression of a drift, but from a physical point of view it is only an up and down movement of the water. Since the pilot approaches in crosswinds, these waves coming from the side are particularly deceptive for the pilot. It is best to look for a fixed optical fixed point on land. When landing in water, the upwind swimmer (facing the wind) must first be touched down, just like on land. Furthermore, ailerons are applied to the wind for landing and when gliding in the water.
The moment when the aircraft "sits" in the water, it is most unstable and tends to turn into the wind, especially as the rudder effect decreases with decreasing speed.
A special landing technique that is only possible with seaplanes is the downwind arc technique. Many pilots counteract the wind vane effect with a deliberate slight curve to leeward. As soon as the aircraft is in the water, the water rudders can be extended. They can be used to steer, as the "runway" for seaplanes is usually much wider than on land. A curved approach path is flown with the convex side facing the wind (to windward). The bow starts at a slight angle into the wind, at the apex of the bow you fly parallel to the wind, and at the end of the curve you fly at a slight angle with the wind (downwind). Through this turn, a slight centrifugal force is constantly generated, which is directed against the cross wind. In order to still generate sufficient centrifugal force, the arc must be flown closer and closer towards the end of the landing, as the aircraft becomes slower and slower. This landing technique also requires appropriate training and experience from the pilot.
Individual evidence
- ↑ a b Report of the Federal Bureau of Aircraft Accident Investigation ( PDF ( Memento of the original from July 2, 2010 in the Internet Archive ) Info: The archive link has been inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this note. ) accessed 02/2011
- ↑ Skyhawk - Model 172R - Information Manual, Cessna Aircraft company, 1996, Section 4: Normal Procedures, 4-30: Crosswind Landing
- ↑ Piper Seminole Information Manual - PA-44-180 (from serial number: 4496001 and higher), Piper Aircraft Inc., 1995, Section 4: Normal Procedures, 4-37: Normal Landing
- ↑ crosswind landings ( Memento of the original dated December 3, 2005 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
- ↑ FliegerRevue May 2010, p. 36, Computer caused a near disaster
literature
- Alan Bramson: The Art of Landing . Motorbuch Verlag, Stuttgart 1987. ISBN 3-613-01010-0
- Private pilot maneuvers . Jeppesen Sanderson, Englewood 1997. ISBN 0-88487-239-4
- Boeing Flight Crew Training Manual. Boeing Commercial Airplanes, Seattle Wa 1983ff.
Web links
- crosswind certification process
- flightsafety.org crosswind (PDF file; 162 kB)
- www.fly-safely.org
- Tailwheel Crosswind Operations
- Crosswind Landing Simulator
Videos and photos of cross wind landings on a tire:
- Videos of different crosswind landings: [1] , [2]
- Boeing 777 video
- Airbus A320 photo
- Boeing 737 photo
- Airbus A319 photo
Video of a crosswind landing of the Boeing B-52: