Landing refers to the controlled landing of a spacecraft, aircraft or watercraft on the surface of the earth , usually on a designated landing site . As a rule, the flight is concluded with the flight maneuver landing after the flight phases descent and approach . If the landing approach or landing has to be aborted, the missed approach follows .
Landing of an aircraft
According to the ICAO definition, landing is the flight phase from interception at the end of the approach to standstill or slow taxiing or until the start of a go- around . During this flight phase, the total energy ( kinetic + potential energy ) that the aircraft possesses at the beginning of the interception must be reduced in a targeted manner. Landing against the wind reduces the touchdown speed, which is between about 60 km / h ( glider flight ) and 300 km / h ( scheduled flight ). The remaining energy must be dissipated on the ground.
The landing of an aircraft is composed of the phases intercepting (break) , the flare (flare) , placing (touchdown) and rolling (rollout) together.
Before the landing phase, the speed is reduced to the safe approach speed during the approach . This must have sufficient reserve for stall speed . As the optimal approach speed which applies to aircraft engine stall speed multiplied by factor 1.3. This speed is called the reference speed (V REF ). Depending on the aircraft type, half or a third of the wind speed and any gusts of wind are added to this. However, the speed must not be higher than the maximum speed for extended landing flaps (V FE - Flaps Extended) and extended landing gear (V LE - Landing Gear Extended). This speed is called the target speed (V TRG - Target Speed or V APP - Approach Speed). In commercial aviation, these speeds are specified before each landing approach in the so-called approach briefing, since the stall speed is weight-dependent and must always be determined up to date. In the case of light aircraft , a safety reserve may be added to the reference speed, for example in the case of strong winds. For gliders, the landing speed is the speed of best glide (V Y ) plus 10% (in headwinds or turbulence plus 20%). Since a go-around is not possible with gliders , the increased speed serves as a safety reserve.
While light aircraft mostly land with the engine idling, this is not used for larger aircraft. The cause lies in the aircraft's good glide ratio, which is disadvantageous for landing, and the associated difficulty in reducing speed. The risk of flooding would be too great. For this reason, a trick is used: In the higher levels of the high-lift aids (landing flaps), these not only generate increased lift, but also intentionally high air resistance. The sliding angle of usually 3 ° can then only be maintained by giving additional thrust. The speed can now be very effectively influenced and kept constant by the combination of thrust and trim. Another advantage of jets is the fact that in the event of a go-around maneuver, the engine's acceleration time is significantly reduced, which would otherwise be four to seven seconds from idling to maximum speed. Most planes have a landing thrust of around 45–65% N1. When initiating the interception arc, the thrust is usually reduced to idle.
The interception ( round out or break ) means the transition (interception arc) from the approach ( descent ) to an almost horizontal flight.
In the subsequent flare (flare) the flight speed is gradually reduced in light aircraft, and the aircraft is with minimum momentum. As the airspeed decreases, the lift is increased by increasing the angle of attack. Since this also increases the resistance on the wings, the angle of attack must be increased more quickly as the speed decreases.
A commercial aircraft is approached at the approach speed V APP . After passing through the landing threshold in 50 feet in height which is in a dependent on the aircraft type Abfanghöhe with a slight increase in the angle of attack rate of descent reduced and the aircraft is out of the flare with that of the pulling up the aircraft nose resulting inclination of the aircraft longitudinal axis relative to the horizontal ( pitch ) on.
There are inconsistent recommendations for putting on the water.
The higher the stall speed of the aircraft, the higher the touchdown speed and thus also the remaining energy that has to be dissipated on the ground.
Is dependent on the required landing distance ( landing distance ), the distance from the touchdown point to a stop. In order to shorten this, generously dimensioned brakes are used in large aircraft - and brakes which can be cooled in some aircraft types . The aerodynamic resistance of the extended landing flaps remains effective. In order to prevent the aircraft from taking off again briefly (jump landing) due to the high lift coefficient (due to the flap deflection), the so-called spoilers are activated immediately after touchdown in order to destroy the lift and increase the drag even further. In commercial aircraft, the spoilers are controlled by a complex logic that checks different conditions depending on the aircraft type. In addition, many propeller and jet engines offer the option of increasing the braking effect by reversing thrust . In the civil sector, braking parachutes are rarely used. B. the Caravelle and Tupolew Tu-104 were available.
The required landing distance ( landing distance ) is the entire distance from the runway threshold ( threshold ) to a standstill, which may be at m jets with high approach speeds over 2000th This depends not only on the speed, but also on the weight and the wind. Pilots who have to make do with very small landing areas ( bush pilots ) use special short landing techniques. As a rule, this means reducing the reference speed to just above the minimum travel. Carelessness in the landing approach means severe sagging and, in the worst case, tipping over one of the two wings. Short landings require high concentration and not too unsteady wind.
A landing can (except for gliders) be canceled in almost any phase. This is referred to by start ( go-around ) or missed approach . Even after touching down while rolling out, you can still restart as long as no reverse thrust is activated (if available). The flight maneuver is then referred to as touch-and-go .
When a military aircraft lands on an aircraft carrier, there is no interception or float. Shortly before touchdown, the engine is brought to full power in order to shorten the time until the engine reacts and delivers full power in the event of a go-around maneuver. The approach ends at the touchdown point and goes straight to taxiing. A safety rope, into which the hook of the carrier aircraft hooks, withdraws its kinetic energy from the aircraft. If the safety hook grips a safety rope, the aircraft is braked and the pilot immediately throttles the engines. The aircraft and pilot experience enormous braking acceleration during the abrupt braking maneuver. A landing attempt in which the safety rope is missed and a go-around with full thrust is necessary is called a bolter (rivet).
For take-offs and landings of all aerial sports equipment and aircraft, there is an airfield obligation in Germany with the exception of free balloons. An external landing permit is generally granted for gliders.
An alternate landing is the normal landing of an aircraft that is not carried out at the destination airport , but at an alternate airport . In the event of an alternate landing, a fuel reserve must be carried for all flights, whether private or commercial, which corresponds to the normal flight distance from the destination airport to the alternate airport +30 minutes. The alternative landing is rarely an emergency landing, which requires an air emergency during the flight.
Reasons for an alternative landing can be:
- short-term closure of the destination airport
- too bad weather conditions
- Long flying in holding loops
- reaching the vicinity of the destination airport too late, e.g. B. at night flight ban .
An outside landing is generally always used when the ground contact of a landing aircraft or parachute jumper does not take place on an approved runway (or the landing area) or outside the available landing stretches of an operating airfield, but, for example, in the outdoor area, on a street or on a closed airfield.
When skydiving, adverse wind conditions are usually responsible for the fact that the target field cannot be reached; On the other hand, there are also planned foreign landings there, which must, however, be announced in advance.
In gliding , outland landings are not uncommon, since gliders can only use their altitude as propulsion energy, which they usually reach via updrafts . If a glider can no longer find any updraft at low altitude away from an airfield, it has to land outside and is later picked up by a vehicle. This is often dramatized and completely inappropriately referred to as an "emergency landing" or even a "crash" in the reporting.
A safety landing is when the pilot decides to land in order to avoid an impending emergency that has not yet occurred at the time of this decision. The pilot has enough time to fly to a suitable airfield or to look for a suitable area for an outland landing.
Reasons for a safety landing can be:
- Unexpected weather phenomena that make it impossible to continue or turn back
- Instrument failure
- Unusual behavior of the engine (but not yet an engine failure)
- During the flight it is found that the fuel is no longer sufficient to reach the planned airport
- During a visual flight without a night flight authorization , it is determined that the next airport can no longer be reached before dark
- Failure of an engine in multi-engine machines
- Illness without acute danger to life
- Pilot feeling unwell
- There are people on the ground who are in great danger and need help
A safety landing must not be hindered. The approval of the aviation authorities for a restart is explicitly not necessary. The owner of the land on which the landing was made must not hinder the restart. However, the pilot has an obligation to provide information to the property owner (information on the owner and proof of insurance in accordance with Section 25 LuftVG ).
An emergency landing is when a landing was forced by an emergency . Reasons for this can be:
- Fire on board
- serious or unclassifiable defects or damage to the aircraft discovered during the flight
- acute lack of fuel
- Storms and turbulence
- severe engine problems
- Failure of all engines
- Problems with the chassis
- Acutely life-threatening illness or injury to a passenger or crew member
- Both pilots are unwell
In the best case scenario, the emergency landing takes place on an airfield; if this is not possible, on open terrain ( external landing ) or as ditching on water surfaces. It is sometimes accompanied by extensive rescue services on the ground. After an emergency landing outside of an airfield (in contrast to a safety landing), a restart is only permitted after approval by the responsible State Aviation Authority, Section 25 (2) No. 2 Sentence 2 LuftVG .
A special type of emergency landing is the “medical emergency landing”. If the patient's condition deteriorates significantly while a patient is being transported by rescue helicopter, the helicopter may have to make an interim landing to enable better treatment. In this case, restarting does not require any approval.
A target landing is a landing on a specified area of the runway. It is often one of the evaluation criteria in flight competitions.
Another meaning of target landing is a landing without engine power ( i.e. gliding ) from a fixed height (mostly 2000 ft above ground) onto a fixed landing field for training and testing purposes.
It is required in the pilot's exam and afterwards pilots like to do it for training purposes, as it is a good practice opportunity for external and emergency landings. Above all, the assessment and division of the available height for a gliding flight is practiced: The flight route - often in the form of a shortened traffic pattern - must be chosen so that it ends exactly at the specified touchdown point. In the pilot examination, the target landing must take place within a specified 150 m area of the runway.
A belly landing is a landing with the landing gear retracted , which can lead to considerable damage to the underside of the aircraft. It can be carried out if the landing gear is damaged or the landing gear actuation is defective.
Experience has shown that gliders repeatedly land without landing gear because the pilot forgot to extend the landing gear. Usually, there is only minor damage if you land on a grass runway, but on an asphalt runway, the damage is immense. Many gliders therefore have a warning device ("landing gear warning") that warns the pilot with an acoustic signal if the airbrakes (which are used almost exclusively for landing) are actuated but the landing gear is still retracted. If the airbrakes are used late during the landing approach, however, there is a risk that the pilot will not concentrate sufficiently on the landing when attempting to extend the landing gear at a low altitude and thereby cause damage that is significantly greater than that which would have been caused by a belly landing. Therefore, some pilots or clubs deliberately forego a landing gear warning.
(Engl. In a long-segment long landing ) the aircraft is intentionally significantly behind that provided for the runway touchdown point placed. This can offer advantages in terms of traffic engineering, but it reduces the safety reserves. The decision about a long landing is made by the pilot, either on his own initiative or at the request of air traffic control. In commercial aviation, however, touchdown behind the touchdown zone, which usually ends at 3000 ft (around 900 m) behind the runway threshold, is not permitted.
Advantages of a long landing:
- Reaching a taxiway faster, thereby clearing the runway more quickly so that it can be crossed by other aircraft behind the landing one
- Shortening of the total taxiing distance to the terminal and thus time and fuel savings
- Flying over wake vortices generated by a previously landed aircraft
At some airports there are special touchdown points for light aircraft (up to 5.7 t). In fact, the long landing is the standard practice in these cases.
In crosswind landings, the pilot must maintain the alignment to the runway and remain on the runway baseline against the lateral drift caused by the wind. Crosswind landings place higher demands on the skill of the pilot than landings without significant crosswinds.
Three point landing
The three-point landing is a landing technique for tail-wheel aircraft . The aim is to touch the ground with all three wheels at the same time. The advantage of this landing technique is that due to the high angle of attack ( aircraft nose is pointing upwards), the landing is carried out at the lowest possible speed and the coasting distance is therefore very short.
The nose-wheel planes more common today touch down with the main landing gear first. In the case of tail- wheel aircraft , one speaks of a wheel landing , which offers advantages in strong crosswinds .
Landing with parachute, paraglider, kite
When landing with military or sports equipment, in which the person hangs with leashes on the glider or the wing, the last phase is approached against the wind if possible and the sink rate is reduced. Very shortly before the legs touch the ground, the control lines are pulled strongly in order to quickly brake the glider's movement, as a reaction the pilot is accelerated in this direction for a short moment by the carrying lines running increasingly diagonally upwards and comes in Ideally, bring your feet to a standstill just a little above ground level. When flying a kite, the trapeze is pushed forward.
Umbrellas, which a person soars into the air behind a motorboat, are launched from land or with water skis from the water; these are often landed in the water. The landed person is rescued from a boat with an umbrella.
An automatic load landing system used by the military can pull in the suspension lines a little shortly before contact with the ground in order to reduce the rate of descent of the load.
Wingsuit pilots usually pull a parachute and land with it.
Successful soft landings without an umbrella have so far been carried out in a stack of cardboard boxes and - even without a wingsuit - in a large, high-tensioned net.
Landing of a stunt kite
A two-liner is best landed the most gently at one of the two lateral intersections of the wind edge and the terrain, where it has the lowest speed to the ground. A four-line can be brought to the ground gently using the steering lines, even in the middle of the wind.
Landing a balloon
Tethered balloons are brought to the ground by hauling in one or more lines and disposed of immediately before the lifting gas lands. To do this, by pulling a rip cord, you open a hook-and-loop tear strip that releases the gas quickly enough before wind eddies can blow the half-filled and then particularly sensitive cover against sharp-edged obstacles. Sufficiently heavy anchoring, weighting or holding of the basket is essential as long as buoyancy and wind force are still acting on the shell.
Free balloons can first absorb braking ground contact with a tow rope. An anchor hook - a stereotypical symbolic image - is rarely used, a sea anchor to anchor in a water surface is seldom. Hot-air balloons can open the lid valve and thus save having to open the tear strip when there is little wind. Usually, a ground crew who followed the balloon flight by vehicle put the balloon in a trailer.
Weather balloons burst at a planned height, whereupon a parachute brakes the measuring instruments to the ground. These can be retrieved by finders or through targeted searches.
Landing a spacecraft
In space travel, a distinction is made between “hard” and “soft” landings.
A hard landing is the unrestrained impact of a missile ( lunar or planetary probe ) on the solid surface of a celestial body. As a rule, the missile is destroyed in the process and can only provide data during the descent phase. Penetrators that can survive a hard landing with subsequent penetration into the celestial body are in development; initial tests were unsuccessful.
For the first lunar probes in the USA and the USSR, a hard landing on the earth's satellite was planned several times, but instead there was only one flyby . The accuracy at the start (final speed and direction of the top rocket stage ) was not yet sufficient and was insufficient for hitting the moon on the necessary curved path.
The goal of hard landings was among other things:
- Successful propaganda (especially on the part of the Soviet Union during the Cold War)
- Further development of technology and rail maneuvers
- first exploration of celestial bodies (e.g. close-ups of rangers 7 to 9)
- Exploring their atmospheres and magnetic fields
- Impactors and preparation for subsequent soft landings
- Incomplete braking or atmospheric braking from the 1990s
- Deposition of a penetrator on a minor planet or comet .
In the case of soft landing, the probe or its special landing device is braked before the impact or protected itself (e.g. by an inflatable cover) during the impact. Brake rockets or, if the atmosphere is present, parachutes are used to slow them down . The missile remains intact and can perform tasks on the surface of the celestial body. That is why the soft landing is the preferred option today. On the Venus was in countries of the parachute because of the dense atmosphere often dropped already at high altitude and the lander suggested only slowed down by the drag of about 30 km / h on the surface. So a soft landing can be very hard by our standards.
A stopover is a temporary stop between a departure and a destination airport. It is used either for transfer of airline passengers , for transhipment of cargo , or for refueling of fuel. Some airlines regularly interrupt their flights in order to refuel cheaply with kerosene .
- Flight phase
- Landing on an aircraft carrier
- Side glide
- Landing device for helicopters
- Aviation language
- STOL , VTOL
- ICAO "Phase of Flight" , Definitions and Usage Notes, April 2013
- German air traffic control : PPL questionnaire , status 2009
- Niels Klußmann, Arnim Malik: Lexicon of aviation. Springer, Berlin 2007, ISBN 978-3-540-49095-1