Categories of incidents

To keep the passengers and crew safe, an aircraft experiencing a technical defect or other problem may need to land as quickly as possible.

To keep the passengers and crew safe, an aircraft experiencing a technical defect or other problem may need to land as quickly as possible.

In practice, they most often return to their point of departure and make what is known as a precautionary landing. As the name implies, this is a safeguard rather than an absolute necessity. In most cases the problem is not serious enough to endanger the flight, but pilots – like air traffic controllers – do not take unnecessary risks. As soon as a something goes awry, they contact air traffic control to report the issue. Sometimes the cause is an external one such as a tail strike (the tail of the plane touches the ground during take-off) or a bird strike (birds hit the plane, also usually during take-off). But technical problems are more common: an engine or communication systems defect, say, or a partial loss of cabin pressure (decompression). Upon receiving a report of this kind, air traffic control assists the pilot in any way it can and facilitates a precautionary landing on his or her preferred runway. The reason the pilot can request a particular runway is that only he or she knows what manoeuvres the aircraft is still capable of making. Moreover, the pilot at all times remains responsible for the aircraft and for landing it safely. Air traffic control makes sure that its separation from other aircraft is maintained, to prevent possible conflicts.

An emergency landing occurs after a critical situation arises aboard an aircraft in flight.

The pilot declares an emergency by making a radiotelephony (RTF) call beginning with the words “Mayday, mayday, mayday” or “Pan pan, pan pan, pan pan”. The term “mayday” is used in the case of an urgent, life-endangering situation requiring immediate assistance. “Pan pan” indicates a serious situation in which the safety of the aircraft, another vehicle, someone on board or someone in view is in danger, but with no immediate threat to life or need for assistance.

 

An emergency can have many causes. Depending upon the urgency of the situation, the pilot may decide that he or she wishes to land at the nearest suitable airfield. Where that is will be determined by the type of aircraft, its weight and the cause of the emergency. For example, not every airport can accommodate an Airbus A380 because of its very large size and weight. In preparing their flight plans, pilots always consider possible diversions to suitable alternative airfields. Air traffic control has its own special procedures in unusual situations.

A go-around or missed approach is when a landing is aborted at the last minute, on final approach. Instead of touching down on the runway, the plane overshoots it and climbs to a given height before recommencing its approach and landing sequence from the beginning.

Standard go-around procedures are included in every airfield’s published approach instructions for pilots. In some situations, the air traffic controller needs to provide additional instructions in order to maintain separation from other aircraft. A go-around may be initiated by either the pilot or the air traffic controller. The most common reason for making one is that the aircraft is not stable enough on its final approach. At this point the pilot has to reduce the plane’s speed and height, and put it into so-called landing configuration: flaps open, undercarriage down. If any parameter is incorrect as the runway approaches, the landing has to be abandoned. Unexpected changes in weather conditions during final approach may also force a go-around, as can circumstances on the ground – disruption of the signal from the instrument landing system by the tail of a taxiing aircraft, for instance. Or the air traffic controller may have to withdraw landing clearance because the previous aircraft using the runway has not left it in time. At busy airports like Schiphol, approaching aircraft are lined up as efficiently as possible, but always with a minimum separation of three nautical miles (about 5.5 kilometres). If a landing aircraft fails to clear the runway quickly enough, the one behind may have to make a go-around. For the runway controller, it is important to determine the risk of a conflict with other aircraft as quickly as possible and to give any additional instructions needed to avoid it. The approach controller then has to guide the aircraft affected back into the queue of flights waiting to land.

The horizontal or vertical distance between aircraft in flight is referred to as their “separation”.

Separation minima have been established to maintain air traffic safety, whilst at the same time making optimum use of airspace. Air traffic control is responsible for maintaining these minimum distances between aircraft in its control zone. When two aircraft come closer to one another than the minima allow, the situation is known as a “loss of separation”.

The criteria for separation minima have been designed in such a way that they allow enough time to correct the situation before it presents a serious danger. An air traffic controller faced with a loss of separation must undertake a number of steps in a very short time.

• Detect the loss of separation.

• Identify an effective solution.

• Communicate that solution to the pilot(s) concerned, in the form of instructions regarding their altitude, bearing and speed.

• Ensure that pilot(s) follow these instructions in order that safe seperation is restored as quickly as possible.

To help prevent losses of separation, air traffic controllers have a number technical and procedural aids to warn them when aircraft come too close to one another. These include STCA (short-term conflict alert). Systems aboard aircraft themselves, such as TCAS (traffic collision avoidance system), can also help avoid losses of separation.

As a rule, aircraft are not allowed to jettison or dump fuel in flight. However, an exception is made for safety reasons.

                         

It is the captain who takes the decision to jettison fuel. In some cases this is because the aircraft exceeds its maximum landing weight. That is often lower than its weight at take-off, with fuel accounting for the difference.

 

In many cases, aircraft making precautionary landings have only just taken off. Because of this, they may have too much fuel on board to be able to land safely. Some types are able to jettison fuel, others are not. The latter have to fly circuits over a designated area until they have burnt enough fuel to reach their maximum landing weight.

 

When a pilot reports that he or she needs to jettison fuel, the air traffic controller asks whether that has to be done immediately and how long it will take. The minimum altitude at which fuel can be discharged is 7000 feet, or just over two kilometres, unless safety reasons dictate otherwise. If the fuel has to be jettisoned immediately, the air traffic controller makes sure that neither the aircraft dumping it nor any other planes with a planned route in the area come into contact with it. The discharge zone remains closed to all traffic for at least fifteen minutes.

 

If the situation is less urgent, but fuel still has to be jettisoned in order to be able to land safely, the air traffic controller instructs the pilot to dump it over the North Sea.

Aircraft occasionally run short of fuel, or threaten to. Possible causes include unfavourable weather conditions en route and delays during the flight.

In such situations, the pilot may decide to divert to an airport nearer than the intended destination. As long as the aircraft has the minimum amount of fuel required by law, however, he or she is also free to continue the flight as normal.

 

To alert the air traffic controller to a possible shortage of fuel, the pilot sends a message including a term like “minimum fuel”, “fuel emergency” or “low on fuel”. But since these have no official status in the Netherlands, the controller is not obliged to give the aircraft priority when landing – although, of course, further delays do need to be avoided. Only once the pilot announces a true emergency, with a “Mayday” or “Pan pan” call, is the flight treated as an aircraft in distress. When notified of possible shortage of fuel, though, the controller does inform the pilot of his or her expected approach time and any subsequent changes to that. This enables the pilot to decide if an emergency call is needed after all.

A runway incursion is understood to mean any occurrence at an airport involving an aircraft, vehicle or person being unintentionally in the protected area of a runway that is being used for aircraft landings and take-offs.

What is a runway incursion exactly?

A runway incursion has been internationally defined by ICAO:

 

"Any occurrence at an aerodrome involving the incorrect presence of an aircraft, vehicle or person on the protected area of a surface designated for the landing and take-off of aircraft.”

 

To prevent such situations occurring, prior to accessing the runway, permission must be obtained from the air traffic controller in the tower. The air traffic controller in the tower (runway controller) has various technical and procedural facilities that can warn him or her when the runway is occupied and therefore cannot be used for take-offs or landings. At Schiphol, the Runway Incursion Alerting System Schiphol (RIASS) is active. 

 

Throughout the world, runway incursions are seen as being one of the more important safety themes in which a lot of time and money is invested.

Schiphol 

At Schiphol airport, sustained attention is given to reducing the probability of runway incursions.

The Runway Safety Team (RST) Schiphol is an advisory body within the Integral Safety Management System (ISMS) with representatives from the aviation sector. Runway incursions are the team's most important safety theme and the team’s objective is to arrive at improvement and control measures based on runway incursions that happen and/or on detected trends.

Determining safety risk

In addition to being able to determine whether a certain situation can be classified as a runway incursion or not, the risk associated with or severity of the situation is particularly important. If a single aircraft was involved in a runway incursion, the severity - probability of a conflict - will have been low.

 

Internationally, four different categories of severity of runway incursions (A to D) have been identified. They are visualised below. 

 

How often do runway incursions occur at Schiphol Airport?

 

 

Investigation of causes

All runway incursions at Schiphol are investigated, irrespective of their severity. The most frequently occurring type of runway incursion concerns situations in which traffic is located on a take-off or landing runway without being authorised to be there.

 

The underlying causes are:

• Misunderstanding in the communication between a pilot and an air traffic controller;
• The complicated infrastructure of Schiphol airport;
• The Situational Awareness of a pilot or an air traffic controller;
• Procedures.

Tools to prevent the occurrence of runway incursions

Since 2011, all runways at Schiphol have been equipped with the Runway Incursion Alerting System Schiphol -  RIASS.

RIASS acts as a safety net in the air traffic control tower system. It generates an alarm if there is a possible risk of a conflict between aircraft and vehicles and between aircraft and aircraft on take-off and landing runways and the associated runway entrances and exits. As a result, if possible and necessary, an air traffic controller can take immediate and appropriate measures. Incidentally, the air traffic controller consciously not performing an action can also lead to a resolution of the safety-critical situation.

 

In addition to RIASS, through the course of time, various control measures have been implemented to reduce the number and severity of runway incursions, including:

• The construction of a north taxiway around the Zwanenburg runway to limit the number of Zwanenburg runway crossings;
• The construction of an alternative towing route around the end of the Aalsmeer runway to limit the number of tows crossing the Aalsmeer runway;
• Holding awareness campaigns among pilots;
• Publishing so-called ‘hotspots’ at the airport - locations where a relatively high number of runway incursions occur - on the map material officially used by pilots;
• Installing Runway Guard Lights: flashing lights at all relevant take-off and landing runway entrances and exits;
• Installing additional ground marking and signage near a take-off and landing runway;

• Awareness campaigns, targeted at pilots and the drivers of vehicles.

A bird strike is when one or more birds hit an aircraft.

This usually occurs at low altitudes, and 79 percent of all bird strikes are at airfields. Although a bird’s size and weight are negligible compared with those of a plane, these incidents can still cause considerable damage. In most cases, this is purely superficial, but technical problems can sometimes arise as a result.

At Amsterdam Schiphol Airport, special patrols inspect the runways regularly for dead or injured birds. These have probably been struck by an aircraft. If any are found, air traffic control notifies the pilot concerned so that he or she can decide whether a precautionary landing is needed. Similarly, pilots who suspect a bird strike during take-off or landing report that to air traffic control. The runway is then inspected as quickly as possible.

All modern airliners have pressurised cabins for the comfort of the passengers and crew. The pressure inside them is maintained by compressors, which draw in air and pump it into the cabin.

This is necessary because the atmospheric pressure at high altitudes is too low for people to inhale enough oxygen to stay conscious. By law, an oxygen supply must be provided on all flights, however short, above 14,000 feet. This threshold is lowered to 10,000 feet (about three kilometres) for flights longer than thirty minutes. In a modern airliner, the cabin pressure at cruising altitude is equivalent to that at an elevation of between 5500 and 8000 feet on earth. If pressure is lost at a very high altitude – 40,000 feet (about twelve kilometres), say – the people inside the plane are unable to function normally after only 15-20 seconds. This interval is known as the “time of useful consciousness”. It is for this reason that all aircraft with a pressurised cabin are fitted with oxygen masks, which are released automatically if the pressure drops.

 

The pressurisation system, properly called the Environment Control System (ECS), also provides the cabin ventilation and heating.

 

If a pilot reports a loss of pressure (decompression), air traffic control immediately instructs him or her to descend to a safe altitude (8000 feet or less). At this height the atmospheric pressure is greater, with enough oxygen for the passengers and crew to breathe normally. Aircraft suffering decompression usually make a precautionary landing so that the problem can be dealt with.

Communications in civil aviation are conducted using radiotelephony (RTF).

 

The frequencies used are decided by the International Telecommunications Union (ITU). Civil aviation makes heavy use of the very high frequency (VHF) bands. The maximum distance over which an aircraft flying at high altitude can communicate with a ground station is approximately 350 kilometres.

 

If two-way contact between an aircraft and air traffic control is lost, the situation is referred as a “communication failure”. To determine whether the plane is still able to receive messages, the controller can ask the pilot to perform a specified manoeuvre that can be observed on the radar screen or to enter a new secondary surveillance radar (SSR) code. These are codes used to identify individual flights on radar and are unique to each aircraft.

 

The controller may try to re-establish radio contact by calling the aircraft on the emergency frequency or on one of the published alternative frequencies for the area in question. The pilot can also enter a special SSR code, 7600, which indicates a communication failure.

 

When communication is lost, the pilot follows the standard flight procedures set out in the Aeronautical Information Publication (AIP). In most cases, contact is re-established quite quickly. If it is not, that may indicate unlawful interference with the aircraft – a hijacking.

In the event of unlawful interference with an aircraft, the pilot reports the situation if he or she is able to. For example, the plane has been hijacked or the passengers and crew are in danger due, say, to a bomb warning or a threat of violence.

To deal with such eventualities, the National Co‑ordinator for Counterterrorism and Security (Nationaal Coördinator Terrorismebestrijding en Veiligheid, NCTV) has compiled a special “renegade procedure”. This includes measures to protect Dutch airspace and to deploy military resources to counter a terrorist threat from the air. Meanwhile, civilian air traffic control follows the procedure for an aircraft in distress.

Airspace infringements – aircraft entering areas they are not authorised to be in – are a key safety issue for LVNL. Such incidents pose a substantial risk to both recreational and commercial traffic.

What is an airspace infringement?

Internationally, an airspace infringement is defined as follows.

 

“A flight into notified airspace without previously requesting and obtaining approval from the controlling authority of that airspace in accordance with international and national regulations.”

Frequency

Both the civilian and the military air traffic control services report all airspace infringements to the Aviation Incidents Analysis Bureau (Analysebureau Luchtvaartvoorvallen) at the Human Environment and Transport Inspectorate (Inspectie voor Leefomgeving en Transport, ILT).

 

A total of 1,565 infringements were recorded in civilian airspace between 1 January 2010 and 31 December 2016. In 59 of these cases, there was a substantive risk to operational flight safety. A clear peak is observed in the summer season, when a relatively high volume of recreational air traffic uses Dutch skies.

 

Infringements are reported from all areas of notified airspace, but the majority occur in the vicinity of Amsterdam Schiphol Airport and Maastricht Aachen Airport.

Amsterdam Schiphol Airport

A substantial amount of recreational traffic uses airspace close to Schiphol in the summer, particularly along the North Sea coast. There are also training and local flights over the provinces of Flevoland and Noord-Holland, originating at Lelystad Airport. And the northbound air corridor from Rotterdam via the IJsselmeer lake passes close to Schiphol’s restricted airspace, too.

 

Most of the incidents in this region involve recreational flights unintentionally entering the airport’s approach zone, particularly due to carelessness with altitude. The lower boundary of the approach zone is 1500 feet, whilst the majority of recreational traffic flies at between 1200 and 1500 feet – that is, within just 300 feet of that boundary. It therefore only takes a minor deviation from the planned flight level to penetrate the zone from below. Common causes include updraughts – a frequent occurrence in the summer months – steering errors and incorrectly calibrated altimeters.

 

A safety risk arises when there is also low-flying commercial traffic in the vicinity. And because Schiphol is one of Europe’s busiest airports, with between 106 and 110 movements per hour, there is a real danger that an infringement of its airspace could compromise safety.

Maastricht Aachen Airport

Most infringements in the vicinity of Maastricht Aachen Airport are caused by the relative complexity of the airspace in the area. East-west and west-east flights between Germany and Belgium frequently forget to contact air traffic control in Maastricht when crossing the narrow strip of Dutch territory separating them. In other cases, careless navigation results in an aircraft briefly entering the Maastricht control zone.

 

A total of 518 infringements were recorded around Maastricht Aachen Airport between 1 January 2010 and 31 December 2016. Again, these are more common in the summer season than in the winter.

Causes

Research shows that there are various underlying causes of airspace infringements.

• Inadequate flight preparation.

• Use of outdated navigation charts.

• Use of an outdated navigation database.

• Navigational errors or loss of situational awareness.

• Excessive pressure of work in the cockpit.

• Inadequate access to information.

• Inexpert use of radiotelephony.
  
  

Prevention is better than cure

In the National Airspace infringements Working Group the problem of airspace infringements is periodically discussed and are measures developed. As well as members from the ministry and LVNL, this includes representatives of the Aircraft Owners and Pilots Association Netherlands (AOPA), the Royal Netherlands Aeronautical Association (Koninklijke Nederlandse Vereniging voor Luchtvaart, KNVvL), the Human Environment and Transport Inspectorate (Inspectie Leefomgeving en Transport, ILT), Royal Netherlands Air Force High Command (Commando Luchtstrijdkrachten, CLSK), the Aviation Section of National Police Services Agency (Korps Landelijke Politiediensten, KLPD), the Dutch Civil Airports Association (Nederlandse Vereniging van Luchthavens, NVL), the Netherlands Association of Commercial Aviation (NACA), the Royal Netherlands Meteorological Institute (Koninklijk Nederlands Meteorologisch Instituut, KNMI) and the National Aerospace Laboratory (Nationaal Lucht- en Ruimtevaartcentrum, NLR).

 

In recent years, the following measures have been taken

• Regular reports and trend analyses from the Aviation Incidents Analysis Bureau (Analysebureau Luchtvaartvoorvallen).

• Harmonisation of reporting protocols for civilian and military air traffic control organisations.

• Assessment of European recommendations.

• Active communications targeting recreational pilots.

• Compilation of an enforcement covenant, with both preventive and reactive components.

• Combining aeronautical information from LVNL and the KNMI on the LVNL website.

• Advice to monitor the flight information frequency when flying below Schiphol airspace.

• Rezoning of the airspace around Maastricht Aachen Airport.

• Compilation of a code of conduct for recreational avaiation.

• Reassessment of training requirements.

• Development of technological support facilities.
  
  

After the downward trend that was seen from 2010, in 2016, the number of reported airspace infringements rose once more for the first time. All of the parties must have a proactive attitude, linked to structural improvements, to manage this safety risk.

When used improperly or in a controlled area, drones pose a risk to air traffic safety. For that reason, we have developed the GoDrone app and the website godrone.nl to show drone operators where you can and cannot fly your drone in the Netherlands. This is an example of how we enable aviation together. The free app is available for download in the Apple Store and Google Play store.

 

This page on lvnl.nl, as well as in the GoDrone app and on godrone.nl, offers more information about how to use drones safely, so unsafe situations involving drones can be avoided. The following links provide information about the consequences if you fail to follow the rules for flying a drone.

 

If a pilot reports seeing a drone, the air traffic controllers:

• Warn any pilots flying in the area;
• Determine whether changes need to be made to the runway use and possibly the routes of aircraft in the surrounding area – should the information provided by the pilot call for this;
• Notify the Police Aviation Service for law enforcement purposes.

Reports

Air traffic controllers are informed of drone sightings by pilots. These pilots give an approximation of where they spotted the drone. They often indicate in this context that it is difficult to give an accurate estimate of the altitude that the drone is flying at and its distance from the aircraft. Drones are so small that they cannot be seen from the control tower. Air Traffic Control the Netherlands (LVNL) does not have any information that can be used for further investigation into a drone sighting. The only details at its disposal are those provided by the pilots.

Legislation and regulations

The law prohibits the operation of drones in controlled airspace. In the case of Amsterdam Airport Schiphol, this involves an area of some 15 km around the airport. This area includes recreational areas like Amsterdamse Bos, Spaarnwoude and Vinkeveense Plassen.

 

Further information on regulations relating to drones can be found at: www.rijksoverheid.nl/drones.

Numbers

Reported at LVNL ATC unit	2016	2017	2018	2019	2020
Schiphol, Tower and Approach	31	36	32	33	11
Rotterdam, Tower and Approach	3	7	3	4	7
Amsterdam Area Control Centre	4	5	6	1	1
Amsterdam Flight Information Centre	3	-	3	-	-
Lelystad Airport, Tower	-	-	-	-	3
Maastricht Aachen Airport, Tower and Approach	2	1	1	-	3
Groningen Aiport Eelde, Tower and Approach	2	5	1	1	2
Total	45	54	46	39	27