A variety of systems are available. These generate additional safety barriers, thus reducing chances of an accident even further.

Below you can find more information about a number of these systems.

Runway Incursion Alerting System Schiphol - RIASS

RIASS acts as a “safety net” in the system of tower-led air traffic control at Amsterdam Schiphol Airport, warning of potential conflicts between aircraft or with vehicles on the runways and at their entrances and exits.

RIASS generates two kinds of alert: alarms and warnings. An alarm indicates that there is an imminent danger of collision and the air traffic controller must respond to the situation immediately. As far as possible, however, an alarm is preceded by a warning. This gives the controller the opportunity to determine whether the risk of a collision might arise. The system is only able to generate alerts in respect of aircraft and vehicles fitted with a working transponder.

Short-term conflict alert - STCA

STCA acts as a “safety net” within the air traffic control system – the main tool used for the management of flights crossing the Netherlands at high altitude (up to flight level 245, or 24,500 feet) – by warning of potential losses of separation shortly before they actually occur. It only produces alerts, however, and does not resolve the situation.

Air traffic controllers themselves are primarily responsible for detecting possible losses of separation. In the photograph below, the white lines are so-called “speed vectors” indicating the expected positions of the aircraft concerned in one minute’s time. Because these are converging, a loss of separation is possible unless the controller issues instructions to keep the flights at a safe distance from one another.

Mode S Enhanced Surveillance

This system is used to transmit a variety of information from the aircraft to the ground.

Now implemented in many cockpits, this form of surveillance ensures that any miscommunication about altitude is detected before it becomes an issue. At LVNL we use the Pilot Selected Level (PSL), which allows the air traffic controller to check that the programmed flight level is the one the aircraft has been cleared to fly at.

Track label information

A track label – the green text on a radar screen – displays information from the system flight plan and data from the aircraft’s transponder. This includes the altitude entered into the autopilot and the one the aircraft is cleared to fly at, so that any difference between them can be seen at a glance.

Proximity warning

In the approach zone to Amsterdam Schiphol Airport and in the area under the responsibility of general air traffic control, LVNL uses the Area Proximity Warning system.

When this function was introduced, it was configured in such a way that all traffic is displayed on the radar screen but with flights below a certain altitude – much of it so-called “general aviation” not directly managed by air traffic control – indicated using a smaller, dimmer symbol (icon) than those operating above this predetermined level. This difference ensures that the controller is not distracted by traffic he or she is not responsible for.

If and when such “uncontrolled” traffic does become relevant to controller’s operations, its symbol becomes bigger and brighter to draw attention to a potential unauthorised penetration of restricted airspace.

In the photograph below, the large track symbol represents flight AZA114 – an airliner. The two smaller ones are light aircraft flying below the altitude range for which the air traffic controller is responsible. But were they to climb into that range, their symbols would brighten and enlarge.

(Enhanced) Ground Proximity Warning System

GPWS is widely used in commercial aviation to warn pilots that they are flying too low and so risk a so-called controlled flight into terrain (CFIT) – that is, a crash in which an airworthy aircraft under the control of its pilot hits the ground, the water or an obstacle.

Pilots are often unaware of an impending CFIT until it is too late to take preventive action. GPWS is designed to warn them in time. It uses a radio altimeter to measure how high the plane is flying, and sounds an alarm if it descends too close to the ground. At low altitudes the system also monitors wind direction and speed, along with a number of other parameters, so as to provide the pilot with an early warning of such phenomena as wind shear.

Traffic Collision Avoidance System - TCAS

Most passenger aircraft today are fitted with TCAS, a system that warns pilots if they come too close to other traffic.

As the name suggests, TCAS is intended to prevent mid-air collisions. Functioning independently of air traffic control and on-board navigation systems, it provides two levels of alert: a “traffic advisory” (TA) and a “resolution advisory” (RA).

These are activated according to the time left before a potential collision. A TA notifies the crew that other traffic is in the area, but the responsibility for maintaining its separation remains with air traffic control. An RA warns of an impending conflict – a flight-critical situation – and issues orders to climb or descend, which the crew has to follow. As such, an RA overrules instructions from air traffic control. In addition, TCAS provides pilots with an overall picture of other traffic in the area on a cockpit display.

Go-around detection system

LVNL has integrated an alarm into the air traffic control system that will sound when an aircraft executes a go-around. Unique in the world, this system will emit an audible alarm and show a warning on the radar screen, decreasing the chances that an unsafe situation will occur. LVNL is constantly improving the safety of air traffic in Dutch airspace.



A go-around occurs regularly and is a standard procedure. A go-around is executed approximately 350 times per year, over a total of 230,000 landings at Schiphol. In the event of a go-around, the aircraft’s landing is aborted. This could be due to various reasons, such as exceptional weather conditions, technical circumstances, or a situation in which the previous aircraft is still on the landing runway. It is also possible that the cabin crew of the aircraft had not been able to make all necessary preparations for the landing. A go-around will be executed at the initiative of the pilot or air traffic controller, depending on the situation.

The air traffic controller gives instructions to inbound and outbound aircraft from the air traffic control tower at Schiphol. In order to alert the air traffic controller more specifically to a go-around, an automatic system has been developed that will both emit an audible warning sound and show a warning on the radar screen in case of a go-around. It has happened in the past that an air traffic controller saw that an aircraft had hit the runway, but a go-around was eventually still executed. That has led to risky situations.

Runway system at Schiphol

Schiphol has take-off and landing runways that can be used in various wind directions. Several of those runway combinations can lead to air traffic intersecting in airspace. Since a go-around is never planned, intersecting air traffic is always unexpected. That is why it is very important to have an excellent overview of the situation.

LVNL developed the Go-Around Detection System itself. The system has been tested and evaluated extensively. The air traffic controllers working from the air traffic control tower have been trained to use the system. The pilot study was carried out in part by NLR and was made financially possible by the Knowledge & Development Centre Mainport Schiphol.