New tools in the arsenal to prevent runway incursions – RWSL and FAROS

On 16-03-2010, in Life around runways, by steve

Although take-offs and a landing from and on taxiways had filled the news recently, the problem of runway incursions is much more of a problem and in spite of major efforts on the part of all concerned, pilots, air traffic controllers and ground vehicle drivers, it refuses to go away. Not that there are no achievements but in Europe there are more than 2 incidents on average per day and an airport like Charles De Gaulle in Paris has in excess of 30 runway incursions per year! The situation is not much different in the US either.

We all know the traditional warnings that come into view as we approach the runway. Red stop bars across the taxiway, flashing yellow lights on the side, markings and signs… all meant to say: beware, you are approaching a dangerous place, proceed with care. The same message is repeated countless times during basic and recurrent training yet aircraft and ground vehicles regularly blunder onto the runway, flashing lights and stop-bars notwithstanding.

The FAA and Lincoln Labs in the US have developed a new set of tools called the Runway Status Lights (RWSL) System and Final Approach Runway Occupancy Signal (FAROS). Both systems use outside light cues to warn pilots and drivers of unsafe conditions while also providing appropriate warnings in the control tower.

In this day of digital link communications and moving map displays on board many aircraft, why would anyone want to introduce a system that uses light signals as a warning? If pilots and drivers ignored the lit stop bar and the yellow flashing lights, will they heed this new system?

Like so many things in life, RWSL and FAROS represent a compromise between the need to field an effective system as soon as possible and the maximum effectiveness in preventing runway incursions such a system can achieve. An in-cockpit warning of an unsafe maneuver would of course be preferable from an effectiveness point of view but the introduction of any such system would take years because of the slow pace of retrofit action and would also be costly, especially for aircraft not equipped with digital link capability. Ground vehicles would also pose an additional complication and cost. Considering this, not many options are left and the light cue based solutions offered by RWSL and FAROS suddenly look fairly logical. The two systems also meet the requirement calling for solutions that do not disrupt the normal operational practices of the airport.

So what are RWSL and FAROS really about?

RWSL indicates to pilots and vehicle drivers if they would be in conflict with another aircraft or vehicle if they moved beyond the runway holding point/hold line or began its take-off.

The RWSL system uses integrated information from terminal and airport surface surveillance information to determine the presence and movements of aircraft and vehicles in the vicinity of and on runways.

The information provided to the pilot and vehicle drivers is in the form of light cues, lit and extinguished automatically by the system. Red Runway Entrance Lights (RELs) are illuminated if the runway is unsafe for entry or crossing and red Take-off Hold Lights (THLs) are illuminated if the runway is unsafe for departure. The lights are repeated on the tower visual displays.

Assuming a surveillance and processing system that works correctly, the effectiveness of the system is predicated on humans (pilots and drivers) correctly observing and interpreting the light cues and implementing the appropriate actions (e.g. stopping the vehicle) on a timely basis.

The Final Approach Runway Occupancy Signal (FAROS) has been specifically developed to notify pilots on final approach to land of the runway status. FAROS is also a light cue based system and uses the Precision Approach Path Indicator (PAPI) as the signal source. If the runway is unsafe to land on due to the presence of another aircraft or ground vehicle, the PAPI flashes (normally the PAPI shows four steady lights that may be individually red or white, depending on the aircrafts position relative to the glide-path). FAROS also provides a signal of the unsafe condition in the tower. This signal is a red bar placed across the runway threshold on the tower visual display and also a voice warning when the situation becomes critical. FAROS also is automatically controlled and there is no need for controller action to trigger FAROS or to cancel the warning.

The effectiveness of FAROS in preventing incidents is predicated on the pilot perceiving the flashing lights and properly interpreting its meaning as well as properly following the prescribed procedures that may lead to a go-around having to be initiated.

FAROS and RWSL together have the potential of providing a complete warning system that serves both arriving and departing traffic.

Trial runs in the USA

Between 2005 and 2009, RELs and THLs were installed at Dallas/Fort Worth International Airport (DFW) and Los Angeles International Airport (LAX); and RELs were installed at San Diego International Airport (SAN). With continued support from MIT Lincoln Laboratory, the FAA has extended operational evaluations of runway status lights at these test airports indefinitely.


In the meantime, a new element, the Runway Intersection Light (RIL) has also been added to the arsenal (tried at Boston Logan airport). The RIL warns when it is unsafe to cross a runway.

FAROS was also implemented at Dallas Fort Worth airport.

Are they any good?

The feedback from both pilots and ATC is unanimously positive. The runway incursion rate at DFW airport was reduced by 70 %, a major achievement by anybody’s standards. The FAA is planning to deploy these systems at 22 US airports by 2011. There is also some movement in Europe, Paris CDG airport, on the advice of its Local Runway Safety Team, is planning to evaluate the local implementation of both new tools.

Unintentionally ignoring a modest set of flashing yellow lights or even a stop bar can happen, not noticing the sea of red of a THL, REL or RIL or the flashing lights of PAPI is probably impossible.

It is about time…

Overview of the RWLS and FAROS environment

You can find more information on RWSL and FAROS here.

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