Make Sense of Stop Bars

2 September 2009 (Last Updated September 2nd, 2009 18:30)

Increasingly common at major airports, stop bars can be powerful tools in preventing runway incursions. Yet the rules governing their use are causing concern among air traffic controllers. Future Airport talks to Bert Ruitenberg of International Federation of Air Traffic Controllers' Associations, who wants the International Civil Aviation Authority to clarify its intentions.

Make Sense of Stop Bars

Runway incursions, which can occur for many reasons, in any weather conditions and at airports of all sizes, can be avoided. However, the number of such occurrences is increasing. In 2001, the ICAO Air Navigation Commission took action, resulting in the development of its Manual on the Prevention of Runway Incursions. However, some of the statements in this document have left air traffic controllers concerned about the interpretation of the guidelines.

The manual states: "... runway incursions may take place in all visibility or weather conditions. The provision of stop bars at runway holding positions and their use at night and in visibility conditions greater than 550m runway visual range can form part of effective runway incursion prevention measures."

The aviation industry has welcomed the emphasis that the ICAO Air Navigation Commission has placed on solving the continuing problem of runway incursions. Improving safety in and around airports will always have a positive impact, yet the detail of the actions taken has raised some important questions yet to be answered.

The Global Airport Domain Team of the International Federation of Air Traffic Controllers' Associations (IFATCA) recently conducted a survey of stop bar use at major airports around the world, the results of which were published at the end of last year in the IFATCA Stop Bar Survey Report. The report marks the first step in IFATCA's extensive Stop Runway Incursions awareness programme for controllers, and highlights the need for much greater clarity about the use and operation of stop bars, which consist of a row of lights that an aircraft must not pass, and are a familiar feature in many international airports.

"As long as there are airports where pilots are expected to cross active stop bar, danger exists."

"The minimum ICAO requirement for the application of stop bars is for runways that are intended to be used with Cat 2 ILS operations – runways with RVR values of less than 550m," says the report's principal author Bert Ruitenberg. "If this requirement is applied at more airports, the use of stop bars will also become more widespread. Apart from that, airports may choose to implement stop bars as a safety tool under all conditions, although cost may be the limiting factor in many cases, just as the lack of unambiguous provisions from ICAO may currently be a limiting factor."

Clarity and consistency

As of now, the model governing the ownership and operation of stop bars varies between airports, which could potentially compromise safety under certain conditions, and there is clear concern among air traffic controllers.

"The most significant problem is that at some airports stop bars cannot be switched off by controllers at positions where aircraft and vehicles are expected to cross them," says Ruitenberg. "As long as there are airports where pilots are expected to cross active stop bars, either with or even without a specific instruction from ATC, the danger exists that pilots will not stop at a stop bar when they are supposed to, as might be the case after a taxi routing error during low visibility operations."

Runway incursions certainly occur, but recent incidents have not been severe. However, the industry should certainly act before a major problem, such as happened in the past at Milan Linate and Tenerife, occurs again. "Recently, there have been several runway incursions at various airports, but fortunately they have been mostly category D – the lowest severity – and have not resulted in any injury or damage," Ruitenberg notes.

"Once the ICAO provisions for stop bar-related procedures are less ambiguous and more consistent across the various documents, it becomes a training issue for pilots, vehicle drivers and controllers. Airport authorities, which are the owners of nearly all stop bars, should ensure that stop bars are made switchable where required and, with the ATC authorities, they should develop and implement a stop bar contingency procedure involving the use of a Follow Me vehicle."

Ruitenberg does not doubt the worthiness of ICAO's efforts, but is adamant that there will be concern and confusion until a clear and consistent set of rules is in place that ensures that same policy on stop bars at every airport.

"Stop bar lights are a familiar feature at many international airports."

"The purpose of ICAO provisions is exactly that," he says. "My interpretation would be that airports have a certain degree of discretion on whether to apply stop bars or not and, if so, also the conditions when they are activated, but pilots and vehicle drivers should never cross an active stop bar anywhere, and stop bars should be switchable at positions where aircraft and vehicles are expected to cross them. In principle, an aircraft should never cross an active stop bar unless there is an emergency, and even then I can't easily think of an emergency where it would be a good idea for an aircraft to enter a runway and cross an active stop bar while doing so.

"If the issue is a stop bar failure, however, then we get to the contingency procedure case. The application of a contingency procedure involving the use of a Follow Me vehicle to assist aircraft over a stop bar that cannot be switched off is an exception to the rule that an active stop bar should never be crossed."

Ruitenberg also believes the focus should be firmly on operation policy, and that ownership of the stop bars should be a side issue. "I think this can be left to local implementation, as long as it is understood that aircraft and vehicles shall never cross an active stop bar," he says. "This probably means in most cases that ATC shall operate the stop bars."

Forging the future

There are many instances in which airports have installed stop bars and their use confirms the intentions of the ICAO manual's directives. For Ruitenberg, these should serve as an object lesson for other airports, as they ensure that pilots and vehicle drivers know they should respect active stop bars and allow air traffic controllers to switch off a stop bar when clearing an aircraft or vehicle to proceed. Nevertheless, he feels there is still much to be done to ensure that a clear set of guidelines exists for air traffic controllers that will resolve any ambiguity around the use of stop bars.

"An aircraft should never cross an active stop bar unless there is an emergency."

IFATCA has submitted a working paper to the ICAO Operations Panel (OPSP), in which it proposes to harmonise the provisions in numerous ICAO documents. The OPSP has since referred the matter to the visual aids working group of the Aerodrome Panel, which will meet later this year. Meanwhile, Ruitenberg believes the industry should continue to collaborate more closely in order to limit runway incursions and improve safety.

"Aerodrome owners have to supply the needed ground infrastructure, and need to be convinced of the value in making changes to existing infrastructure, like other members of the aviation community do," he says.

"Airspace users operating at the most critical stages of their flight – landing and take-off – have to interface with a number of services, both airside and landside, and usually have the most factors influencing the predictability of their own operations. Many airports are creating runway safety teams and it is important that air traffic controllers are members of these teams. The cooperation requires the kind of collaboration that demands pragmatism and compromise by all involved. IFATCA commits itself to being involved in the process and the consequences."