Runway Incursions

by Bryce Fisher, Manager, Safety Education and Promotion, Safety Services

Some things happen in waves with peaks and troughs, resulting in a pattern that is repeated over and over again in time. Some safety issues, it seems, display similar characteristics. Take runway incursions. At one point, their number reached an alarming level — a peak. Studies were conducted and changes, such as the readback of hold-short instructions issued by air traffic controllers, were institutionalized. These changes resulted in a reduction of runway incursions to a better level — a trough. Now it seems another wave, perhaps larger than previous ones, is looming on the horizon.

In 1999, both Transport Canada and NAV CANADA noted a rise in the number of runway incursions at Canadian airports. Each commissioned studies to analyze the phenomenon, confirm the trend, identify contributing factors and make recommendations for their redress. (An article from NAV CANADA on runway incursions will appear in the next issue of ASL.)

The Transport Canada study team found that, from 1996 to 1999, the number of runway incursions reported at Canadian aerodromes increased by 145%. While not included in the report, the figures for 2000 kept rising: 368 incursions were recorded for the year, representing a 40% increase over 1999.

These figures clearly indicate that the number of runway incursions at Canadian aerodromes has increased sharply in recent years and is continuing to do so.

Figure 1

What has Contributed to this Increase?

According to the Transport Canada report, a number of factors that are potentially responsible for this upward trend include traffic volume, capacity-enhancing procedures, airport layouts, complexity and, not surprisingly, human factors.

Traffic Volume — From 1996 to 1999, the average traffic volume at Canadian aerodromes increased by approximately 9.3%. Some airports have recorded even higher rates of growth, especially at peak hours.

But the Transport Canada study team concluded that the relationship between volume and incursion potential is not so simple.

Using a single-runway model, the possible number of runway incursion scenarios can be calculated for a given number of aircraft on the manoeuvring surface.

Table 1 — Runway Incursion Potential, Single-runway Operation

As shown in Table 1, it becomes immediately apparent that the potential for a runway incursion increases more rapidly than traffic volume. For example, a 20% increase in volume (four to five aircraft) — typical of the volume increase since 1996 — represents a 140% increase in runway incursion potential.

In keeping with the laws of probability, and in the absence of significantly improved safeguards, an increase in the potential for runway incursions can be expected to be associated with an increase in actual runway incursion events.

Capacity-Enhancing Procedures

To accommodate the increase in traffic, procedures such as parallel runway operations, simultaneous intersecting runway operations (SIRO) or land and hold short operations (LAHSO) and intersection departures were introduced at many airports.

Once the effect of these procedures was computed, it was found that capacity-enhancing procedures have a compounding effect on runway incursion potential.

By virtue of their complexity, these procedures offer more ways in which a conflict can develop, as illustrated in Figure 2. Though not shown here, intersection departures and/or a three-runway SIRO will further increase the complexity and create yet more opportunities for a runway incursion.

Figure 2

Two conclusions can be drawn from this analysis. First, as traffic volume increases, runway incursion potential increases more rapidly when capacity-enhancing procedures are in effect than when they are not. Second, if traffic remains the same, the potential for runway incursions increases when capacity-enhancing procedures are put into operation.

Airport Layouts

To absorb current and forecast increases in traffic, many airports have embarked on ambitious projects to improve existing infrastructure. But in many instances, these have resulted in a yet more complex aerodrome environment. This, the study team concluded, is further exacerbated by inadequate aerodrome design, marking and lighting standards; the lack of standard taxi routes; and the availability of improved aerodrome diagrams.

Complexity

The effects of increased traffic volume, capacity-enhancing procedures and physical layout may simultaneously exacerbate the runway incursion potential at a particular aerodrome.

There is some evidence to suggest, however, that the combined influence of these factors — the overall complexity — is greater than the sum of its parts. It is typically against a backdrop of high complexity that second-order effects, such as reduced visibility, unfamiliarity or momentary distraction, become the last link in the chain of events that could lead to a runway incursion.

Human Performance

While traffic volume, capacity-enhancing procedures and aerodrome layout may increase the potential for a runway incursion, human error is the mechanism that translates this potential into an actual occurrence.

Complexity, lack of familiarity with airport layout, communications difficulties, distractions and other factors all contribute to making flight crew and air traffic controllers more vulnerable to committing errors.

Is There Hope?

The Transport Canada study team made 23 recommendations to reduce the frequency of runway incursions. NAV CANADA also conducted a study to identify actions the industry could take to prevent runway incursions. Its study generated 27 recommendations.

Many of the recommendations from both reports have been implemented or are being implemented. Some require institutional changes, such as rules and standards, and will take some time to take effect. Others, such as air traffic control procedures, have already been implemented.

The Incursion Prevention Action Team

To oversee the implementation of the common recommendations from both studies, monitor and analyze runway incursions and remedial actions, and develop an awareness program, NAV CANADA and Transport Canada formed the Incursion Prevention Action Team (IPAT).

The aforementioned incursion awareness campaign (of which this article is part) is being designed to inform all sectors of the industry of the hazard of runway incursions and to publicize measures that can be taken to prevent them. Watch for more articles and updates in upcoming issues of the ASL.

In time, it is hoped these efforts will reduce the probability and consequences of runway incursions. Transport Canada’s complete report can be viewed or downloaded from http://www.tc.gc.ca/CivilAviation/SystemSafety/Pubs/
tp13795/menu.htm. NAV CANADA’s report can be read or downloaded from its Web site at http://www.navcanada.ca/navcanada.asp.