The communications related aspects of runway incursions

On 31-03-2010, in Life around runways, by steve

More than two incursions a day…

Few other incidents return with the grim and persistent regularity of runway incursions. A lot of effort by all concerned has resulted in a reduction of the total number of incidents but there are still, on average, more than two runway incursions in Europe per day. Clearly, there remains a lot of work to be done.

But what exactly is a runway incursion? According to the definition provided by the International Civil Aviation Organization (ICAO) a runway incursion is “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.”

Of course the words “incorrect presence” cover a wide range of possibilities from part of an aircraft sticking into the protected area to a vehicle or aircraft being entirely in the path of an aircraft landing or taking off. The dangers need no explaining… The reasons why highly trained professionals like pilots and controllers and less well trained but still “aerodrome aware” vehicle drivers make mistakes leading to runway incursions provide a telling story with roots in human psychology, engineering, traffic design, information technology and one may dare to say, on occasion Murphy’s law.

Focus on communications

A lot of work has been undertaken to analyze the causal factors of runway incursions and to define actions to eliminate or at least reduce those causes. A recent study focused on the role communication breakdowns have in runway incursion events. The following is an edited account of what this study has found. It is not the intention to generalize the results but the lessons are certainly worth consideration by all airports.

It has been known for a long time that improper use of phraseology leads to all kinds of operational errors, runway incursions among them. But of course the term “communications” need not be limited to addressed or broadcast radiotelephony. The relationship between an aircraft or ground vehicle and air traffic services involves multiple interactions where information exchange takes place via several channels (ATIS, AIS, telephone, printed documentation, training, briefing, etc.). All of those represent a form of communication and as such, can have errors in them that may lead to a runway incursion.

This reasoning led to communications being defined for the study as referring to any active or passive presence involving transfer of information by and between humans or machines, whether analogue or digital, visual, verbal, written or electronic, irrespective of its timing, which had or could have an influence on the evolution of events that led to a runway incursion. In this respect, the lack of information transfer, when in fact there should have been such transfer, is also considered as belonging to the concept of communication as understood in the study. This definition is a roundabout way of saying that the study aimed to catch all events where information transfer of any kind (or the lack of it) was at fault.

A representative sample

Frequent as they are, it is not always easy to come by a representative sample of runway incursion reports. While they are in the public domain in some European states, in others they are subject to strict data protection laws. What is common in all cases is the willingness to share incursion related lessons learned… but getting the raw data is a tough assignment.

The difficulties notwithstanding, 5 years’ worth of incursion data covering the period 2005-2009 and comprising 482 events was scrutinized. The airports concerned were a good cross section of the European scene from busy hubs to moderately busy regional airports.
The broad airport coverage brought with it a nicely balanced set of aircraft types and operators, making the sample sufficiently representative.

Where communications played a role…

Initially there was some concern as to how it will be possible to isolate communications related events. How would one deal with cases where several causal factors interacted to create the incursion event.

In practice the overwhelming majority of runway incursions turned out to be the result of a single cause in simple circumstances and multiple causes were more the exception than the rule. Finding the target cases was not difficult. Evidently, aviation’s multi-layered safety system was lacking in the case of runway incursions. Single errors should not lead to potentially catastrophic events…

Is there “incursion” weather or time of day?

Intuitively one tends to think that getting lost and wandering onto an active runway would typically happen in poor visibility or at night or both together… In fact in reality most runway incursions happen in broad daylight and fair to unlimited visibility!

Of the communications related events studied, only 11 % occurred in airport IMC conditions but even there cloud-base and visibility were not really critical and certainly did not play a role in causing the event. The same is true of the 20 % of events that happened at night.

Could it be that the perception of something sinister lurking in thick fog or under the darkness of the night makes us more careful?

What about traffic complexity?

Air traffic controllers know full well that near misses and mid-airs usually occur in the simplest circumstances when only the two aircraft involved in the incident are around. The same tends to be true for runway incursions. Traffic complexity does not seem to play any role at all.

Are there incursion prone aircraft types or operators?

Focusing on communications as this study did, it was not difficult to notice that not all flight crews were equally proficient in the use of the English language and standard phraseology. However, it was not possible to identify worst of class companies. The best and the worst seem to be contributing about equally.

The perception that small aircraft cause more trouble than bigger ones was also not borne out by this sample. Boeing 737 and Airbus A320 family aircraft figured in the show much more often than did Cessna’s and the like.

There is clearly an issue with ground vehicles, however. Compared to their numbers (much lower than the number of aircraft) ground vehicles were involved in events at a rate that should raise some warning flags across the board. As you will see, even the airport fire brigade may need a few refresher courses on how to approach the active runway when they are not actually responding to an aircraft emergency…

What the events tell us

As you will see, the events encompass a wide range of communications related causes, some quite unexpected. Each event had a story to tell and serves as a pointer as to where more effective action is needed to further reduce the incidence of runway incursions. Here are the most prominent examples.

  • Phraseology use

These cases involved slight or not so slight variations on the standard phraseology, the use of phrases that are not at all part of the standard and using local language expressions, sometimes mixed in with English.

Saying “Expect departure three miles behind the Airbus” was obviously not a good idea, an aircraft lined up thinking the phrase meant “Behind the Airbus, line up”.

The phrase “Report ready for departure” sounds innocent enough, but issued to an aircraft approaching the runway, it was taken as a line-up clearance with a runway incursion the result.

  • A properly given clearance or instruction is misunderstood or ignored

One would think that a clearance or instruction issued using the proper phraseology and procedures should not result in problems. Yet, on a number of occasions such a clearance or instruction was followed by totally unexpected behavior of the aircraft and vehicles concerned.

In some cases things went out of hand twice in a row, with the pilot failing to read back the instruction and the controller not challenging it. After this of course almost anything can happen.

One can probably better understand the debate that rages around pilot duty times when an aircraft having been instructed to hold short of the runway just taxies on and when instructed to stop, it stops with the pilot apologizing “it was a very long day…”

When an aircraft carries out the action authorized in a clearance issued to another aircraft is bad enough… but what about the bus service which started to move, entering the runway on the strength of a clearance issued to the snow removal vehicles?

  • Lack of awareness of or ignoring the protected nature of runways

One would think that anyone who has had the opportunity to stand beside a runway when even a medium size aircraft rolls by landing or taking off would need no special briefing why it is not a very good idea to get in the way of such a beast… Yet even seasoned airport drivers occasionally blunder onto the active runway. What can then we expect from the drivers of outside contractors who are allowed near runways after just a short briefing on the dangers?

Apparently even having a dedicated safety watch post is no guarantee of success… The contractors for the construction work must have thought of everything, yet the tower was never told of what was being done… until someone managed to become a runway incursion, safety post notwithstanding.

When an aircraft called for a doctor, the fire brigade responded, transporting the doctor, and dashing across the active runway without clearance from the tower. On another occasion the fire brigade took some of their gear for a test drive and entered the active runway without clearance. Now if they thought this was ok to do, what do you expect from a simple follow-me? Well, exactly, they and some other airport vehicles seem to be regular, though unauthorized, visitors on runways everywhere.

  • Failure to respond to an erroneous read-back

The requirement to read back certain information is there obviously to catch misunderstandings. It is part of the layered safety arrangements. It would appear however that listening to the read-back sometimes becomes a formality with the attention of the controller already taken up by something else. Once such a slip happens, there is no third safety layer to prevent an incident.

Two runways, two aircraft, one on each runway… they both responded to the take-off clearance issued to just one of them and the controller never noticed.

On another occasion, an aircraft was given hold-short instructions. The read-back was incomplete but it was not challenged. The aircraft subsequently lined up without clearance.

  • Loss of awareness of the world outside the cockpit

The cockpit is a busy place most of the time and when taxiing for take-off, the number of tasks to be carried out is one of the highest of all phases of flight. At the same time, the aircraft has to navigate often complicated taxiway systems, possibly cross runways… In other words there is no room for not keeping an eye on the outside environment. Yet it happens regularly that the flight crew is apparently so absorbed in the cockpit chores that they just roll past holding points, onto runways and even fail to respond to frantic transmissions from the tower, shouting their name.

This must have been the case when an aircraft taxied clear through the holding point and afterward claimed that they had not seen the markings, the lights… nothing.

  • Vehicle driver not familiar with the airport

Basically there are three types of ground vehicle drivers who operate on an airport. Old hands employed by the airport or a company with a location at the airport who have been there for a long time and who you would expect to be familiar with the airport layout and the applicable procedures; new hires who will have received some training or at least a briefing and who may even had to take an exam but whose knowledge is still relatively shaky; and drivers of companies hired to carry out specific tasks and whose knowledge is often questionable and awareness of the dangers is minimal if it exists at all. One would think that it is the last two types who are involved in most of the runway incursions and indeed they are. But even the seasoned hands contribute at a rate that is cause for concern.

That a driver with his airside license just one day old gets disoriented and crosses the threshold of the active runway several times is perhaps not so surprising even if it should not have happened. Another driver managed to surpass his colleague when he went out on the field without even elementary familiarity of its layout, got several concrete instructions which he acknowledged… and then proceeded his own way as if the Tower had not said anything. In short order he too became a runway incursion…

  • Wrong assumptions

One does not need to think in an aviation context to experience the dangers of replacing the certainty of knowledge with assumptions. It is a curious aspect of human psychology that seems to abhor vacuum and so forces us to fill a lack of knowledge with assumptions. The correctness or appropriateness of the assumption does not really play a role. In extreme cases, the strength of an assumption can even override the visible facts of reality. When operating aircraft, assumptions can be (and have been!) deadly.
There have been several cases where vehicles and aircraft entered a runway which was not at the time the runway in use assuming that there was no need to ask for clearance to cross such a runway…

In another case, the flight crew assumed that the information from the Automatic Terminal Information System (ATIS) was always absolute and if the ATIS said a runway was closed, then it was closed and could be crossed without clearance. The ATS authority assumed that it was clear to everyone that the ATIS broadcast and reality may be a few minutes out of synch and hence flight crews will not assume that they can do anything without a clearance, just on the strength of the ATIS broadcast…

  • Faulty documentation

Perhaps the least typical but it has happened… Documentation on board an aircraft showed a runway closed when in fact it was open. The aircraft crossed the runway without clearance and a runway incursion event was the result. Of course the documentation was only a contributing factor to the event but still… Documentation should not have errors in them.

What about the top non-communications related causes?

Focusing as the study was on communications related events, the authors were curious what the top three non-communications related causes of runway incursions were. Enquiries revealed that in the complete list of events, the top two by frequency of occurrence are confusing signs and markings and intersecting/closely spaced parallel runways with the third place being taken by phraseology use… so they were back in the context of the study! But the top two non-communications causes are very interesting.

If an airport finds that incidents occur regularly at or around a particular location, the place will be designated as a hot-spot and marked on the map. This is a good first step of course but the next thing they need to think of is how to eliminate that hot spot. And this is where the lessons from studying runway incursions come in handy.

On the top of the list of causal factors is confusing signs and markings. So the first thing to look for is just how good, or rather poor, the signs and markings are around the hot-spot. They will of course all meet the applicable ICAO provisions but that is not enough to keep people out of trouble. The location, orientation, composition, repetition etc. of the signs and markings all play a role in helping or, in this case, confusing the flight crew and vehicle drivers. Experience shows that in many cases just a slight rearrangement of things works magic and the incidents, at least at that particular position, become history.

Closely spaced parallel runways are another story. What seems to be happening there is that an aircraft lends, leaves the runway via a rapid exit taxiway (RET) and almost before they know it, they have to stop the get cleared to cross the parallel runway… in many cases, they overshoot the holding point and become a runway incursion on the parallel runway. Logically this should not be happening because the charts show clearly that there is another runway yet the problem figures in the top two of all runway incursions. Perhaps a slight modification of the geometry of the RETs or some kind of new signs and markings, with eventually a warning light might be what is needed to eliminate this particular danger.

What conclusions can we draw from this study?

The events studied as being communications related show clearly why it was a good decision to use a wider definition for the term “communications”. The study captured events that may have been allocated to other, less well fitting categories if the traditional definition had been used and possibly remained invisible. However, it is now possible to address the issues discovered in a complex manner, using the power of communications theory in the widest sense of the word. The synergies between the solutions that will need to be applied will help in increasing their overall effectiveness.

Not unexpectedly, the largest contributor to runway incursions from a communications point of view is the improper use of phraseology and the related procedures. In fact, this is the third most frequent cause of runway incursions in general.

Looking at the other communications related causes, it is easy to see that better training and more discipline in daily operations could eliminate or at least reduce the incidence of these types of incursions.

But this is exactly where the problem is. The top cause of non-communications related incursions was found to be confusing signs and markings. Figuring out how to improve the signage is relatively easy. Enforcing discipline and improving training across the board is anything but…

Obviously there is a major challenge here requiring the cooperation of all concerned. The study, with its unconventional definition of communications, has highlighted the issues and has provided guidance on where the mitigating measures should be focused so the initial direction has been set.

What needs to be done is not rocket science. Better training and more discipline regarding the use of the sterile cockpit concept and insisting on complete and correct readbacks should go a long way towards reducing the incidence of communications related runway incursions.


You can read about technology solutions aimed at preventing runway incursions here.

You can find a lot of useful information about preventing runway incursions in the EUROCONTROL runway safety portal  here.

Looking for runway incursion training videos? Click here.

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  1. Ed says:

    Good article!

  2. [...] me say that as a former air traffic controller who has also done quite some work on analyzing the causes of runway incursions, I am especially sensitive to the importance of using proper phraseology in [...]

  3. [...] the wrong frequency or does not respond to controller instructions for some other reason (problems often seen in runway incursion incidents), it is almost totally useless. Having said this, of course any system [...]

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