Hearing what they expected to hear?

October 6, 2009

Multimedia Features

View an animation that recreates this runway incursion.

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General Edward Lawrence Logan International Airport in Boston is a complex operation with multiple runways and ground operations that can be especially challenging. The complexity can rise significantly when changes are taking place and different people have different expectations of what they believe is occurring.

We join the event one night as a Cessna Citation, call sign LJ6, is trying to depart with the least amount of delay. The ground controller assigns Runway 27, which was not the primary departure runway, and LJ6 asks if that will get them out faster. Responding, “Yes,” the ground controller then instructs LJ6 to taxi to Runway 27 via taxiways Charlie and Delta, hold short of Runway 33L, and monitor the tower. LJ6 reads the clearance back correctly, taxies out as instructed, stops short of Runway 33L on Taxiway Delta, and waits patiently for further instructions from the tower.

So far everything is going according to plan and things are probably looking pretty good on LJ6’s flight deck. But did that perspective establish an expectation on the part of the two pilots, anxious to depart with minimum delay, taxing out with the belief they had to do things in a hurry? Were they already ready to “hear” what they were expecting to hear?

Meanwhile, at least four other aircraft are on the tower controller’s frequency holding short of Runway 27 on Taxiway Charlie. The tower controller is advising each aircraft to expect Runway 33L and to hold short of Runway 27.

In the control tower, the ground controller is standing next to the tower controller and they are both watching the traffic begin to back up. The need to get the aircraft moving is increasing as Taxiway Charlie becomes congested with waiting aircraft. Ironically, the use of multiple runways, designed to increase traffic volume, can create this type of temporary bottleneck. One of the hidden risks that can occur under these conditions is that a controller’s focus may shift to the perceived “problem area,” in this case Taxiway C at Runway 27. It’s a normal controller response to identify the problem, solve it, and move on to other tasks. But sometimes that momentary shift in focus changes the risk level. An analogy would be a pilot’s instrument scan becoming narrow as cockpit workload increases—ever find yourself staring at the attitude indicator? The same thing can happen to an air traffic controller.

As you watch the animation you will see the line of aircraft holding short of Runway 27 at Taxiway Charlie. If you look on Taxiway Delta, right next to Taxiway Charlie, you will see LJ6 continuing to patiently hold short of Runway 33L exactly where he is supposed to be. In all likelihood the crew is also spring loaded to execute the next clearance they are expecting to hear—to “cross Runway 33L” for their expedited departure off of Runway 27. Their level of expectation is a potential risk factor they may not recognize.

Listen to the voice of the local controller in the animation. Sometimes voice, like body language, can send signals we can use to our advantage. Perhaps the signal is one of increasing traffic complexity. Perhaps it is a signal that the operation is getting busy. In either case, it may offer a barometer of changing risk levels.

Because of the number of aircraft on Taxiway Charlie waiting to cross Runway 27, it’s very possible that the tower controller may not be able to see LJ6—another indication of potentially increasing risk.

In the control tower, information is passing hands quickly, either through electronic means, verbally, or on paper flight strips. Coordination is becoming more complex as the controllers orchestrate the ballet that is occurring on the surface and in the air. It is very easy to look down and see a call sign but say something else. We’ll hear an example of this in the animation when the local controller instructs “Jet Blue 489” to taxi into position and hold but it sounds like “Jet Blue 49.” However, instead of confirming the call sign, the crew elects to respond to the transmission as “Jet Blue 49” and another element of risk is added. Regardless of whether this was caused by speaking too fast, ‘;clipping’ the transmission, or misspeaking the call sign, it still impacts effective communication. Whether or not this made a difference we can’t say, but it might have been an opportunity to mitigate risk that was lost.

So, what is the situation now? If we were in the control tower and looked out the tower window we would see a line of aircraft holding short of Runway 27 waiting to taxi across to get to the departure runway. We hear the local controller instructing everyone to hold short of Runway 27 on Taxiway Charlie…transmissions are happening faster and faster...we see a lot of aircraft near the intersection. Then we hear the tower controller say, “LJ6 taxi across Runway 27.” We hear the aircraft clearly read back “taxi across Runway 27,” and then we watch the aircraft taxi across Runway 33L just as the Jet Blue aircraft begins his takeoff roll. This was the final increase in risk.

What could have happened? Use of multiple runways and traffic flows are normal events that happen every day across the country. What made this time different?

Let’s try to look at the event from the perspective of LJ6. When the aircraft was originally issued instructions to taxi to Runway 27, there was probably a hope and expectation it would allow them to depart faster—clearly a clue that somebody was in a hurry. Although they very patiently waited at the hold short line, there may have been a conversation going on in the aircraft about delays, schedules, or other distractions. Could those types of distractions, combined with their expectations, have made them forget they were holding short of Runway 33L? Were they primed and ready to hear what they were expecting to hear?

Historically, it’s never just one thing that causes an event; it’s always a buildup of seemingly little things that combine to cause the event. Sometimes the solutions are changes in procedures or technology. Sometimes they are very simple, often times very complex. Sometimes it’s hard to tell.

Years ago, a very wise pilot described what he did when he was entering a busy airport environment: He moved the seat forward a notch. That simple step was his acknowledgement that things were going to get busy and he needed to devote his complete attention to conducting the flight. One of the many solutions to reducing runway incursions may be as simple as moving our seats forward a notch—it could be our mental checklist item, reminding us to devote our full attention to careful surface movement.

Tom Lintner is an airline transport pilot, CFI, and air traffic controller who works with the FAA’s Office of Runway Safety.