Runway safety as a function of time

May 2, 2009

Multimedia Features

View an animation that recreates this runway incursion.

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When things are busy we’re all focused on the task at hand. We may be at the controls of an aircraft, sitting at a radar screen, or scanning an airport and traffic pattern from a control tower. But we’re all maintaining our focus on safety, looking for increasing levels of risk, and mitigating them before they impact safety.

However, when things slow down and we have too much time on our hands, our level of attention may be affected. It’s a weekday in December at the Moline, Illinois, airport. The weather was IFR, visibility one-quarter mile in fog with a runway visual range (RVR) of 2,000 feet. In the control tower, traffic was light enough to combine the tower and ground control positions for slightly more than an hour to allow new controllers to receive training.

As the animation starts we hear a clear, deliberate, “textbook” example of phraseology between an airport vehicle, “Truck 3,” and the tower controller. Truck 3 requests clearance to go out onto the runway to work on some of the lights. It seems like an ideal time for the tasks—no traffic, poor weather greatly reduces the possibility of impacting VFR operations, and it’s lunchtime. The controller clears Truck 3 to the requested area to work on Runway 9 near Taxiway Hotel 1.

It takes Truck 3 approximately seven minutes to travel to the work site. Approximately 21 minutes later Citation N257AL calls the tower to request departure. Unbeknownst to the personnel involved in this event, those 28 minutes of elapsed time have increased the level of risk at Moline. Situational awareness of the traffic has been lost as a result of inactivity.

As Citation N7AL taxies out, there is a focus on the weather conditions and arrival traffic that could impact the departure off of Runway 9. The tower controller advises N7AL of changing RVR and requests information on the pilot’s required weather minimums.

Approximately three minutes after beginning to taxi, N7AL approaches Runway 9, which is not visible from the control tower, and requests confirmation that they are cleared to cross the runway. This is a great call by the Citation since the crew recognized the risk that a clearance may have been forgotten.

In the control tower, coordination is taking place to allow N7AL to depart before an arrival to Runway 27 becomes a conflict. A departure heading off of Runway 9 is relayed to the Citation. The controller’s attention is focused on the departure, the changing weather, the inability to see the runway from the tower, and the arrival. Truck 3, still parked on the side of Runway 9, has been forgotten.

Citation N7AL is issued takeoff clearance. With an RVR of approximately 2,000 feet and Truck 3 parked on the grass 1,500 feet from the departure end of the runway, N7AL has little chance of seeing the vehicle. As the aircraft continues the takeoff and observes the vehicle, the crew advises the tower of the situation. Fortunately, due to Truck 3’s position, there was little if any chance for a collision, but the animation’s audio track indicates surprised recognition by the controller.

Would this have happened if those 29 minutes did not transpire between Truck 3 going out to work on the lights and N7AL’s takeoff? Perhaps. But how do we control that?

This animation presents a situation whereby the crew of the aircraft did not contribute to the incursion. But were there things N7AL’s pilots, or any other crews, could have done to minimize the risk? Many factors led to the event but the poor visibility may have been the most significant, especially since it eliminated the tower controller’s ability to scan the runway. Would it have been possible for the departure to scan the runway while it was taxiing for departure? Perhaps, but the flight deck is a busy place when preparing for a low-visibility departure.

Could the airport have done anything differently? Could it have established a procedure where maintenance is not done under certain weather conditions? Perhaps a practice of always having vehicle headlights on and the vehicle facing in the direction of the runway might have made a difference. It’s difficult to say.

We may find that while we wait for additional technological enhancements to help us identify and manage risk, one of the most difficult tasks for everyone who is involved in runway safety will be maintaining situational awareness. We may also find that, although it may seem counterintuitive, periods of slow traffic can present high levels of risk.

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