Monday, October 18, 2010

Taxi via Delta, Juliet ...

The main goal of any runway or taxiway safety initiative is simple: Prevent aircraft from running into each other whether they are taxiing, taking off, or landing. The FAA announced there were just 12 runway incursions for the 2010 fiscal year (ending in October), a 50% reduction from the previous year. The FAA's press release attributes the drop in runway incursions to new technology at airports, improved signage and markings, and improved pilot training on runway conflict scenarios. Surely all those capital improvements and increased pilot training helped reduce runway incursions, but there are low-cost improvements, too. There have also been FAA safety initiatives that may actually decrease safety as well as some widely used procedures that need to be changed.

Who's in Charge?

The dominant paradigm in aviation is to have an air traffic controller be the authority that manages conflicts, prevents collisions, and keeps the big picture. The ground controller gives instructions to pilots and flight crews and those guys and gals follow those instructions. Problems can still happen when pilots or controllers are confused or tired and make mistakes. Here's a simulation of a situation that occurred at Theodore Francis Green Airport during low visibility at night. A United flight crew makes a wrong turn while taxiing to the terminal, which takes them back to the active runway. The situation gets worse when the United crew realizes something is wrong, but twice they identify their position incorrectly to the tower controller. The tower controller loses The Flick and in the end, a US Airways crew makes a wise choice that averts disaster. (I chose this particular re-creation because it doesn't edit out the transmissions that reveal the tower controller's frustration, which I think figures prominently in this incident.)

This incident was probably the reason why Theodore Francis Green was one of thirty some airports where Airport Surface Detection Equipment, Model X (aka ASDE-X) was installed or will be installed to help  controllers keep The Flick during low-visibility situations. Pilots operating on taxiways or runways set their transponders to squawk altitude and the controller sees each aircraft's position on a color display. This is surely a welcome addition in low-visibility situations.

Where You At?

A supporting approach to the Controller is the Boss paradigm is to provide rules and a clear context to pilots and flight crews so they can prevent conflicts on their own initiative. Several years back, an experimental system was tested at the Concord airport that involved placing sensors in the taxiway pavement at hot spots - locations on the airport where history had shown pilot were likely to get confused. When an aircraft taxied onto one of the sensors, a low-powered transmitter would broadcast a recorded message of the pilot's position and the pilot received these messages through their marker beacon receiver.

Though this was a clever use of existing avionics equipment, this system was expensive to install. Pavement had to be ripped up, sensors placed, and pavement reapplied. I tried this system several times and found that it worked, but there were limits to its usefulness. A disoriented or confused pilot still had to interpret what the recording was saying, find their position on a taxiway diagram, and then get un-confused. The system was deactivated after about a year, if memory serves me.

One safety enhancement left out of the FAA's press release was an important change that became effective in June of this year: New air traffic control phraseology for issuing taxi instructions. The gist of these changes was that ground controllers were required to explicitly provide the taxiways that pilots were to use when repositioning or taxing for takeoff. Prior to this, controllers were not required to specify a taxi route and (here's the amazing part) clearance to cross any runways along the way was implied. This procedure had the advantage of requiring controllers to say less, but this always seemed like a recipe for trouble. Add to this some controllers' tendency to be ... impolite when under stress and you can have a really bad situation.

At one airport where I teach, approval was provided years ago for a large corporation to construct a hangar that blocked the line of sight between the tower and portions of two taxiways that cross a runway. So ground controllers would tell aircraft "taxi to the Old Tees via Delta, hold short of runway 15 and report holding short." Some controllers are extra careful and add "That area is not visible from the tower." After hearing this countless times, pilots taxiing in that area became accustomed to stopping at the runway and reporting to the ground controller.

There was a particular air traffic controller (long since retired) who had a widely recognized reputation for being terse and impatient (I'm being nice here). At the conclusion of a long night flight, my student requested taxi clearance from this controller, but missed what the controller actually said: "Cessna 123, taxi to the Old Tees via Delta." There was no mention of holding short at the runway. The airport was dead quiet and as we approached the usual hold short point, my student put on the brakes. Confused, he asked me "Did he tell us to hold short?"

Thinking this to be one of those teachable moments, I offered "Anytime you are in doubt, you should ask." So he reported holding short. The controller let loose with a verbal fusillade the likes of which few of us have heard on frequency. My student turned to me, his mouth was open, but no words were coming out. During the debrief, I spent much time trying to undo the damage done by the controller, explaining to my student that he had indeed acted correctly and the controller's response was both unprofessional and contrary to safety. Visibility to the area I mentioned should not be a problem once the new control tower is completed. The new tower will replace the two, separate towers and will be more centrally located (near the FedEx ramp).

Another change has been the FAA's long-anticipated adoption of the ICAO phraseology Line up and wait. The old phrase "Taxi into position and hold" was often elided to "position and hold" and could be easily confused with the phrase "hold your position." This phraseology change is certainly a step in the right direction and required no expensive equipment to be installed.

Enhanced Centerline, Runway Guard Lights

The enhanced centerline became a Part 139 standard a couple of years ago. The idea was to make a taxiway centerline change appearance as an aircraft approaches a hold short line at a runway crossing. While the motivation for this change was safety, it's my feeling that the enhanced centerline is actually visual noise. Assuming there are no other unusual surface markings nearby, the enhanced centerline may help a flight crew avoid blowing through a hold short line. In areas where taxiway edge markings and patched pavement exist, all the dashed lines can become a confusing distraction.

Can you find the Enhanced Centerline?

Flashing runway guard lights can be installed adjacent to a hold short line or they may be embedded in the pavement prior to the hold short line. When these lights are embedded in pavement, they can actually obscure the runway centerline unless lead-in lights are also installed. Lastly these lights aren't the best for preserving night vision adaptation.

Taxi My Frequency

A very hazardous procedure that is often used by ATC is having one controller at an airport running both tower and ground frequencies. While this may save money by having one person doing two jobs during off-peak hours, it a dangerous practice. With one controller listening and transmitting on two frequencies, pilots and flight crews are robbed of The Flick because they can only hear one side of the conversation. This was a contributing factor to a near collision I had while taxiing one night.

I'd called ground to taxi to parking from the fuel island and received my clearance. As I began taxiing I saw a business jet rolling out on the runway parallel to me. The jet taxied clear and I heard the controller ask the jet where they were headed, but since the jet was still on the tower frequency I didn't hear their response. I did hear the controller tell them "You can taxi either route" and my spidey senses started tingling.

Sure enough, the jet chose the route that had it headed right toward me, the controller hadn't mentioned my presence to them, and they didn't appear to see me. I turned on my strobes and poured on the coals. The jet missed hitting me by a few feet and the irony was at the time, we were the only two aircraft on the airport. I mentioned to the controller that we'd nearly had a collision to which he simply replied "Roger." Had there been a separate ground controller and had the jet been on the same frequency that I was on, everyone could have cooperated to prevent a conflict. The FAA really needs to stop this practice of one controller running multiple frequencies because, quite frankly, it's dangerous.

More Progress Needed

The drop in runway incursions is a significant achievement. The latest hi-tech and high-cost initiative is NexGen and ADS-B, which we're told will enhance safety, reduce airline delays and prevent athlete's foot. Hopefully the folks at the FAA (and their contractors) will keep in mind that along with these expensive solutions, there are still many simple, low-tech, and low-cost changes that can provide significant safety enhancements. Of course that means that pilots, controllers, and the FAA must have the will to change old habits.


Marc said...

I agree that having one controller work both positions can be problematic. There have been a couple times where I have flown into an airport that had combined positions, but ATIS announced that all traffic use the tower freq. If someone would call up on ground, the controller would ask them to "change to my frequency on ." I thought this was a pretty great way to handle the combined positions.

John Ewing said...

Okay, I have fat fingers. I inadvertently tapped on delete when I meant to tap on publish and Blogger doesn't let you undo. So here's Ron's comment:

Ron has left a new comment on your post "Taxi via Delta, Juliet ...":

If it was me, I would have asked the controller who berated your student for a phone number where I could contact him or his supervisor after the flight. Not only was it unprofessional and contrary to safety, but now that student might be gun-shy about asking for clarification from a controller. Years from now some accident could occur which could be linked to how badly the controller (a rather faceless authority figure to many students) treated the student pilot. Primacy at work.

I really hate it when controllers let loose on pilots. I see it a lot with instrument students in busy metro areas. It's very difficult to have any faith in the performance of a controller who is loses control of themselves while on duty.

I think one of the root causes of this sort of thing is that controllers are no longer pilots. They have no idea what it's like to be on the other side of the radio. Controllers should be flying with pilots, and pilots should be observing what controllers have to deal with. That simple exchange would virtually eliminate these kinds of things. And even in cases where they don't, at least the pilot will understand how busy the controller might be or how long and stressful their day might have been.

And I'll add my voice to the chorus of disapproval about a single controller working multiple frequencies.