I was talking recently with my friend Darryl, a budding private pilot close to solo, about takeoffs and landings. Darryl was lamenting the difficulty of staying on the runway centerline all the time and was wondering how important it really was. Darryl's shock was apparent when I defended the centerline like it was my little sister.
Are you a centerline person? Or are you the reason that they made airways eight miles wide and runways three miles long? We're supposed to be centerline people — it's where we were born to be. OK, maybe it's more of a guideline — as long as we land on the runway. OK, maybe more of a suggestion — as long as we touch down on the airport, that's fine. OK, maybe forget the whole centerline thing — as long as we land within sight of the airport we'll call it good.
The centerline is about precision in your flying. It's about hitting the spot. It's about being where you said you'd be. Even more important, because obstacle clearance and air traffic separation are based on the centerline, it could be the only thing keeping you safe from the rocks and other airplanes. And when we talk centerlines, we aren't just talking runways. The centerline concept also applies to taxiways, airways, approaches, touchdown zones, and more — everything you do in flying.
Taxiway centerlines
My friend Kelly was returning to his home field late one night after flying his friends to a nearby airport for dinner. He knew that the taxiway centerline was his best chance to get through the obstacle-ridden ramp dent free, and unlike many pilots, he had no aversion to the little yellow line. As it was the end of a long evening, Kelly was excited about following the little yellow line right to his tiedown spot. However, like a prisoner caught in the act of escaping, Kelly was not excited about the blinding security spotlight that met him as he taxied in. Kelly put up his hand to ward off the glare, but unfortunately that did not ward off the smack — those runway hold-short signs are not nearly as short as they look.
Kelly got out to survey the damage. Hole in the leading edge of the left wing: Sign 1, Wing 0. The security spotlight was used to identify after-hours aircraft operations for potential noise violations (which they got when Kelly saw the hole in the wing), and while warding off the security spotlight Kelly had drifted off the taxiway centerline right into the hull-damage section of his insurance policy. On the upside, the security folks paid for the damage to the airplane — apparently, blinding pilots and running airplanes off taxiways are not the sole jobs of after-hours security. On the downside, stupidity rarely happens in a vacuum — it's pretty much guaranteed you'll have friends around to witness every stupid move you make.
Runway centerlines
As we all know, anything you can do on a taxiway you can do on a runway a whole lot faster. A few years ago, a Gulfstream business jet landed at Van Nuys (near Los Angeles) on a relatively unused section of the runway near the departure end. Unable to stop in a timely manner, the pilots took the road less traveled through the FBO ramp, across the street, and onto a golf course, yelling "fore" and "playing through" as appropriate. Great effort to ensure a quick tee time, but not the best way to stop the airplane.
When I arrived at Van Nuys about a week later I noticed one of the FBO folks scrubbing something off the ramp. It took me a second to realize that he was scrubbing off the skid marks leftover from the unfortunate arrival (and departure) of the Gulfstream — and that the marks went right underneath my airplane. I looked around and saw many airplanes (including mine) and people (including me) that would have been damaged if the Gulfstream had picked that moment to plow through the unsuspecting ramp. Very disturbing.
A year or so later an airliner used the same approach at Burbank, which ironically, is right next door to Van Nuys. The pilots touched down at a very high rate of speed in a place where there were few other tire marks. This caused them to depart Burbank on runway heading (which works way better when you're airborne) through a barrier (that had always looked pretty substantial to me) and across Hollywood Way to the gas station across the street. Some pilots will go pretty far to get cheap gas and apparently they had heard that gas was cheaper off the airport. No word yet on that autogas STC for the 737.
Hitting the centerline is great, but it doesn't do much good if you completely miss the touchdown zone. When I land, I never want to look back and be able to identify my tire marks on the runway. If I can, I either left some serious skid marks or I boldly touched down where no one had touched down before. There's a time to be special and there's a time to just land where everyone else does.
Airway and approach centerlines
Sometimes it's completely appropriate to approximate, but on an airway, the world expects us to be perfect. Not flying English style (down the left side of the airway) or American style (down the right side of the airway), but good pilot style — down the centerline. Flying the centerline is often the only way to ensure separation with other aircraft and terrain. Think about it; if you are on the centerline of an airway that is eight miles wide, you should be separated from an airplane on a neighboring airway by at least eight miles. If you both ignore the centerline and fly one foot from the edge of your respective airways, you might be 16 miles apart (optimist) or you might be two feet apart and in each other's grill (pessimist).
My friend was doing an ILS to 10R in Portland, Oregon, one foggy winter morning in a Cessna 310. It had already been a long flight and he was a little tired. And, as a newly minted instrument pilot, he was not the most confident of IFR aviators. ATC piled it on with a late descent and a fairly radical turn onto the localizer, and my friend never quite recovered. While he tracked the glideslope perfectly all the way down, the localizer needle went back and forth like the dining-room lamp in an earthquake. Full deflection right, full deflection left ... yikes. Thanks more to dumb luck than skill, it just so happened that he intercepted visual conditions, minimums, and the centerline all at the same time. He made a 20-degree left turn and landed right on the centerline. I have since been informed that this kind of navigation is called having the needle "transiently centered." Transiently centered apparently is a term for that one instant when the needle is centered as you go from full deflection left to full deflection right, blowing across the centerline you meant to track. Probably wouldn't want to be using that term on your next checkride.
Do-it-yourself centerline
All that said, it may not always be prudent to blindly follow the centerline right through hazardous weather or traffic. For one bizjet crew, it was just another beautiful day in Boston with that kind of IMC weather that teases you with occasional glimpses of the airport. Unfortunately, a thunderstorm had inconveniently set up house just to the left of the final approach course to Runway 4R, making it difficult to get into the airport. The only way to safely get past the storm and into Boston was to deviate almost two full dots to the right of course. Our friendly bizjet crew (and several other airplanes) did this, got around the storm, returned to the localizer centerline, and everything was fine. It worked great for them, but as a general rule, be real sure what you're doing before you try this at home.
Just a few weeks ago I was a passenger on an airline flight into Orange County, again near Los Angeles (the L.A. area is home to three of the top 25 busiest airports in the world), a place where you instinctively fend off other airplanes like mosquitoes at Oshkosh. About five miles out on the ILS to Runway 19R the airplane abruptly went up, paused, then went right back down, landing uneventfully a couple of minutes later. The aircraft had responded to a TCAS (traffic alert and collision avoidance system) resolution advisory to avoid another airplane and had managed to stay within the glideslope the entire time. I have to admit, in this era of fee-happy airlines, I was impressed — rarely do you get to experience a zero-G roller-coaster ride so close to the ground on purpose, and all at no extra charge.
The wrong centerline
Being on the centerline is great, but we have to be on the right centerline to stay out of trouble. Following the wrong centerline can get us in serious trouble. Not normal trouble, but serious trouble. A few months ago, an airline crew allegedly deviated from its departure clearance leaving Washington, D.C.'s Ronald Reagan Washington National Airport to the northwest from Runway 1. Instead of turning left, our airline friends went straight ahead, tracking the runway centerline to the evening news and aviation infamy. If you've ever taken off from Washington National to the north on Runway 1, you know that you only have to remember one thing. Not that the capital of Iceland is Reykjavik (though that is always great for Trivial Pursuit), but that whatever else happens on departure, turn left. If you see a mushroom cloud, turn left. Even if you are a dyed-in-the-wool Republican, turn left (don't think of it as left, think of it as really, really far right). Even if you see Elvis, turn left; otherwise, you'll get a great view of the White House, Capitol, and several anti-aircraft batteries on your way to doing the "Jailhouse Rock" in the aviation big house.
Big-sky theory
With air traffic increasing we can no longer rely on big-sky theory for aircraft separation. We have to find ways to fit more airplanes into crowded en route and terminal environments, making holes today where yesterday there were none. As we do this, the buffer zones around airplanes and centerlines will become thinner and thinner.
Precision runway monitor (PRM) approaches are a way for certain airports to fit more airplanes in less space by running simultaneous (usually ILS) approaches to parallel runways with less than the usual amount of IFR separation. This can be a big help to busy airports that have runway layouts that drastically lower capacities when the weather no longer warrants visual approaches. However, this improvement does not come without a cost — PRM approaches require special ground equipment, procedures, and training for both air traffic controllers and pilots.
Controllers make it work by assigning an additional "monitor" controller whose sole purpose is to watch you, and just you, every second, all the way to the runway. The controller uses a special high-update radar (call it "we can figure out you're doing something stupid sooner" radar) and extra frequencies to allow ATC transmissions to the cockpit at any time. Deviating from the centerline even a little bit results in an immediate go-around. Pilots make it work by being familiar with PRM, watching a video that describes special missed approach procedures, and accepting the approach when it is offered. Minneapolis, Philadelphia, and St. Louis are the only PRM facilities now, but PRM is coming to San Francisco and perhaps a big airport near you in the future.
Flying down the narrow and mountainous Gastineau Channel into Juneau, Alaska, can be one of the most dangerous approaches around. However, utilizing the benefits of required navigational performance (RNP) technology, Alaska Airlines developed an approach that is legal, safe, and a huge improvement over what was there before (nothing). It is an approach that would be impossible by any other means.
RNP procedures get airplanes into and out of lots of places they couldn't go before. An RNP approach is like an ILS approach with the ability to go around corners. With no ground-based localizer, glideslope, or ATC requirements, RNP differs from PRM in that all of the required equipment is already on the airplane. If the airplane is equipped properly and meets the RNP for that procedure, it can fly it.
Replacing nonprecision LDA, VOR, and NDB approaches with RNP approaches provides significantly lower minimums with no additional cost. Because RNP procedures don't have the straight-line and line-of-sight limitations of procedures using ground-based navaids, they can wind around and over obstacles that on a traditional instrument approach would result in much higher minimums — if the approach were even possible. You think the centerline is important using PRM and RNP? If you're lucky, deviation from the centerline results in a go-around; if you're not, it results in a whole lot of inappropriate contact with traffic or terrain.
Do I need the centerline today?
What does the centerline mean to you? Is it:
- A guideline?
- A dream?
- Where you fly all the time, day or night?
- Someplace you've never been but hope to be someday?
Your comment may be, "I don't need the centerline today," but what about tomorrow? Maybe today you're a private pilot. Maybe tomorrow you're flying the left seat of a Boeing 777 at the financially solvent airline of your choice. As you move up the ladder and into more complex airplanes — whether the product of some incredibly well-thought-out career progression or just an upgrade from a Cessna 152 to a Cessna 172 — the tolerances for error get smaller and smaller. Put a Helio Courier on a 150-foot-wide runway and you can pretty much land in any direction you want. Put a heavy jet on that runway and it suddenly looks a lot smaller. And if you lock a brake or lose an engine at the wrong time, you won't even remember seeing the runway.
Defend the centerline like it was your little sister. Don't give it up for anything. If you're a few feet off, get back on. If it's a challenge, keep after it. Whether you are carrying 400 people you don't know or your own family and friends, your commitment to the centerline in everything you do should be the same. Don't settle for close enough, because once you accept less than your best it will become the norm. Don't lower your flying skills to the conditions; if the conditions don't demand your best, make sure that you do.
Marc K. Henegar flies a Boeing 737 for Alaska Airlines.
Related Articles
