Turbine Pilot

GNE: Sweat the small stuff

It was a near miss of epic proportions. Two wide-body jets, a Boeing 747 and a Lockheed 1011, crossed paths over the North Atlantic with what was later estimated by the crews involved to be a scant 50 feet of vertical separation.

A friend of mine, whose parents happened to be passengers on the 747, said afterward that her mother had watched from her window seat as the L-1011 slowly converged. Believing that the pilots were aware of each other's positions, she was delighted (at first) for the unexpected photo opportunity and took several air-to-air snapshots as the jets drew closer.

The pre-TCAS (traffic alert and collision avoidance system) incident took place in July 1987, and but for a fortuitous Fate Is the Hunter piece of last-minute good karma (more on that later), the outcome could easily have been different. When the ensuing investigation finally wrapped up, the near tragedy was attributed to a gross navigation error (GNE) on the part of the L-1011 crew. Like most aviation mishaps and near misses, this one resulted from a chain of events that was allowed to progress far past the point where the incident should have been prevented. The first mistake occurred when a waypoint was entered incorrectly into the inertial navigation system during the crew's preflight preparations. That error was compounded when they subsequently failed to utilize other procedures designed to catch just such a mistake.

According to the FAA, a GNE occurs when an aircraft is displaced 25 nm or more laterally from its cleared track. Although infrequent, the majority of GNEs have occurred in North Atlantic track (NAT) airspace. In 1998, for instance, 28 GNE events were recorded out of more than 317,000 aircraft movements in the NAT route structure. Air traffic controllers were credited with helping to prevent 77 others that same year.

Aircraft operating between North America and Europe utilize a high-altitude route system with parallel east-west tracks separated by one degree of latitude, or 60 nm. Much of the NAT airspace lacks radar coverage, but an increasing number of oceanic flights now utilize automatic dependent surveillance systems that allow controllers to determine aircraft position and speed information via satellite. This is expected to help reduce the number of GNEs that occur, since observed position errors can be caught by controllers before they progress to GNE status. Other improvements, such as the increasing use of datalinked flight plans that minimize the chance of data entry errors, are helping as well.

Not long after the 1987 incident, another equally egregious GNE occurred on an air carrier flight from Newark International Airport (recently renamed Newark Liberty International Airport) to the island of St. Thomas in the U.S. Virgin Islands. This one didn't result in a near midair collision, but it could have ended in a fuel emergency or even a ditching.

Soon after beginning the over-water portion of the flight, about 10 minutes after takeoff, New York Center assigned the Boeing 727 crew a southeasterly heading for traffic. The crew was told to expect on-course routing shortly from the next controller. For some reason the crew missed the hand-off to the next frequency, although the first controller apparently believed the hand-off had occurred. The aircraft maintained the assigned heading and eventually flew out of both VHF radio and radar range of New York Center.

The Boeing was equipped with dual omega long-range navigation systems that had been correctly programmed for the route of flight. The planned route was via Alpha 300, a north-south oceanic airway that passes 227 miles west of Bermuda. However, the crew apparently didn't think to question the heading assignment or wonder why the "expect" clearance had failed to materialize. They never engaged the NAV mode of the autopilot, which would have allowed them to fly the programmed route. Instead they continued to operate the autopilot in heading mode as they passed nearly 200 miles to the northeast of Bermuda, on the edge of that island's radar coverage.

Just how long they might have continued out to sea in the wrong direction is anybody's guess, but fortunately for them and their passengers the error chain was finally broken. Following a telephone call or two, Bermuda controllers were able to figure out who the mystery target was. The crew, reached by HF radio, was no doubt surprised to learn they were more than 400 miles off course.

Perhaps the most infamous GNE in modern times is linked to the ill-fated Korean Airlines Flight 007 of August 31, 1983. The Boeing 747 departed from Anchorage, Alaska, headed to Seoul, South Korea. Along the way it penetrated Soviet airspace without permission, and was subsequently shot down by a Soviet fighter pilot. Various conspiracy theories have since suggested the crew's incursion into Soviet airspace was intentional. But the most compelling (and reasonable) explanation I've seen suggests the crew left the autopilot in heading mode after departure, rather than engaging it in the INS NAV mode. Just as in the 727 incident, the aircraft never tracked over the oceanic waypoints that had been programmed into its navigation system.

Long-range navigation systems have been used for decades in airline and corporate flight operations. Along the way these heavy-iron operators have developed procedures designed to keep pilots from making the kinds of mistakes described above. When used as intended, the procedures work very well. It's when they aren't followed to the letter that the chance of error increases. Most GNEs, in fact, are eventually pinned on the pilots involved. Boilerplate language attached to the oceanic clearance needed to enter NAT airspace reminds crews that 80 percent of such errors result from poor cockpit procedures. It further admonishes them to carry out proper waypoint verification procedures.

But lest you think it's only airline crews that make such mistakes, I should note here that the granddaddy of all navigation errors is attributed not to an air carrier crew but to a general aviation pilot, Douglas "Wrong Way" Corrigan. On July 17, 1938, he took off from New York, ostensibly headed to California. Instead he arrived in Ireland a little more than 28 hours later, blaming the "error" on a faulty compass.

Stripped of his pilot license by angry Civil Aviation Authority officials who had turned down his original request to make the transatlantic crossing, he stuck to his story and became something of a folk hero when he returned to America.

It's only in more recent years that true long-range navigation has filtered down to the masses in the form of affordable GPS units. Probably no single technology has ever been more warmly embraced by the general aviation flying community. It's powerful, dead-on accurate, and getting easier to use every day. In fact, GPS works so well that it's easy to forget these units can fly us to the wrong point in space as easily as the right one. It all depends on what we tell — or forget to tell — them to do.

Given the ramifications of aviation faux pas in the United States nowadays, an error saved is more meaningful than ever. And a gross navigation error isn't required to blunder into an uncharted TFR or prohibited airspace. A small one may be all it takes. While many GPS units display special-use airspace and can warn of your impending entry into the nearest Class B, don't depend on that feature alone to save your bacon. TFRs likely won't be depicted, for example, and if you don't have the latest database update, it's possible the airspace dimensions may have changed since the last time you flew the route. A few precautions can easily prevent most such mistakes:

• Like the carpenter who measures twice and cuts once, always double-check waypoint entries, especially latitude and longitude coordinates, the most susceptible to error. Do so when you are not rushed with other cockpit duties. If there are two pilots, cross-check each other's entries independently.
• Keep appropriate charts handy to increase awareness of terrain clearance, airspace, and diversion options should your GPS or anything else you depend on for safe flight fail.
• Use a hard copy of the flight plan as a tool to track your flight's progress. Computer-generated flight plans are readily available nowadays. If all else fails, it probably contains all heading, wind, and time information you need to continue the flight using dead reckoning alone if need be.
• If the autopilot can fly a GPS-programmed route in LNAV (lateral navigation) mode, be sure to positively engage the right mode. Pushing the button doesn't guarantee the mode actually changed from HDG to LNAV, for example.
• Get the latest information on special-use airspace before you fly. You may have planned a route around or above such airspace, but weather or other contingencies can force a change of plans. Then you could find yourself in a round of "Battleship," where you try to guess the location of TFRs and the FAA tries to guess your N number when you transgress one.

And now back to that North Atlantic near miss. Throughout the first several hours of the flight, the 747 captain's altimeter had consistently indicated about 50 feet lower than the first officer's, the flying pilot. When the first officer left the cockpit for a break, the captain, bothered by the disparity, effected a slight climb so that his altimeter would indicate the exact assigned altitude. Not long afterward the L-1011 passed an estimated 50 feet below them, close enough for its bow wave to nudge the Boeing.

Serendipity? Perhaps, but sometimes it just pays to sweat the small stuff.

Vincent Czaplyski holds ATP and CFI certificates. He flies as a Boeing 737 captain for a major U.S. airline.