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Transocean Trips Demand Navigational Diligence

Despite GPS-equipped cockpits and the growing use of data link, pilots flying oceanic trips need to keep on top of their game to avoid the most common navigation errors.

"When you look at a gross navigation error (GNE), which is defined as being more than 25 miles off course, business aircraft account for 20 percent of them on North Atlantic routes, even though they represent just 5 percent of the total traffic," said Bill Stine, NBAA director of international operations.

According to David Maloy, a flight operations inspector in the FAA's Boston Regional Office, the main scenario that leads to a GNE is a "re-clearance," or change in the clearance previously received by the crew.

“Avoiding the scenarios described here comes down to training.”

"When re-clearance occurs, you have to do certain crosschecks, such as updating your FMS [flight management system] to confirm the new latitude and longitude, Maloy noted. "You also have to verify that you have entered into the computer the new magnetic course or heading, as well as a distance check, which you have to independently compute as a result of the new clearance. If you don't, the computer has incorrect information."

Another over-ocean navigational error includes insufficient longitudinal separation – when the aircraft is less than 10 minutes behind another at the same flight level. In that regard, Maloy cited an example that he called unique to business jets.

"When a pilot has been given clearance to ascend to a specific flight level, he initiates the climb but cannot reach the flight level for aircraft performance reasons, and levels off at a lower flight level without informing ATC in a timely manner, as he is required to do. That can mean he is closer than 10 minutes to another aircraft already at that same flight level."

The other major oceanic error involves large-height deviation, in which the aircraft is more than 300 feet off its assigned altitude. In some cases, explained Maloy, it occurs during a conditional clearance. 

"What happens is that ATC gives you clearance to climb to another flight level, and here the issue is the meaning of the words 'at' and 'by.' The controller could say, 'ascend to a certain flight level at the specific waypoint,' which means that you don't initiate the ascent until you actually reach that waypoint. But, the controller could tell you to initiate the ascent by a certain waypoint, which means you start your ascent so that when you reach the waypoint, you are at the specified altitude. Some pilots will interpret 'by' to mean 'when I get there.' I advise pilots to be very careful of a conditional clearance and to understand when to initiate the flight level change. It is causing problems and leading to a number of errors."

Avoiding the scenarios described here comes down to training. "Pilots have told me that they don't get enough training in ground school about avoiding oceanic airspace errors," Maloy said.  "Others have said that they thought the [GPS and datalink] technology on the aircraft would help them avoid errors. But it still comes down to basic human errors."

Maloy said the FAA recommends that pilots train consistently to ICAO Document 007, "Air Navigation in and Above North Atlantic MNPS Airspace," which contains procedures applicable to over-ocean flying anywhere.

David Stohr, president of Air Training International Ltd. in Texas, attributes errors to lack of knowledge of rules and procedures, and not following standard operating procedures. "This is a training-related issue," he stressed. "The training should not be structured toward getting the crews to recite the procedures, but to give them the ability to execute the procedures and, when able, to practice those procedures in a simulator as often as time and scheduling permit."

For More Information

NBAA Members may access NBAA's Oceanic Flight Information page (Member password required).

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