ASRS Directline

  Issue Number 1 : March 1991

Time Allocation and Navigation Errors

by Roy Chamberlin


The ASRS program has just celebrated its 13th year of operation and it is interesting to note that there are still an uncomfortable number of track deviations on over-water flights being reported. Even one would be uncom fortable to the individuals involved.

Common Threads

Incorrect Waypoint Entry

There do seem to be a couple of common threads within most of the track deviation reports. The first is that the wrong coordinates were placed into the primary INS or Omega navigation unit, yet these were not identified as being incorrect.

States one reporter:

In another report, the pilot explains:


The second thread is that input of erroneous data occurred at periods of high activity (usually a re-route with the associated INS updates) coupled with other distractions that added to the workload of the flight crew. In an example of re-route activity, one reporter writes: "Our flight appeared to be totally routine until approaching [VOR]...At that time we received a track change re-route....I immediately asked the flight engineer for the track message to update the INS's....A radio frequency change to [Center] took place in a few moments....I then began to complete the remainder of my paperwork involved with a track change...."

Sometimes there seemed to be too many changes. In the reporters own words:

And sometimes distraction has its origin in normal routine: "...Captain was having breakfast" at the same time a re-route and frequency change occurred, which appears to have taken him out of the loop. The error was not caught in time to prevent a major track deviation. "[Center] gave us a 90 degree correction to the right...and advised us we were off course and in [foreign and unfriendly] airspace."

Tying The Threads: Critical Phase of Flight

Because the developing conditions experienced by these flight crews were not extraordinary, they did not recognize that high workload compounded by distraction produced a situation of overload. In the analysis of many previous reports where the flight crews were placed in situations of overload, important numbers and information tended to be disregarded or discarded. The pilot might look, but he or she did not recognize a discrepancy. In each of the situations presented, the flights were viewed as normal or routine by the flight crews, but were actually near, or in, a critical phase of flight.

The Solution: Time Allocation

The solution to the problem of task overload lies in not trying to do too much at one time. Pilots are advised to delay some tasks to a time when proper attention may be devoted to that task. (ASRS has a term for this--we call it "Misplaced Duty Priority.") In the analysis of one of the reports used in this article, had the flight crew performed only the minimum necessary items at the time of the re-route, such as entering the next required waypoint and completing the gross error check, they would likely not have been overloaded.

In summary, available time should be allocated to the task with the greatest priority. As soon as that task has been satisfactorily handled, another task will now have the greatest priority. Pilots are advised to avoid the tendency to rush or hurry through a given task.

For those airlines that do not already do so, the problem of time allocation should be addressed in recurrent or initial training guides, and emphasis should be given to the hazards of "tunnel vision" during critical phases of flight.

Transoceanic deviations most likely started with Columbus who was highly praised for finding the New World, when all he wanted was to find the Northwest passage. Upon returning to Spain he told Queen Isabella, "The Center gave us a call..."

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