In 1992, the FAA began investigating whether it would be possible to decrease the distance between the long, parallel runways at the Los Angeles International Airport (LAX) and still maintain safe separation between aircraft on approach to the airport. If the space between the runways could be reduced, it would allow the construction of more runways on the airport, which would boost the airport's capacity. Since LAX controllers typically assigned airliners long, straightin approaches from 30 or 40 miles away, however, analysts needed information on how accurate the standard Instrument Landing System (ILS) signal was at those distances in order to determine whether more closely spaced approach courses would be safe.

In order to gather that information, the FAA enlisted the assistance of the TSRV 737. The NASA 737 had the ability to gather extensive data on the ILS signal characteristics, and its computers could also design and fly precise, complex navigation routes that could cover the entire signal range. Specifically, the FAA wanted the airplane to fly evenly spaced, descending "S" turns across the ILS signal, starting from a point 30 miles away from the airport. One of the NASA researchers dubbed the backandforth navigation course a "boustrophedonic" flight path, which sounded very impressive and technical. It was not until some time later that the other engineers looked the term up in the dictionary and discovered that it meant simply, "as the ox plows." [Ref 8-21]

The Los Angeles ILS modelling research took place from April 13, 1992. The flights had to be conducted in the middle of the night so the experiment would not interfere with the normal airport traffic, but they were uneventful and obtained the ILS data the FAA analysts needed to explore expansion options at LAX. The experiments also allowed NASA researchers to compare the accuracy of a differential global positioning system (GPS) signal against that of the ILS, so both the FAA and NASA obtained some valuable information from the research.

An electronic display of "boustrophedonic" flight path the 737 created and followed to map the ILS signal at the Los Angeles International Airport.

The ILS modelling work at LAX was not a large or complex research project. Nevertheless, it involved a task that would have been difficult or impossible for any airplane without the TSRV's unique equipment and capabilities to perform. The NASA airplane, on the other hand, was able to complete the research relatively easily and in a timely manner. The LAX flights demonstrated once again that the TSRV 737 could support not only ATOPS programrelated research, but a variety of other tasks and research efforts for NASA, industry, and other government agencies. [Ref 8-22]