Giving “X” a New Look
Engineering X-perts from the FAA’s William J. Hughes Technical Center continued with the next stage of testing to determine the most effective intensity, size, and flash rate for runway closure markers at airports.
By D. Gagnon, FAA
“X” is getting a new look, but probably not the one you’ve already seen. This summer, researchers from the FAA’s William J. Hughes Technical Center gathered at a naval air testing facility in Lakehurst, New Jersey to gauge the effectiveness of lighted “X” runway closure signs that signal to pilots that a runway is closed.
FAA researchers recruited 32 volunteer pilots — 16 in each age group — to provide feedback on the visibility of the runway closure lights from an observation deck roughly 1.5 miles away from the end of the U.S. Navy facility’s runway.
“Reducing surface safety risk remains a top priority for the FAA and this important research is going to help reduce that risk.”
— Shelley Yak, director of the FAA Technical Center, the nation’s premier aviation research facility, in Atlantic City, New Jersey.
In 2016, the FAA requested a study to test and evaluate the effectiveness of the runway closure markers after pilots reported the lights being too bright at night, causing some to be unable to make out their shape. That study concluded that further research was needed to determine the best maximum and minimum intensities of the runway closure markers for both nighttime and daytime to enable pilots to see and identify the markers.
The first stage of the research began in 2019, when the FAA tasked the National Institute of Standards and Technology (NIST) to conduct a nighttime vision simulation with 20 pilot participants. NIST engineered a scale model in a laboratory using mirrors, and tested the intensity of the lamps in complete darkness.
The NIST laboratory experiment concluded that the current recommended minimum nighttime intensity of 2,000 candela (cd) is too high, caused glare, and made the “X” shape difficult to recognize. The NIST experiments theorized that the best nighttime visibility occurs at intensities much lower than previously speculated, between 100 cd and 300 cd for both LED and incandescent lamps.
These findings were the first step in understanding the effectiveness of the current design of runway closure markers, but were conducted in a completely dark laboratory environment. Therefore, the next step brought FAA researchers to Lakehurst, NJ to test the NIST findings in a real-world setting, gathering data for both daytime and nighttime.
“One of the advantages of this location was the minimal ambient lighting surrounding the runway, which was similar to the conditions during the NIST study,” said Darian Byrd, the lead researcher on the project.
The goal of this completely ground-based phase of research was to narrow down for further testing:
- The minimum and maximum intensities of the runway closure markers during daytime and nighttime operations;
- The optimum intensity to recognize the “X” shape; and
- The effectiveness of various flash rates (synchronous vs. asynchronous, etc.).
In addition, researchers included tests to determine whether LED bulb intensity was visually consistent with incandescent bulbs, since runway lighting is shifting to be more sustainably LED based.
Each ground test took place over 3 days (day and night). During each test case, the paid observers evaluated the runway control markers from the observation tower 1.5 miles away, and were instructed to note the intensity, glare, and flash rates of each of several models of runway closure marker, which varied in size, intensity, and type of bulb.
Now that these ground-based tests have concluded, researchers are compiling the results and preparing recommendations for the next phase, which will be actual flight testing. However, the results from this ground-based testing will help the FAA to narrow down which specific intensities and flash rates to test during the more complicated and costly flight-testing phase.
“We needed the data from this phase of the testing to really help make the right decisions for that critical final phase. We’re ensuring that, when we begin doing test flights, we will be able to do so more efficiently with fewer possible configurations,” said Byrd.
