Japan Dragged 13 Feet Closer to U.S., but Instrument Approaches Survive

Updated March 19, 2011

First, the bottom line: your use of GPS for aerial navigation or approaches will not be affected by the geographical shift of Japan due to last week’s earthquake and tsunami. The extent of the unusual land mass movement varied, but the average shift was about eight feet.

“Really, that kind of shift would drop into the insignificant bucket for aviation GPS use,” said Bill Stone, avionics products manager for Garmin International, maker of numerous GPS devices. “Japan doesn’t have any public LPV [localizer performance with vertical guidance] approaches or any WAAS [wide area augmentation service] anyway, so even a 13-foot shift would be down in the noise.”

Of course, numerous airports and ground-based NAVAIDs in Japan were affected by the earthquake and tsunami that happened earlier this month. The earthquake was the fourth- most powerful anywhere on earth since 1900, with a Richter scale reading of 9.0. The last step on the Richter scale is 10.0, which has never been recorded, but would be expected to cause “possibly planet-wide destruction” according to the rating scale. The quake shifted a portion of the Japanese main island 13 feet closer to the United States; it and the resulting tsunami have so far claimed at least 7,000 lives, with more than 11,000 people still listed as missing.

But ground-based instrument approaches not ruined by the quake, tsunami or loss of electrical power are still operational. Ted Thompson, corporate technical leader for aeronautical charts and displays at Jeppesen, said all instrument approaches, both precision and non-precision, are built with tolerances that would absorb position or elevation changes such as those caused by the earthquake. He added that the Japanese Civil Aviation Bureau (JCAB) uses the same terminal instrument procedures (TERPS) guidance used by the FAA in building instrument approaches.

According to both Stone and Thompson, no NOTAMS related to either enroute or approach charts have been issued by the JCAB and none are expected. Several NOTAMs have been issued for other aviation-related issues, including airport closures. One NOTAM establishes a 30 kilometer “no fly” zone around the crippled nuclear power plant Fukushima Number One.

“It’s about what we would expect after such natural disasters such as the earthquake and tsunami,” said Thompson. “Other than those, there just isn’t any ‘out of the ordinary’ information coming out of Japan right now.” He said that Jeppesen maintains close contact with civil aviation authorities in 220 countries around the world, including Japan, and uses charting information provided by those governments in creating Jeppesen charts.

Along with ‘quake and GPS’-related pilot queries on NBAA’s Air Mail discussion lists, a concern was voiced about the increase in the speed of the earth’s rotation, since GPS accuracy depends on exact time, as measured by an atomic clock.

“The speed increase won’t affect atomic clocks at all,” said Stone. “Atomic clocks are independent of the earth’s rotation speed, unlike us humans.” He explained that there are two separate accepted definitions of time: atomic clock time, which defines one second as 9,192,631,770 cycles of the cesium-133 atom and a day as 86,400 of those seconds, and “human time” based on the rotation of the earth.

“We humans like to see 60 seconds in a minute, 60 minutes in an hour and 24 hours in a day,” he said. “For us, a day is one rotation of the earth. But one earth rotation is almost never exactly 86,400 atomic seconds, so a consortium of astronomers called the International Earth Rotation and Reference Systems Service adds or subtracts a ‘leap second’ when needed to make up the difference.”

Thompson said he expects that the Japanese government will start the process of re- surveying various aeronautical facilities and fixes once the immediate crises have passed. “Of course this earthquake and tsunami are unique events, but I would expect, based on previous situations, it will be months if not a year or more before we would see any permanent charting changes come through Japan’s aeronautical amendment process.”

It could be that the wait before correcting thousands of latitude and longitude coordinates will be a good thing in the long run, because land shifts from this earthquake might not be over. Japan continues to experience frequent and substantial aftershocks, so GPS coordinates could still shift. “Therefore, it may be months or even a year before GPS maps of the area can be considered accurate,” said Rebecca Pearson in a blog on the GPS City Buzz web site.