Always trust the GPS?

This happened about 15 years ago in South Africa. My wife, two children, and I were launching on a three and a half week flying tour of South Africa, Botswana and Zimbabwe arranged by Hanks Aero Adventures of Johannesburg. I had spent two days getting my South African pilot’s license and we were ensconced in a rented Cessna 206 with a cargo pod and STOL kit. For navigation, we had an extremely thorough trip package prepared by Hanks plus the latest Garmin GPS. In addition, we had the US Department of Defense paper charts which are about all you can get in some parts of the world.

Tuli airport
The airport at Tuli – easy to miss if your GPS has a bad day.

Leaving Johannesburg, our first stop was a camp called Tuli Block, a private game reserve about 300 miles north across the Limpopo River in Botswana. It was a dirt strip bulldozed out of the bush and three to four miles away from the camp itself. The instructions were to find and buzz the camp and a Land Rover would be sent to pick us up.

I punched the identifier for Tuli Block into my GPS and it came up, instructing me to fly a heading of 273 degrees for 300 miles, which would put us well into the Kalahari Desert searching for a non-existent dirt strip in the bush. Not a good outcome. Thinking I had made an entry error, I reentered the identifier and got the same result. Third try? No change. I handed the GPS to my son who is also a pilot and he repeated the process and got the same error.

So we pulled out Hanks’ trip pack, entered the lat/long coordinates of Tuli Block, found the right course and were on our way. Even so, when we arrived at the destination, it took five minutes or so of looking to locate the dirt strip and camp. If the erroneous database had been off just a few degrees instead of 90 degrees, I would have failed to recognize the error and we could have searched the bush until our fuel ran out with no luck.

That night I sat down with the GPS and cross-checked each identifier of each camp we were to visit against its lat/long and verified the accuracy. When we got back to Johannesburg I checked my GPS against Hanks’ and found the same error for Tuli Block in his database.

A freak occurrence? Two years ago my son and I were flying his Bonanza to northern Saskatchewan for a fishing trip on a remote island. Our last fuel stop was a place called The Pas in Manitoba. Leaving Winnipeg, we entered the identifier for The Pas and it looked to be about the right heading and distance, so off we went. Seventeen miles before arriving at the GPS destination, we flew over a town and airport that looked suspiciously to be the right place (there aren’t a lot of towns and airports in this part of the world) but we continued on to the GPS destination with the predictable result – lots of trees and bush but no airport. We turned around and returned to The Pas where we refueled and continued to our destination.

Suppose we had been IFR? Suppose The Pas had been overcast and we didn’t see it? This was exactly what scared me in Africa – a small but potentially deadly error. Fortunately there was an alternate within reach of our fuel supply but once again a bad database could have produced disastrous results in a wilderness. We go to remote places – from the Arctic Ocean to the Amazon – there isn’t much room for error and twice is two times too many.

How do you protect against a database error? We’re all flying on Jeppesen data so I guess if you’re going to an unfamiliar, remote spot, all you can do is double check against the lat/long and hope that the data used for moving maps comes from a different source.

12 Comments

    • Sir, Only visual conditions and in area that provides recognizable landmarks. Large areas of jungles, large areas of deserts, absence of roads and rails and harbors or major lakes absemce of lighted town or city areas, absence of lighthouses, absence of commercial radio stations to take a heading on angle on, and lack of VOR broadcast, can make visual recognition of place very very unlikely. Celestial navigation is lost art and is useful only at night in clear sky to only a few knowledgable people.
      Being lost while flying without clues can create terrible outcomes.

      • Actually shooting a noon sight of the sun with a sextant works very well. It is the only means of getting latitude and longitude with one celestial body with a sextant that I am aware of. I had a hard enough time getting fixes with my sextant on a small boat – I don’t think it would be possible in a small plane – certainly not if you were operating solo.

        With the errors possible in electronic navigation devices, it certainly pays to keep up with your dead reckoning when in the outback.

  • In 2001 while preparing for a trip back to KPSP I found that the Lat/Long for the airport out of the AF/D (FAA Airport Facilities Directory) was 5 miles to the south of KPSP. The Jeppesen database was correct but the printed information in the printed reference was not. I called Jeppesen and they corrected their printed material in 24 hours, notification were sent out soon after. The FAA corrected the AF/D 3 or 4 printings (6 to 8 months) later.

  • What to say? Perhaps with the proliferation of EFBs and frequent updates, in the first world maybe coordinates are fine these days.

    Who knows?. An educated guess would be that they are not in 100% of cases. 100% pretty much never happens.

    If at all concerned though, take your paper chart and with some straight edge work determine your own lat/long and plug it in to the GPS. Presumably if your destination is plotted incorrectly on the paper chart you could tell. If not, well…..

  • I know we all love a cautionary tale in flying, but how about the rest of the trip? Seems like flying yourself around southern Africa would be a story worth telling.

    Hope that story is coming soon.

  • I taught many of Hanks Aero Adventure visitors, his data pack is fantastic, the error here is not the GPS but the fact that people are not using maps! In South Africa it is standard to teach plotting using long/lat. Also the 1:1000000 maps are good, they just don’t have every bush strip on them! GPS IS AN AID to navigation NOT a primary!

  • I have avoided some GPS pitfalls by flying the route on my computer with the Garmin Flight Simulator.
    In remote areas I use a backup Garmin Etrex plugged into Laptop with terrain map.
    I fly frequently in Adirondaks and I find Topographic maps and compass very helpful.
    And of course it is always best to fly with someone who has flown the route before.
    And as always, preplan, preplan, preplan….did I mention plan B, C….

  • When I started using a GPS it only worked for four hours a day and all the waypoints had to be entered by hand. (Trimble) Then it was essential to compare your GPS position with the map and write down your heading and ETA often. We’ve just gotten complacent with all our gadgets nowadays and it’s going to bite a few yet.
    Next time you fly, don’t turn the GPS on, you’ll find it much more rewarding especially as your friends won’t believe it can be done.

  • I too have flown over the Kalahari Desert and Canadian wilds. My verifier is Google Earth. Locate a destination airstrip with GE and check that its coordinates agree with your GPS database. If not enter a user waypoint. I also print some photos of the area as an aid to picking out the camp and/or airstrip when arriving.

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