Datum lessons learned

Here’s a quick story from my Forest Service firefighting days that illustrates the importance of being aware of datums. A fire was reported in a mountainous area of eastern Oregon, and my partner and I helicopter-rappelled in to put out the fire. Because the fire was bigger than expected, we requested some smokejumpers to assist. They were down from Alaska, helping out during the lower 48’s fire season, and they all had new handheld GPS receivers, which were pretty state of the art back then (1998). The fire continued to grow, and we called in a small air tanker to stop the fire’s spread. One of the Alaska jumpers pulled out his GPS unit, and we called in an exact set of coordinates for the pilot to hit. As the tanker approached, the pilot radioed us, asking whether we were sure that was where we wanted the retardant to go. Turns out that the jumper still had his GPS unit set with an Alaska map datum (that didn’t match the local datum on the pilot’s GPS receiver), and the coordinates that the Bureau of Land Management (BLM) jumper gave were on the other side of the ridge, nowhere near the fire. Fortunately, the pilot used his own initiative and dumped his load right where it needed to go.