ADVANCED SEARCH: FIELD LINES, LANES AND WHERE THE MINUTES ACTUALLY GO

The Technique

1. Everything here rests on one fact about the physics, and most riders have it wrong. A transceiver transmits from a small antenna as a **magnetic dipole**, and the field it makes is not a set of straight lines radiating outward. The flux lines leave one end of the antenna, bow outward and curve back into the other end, like the wings of a butterfly or water arcing out of a fountain. Snow, bodies, rock and your aluminium shovel barely affect it, which is why the thing works at all.
2. **So the arrow on your screen does not point at the buried person. It points along the curved field line you are standing on.** This is not an interpretation, it is what the manufacturers say: Mammut's Barryvox manual states the arrow "leads the rescuer along the field lines and therefore usually in a curved line to the buried subject". Only in the special case where you happen to be standing on the axis of the buried antenna does it point straight at them. **Follow the arc. Do not cut the corner**, because cutting the corner is leaving the information and guessing.
3. **And the distance number is not a distance.** It is an estimate derived from signal strength along that curved line. Mammut describe it as indicating "the maximum possible distance to the buried subject". Genswein, of the Swiss institute SLF, is blunter still, calling it "an indication of a tendency" that can vary widely from real distance depending on how the two antennas happen to be oriented. **It reads long, never short**, it is worst at long range, and it gets more trustworthy the closer you get.
4. Hold those two facts together, because they explain the biggest mistake capable riders make on a big debris field. **When two searchers both pick up what looks like the same signal, the instinct is to converge on each other and triangulate a fix from the two distance readings.** It feels obviously right: two bearings beat one. It is wrong, and it is worth understanding exactly why.
5. **Both readings are inflated, so you are intersecting two circles that are each too big**, which pushes the crossing point away from the line between the two searchers rather than onto the victim. The inflation is not even equal between them, because whoever is standing broadside to the buried antenna over-reads more than whoever is closer to its axis, so the fix also drifts sideways. Worst of all, **the errors are largest at long range, which is precisely the moment two searchers first both hear the signal.** You are computing a position from the least reliable numbers the system ever produces.
6. Then there is the cost. **Two adjacent searchers converging vacate two adjacent lanes at once**, tearing a hole in the swept ground at least two lane widths wide, and they arrive together at one victim while others lie unsearched. The path they walk converging is a shrinking wedge, not a search pattern. And a pair walking toward each other with transceivers is a textbook way to end up chasing each other's units rather than a victim.
7. **The recognised method is the opposite, and it is simpler: hold your lane.** The technique is called Searching in Parallel, published by Edgerly and Conway in The Avalanche Review. Lane width is roughly the debris width divided by the number of searchers with transceivers. Everyone walks their own lane down the fall line and **abandons it only when their own reading drops below their lane width**, meaning the signal is genuinely theirs rather than a neighbour's. Communication stays minimal: signal acquired, distance dropping in ten metre steps, lane abandoned, probing, depth.
8. When two people do hold the same signal, the answer is not negotiation and not convergence. **One takes it, the other returns to sweeping the rest of the avalanche.** That is Mammut's own instruction in their manual, and it is the direct answer to the scenario. A leader ideally walks behind the line without searching, keeps lanes honest, and rewidens them as people peel off to probe and dig.
9. **On multiple burials, do not trust the marking button alone.** Large scale field testing at Davos found novice searchers failed to find the third buried transceiver in **about a third of all attempts across the five devices tested**, and in roughly forty per cent of attempts on the four worst performers, with individual devices ranging from thirty to nearly sixty per cent. **The cause is signal overlap rather than clumsy button pressing**, which means it is not something you can simply be more careful about. So marking is a convenience with a known failure rate, and you need a fallback you have practised: **micro search strips**, or the three circle method, where you walk circles of increasing radius around a found victim to pick up the next. The advanced rescue lesson in this library goes through the failure in detail.
10. **The honest tool for telling one burial from two is your ears, not your screen.** When signals overlap the display is the first thing to become useless, showing a frozen distance or a stand still message. The discriminator the literature endorses is the analog tone: stand still, listen, and count the beep patterns against the distance shown. Worth knowing too that renegade signals from people on the surface who never switched to search cause more chaos in real incidents than multiple buried victims do, which is why the trailhead check and the search-mode discipline matter so much.
11. **Now the part that should change how you train, because it is where the time actually goes.** It is not the coarse search. A 2025 randomised simulation found probing took around forty five seconds when the fine search had got within about a metre, and around one hundred and sixteen seconds when it had not, and excavation dominates total rescue time in Edgerly's ISSW work. **Sloppy fine search and slow digging are what kill people, not slow walking at the start.** So train the last three metres and train the shovelling: strategic shovelling in a conveyor, rescuers spaced about a shovel length apart down the fall line, rotating the lead every twenty to forty seconds.

Common Mistakes

Cutting across the arc to "save time". Fix: the arrow follows the field line. Cut the corner and you leave the guidance and start guessing.

• Treating the distance number as metres. Fix: it reads long, especially far out. It is a tendency, not a measurement.
• Converging with a mate to triangulate a signal. Fix: hold your lane. One person takes the signal, the other keeps sweeping. Converging costs two lanes and computes a fix from the worst numbers available.
• Relying on the marking button in a multiple burial. Fix: it has a documented failure rate. Have micro strips or the three circle method practised as a fallback.
• Deciding one victim versus two off the screen. Fix: stand still and use the analog tone. The display is the first thing overlap ruins.
• Training the walk and neglecting the dig. Fix: the minutes live in the fine search and the shovelling. Drill those.

The Drill

The lane discipline drill. Bury two transmitters on a wide safe slope, set lane widths as debris width divided by searchers, and run it with a leader who does not search. The rule of the drill: nobody leaves their lane until their own reading is below their lane width, and if two people hold one signal, one continues and the other goes back to sweeping. Then time the last three metres and the dig separately from the walk. Most groups find the walk is fine and the last three metres are ugly.

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