Lesson 5: Stages of a Transceiver Search

Trained AvSAR responders should be able to quickly and effectively conduct a transceiver search. Responders must also maintain situational awareness and be able to guide and direct other responders on scene. Although circumstances are different in every incident, the basic search procedures and the stages of a transceiver search are the same in all scenarios.

Stages of a transceiver search:

Assessing Further Hazard

Upon arrival on the scene of an avalanche incident, responders must:

Quickly determine how many people are missing
- If the avalanche was unwitnessed, or occurred to another party, never make assumptions about the number of burials
Evaluate the potential for further avalanches
- In many cases, the main avalanche danger will have been minimized with the first avalanche, but there will be some instances where the run-out zone may be exposed to further avalanche danger from multiple start zones. The risk must be evaluated with respect to the likelihood and consequence of a further avalanche balanced against the chance of live recoveries.
Post a lookout if there are enough responders.
Clearly define escape routes to help mitigate the risk of further avalanches.

In an organized rescue where the probability of a live recovery might be low due to the amount of time elapsed, performing avalanche control before exposing numerous rescuers to the slope may be the preferred option.

Last-Seen Point

If a responder has seen the subject disappear and is above that point, the first action should be to immediately proceed to that point and mark it with two crossed poles. In an unwitnessed burial, interviewing other members of the group and evaluating entry tracks may help refine the likely search area.

Remote Triage – High-Priority Search Area

Remote triage refers to the process of prioritizing resources to maximize the number of survivors when rescuers do not have direct physical access to the subjects. It begins as soon as the safety of the rescue party has been considered, and before any search actions begin.

When the search area is larger than can be searched with the available rescuers in parallel, it is important to focus efforts first on locations with the highest survival chances (high-priority search areas). These search areas include likely burial areas such as benches, above trees, inside corners, or at the bottom of run-out zones. Tracks and surface clues may help identify high-priority search areas in unwitnessed events, or in avalanches with no last-seen points. Areas where the subject could have sustained fatal injuries (i.e. from falls over cliffs, impacts with trees or terrain) are lower priority than areas where the run-out is smooth and survival chances are greatest.

Initial Response

In most cases, search members will have varying levels of response skill and capability, and may be experiencing some degree of shock. Some may be partially buried or injured themselves, or the group may be spread out over the terrain.

Everyone on the scene should participate in the search activities unless acting as the avalanche lookout, however it is beneficial to have someone take charge of the scene.

For the group leader, they must do the following:

Assess further hazard and make their go- or no-go decision.
Ensure good communication to quickly determine the number of people involved and their last-seen points.
Ensure that all rescuers switch their transceivers to receive mode.
Ensure that all rescuers switch off interference devises and move them to their bags.
Determine the search area boundary and high-priority search areas.
Make sure the scene is not contaminated with rescue equipment and personal belongings. All rescuers should keep their gloves and packs with them at all times.
Delegate specific functions to others as required (e.g. signal- and visual-clue search, fine search, assembly or rescue equipment).
Maintain an overview of the search action.

For the initial transceiver searchers, they must do the following:

Quickly search the likely areas below the last-seen points, and areas with highest survival chances first.
Move quickly with their transceivers in receiver mode, listening for a signal and maintaining good situational awareness while looking for visual clues and stopping to listen for shouts.
Direct other responders to the area where the fine searches and extrications will be required. In an avalanche incident, it is not uncommon to have partially buried subjects who do now need to be found by a transceiver but just need shovelling out.
In the case of multiple burials, make a triage decision to decide whether it is best to continue with the high-priority action of search the whole deposit for everyone, or to stop searching briefly to deal with the first extrication.
Continue to search the entire deposit in order to allocate rescue resources to subjects with the highest chance of survival.

Signal Search

A signal search is the first phase of a transceiver search. The purpose is to quickly search the avalanche deposit in order to acquire a signal. The searcher should be running or skiing.

During this phase, it is important to maintain an appropriate search-strip width. Search-strip widths vary between different transceivers; manufacturers provide recommendations for each model of transceiver. The recommended search-strip width represents double the maximum effective range of the transceiver with a non-optimal orientation between the transmitter and receiver antennas, and with a 98% likelihood of detections.

Using the widest search strip possible will result in optimal coverage of the search area, and provide the highest survival chances. However, it may be prudent to reduce the search-strip width for the following reasons:

Situations with many searchers.
Difficult terrain or snow conditions that impede the search.
Traps such as crevasses, creeks, or terrain barriers that will reduce the effective range.
Indications of interference.
If directed by the search device.

While performing the signal search, searchers should rotate their transceiver through all three dimensions at 1-second per dimension. The rotation should be done near the ear, while the rescuer looks at where they are walking. If a signal is detected only when the transceiver is orientated vertically, this means that the buried transceiver is orientated vertically as well. The searcher should continue until they can hold a signal while their transceiver is orientated horizontally, however they may be able to approximate the signal direction if they can get two points where the vertical orientation can resolve a signal.

There are two primary search patterns used in the signal search: a ziz-zag search pattern, and a straight-strip search pattern. The zig-zag search pattern is the preferred method with only one searcher and is commonly completed on skis. The searcher must ensure that the wide part of the triangle does not exceed the search-strip distance. Using the zig-zag search pattern requires that each leg of the search pattern ends at the edge of the deposit. The straight-strip search pattern is done with multiple rescuers covering the entire deposit at the same time.

Single Searcher:

Multiple Searchers:

Coarse Search

The coarse search begins once a signal is obtained. The searcher continues to move rapidly in this phase, slowing down only as the distance gets below 10 meters. As the coarse search progresses, it is critical for rescuers on skis to balance between search speed and search precision. In the last stage of the coarse search (<10 meters), it is very easy to overshoot the burial site and lose time by having to walk back uphill. In particular, the last 5 meters of the coarse search should be conduced very slowly (transitioning from a coarse search to fine search).

The procedure for rescuers conducting a coarse search is as follows:

Hold the transceiver horizontally in front of you. Allow the read-out and/or audible clues to lead you along the flux line. Initially the direction indicator may lead you the wrong way along the flux line. If the distance indications are going up, turn back 180 degrees (some transceivers actually display a 180-degree warning).
If the first signal cannot clearly be followed (due to the effects of fuzzy range), then follow the established search-strip pattern until reliable distance and direction indications are received.
Clearly communicate to other rescuers when you acquire a signal so they can respond with shovels and probes.
If multiple signals are received during the coarse phase, add this information to your mental map of the situation. This will help you determine the size of the area on which to apply multiple-burial search strategies.

Fine Search

The fine search is done at a slower pace to provide the most accurate distance indication. The searcher holds the transceiver close to the snow surface and begins a series of right-angle ‘brackets’. Then, the distance minimum on each bracket is determined. Two or three right-angle brackets may be required to effectively determine the final location. It is important that the searcher holds the search transceiver at the same orientation and close to the snow surface in order to avoid changes in reception due to antenna orientation. The searcher must also complete each bracket fully by going past the lowest distance point until the distance indication begins to rise again.

The final fine-search location point may not be exactly above the buried subject due to the bending of the flux line. If there are multiple searchers converging in the fine search, it is not efficient for all searchers to continue with the transceiver search. One proficient searcher should finish the fine search and pinpoint, while someone begins probing systematically above. Other searchers should begin shovelling just below the pinpointed location.

With shallow burials (<1m), it is important to not waste time with bracketing. It is more efficient to start probing. Additional brackets only result in small gains in accuracy and can be very time consuming. Immediate proving will lead to the buried subject much more quickly at this stage of the search.

Pinpointing

Square Probing. Square probing is the current best technique at pinpointing the exact position of the buried subject.

Probe perpendicular to the slope angle. The transceiver signal travels to the shortest distance, which is 90-degrees to the surface.
Use probe spacings of 20-25cm.
Do not revert back to a fine search. Continue to probe until a probe strike is made.
Leave the probe in the snow to mark the subject’s precise location.
Avoid stepping on the top of the subject (especially in the case of shallow burials).

Square probe using the following steps:

Stand where the strongest transceiver signal was found.
Probe Centre, Left, Right.
Probe Front-centre, Front-left, Front-right.
Take a step back, and probe Back-centre, Back-left, Back-right. This completes the first square.
Take a step back. Begin probing clockwise around the first square to complete the second square. Start from the Back-Centre so the final strike would be clear to see. Strike with the probe between your feet.
If two squares yield no strikes, return to the centre, rotate 45 degrees, and repeat with a reduced probe spacing.

Position Probing. Performed after a probe strike is made. Knowledge of the subject’s position is desired to facilitate shovelling and to more efficiently access the subject’s airway. This operation must be done quickly because time is of the essence.

Leave the probe in the snow to mark the strike.
Continue using the spiral method with additional probes to establish the person’s orientation and detailed position.