Recognizing from your side that the fix has stopped being worth having, and moving on without stopping.
Reading: about 10 minutes · Field drill: about 45 minutes
Bottom Line Up Front
Three things can go wrong with a position and they are not the same problem. Degraded means the fix is worse than usual and the device mostly knows it. Denied means you are not getting a usable fix at all, or the one you are getting is false. Dead means the device is off, flat, broken, or deliberately shut down.
Dead is the easy one. Degraded is manageable with the habits from Lesson 06. Denied is the dangerous case, because a spoofed position is confident, plausible and wrong — and nothing on the device will tell you. This lesson covers what each looks like from the user’s side and what to do, ending where the course has been pointing all along: the step down to map and compass, taken without halting.
Scope note: this covers recognizing and responding to interference. It does not cover causing it, which is illegal and outside this curriculum.
Recall Check · L01
From Lesson 01, since this lesson is about recognizing them: which condition produces a position that jumps while you stand still?
1. Degraded
Degradation is ordinary. Canopy, terrain, buildings and a poor spread of satellites all worsen a fix in ways Lesson 01 described, and the device usually reflects it honestly — the accuracy figure climbs, satellite count drops, the position wanders.
The right response is proportional rather than dramatic. Widen your tolerance, verify more often against terrain, and stop asking the device for precision it is not currently able to give. A fix good to thirty meters is still enough to confirm which drainage you are in; it is not enough to call a landing site.
Two useful moves: give the device a better view of the sky, even briefly, by stepping into a clearing or onto a spur; and if you are working somewhere with an augmentation signal, remember from Lesson 02 that its integrity warning is the part that matters — it flags a satellite broadcasting bad data within seconds, which is a class of problem the receiver cannot detect alone.
Knowledge Check
What is the correct response to a fix that has degraded under heavy canopy?
2. Denied
Denial comes in two forms and they present very differently.
Interference that stops the fix
Signals are drowned out and the device cannot compute a position. From your side this looks like loss of fix in terrain where you would expect a fix, satellite counts collapsing across the board, and every device in the group failing at once in the same place. The device is not lying to you; it is telling you it has nothing.
The response is straightforward because you know you have a problem: navigate by other means, note where it started and stopped, and expect it to be geographic — interference has an area, and walking out of it usually restores the fix.
Interference that fakes the fix
The harder case is false signals strong enough to override the real ones, so the receiver computes a position that is wrong and reports it with complete confidence. This is the failure mode the entire course has been circling, arriving from outside instead of from a setting.
From the user’s side, the tells are indirect:
What you notice
Why it is suspicious
The position disagrees with terrain, and the fix looks healthy
The Lesson 06 signature. It has other explanations — check the cheap ones — but this is the first symptom.
The position jumps a long way and stays there, plausibly
Real errors wander. A clean transfer to somewhere consistent is different in character.
Several devices agree with each other and disagree with the ground
Agreement between receivers is not confirmation. They see the same sky and can be fed the same false signals.
Reported time is wrong
Position and time come from the same solution. A clock that has shifted is a strong indicator.
Accuracy reads unusually good for the conditions
Suspiciously clean is a tell. Real ground rarely produces perfect numbers under canopy.
Notice that none of these come from the device warning you. Every one is a comparison against something outside it: the terrain, the clock, your own expectation. That is why the verification habit is the countermeasure, and why multi-constellation hardware helps without solving it — more systems raise the effort required, and a determined source can cover them all.
Knowledge Check
Three members compare devices and all three show the same position, which does not match the terrain. What does the agreement prove?
3. Dead, and the things that get you there
Flat batteries, cold, water, a drop onto rock, or a deliberate shutdown under the postures from Lesson 08. The device stops. This is the easy case precisely because it announces itself.
Most of the work here is preventive:
Match battery chemistry to conditions. From Lesson 03: lithium in the cold, and carry spares you can actually swap in the dark with gloves on.
Know your real endurance at the settings you actually use. All systems and multi-band cost significantly more than a basic mode, and a number from the box is not a number for your configuration.
Load offline mapping before you leave. Worth being precise about a widespread misconception: a phone’s receiver does not need cell service to compute a position. It needs the network to download assistance data quickly and to fetch map tiles. With maps cached in advance, a phone in airplane mode still fixes and still shows you where you are on a map.
Keep the paper current. The map with the route marked and the grids written is the thing that makes a dead device an inconvenience.
Knowledge Check
A member says their phone is useless for navigation once cell service goes down. What is wrong with that?
4. Stepping down without halting
The PACE plan from Lesson 01 exists for this moment, and the measure of it is not whether you can navigate on map and compass — NAV-02 covers that. It is whether the change of method costs you a pause or an incident.
Step 1Fix your last known pointThe last position you confirmed against terrain, not the last one the device displayed. Mark it on paper. → Step 2Account for sinceRough direction and distance traveled since that point. Minutes and pace, not precision. → Step 3Confirm on the groundEstablish where you are by terrain before continuing. This is the step that must not be skipped. → Step 4Continue on the planSame route, same turning points, different instrument. The plan does not change because the method did.
Step 1 is the one that decides how expensive this is. If you have been verifying at checkpoints, your last confirmed point is minutes behind you and the step down is trivial. If you have been following an arrow for two hours without looking up, your last confirmed point is the trailhead, and everything since is guesswork.
The cost of losing the device is set long before you lose it — by how recently you last confirmed position, and by whether the plan exists on paper. Both are decided in calm conditions, which is the whole argument of this course in one sentence.
Knowledge Check
Two members lose their devices at the same moment on the same leg. Why is the step down cheap for one and expensive for the other?
What to carry out of this lesson
Degraded is the device being honest — widen tolerance and verify more often rather than abandoning it.
A spoofed fix is confident, plausible and wrong. Every indicator of it is a comparison against something outside the device.
Several devices agreeing is not corroboration. They see the same sky and can be fed the same false signals.
A phone receiver needs no cell service to compute a position; the map underneath it does. Cache the maps beforehand.
How expensive the step down is was decided before it happened, by how recently you last confirmed position on the ground.
Field Drill
Rehearse the failure rather than reading about it.
Mid-leg, without warning from yourself, put the device in a pocket and treat it as dead. Run the four steps. Time how long until you are moving again on the plan.
Repeat having deliberately not verified for the previous thirty minutes. Compare the two times. That difference is the value of checkpoint discipline.
Put your phone in airplane mode in your operating area and confirm it still fixes and still shows a map. If it does not, cache the maps now.
Run your device down at the settings you actually use and record the real endurance. Write it on the settings card.
Answer all four knowledge checks to unlock Lesson 10