Offline trip planning: what to save, test and leave behind before a hike

Planning a hike without mobile signal means deciding, before you leave, how you will find your way, keep the phone working, track the time and tell someone where you are. Most of that is done at home, while the network is still available to download, test and confirm things.

Save maps and test them in airplane mode

Download the map area for the whole route, with a margin on each side, in the mapping app you already use. Then switch the phone to airplane mode and open the map. Check that the route, the trailhead and the nearest road are all shown, and that the map still loads when you zoom in to the detail you will need on the trail. A saved area that only loads at the zoom level you chose is still useful, but you should know its limit before you leave.

Carry a paper map and a compass as well. A phone can fail, run out of battery or get wet, and a paper map does not depend on any of them. The map scale guide covers how distances on a map relate to the ground, and the true north and magnetic declination guide covers why a compass bearing and a map bearing can differ. Practise with both before the trip. The navigation item in the ten essentials covers the wider list of kit.

Check that position works with the phone offline

Once the maps are saved, test whether the phone can still show your position. Turn on airplane mode, open the saved map and look for the position marker. Walk a short distance, or stand at a point you can identify on the paper map, and check that the marker moves to the right place. Note how long the marker took to appear and how much battery the test used.

Do the test at home, where the settings can be changed and help is a phone call away. If the marker does not appear offline, plan to navigate with the paper map and compass, and treat the phone as a backup.

Save the Trailwright pages you need

The Trailwright field pack is meant to be saved while the phone is connected. Save it at home, then check it in airplane mode before you go. Open the tools you expect to use, change one input, and confirm that the result updates. Saved scenarios stay on the device that saved them, so a scenario saved on one phone does not appear on another.

Solar coordinates are never saved. Write down the latitude and longitude of the trailhead and of the camp on paper if you will need sun and daylight times in the field. The tools index lists every calculator, and each one states its own inputs and limits. Choose the ones that match the trip. A short walk on a marked trail needs fewer than a multi-day route through remote ground.

Budget the battery in watt-hours

Battery packs are labelled in milliamp-hours (mAh), but devices use energy in watt-hours (Wh). The Trailwright power budget tool converts one to the other using the cell voltage and an assumed end-to-end efficiency. The usable energy from a pack is:

usable Wh = mAh ÷ 1000 × cell voltage × efficiency

The mAh to Wh guide works through that conversion in more detail, and how many phone charges turns the figure into a practical count. Cold weather is a separate question, covered in the battery guide for cold weather, which matters if the trip is in winter.

usable energy = 10,000 ÷ 1000 × 3.7 × 0.80 = 29.6 Wh
demand        = 2 W × 4 h × 3 days = 24 Wh
balance       = 29.6 − 24 = 5.6 Wh

The balance is positive, so the pack covers the assumed use with 5.6 Wh to spare. That margin is small. A slightly higher draw, a cold day or a pack that is older than its label would use it up, so the budget should be checked against a figure you have measured on the same phone and settings.

Note daylight and set the turnaround for each day

Write down sunset and civil dusk for each day of the trip, at the place you will be. The Sun & daylight tool gives both times, in UTC, so convert them to local time before writing them down. The sunset and remaining daylight guide explains how to use those times on the trail.

Then set a turnaround time for each day, worked back from the finish time. The turnaround time guide sets out the arithmetic, and the Trail time tool estimates the walk back. Put the turnaround on the trip plan, so that the person holding it knows the times that matter.

Leave a trip plan with someone reliable

The National Park Service advises that you tell someone where you are going and when to expect you back. A trip plan is the written version of that advice. It should give the route, the names of everyone in the party, the vehicle and where it will be parked, the expected return time, and the time after which the person holding the plan should raise the alarm.

Choose someone who will act on the plan, and agree the alarm time with them in advance. Give them a copy of the map area, not only a description. Confirm by message that they have it before you leave the signal. Tell them when you are back, so that they do not start a search for a trip that has finished.

Plan for calls and emergency messages

Without a mobile network, an ordinary phone call may not connect, so the offline map is for navigation only. The National Park Service lists a two-way satellite messaging device among the extra items some activities need, in addition to the ten essentials. Treat it as a separate item to carry, charge and test before the trip.

The NOAA SARSAT programme says that Cospas-Sarsat 406 MHz beacons are capable of transmitting a distress signal thousands of miles into space. Beacons are for emergencies. They do not replace the trip plan, the turnaround time or training in first aid and route finding. Check the current rules for any beacon you plan to carry with the agency that issued them.