Solo skydiving demands the highest level of reliability from every piece of equipment, and the altimeter is no exception. A dual‑redundancy altimeter system ---typically a primary electronic altimeter paired with a backup analog or separate digital unit---provides a safety net in case one device fails or gives an erroneous reading. This guide walks you through the complete process of mounting, wiring, and calibrating a dual‑redundancy altimeter setup, from pre‑jump checks to post‑jump verification.
Gather the Right Gear
| Item | Why You Need It |
|---|---|
| Primary electronic altimeter (e.g., MIRAGE 2000 or CIR 400) | Provides high‑resolution altitude data, barometric trend, and integrated dive computer functions. |
| Backup altimeter (analog Famous or second electronic unit) | Independent measurement line; works even if the primary loses power. |
| Dual‑mount harness platform (e.g., Altiplatform 2‑in‑1) | Allows both units to be clipped securely without adding bulk. |
| Quick‑release clips / Velcro straps | For rapid removal in emergencies. |
| Altimeter mounting brackets and screws (stainless steel) | Ensure the units stay level and vibration‑free. |
| Calibration barometric pressure gauge (0--110 kPa) | Needed to set absolute altitude correctly. |
| Hand‑held pressure sensor (optional) | For on‑site verification of barometric pressure. |
| Torque wrench (3--5 Nm range) | Prevents over‑tightening of brackets. |
| Small screwdriver set (Phillips & flat) | For adjusting any set‑screw calibrations. |
| Safety checklist (paper or digital) | Keeps you from skipping essential steps. |
Pro tip: Invest in a single‑piece mounting platform that positions the primary unit directly above the backup. This geometry minimizes the chance that a single impact will knock both devices off‑axis.
Prepare the Harness
- Lay the harness flat on a clean surface, zip it open, and inspect all stitching and webbing for wear.
- Locate the left and right leg loops -- most dual‑mounts are centered on the left hip for right‑handed jumpers.
- Thread the mounting platform through the front D‑ring, ensuring the platform sits flush against the chest‑to‑leg line.
- Secure with the quick‑release clips but leave them slightly loose (about 1 cm clearance) so you can adjust the tilt later.
Mount the Primary Altimeter
- Attach the primary unit to the top slot of the platform using its dedicated lock‑pins.
- Align the display so it faces outward and is readable when you're in the "mouth‑to‑chin" position.
- Tighten the lock‑pins with a torque wrench set to 3 Nm . Over‑tightening can warp the internal sensor.
- Run the power cable (if the primary requires an external battery) into the harness's internal pocket.
Mount the Backup Altimeter
- Slide the backup unit into the bottom slot, ensuring the dial (for analog) or screen (for digital) faces the same direction as the primary.
- Fasten the secondary lock‑pins at 2.5 Nm.
- If the backup is analog , verify that the needle rests at "0" when the unit is level. Adjust the set‑screw on the back of the case if necessary.
Wiring & Power Management
| Connection | Steps |
|---|---|
| Primary battery pack | Connect to the primary's power port, route the cable under the harness straps to avoid snagging. |
| Backup unit (if electronic) | Use a separate, low‑profile battery; keep it isolated from the primary's power line. |
| Redundant power switch (optional) | Install a small two‑position toggle on the platform to quickly disable one unit for testing. |
- Secure all cables with small zip‑ties, leaving enough slack to accommodate harness movement.
- Label each connector with heat‑shrink tubing (e.g., "P‑BAT" for primary, "B‑BAT" for backup).
Calibrate Barometric Pressure
6.1. Set the Reference Pressure
- Obtain the current sea‑level pressure from a reliable source (local airport METAR, handheld weather radio, or a calibrated barometric gauge).
- Enter the value into the primary altimeter's setup menu (usually under "Barometric Calibration").
- Repeat the same entry on the backup unit (most analog backups have a small screw‑type pressure reference; turn it clockwise for higher pressure, counter‑clockwise for lower).
6.2. Verify Altitude at Ground Level
- Stand on flat ground (elevation known, e.g., a field with a surveyed benchmark).
- Check the displayed altitude on both units. They should read within ±50 ft of the known elevation.
- If readings differ , adjust the backup's set‑screw in 0.5‑turn increments until the discrepancy falls within the tolerance.
6.3. Temperature Compensation (Optional)
Some electronic altimeters allow input of ambient temperature. Use a handheld thermometer to input the current temperature to improve accuracy, especially on hot days.
Functional Test (Pre‑Jump)
- Power on both units and verify that LEDs/indicators light as expected.
- Simulate a rapid descent by stepping off a low platform (2--3 m) while holding onto a safety line. Observe whether both altimeters register a descent of at least 10 ft.
- Check the "low‑altitude alarm" on both units (often a vibrating buzzer). It should activate at the pre‑set threshold (e.g., 1 500 ft).
If any unit fails to alarm, repeat the calibration steps or inspect the sensor for blockage (dust or moisture).
Post‑Jump Verification
After each solo jump:
- Power down the units and record the final altitude displayed on each.
- Compare the readings ---they should be within ±30 ft. Larger discrepancies may indicate sensor drift.
- Log any anomalies (e.g., missed alarms, erratic needle movement) in a jump logbook.
Schedule a full recalibration after 10 jumps or after any significant temperature change (> 15 °C) that could affect the barometric sensor.
Maintenance Checklist
| Frequency | Action |
|---|---|
| Before every jump | Visual inspection for dents, loose pins, and cable wear. |
| Weekly | Verify battery voltage (≥ 3.5 V for Li‑Ion, ≥ 1.5 V for alkaline). Replace if below. |
| Monthly | Clean the sensor ports with a soft brush; avoid solvents. |
| Every 6 months | Re‑calibrate barometric pressure using a certified gauge. |
| Annually | Send both units to the manufacturer for a full diagnostic check. |
Troubleshooting Common Issues
| Symptom | Likely Cause | Remedy |
|---|---|---|
| Altimeter reads a constant high altitude | Barometric pressure entry error | Re‑enter current sea‑level pressure; double‑check the source. |
| Needle on analog backup jumps erratically | Loose set‑screw or magnetic interference | Tighten set‑screw; keep magnetically noisy equipment (e.g., phones) away. |
| Primary unit fails to power on | Battery connection broken | Reseat battery connector, replace battery if voltage low. |
| Low‑altitude alarm does not sound | Alarm threshold set too low/high | Adjust the alarm threshold in the menu; verify speaker/buzzer integrity. |
| Discrepancy > 200 ft between units | Sensor drift or damage | Conduct a full recalibration; if discrepancy persists, replace the faulty unit. |
Safety Best Practices
- Never rely on a single altimeter---the whole point of redundancy is to have a back‑up.
- Perform a "two‑hand check" : after you clip in, reach for both units with each hand, confirming they are locked.
- Carry a spare battery for each unit in a separate pocket.
- Practice emergency procedures on the ground: simulate a scenario where the primary fails and you must switch to the backup.
Conclusion
Installing a dual‑redundancy altimeter system is a straightforward yet critical task for solo skydivers who demand the highest safety margins. By following the step‑by‑step mounting process, calibrating both units against a reliable pressure reference, and maintaining a disciplined verification routine, you can trust that your altitude data will be accurate and dependable---every jump, every altitude, every landing.
Remember: equipment is only as good as the procedures that support it. Keep your checklist handy, stay methodical, and enjoy the freedom of solo flight with peace of mind.
Happy jumping!