GNSS in VFR practice

GNSS (especially GPS) has revolutionised VFR navigation — moving-map apps on tablets are standard today. But: pilotage and DR remain a mandatory foundation. This lesson covers practical use and pitfalls.

Moving-map apps and EFB

EFB (Electronic Flight Bag): tablet- or smartphone-based assistant.

Popular VFR apps:

SkyDemon (UK/EU, very popular in Europe, ICAO 1
integrated)
ForeFlight (USA, widespread)
Garmin Pilot (USA, well-integrated with Garmin hardware)
EasyVFR (NL, Central Europe)
Air Navigation Pro
AvPlan (Australia)

Features: moving map, route planning with weather/NOTAMs/airspaces, METAR/TAF, wind & performance, logbook, some with ADS-B Out/In.

Advantages for VFR

Reduced workload — no plotter measurement in flight.
Real-time position — no need for 1-in-60 in flight (but: understand it anyway).
Instant NOTAM/weather updates via internet/4G.
Traffic display via ADS-B → situational awareness.

When using GNSS, especially on VFR flight, observe:

A comprehensive flight plan is still required (PLOG, pilotage, DR).
GNSS exclusively serves to support and monitor conventional terrestrial navigation.
GNSS cannot replace the obligatory sufficient visual flight weather conditions — visibility and cloud-base minima must be respected at all times, even with perfect GPS.

→ Result: GPS is an aid, not a replacement. The pilot must respect VFR minima, perform pilotage, and have a complete PLOG.

Risks and limits — GPS loss

What if GPS fails?

Accumulated knowledge gone — no heading/GS display.
Take over with pilotage: paper ICAO chart and PLOG on the knee.
Use the last confirmed waypoint as starting point, continue DR.

Causes of GPS loss:

Receiver failure or tablet power loss.
Jamming: military exercises (NOTAM!), conflict zones.
Spoofing: false signals — rare but rising.
Solar storm: ionospheric disruption.
Multipath / masking: deep valleys, dense forest, tunnels.
Signal shadowing by aircraft parts (see GNSS basics lesson).

Directional gyro — set before take-off

An important pre-take-off action: the directional gyroscope is correctly set before take-off with reference to the published magnetic direction of the runway:

Pilot positions the aircraft on the runway (at the threshold or holding point).
Sets the DG knob so the DG indication matches the published magnetic runway direction (RWY heading from the VAC chart).
Example: Runway 27 → magnetic direction 270° → DG set to 270°.
This completes the initial synchronisation with the magnetic compass before flight.

Switch avionics on only after engine start

Only switch on navigation equipment after engine start to prevent damage from voltage spikes:

During engine start the starter draws heavy current → bus voltage can momentarily dip.
Sensitive avionics (GPS, radio) can be damaged by this spike.
→ Avionics master OFF for start, then on after bus voltage stabilises.

Golden rules of GNSS use

Never the sole navigation source — paper chart and PLOG always with you.
Study the chart before the flight — even with EFB, the pilot must know the route.
Backup power: second tablet, power bank, hard-installed GPS.
Mental track with pilotage parallel to GPS — if GPS and visuals disagree, check immediately.
Pre-flight NOTAM check for GPS jamming — Central Europe and Mediterranean increasingly affected since 2022.
Avionics on only after engine start.
DG synchronised with runway direction before take-off.

Database currency

Important: the GPS database must be current!

AIRAC cycle: 28 days.
Outdated database can lead to outdated waypoints, airspaces, approach procedures.
For IFR legally mandatory (EU 965/2012, NCO.IDE.A.190).
For VFR strongly recommended.

ADS-B in VFR practice

ADS-B Out: aircraft transmits its position, altitude, speed. ADS-B In: receives positions of other ADS-B-Out-equipped aircraft.

Benefit ADS-B In for VFR: traffic-conflict detection even in VMC — sees other ADS-B-Out aircraft on the chart before visual contact.

Recommendations for PPL training

First 10 cross-country flights WITHOUT GPS (only DR + pilotage) → foundation.
Then introduce GPS as augmentation, not replacement.
Periodically switch GPS off in training — anti-addiction drill.

GNSS in practice for VFR