Static electricity in the aircraft

Static electricity builds up when the aircraft and its environment develop different electrical potentials — through:

Friction of the airframe with air molecules, water droplets, ice crystals, dust in flight,
Friction during refuelling (fuel flowing through hose),
Movement on the ground (tyres on asphalt),
Thunderstorm fields (induction from charged clouds).

Effects of static electricity

1. Radio interference (precipitation static, P-Static)

Charge built up in flight by ice crystals/rain discharges via the antennas → crackling, noise, possible radio failure.
Particularly affects VHF communication and ADF/NDB navigation.

2. Instrument disturbances

Some instruments and EFIS displays respond to electrostatic fields.

3. Fire/explosion during refuelling

A spark during refuelling can ignite fuel vapours (AVGAS, Jet-A).
Classic cause of fires, hence strict bonding requirements.

4. Pilot risk

Touching a charged aircraft after landing can cause a shock — rarely dangerous but unpleasant.

Protective measures

Static dischargers

Construction: small rods of carbon fibre or tungsten micro-fibres at the trailing edges of wings, elevator, fin and ailerons.

Principle:

The fine fibre tips have very small radii → high field concentration.
A corona current flows from the tips, weakly and continuously releasing charge to the surrounding air.
Prevents discharge through the antennas or other paths that would cause radio interference.

Pre-flight inspection: static dischargers must be present and undamaged; broken rods should be replaced.

Grounding during refuelling

Before every refuelling the aircraft must be electrically grounded — a worldwide requirement and one of the most important safety procedures in aviation.

Procedure:

Aircraft ground to the fuel truck or grounding point:
- Ground cable from the fuel truck's earth point to the aircraft's grounding point (landing gear leg or grounding tab on the wing leading edge).
Bonding between aircraft and fuel nozzle:
- Additional ground cable between the fuel hose nozzle and aircraft grounding point.
Only then open the fuel cap and insert the nozzle.

Why two connections?

During refuelling, fuel flow through the hose and filter creates a charge on the hose and filter.
Without a continuous electrical connection between aircraft and fuel truck a spark can occur when inserting or removing the nozzle.

Self-fuelling / mobile fuelling: similar rules; the aircraft must be connected to the fuel source via ground cable before fuelling.

Before entering the cabin

In dry air a pilot may receive a spark when touching the airframe. Recommendation: place a hand first on a metal frame on the ground to dissipate any charge slowly.