10.5 Clouds, Cumulonimbus, Lightning & IP43

Reading Clouds

Clouds show moisture and atmospheric motion. Observe amount, base, type, development, movement, and trend. Low cloud can remove VLOS at modest height. Ragged fast-moving cloud can indicate strong flow. A lowering base with temperature and dew point close can precede mist or fog.

Cumulonimbus

Cumulonimbus (Cb) is the deep convective thunderstorm cloud, often with a tall cauliflower form and anvil top. Hazards include:

• lightning;
• heavy rain, snow, or hail;
• strong gust fronts and sudden direction changes;
• severe turbulence;
• powerful updraughts and downdraughts;
• rapid visibility loss; and
• flooding or unsafe ground conditions.

Effects extend beyond the rain shaft. A dry site can receive a sudden cool outflow gust. Small UAS lack the performance and protection for thunderstorm flight.

If cloud towers rapidly, thunder is heard, lightning is seen, or a warning covers the operation, land before the hazard reaches the site.

Lightning and Shelter

Lightning threatens pilot, observer, public, and equipment. Do not remain exposed holding a controller or shelter under an isolated tree. Stop and seek a substantial building or enclosed vehicle under current official safety guidance.

A weather case or ingress code is irrelevant to lightning safety. Do not launch for “one last flight” because rain has not begun.

Precipitation, Icing, and Cloud

Rain and snow reduce visibility, wet electronics, change aerodynamic surfaces, and make launch sites slippery. Near freezing, visible moisture can form ice on propellers or wings. Small contamination changes shape, balance, lift, and vibration.

Entering cloud breaks visual contact and may expose the UAS to icing and unpredictable flow. A green night light does not make it visible through cloud.

Understanding IP43

The syllabus calls out IP43, an IEC 60529 ingress-protection classification. The two digits describe different protections.

First digit: solids

The first digit 4 means protection against solid foreign objects of 1 mm diameter and greater under the test. It does not mean dust-tight.

Second digit: water

The second digit 3 means protection against spraying water up to 60 degrees from vertical under the defined test. It does not mean protection against jets, heavy rain from every direction, immersion, salt water, or condensation.

The rating applies to the tested product and configuration. Open covers, damaged seals, added payloads, wear, or repairs can defeat it. The operating guide may impose a stricter no-rain limit even if one enclosure has a rating.

Rating Boundaries and Maintenance

An IP result is a laboratory classification, not an operational endurance time. It does not state how long the complete aircraft may remain exposed, whether propeller-driven spray reaches an untested angle, or whether water can travel through a moving gimbal, vent, speaker, connector, battery interface, or payload mount. The two digits must be read separately; they are not added together and a higher first digit does not compensate for a low second digit.

Age and maintenance matter. Dirt across a seal, a pinched gasket, a hairline crack, an incorrectly closed battery door, or residue from salt water may create a path that did not exist in the tested configuration. After unexpected wetting, follow the manufacturer’s shutdown, drying, inspection, and return-to-service instructions. Do not apply heat, open a battery, or power the aircraft merely to see whether it still works unless the instructions make that safe.

For exam questions, reject statements such as “IP43 is waterproof,” “4 means four metres of immersion,” or “3 means three hours in rain.” The exact answer concerns solid objects of at least 1 mm and limited water spray up to 60 degrees from vertical under the defined test.

Operational Decision

Ask:

1. Does the complete aircraft have a verified rating, or one component?
2. Is it assembled and maintained in rated configuration?
3. What do manufacturer instructions permit?
4. What intensity, direction, duration, and type of precipitation are expected?
5. Will water affect camera, sensors, battery, connector, link, or visibility?
6. Can VLOS and safe landing be maintained?
7. Would a wetting failure expose people?

Never use a marginal ingress rating to justify 5 m in worsening weather.

Scenarios

Marketing says waterproof. IP43 does not support that. It describes limited tests; follow actual operating limits.

Thunder heard. The storm is distant and the pad dry. Thunder still confirms a lightning-capable storm. Land and seek shelter.

Broken cover. The aircraft was rated, but a port no longer seals. Do not rely on the original rating.

Low cloud. The base lowers over a roof route. Even without rain, VLOS can fail and moisture risk rises.

Remember: Cb = lightning, heavy precipitation, gusts, severe turbulence; IP43 = ≥1 mm solids and spray up to 60° from vertical, not waterproof.