2.4 VLOS, Daylight, Visibility and the One-RPA Rule

VLOS, Daylight, Visibility and the One-RPA Rule

Three of the Standard Operating Conditions — Visual Line Of Sight (VLOS), daylight, and one RPA per pilot — work together as the core see-and-avoid system for remote pilots. They are examined individually and in combination, so understanding the definitions and the reasoning behind them matters.

VLOS — Visual Line Of Sight (CASR 101.073)

Visual Line Of Sight (VLOS) means the remote pilot can see the RPA unaided throughout the flight and is close enough to maintain control of the aircraft in both normal and emergency manoeuvres. The key points:

• Unaided eye only — you may not use binoculars, telescopes, or any optical magnification aid to maintain VLOS. The aircraft must be visible to the naked eye.
• Corrective lenses are permitted — ordinary prescription glasses or contact lenses are not considered an "aid" that disqualifies VLOS. The rule targets magnification, not vision correction.
• Maintain control — VLOS is not just about seeing the aircraft; the pilot must be close enough that, if something goes wrong, they can visually command the aircraft to a safe outcome.
• First-person view (FPV) cameras alone are not VLOS — flying using only an onboard camera feed is Beyond Visual Line Of Sight (BVLOS) and requires an approval.

When the aircraft can no longer be seen unaided, the operation has crossed into EVLOS (Extended Visual Line Of Sight — using observers to extend the visual range) or BVLOS, both of which require CASA approval. EVLOS uses one or more visual observers to keep the RPA (or its surroundings) in sight; BVLOS relies on instruments, sensors, or cameras alone.

Daylight and Civil Twilight

The SOC require operations only during daylight — defined as the period between the beginning of morning civil twilight and the end of evening civil twilight at the location. Civil twilight is the period when the sun is below the horizon but its geometric centre is no more than 6° below it; there is enough light to see unaided and to conduct see-and-avoid. CASA publishes civil twilight times for Australian locations, and flight planning software calculates them automatically.

Operations at night are outside the SOC and require a specific CASA approval. The reasoning is twofold: the unaided eye cannot reliably see an RPA (or surrounding traffic) in darkness, and manned aircraft lighting and separation norms are built around daytime see-and-avoid. A night approval usually requires additional equipment (lights, observers), an ReOC, and an approved safety case.

Note the boundary: civil twilight is not the same as sunrise/sunset. Morning civil twilight begins roughly 20–30 minutes before sunrise (varies by latitude and season), and evening civil twilight ends roughly 20–30 minutes after sunset. A flight at 10 minutes after sunset may still be within evening civil twilight and therefore within the SOC, but a flight 40 minutes after sunset is almost certainly in darkness and outside the SOC. In the southern hemisphere summer at higher latitudes, civil twilight can be very short; in winter it is longer. Always check the published twilight times for the operating location and date rather than guessing.

Visibility: Clear of Cloud, No Fog

Complementary to daylight, CASR 101.095 requires that an RPA not be operated in cloud or in thick fog or in conditions of insufficient visibility to maintain VLOS and see-and-avoid. The practical test: if you cannot see the aircraft unaided, or cannot see surrounding sky well enough to detect manned traffic, you must not fly. Unlike manned instrument flying, RPA operations under the SOC are always visual — there is no "instrument meteorological conditions" capability for a standard RPA flight.

One RPA per Pilot

The SOC limit of one RPA per pilot means a single remote pilot may operate only one RPA at a time. The reasoning is workload and see-and-avoid:

• Operating one RPA already demands continuous visual attention and control inputs.
• Adding a second aircraft splits the pilot's scan, reduces the time each aircraft is in view, and increases the chance of a mid-air collision or loss of control.
• Emergency handling (a motor failure, a fly-away, a low-battery landing) is near-impossible to manage for two aircraft simultaneously.

Operations involving more than one RPA per pilot — sometimes called multi-RPA or swarm operations — require a CASA approval, generally held by an ReOC operator, with a safety case demonstrating how workload is managed (e.g. autonomous waypoint missions with autonomous fail-safes, separate ground stations, or visual observers).

Give Way to Manned Aircraft

Under CASR Part 101, an RPA must give way to manned aircraft. This reflects the principle that unmanned operations yield to manned operations because the consequence of a mid-air collision for a manned aircraft is potentially fatal, whereas an RPA collision risk is generally to people and property on the ground. In practice, give way means: maintain visual scan for manned aircraft, descend or manoeuvre clear if a manned aircraft approaches, and never assume the manned pilot has seen the RPA — most manned aircraft have no detection capability for small RPA. If a collision risk develops, the RPA pilot acts first and decisively.

The give-way rule also means the RPA pilot should avoid operating at altitudes and locations where manned aircraft are known to transit — near aerodrome circuit patterns, along helicopter routes, over hospitals with helipads, and along coastlines where scenic helicopter flights occur. Even when operating within the 120 m AGL limit, an RPA pilot may encounter low-flying manned aircraft (helicopters, agricultural aircraft, emergency services) that are below 400 ft. The response is always the same: the RPA gives way, descends if practical, and lands or holds if a collision risk cannot be eliminated.

Putting the three conditions together — VLOS, daylight, one RPA — the standard remote pilot's operating loop is: keep the aircraft in unaided sight throughout the flight, fly only between morning and evening civil twilight, stay clear of cloud and fog, fly one aircraft at a time, and continuously scan for manned traffic to give way. Every SOC deviation from that loop requires a documented approval.