12.2 Visual Scanning, Visual Observers & Radiotelephony Phraseology

Visual Scanning, Visual Observers & Radiotelephony Phraseology

Quick Summary: Maintaining continuous Visual Line-of-Sight (VLOS) is the cornerstone of Basic RPAS operations under Canadian Aviation Regulations (CARs Part IX). Because drones share uncontrolled airspace with low-flying crewed aircraft—including floatplanes, helicopters, and agricultural sprayers—RPAS pilots must master visual physiology, systematic scanning techniques, and see-and-avoid rules. Under CAR 901.17, the RPA must give way to power-driven heavier-than-air aircraft, airships, gliders and balloons at all times. When operating near aerodromes or communicating on VHF airband frequencies (118.000 to 136.975 MHz), operators must hold an ISED ROC-A certificate and use standard ICAO phonetics and phraseology.

---

Visual Scanning & See-and-Avoid Principles

The primary defense against mid-air collisions is the see-and-avoid doctrine. Because small drones are nearly impossible for full-scale pilots to spot, the RPAS pilot bears the sole legal responsibility to detect conflicting traffic and clear the airspace.

Human Visual Physiology

The human eye relies on two distinct photoreceptor systems on the retina:

• Fovea Centralis (Cone Cells): Located at the retinal center, the fovea covers only a 2° visual cone (roughly two thumbnail widths at arm's length). Packed with cones, it delivers sharp central acuity and color perception in bright photopic conditions. Outside this 2° center, visual acuity drops by over 90%.
• Peripheral Vision (Rod Cells): The remaining visual field contains rod cells, which lack fine resolution and color perception but excel at detecting motion and subtle contrast changes in low light.
• Fixation vs. Saccades: The eye cannot focus while in motion. During rapid eye sweeps (saccades), the brain suppresses visual processing. Approaching aircraft remain invisible unless the gaze pauses in stationary fixations.

Systematic Sector Scanning Techniques

To overcome saccadic limitations, Transport Canada recommends the systematic sector scanning technique:

1. Scan the sky in systematic, overlapping sectors of 10° to 15° wide.
2. Pause the eyes for 1 to 2 seconds in each sector to allow optical fixation and target detection.
3. Overlap adjacent sectors by 3° to 5° so that no visual gaps exist between sectors.
4. Scan the horizon from left to right, raise the gaze 10°, and sweep back from right to left, alternating back to the RPA at regular intervals.

The Constant Bearing, Decreasing Range (CBDR) Hazard

An aircraft on a direct collision course displays Constant Bearing, Decreasing Range (CBDR). The approaching traffic appears stationary in your visual field while growing larger in size. Because there is no relative motion across the retina, peripheral rod cells cannot detect it. Only deliberate sector scanning reveals CBDR traffic in time.

---

Visual Illusions & Physiological Limitations

---

Absolute Right-of-Way Rules (CAR 901.17)

In Canadian civil aviation, right-of-way rules for remotely piloted aircraft are absolute:

• CAR 901.17 Mandate: An RPA must give way to power-driven heavier-than-air aircraft, airships, gliders and balloons at all times. The TC AIM (RPA 3.2.5) restates this as giving way to all other aircraft, including balloons, gliders, airships and hang gliders.
• Pilot Action: Upon sighting or hearing crewed traffic, the RPAS pilot must immediately descend, maneuver away, or land to clear the airspace. Crewed aircraft pilots cannot see small drones, and high closure rates eliminate margin for error.

---

Visual Observer (VO) Roles & Responsibilities (CAR 901.20)

Under Canadian regulations, a Visual Observer (VO) provides dedicated lookout support:

• Definition (CAR 900.01): A visual observer is a crew member who is trained to assist the pilot in ensuring the safe conduct of a flight.
• Reliable Communication (CAR 901.20(1) and (2)): A VO may only be used if reliable and timely communication is maintained between the pilot and each VO throughout the operation, and the VO must report conflicting air traffic, hazards to aviation safety and hazards to persons on the surface in a timely manner.
• One Aircraft at a Time (CAR 901.20(3)): A VO must not perform VO duties for more than one RPA at a time, except for compliant multi-aircraft operations under CAR 901.40(1) or under an SFOC — RPAS.
• No Driving (CAR 901.20(4)): A VO must not perform VO duties while operating a moving vehicle, vessel or aircraft.
• Undivided Attention (TC AIM RPA 3.2.8): Transport Canada advises that if a visual observer must attend to another task, the pilot should use a second visual observer or land the aircraft until that task is complete.
• Unaided Vision: Visual observers must rely on natural, unaided sight. Corrective lenses are permitted; binoculars or cameras may only be used momentarily to identify a target, not for continuous scanning.

---

Aeronautical Radiotelephony & Communication Standards

ISED Regulations & ROC-A Certification

• Airband Spectrum: Aeronautical VHF communications operate between 118.000 MHz and 136.975 MHz.
• ISED Jurisdiction: Radio frequencies in Canada are regulated by Innovation, Science and Economic Development Canada (ISED) under the Radiocommunication Act.
• Licensing Requirement: Operating a transceiver to transmit on aviation airband frequencies requires an ISED Restricted Operator Certificate - Aeronautical (ROC-A). Transmitting without an ROC-A is illegal.

The ICAO Phonetic Alphabet & Number Pronunciation

Aviation demands standard phonetics across voice channels:

Standard Aeronautical Phraseology

• ROGER: "I have received all of your last transmission." (Does not signify agreement or compliance).
• WILCO: "I understand your message and will comply with it."
• AFFIRMATIVE / NEGATIVE: "Yes" / "No".
• SAY AGAIN: "Repeat all, or the specified part, of your last transmission."
• STANDBY: "Wait and I will call you."
• READ YOU FIVE BY FIVE: Transmission received with maximum signal strength (5) and clarity (5).
• OVER / OUT: "Over" means transmission ended and a response is expected; "Out" means transmission ended and no response is expected. Never say "Over and Out".

Emergency Distress & Urgency Signals

• Distress ("MAYDAY"): Spoken three times ("MAYDAY, MAYDAY, MAYDAY"). Indicates grave and imminent danger requiring immediate assistance.
• Urgency ("PAN PAN"): Spoken three times ("PAN PAN, PAN PAN, PAN PAN"). Indicates a condition concerning the safety of an aircraft or person that does not require immediate assistance.
• Aeronautical Emergency Guard: 121.5 MHz VHF is the international civilian distress and urgency frequency.
• Traffic Frequency Monitoring: RPAS pilots operating near uncontrolled aerodromes monitor the Aerodrome Traffic Frequency (ATF) (standard 123.2 MHz unless published in the CFS) or Mandatory Frequency (MF) to track circuit traffic.

---

Practical Exam Scenarios & Common Traps

• The Floatplane on Final Approach: An RPA is flying at 300 ft AGL over a lake when a floatplane approaches to land. The drone pilot must immediately yield under CAR 901.17 by descending or maneuvering clear.
• The Unlicensed Transmission Trap: An RPAS operator buys an airband radio to broadcast position advisories on a local ATF frequency. Transmitting without an ISED ROC-A certificate is a federal violation.
• The Empty-Field Myopia Trap: Staring into an overcast gray sky causes the eyes to focus at 1 to 2 metres, obscuring a converging helicopter until it is too close to avoid.