Air Traffic Control (ATC) Communications for UAS Operators: Radios, Phraseology, and Visual Signals

VHF and UHF Radio Bands (and How You Access Them)

What these bands are

Radio frequency (RF) spectrum is divided into named “bands” based on frequency. Two of the most important bands for aviation communications are:

• Very High Frequency (VHF): frequencies from $30\,\text{MHz}$ to $300\,\text{MHz}$.
• Ultra High Frequency (UHF): frequencies from $300\,\text{MHz}$ to $3000\,\text{MHz}$ (also written as $3\,\text{GHz}$).

Those ranges are general, worldwide engineering definitions—not specific to any single country’s aviation rules. Aviation then uses sub‑ranges inside these bands for particular services.

Why VHF and UHF matter in aviation (and for UAS)

Air traffic control relies on fast, clear, real-time communication. VHF and UHF are used because they generally support line-of-sight communication with good audio quality and relatively simple equipment.

For UAS operations, you may encounter aviation radio communications in a few common situations:

1. Operating near or within controlled airspace where you may need ATC authorization and coordination.
2. Operating on or near an airport environment where manned aircraft are using tower/CTAF frequencies.
3. Supporting a mission with an organization that uses aviation-band radios (for example, public safety operations near helipads or temporary flight restrictions).

Even when you are not speaking to ATC directly (many UAS operations do not), understanding how these communications work helps you interpret what other aircraft are doing and how traffic is being sequenced.

How VHF/UHF aviation communications work (the idea of line-of-sight)

A key concept is that most VHF and UHF communications are primarily line-of-sight:

• The radio waves usually travel in fairly straight paths.
• Terrain, buildings, and Earth’s curvature can block the signal.
• Higher antennas (or aircraft at altitude) can “see” farther.

This explains why a low-altitude UAS on the far side of a ridge might not hear a tower clearly even if the frequency is correct, and why aircraft at higher altitude can often hear ATC from much farther away.

Aviation-specific use of VHF and UHF (what you’ll actually encounter)

While VHF and UHF are broad bands, aviation communications commonly fall into these well-known areas:

• Civil aviation voice communications are commonly on VHF in the aircraft communications band (often encountered as 118.000–136.975\,MHz in many regions).
• Military aviation voice communications commonly use UHF (often encountered as 225–400\,MHz in many regions).

The exact services and channel spacing can vary by country/region, but the big picture stays the same: civil aircraft typically talk on VHF; many military operations have UHF capability.

How you “access” VHF and UHF (practical access, not just theory)

In practice, “accessing” VHF/UHF means you can receive (monitor) and/or transmit on a frequency using approved equipment and procedures.

1) Equipment access: radio hardware and audio chain

To use an aviation radio channel, you need:

• A VHF COM radio (or UHF radio if operating in UHF environments), connected to an antenna suited for that band.
• A push-to-talk (PTT) switch (or equivalent transmit control).
• An audio panel/headset (typical in manned aircraft) or an integrated audio interface (common in some ground stations).

In UAS contexts, direct aviation-band voice radios are more often used by:

• A visual observer team near an airport,
• A mission crew coordinating with a tower (when allowed/required),
• Or specialized operations where the ground crew has an aviation radio.

2) Frequency access: selecting the right channel

Aviation radios typically allow you to:

• Set an active frequency (the one you transmit/receive on right now).
• Set a standby frequency (pre-selected so you can quickly swap).

A common workflow is:

1. Dial the frequency into standby.
2. Double-check it.
3. “Flip-flop” it into active when ready.

That workflow matters because it reduces errors—especially in high workload moments like approaching an airport boundary or switching from approach control to tower.

3) Procedural access: authorization and proper use

Even with equipment, you cannot simply transmit anywhere at any time. Access also includes:

• Knowing which frequency to use (tower, ground, CTAF/UNICOM, approach, center, etc.).
• Using correct call signs and phraseology so your message is understood quickly.
• Following local/regional rules on when UAS operators may transmit on aviation frequencies.

A helpful way to think about it: the radio is like a “shared classroom microphone.” The technical ability to press the button is not the same as having the right to interrupt the class.

4) Monitoring vs transmitting (a key safety distinction)

Many UAS teams—especially near airports—may choose (or be required) to monitor aviation frequencies even if they do not transmit.

Monitoring helps you build situational awareness:

• You learn which runway is in use.
• You hear traffic patterns.
• You can anticipate aircraft that may be descending or crossing near your operating area.

A common mistake is thinking “If I can’t transmit, monitoring is pointless.” In aviation, listening is a major part of risk management.

5) Common radio controls that affect “access”

Even with the correct frequency set, you can still “fail to access” the conversation if your settings are wrong:

• Volume too low: you miss calls.
• Squelch set incorrectly: you either hear constant noise (too open) or miss weak signals (too tight).
• Wrong microphone source (in more complex setups): you transmit but no one hears you (or you transmit on the wrong radio).
• Wrong frequency format: entering $123.45$ instead of $123.450$ typically won’t matter in modern radios, but confusing similar frequencies can.

VHF vs UHF: a simple comparison table

Exam Focus

• Typical question patterns:
  • Define VHF and UHF by frequency range and connect each to typical aviation uses.
  • Scenario questions where you identify why reception is poor (terrain/line-of-sight) even on the correct band.
  • Practical questions about how a pilot/operator selects active/standby frequencies and avoids tuning errors.
• Common mistakes:
  • Mixing up the band definitions (swapping VHF and UHF ranges).
  • Assuming VHF/UHF “go through anything” like a phone signal—ignoring line-of-sight limits.
  • Treating “access” as only “having a radio,” rather than including correct frequency selection and procedure.

Radio Communication, Phraseology, and Light Signals

What “radio communication” means in ATC

ATC radio communication is a standardized way to exchange time-critical information between aircraft and controllers. The goal is not to sound formal—it is to be unambiguous, brief, and repeatable.

In aviation, radio transmissions are usually half-duplex:

• Only one station transmits on a frequency at a time.
• If two people transmit simultaneously, they “step on” each other and both messages may be unreadable.

That drives many aviation habits: pausing before you transmit, keeping messages short, and using structured phraseology.

For UAS, you might communicate:

• Directly with ATC (when operating under procedures that require it),
• Indirectly (another pilot radios ATC on your behalf),
• Or not at all (but still monitor for situational awareness).

Why phraseology is standardized

Phraseology is a set of standard words and patterns designed to reduce misunderstandings. It matters because aviation is full of conditions that make communication harder:

• Noise and weak signals
• Accents and differing first languages
• High workload and stress
• Similar-sounding numbers and place names

Standard phrasing acts like a “compressed language” optimized for safety.

How an aviation radio call is structured

A useful mental model is that most good calls answer four questions in order:

1. Who you are calling
2. Who you are
3. Where you are (as relevant)
4. What you want / what you are doing

Controllers and pilots expect this structure. If you scramble it, they can still understand you—but it costs time and increases the risk of confusion.

Example (general pattern)

Imagine you are authorized to coordinate from the ground near an airport:

• “Tower, Drone Team One, two miles north of the field at $200\,\text{ft}$ AGL, request traffic advisory.”

Even if your exact call sign and permissions differ by jurisdiction, the structure demonstrates the idea: called station, caller ID, position/altitude, request.

Call signs: what they are and why they matter

A call sign is the identifier used over the radio so everyone knows who a message is for. In manned aviation, call signs might be:

• An aircraft registration,
• An airline flight number,
• A tactical/military call sign.

For UAS teams, the call sign may be assigned by the operation, coordinating agency, or ATC arrangement (where applicable). The safety point is the same: use one consistent identifier so controllers can track you.

A common error is changing identifiers mid-mission (“This is the drone… uh… UAS team…”) which forces the other side to spend time confirming who is speaking.

Numbers and letters: making them hard to mishear

Aviation uses conventions for clarity.

The phonetic alphabet

The ICAO/NATO phonetic alphabet spells letters so they sound distinct over static (e.g., “Alpha, Bravo, Charlie…”). You don’t use it for every word—only when spelling identifiers, locations, or codes.

Numbers

In aviation, numbers are spoken in a deliberate way to reduce confusion. The exact conventions can vary slightly by authority, but these ideas are consistent:

• Speak digits clearly.
• Don’t rush.
• Expect to repeat critical numbers.

If you say an altitude, a heading, or a runway, that information can directly prevent a collision—so clarity beats speed.

Readbacks: how ATC confirms understanding

A readback is when you repeat back key parts of an ATC instruction to confirm you heard it correctly.

This is one of the most important safety mechanisms in aviation communication. It catches errors like:

• Hearing the wrong runway
• Confusing altitudes
• Missing a “hold short” instruction

Even outside a cockpit, the habit is valuable: if a controller gives you a constraint (altitude limit, lateral boundary, time window), repeating the key restriction back reduces the chance your team operates outside approval.

Example: what a good readback includes

If you are given a restriction such as “remain north of the runway and below $200\,\text{ft}$ AGL,” a strong readback repeats **north of runway** and below $200\,\text{ft}$ AGL.

Common standard words (and what they actually mean)

A lot of aviation misunderstandings come from using everyday speech instead of standardized terms.

Here are several terms with specific intent:

• “Affirmative” / “Negative”: Yes / No (clearer than “yeah” or “nope”).
• “Roger”: “I received your last transmission.” It does not mean “yes” or “I will comply.”
• “Wilco”: “Will comply.” (Sometimes used, depending on local standards.)
• “Say again”: Repeat your last transmission.
• “Stand by”: Wait; I will call you back.
• “Unable”: I cannot comply with that instruction/request.
• “Correction”: I misspoke; here is the corrected information.

A classic mistake is saying “Roger” when ATC asked a yes/no question. If ATC says “Confirm you will remain below $200\,\text{ft}$,” replying “Roger” is ambiguous. “Affirmative” (or “Negative”) is clearer.

Radio discipline: how to share a frequency safely

Radio discipline is the etiquette and technique that keeps the channel usable.

Key habits:

• Listen before transmitting: make sure you’re not interrupting.
• Pause a moment before keying up: you might otherwise clip the beginning of your message.
• One idea per transmission when possible: it’s easier to copy.
• If you make an error, correct it immediately using “Correction.”

Example: concise vs overloaded transmission

Overloaded: “Tower, Drone Team One, we’re about to launch and we’ll be at the soccer field and then go to the river and we think we’ll be fine and we’ll call you after…”

Concise: “Tower, Drone Team One, request launch approval—operating north of the field, below $200\,\text{ft}$ AGL, duration ten minutes.”

The concise version gives ATC what they need to make a decision.

Handling communication problems (static, blocked transmissions, no response)

When radios get noisy or busy, errors increase. Good practice is procedural:

1. If you didn’t understand, ask for a repeat (“Say again”).
2. If your message is long, break it up.
3. If the frequency is saturated, wait for a gap rather than forcing your call.
4. If you get no response, consider:
   • Are you on the correct frequency?
   • Is the volume/squelch correct?
   • Are you actually transmitting (PTT, mic selection)?
   • Are you blocked by terrain (line-of-sight)?

A common misconception is to keep transmitting louder/longer. That often makes things worse by blocking others.

Light signals (light gun): what they are

A light signal (often called a light gun signal) is a set of colored light indications a control tower can shine at an aircraft (or vehicle) to give instructions when radio communication fails or is not possible.

This system matters because aviation is designed with redundancy—if radios fail, the tower still needs a way to control runway and taxiway movement.

For UAS operations, you should understand light signals for two reasons:

• If you are operating near an airport environment, you need to know how the tower may be directing other traffic (which affects your risk picture).
• In some operations, a crew member may be coordinating near the movement area, where visual signals could be relevant.

How light signals work (the logic)

Light signals are designed to be:

• Highly visible from the tower
• Simple (a small number of colors and patterns)
• Different enough that you can tell them apart under pressure

They use:

• Color: typically green, red, and white
• Pattern: steady vs flashing (and one alternating pattern)

Steady generally implies “cleared/authorized” or “stop,” while flashing often implies “return,” “exercise caution,” or “not cleared.” You still have to memorize the exact meanings, because there are important exceptions.

Standard light signal meanings (aircraft in flight vs on the ground)

Meanings differ depending on whether the aircraft is in flight or on the ground.

Because these are safety-critical, you should treat them as “must know” signals rather than “nice to know.”

Light signals in action: interpreting a scenario

Suppose an aircraft’s radio fails while taxiing out. The tower might use:

• Flashing green: cleared to taxi (keep moving under tower control).
• Steady red: stop (hold position).
• Flashing red: taxi clear of runway (you are in a runway safety area and must exit).

The important skill is not just memorization—it is matching the signal to the phase of operation (ground vs air) and then predicting what the aircraft will do next.

Where students often get light signals wrong

Light signals are easy to confuse because green/red meanings swap depending on context:

• Steady green means “cleared to land” (in flight) but “cleared for takeoff” (on ground).
• Flashing green means “return for landing” (in flight) but “cleared to taxi” (on ground).

A good way to avoid mistakes is to first ask yourself: “Is the aircraft airborne or on the surface?” Then recall the meaning.

Bringing it together for UAS operations

Even if you never transmit on ATC frequencies, these concepts connect:

• Understanding VHF/UHF and line-of-sight explains why you may or may not hear traffic calls—and why a relay (or a better antenna position) can matter.
• Phraseology and readbacks show how aviation keeps communication efficient and verifiable; this mindset improves any operational comms plan.
• Light signals are a reminder that airports have procedures for failures—so you should plan for comm failures in your own operation (lost link, observer-to-pilot comm interruption, etc.).

Worked examples: short, realistic radio exchanges

These examples illustrate structure and discipline. They are not meant to replace local rules about whether you may transmit, but they show what “good” sounds like.

Example 1: Requesting information concisely

• You: “Tower, Drone Team One, one mile east of the field, request traffic advisory—operating below $200\,\text{ft}$ AGL.”
• Tower: “Drone Team One, standby.”
• You: “Standing by, Drone Team One.”

What’s happening: you gave position + intent + constraint; tower acknowledged workload.

Example 2: Correcting yourself cleanly

• You: “Tower, Drone Team One, operating west of the runway—correction—east of the runway, below $200\,\text{ft}$ AGL.”

What’s happening: you didn’t bury the correction; you flagged it immediately.

Example 3: Handling a garbled call

• Tower: “Drone Team One, remain north of—[garbled]—below two hundred.”
• You: “Tower, Drone Team One, say again remain north of what? Confirm below $200\,\text{ft}$.”

What’s happening: you asked a precise clarification question and confirmed the part you did hear.

Exam Focus

• Typical question patterns:
  • Identify what makes a radio call “complete” (who you’re calling, who you are, where you are, what you want).
  • Interpret or choose correct phraseology in a scenario (e.g., which response is appropriate to an instruction).
  • Match light gun signals (steady/flashing, color) to correct actions, with ground vs in-flight distinctions.
• Common mistakes:
  • Using vague acknowledgments (“OK,” “copy that”) instead of clear terms, or using “Roger” to mean “yes.”
  • Failing to read back critical restrictions (altitude limits, hold short, boundary constraints).
  • Mixing up light signal meanings by forgetting to separate in-flight from on-ground interpretations.