Radio Navigation: 5 Latest ATPL Questions Explained
In the Radio Navigation subject, you’ll explore the full range of radio navigation aids used in daily aviation operations. Key topics include the operation and application of the Instrument Landing System (ILS), Performance-Based Navigation (PBN), satellite navigation, and Distance Measuring Equipment (DME).
Explore key subtopics & core concepts of the Radio Navigation Syllabus
The exam places particular emphasis on satellite navigation and PBN. Success requires more than rote memorization — you need a solid understanding of how these systems work and interact.
Overall, Radio Navigation is considered a medium-difficulty subject. Many students find their experience depends heavily on the quality of instruction at their ATO and how up-to-date their instructors are with the latest developments in navigation technology.
In this walkthrough, we’ll review five fresh ATPL Radio Navigation questions, all recently reported from real EASA exams. Each comes with explanations to help you strengthen both your knowledge and exam technique.
Prefer to watch instead of read? You can also follow along with the video version of this walkthrough for a more interactive experience. Let’s get started.
Subscribe to the AirheadATPL YouTube channel and hit the notification bell for weekly ATPL revision videos. Each video helps you tackle the latest challenging questions from all 13 ATPL subjects, straight from recent EASA ATPL exams.
Question 1. MLS vs ILS
Question ID AIR-249965: Which of the following statements about the Microwave Landing System (MLS) is correct?
It operates one of 126 channels within an allocated frequency spread of 960 to 1215 MHz (UHF).
It operates in the VHF band, and the frequency allocation is between 108.1 to 111.95 MHz.
It operates one of 200 channels in the band 5.03 GHz to 5.09 GHz (SHF).
It operates one of 40 channels in the band 329.15 to 335 MHz (UHF).
Correct Answer: It operates one of 200 channels in the band 5.03 GHz to 5.09 GHz (SHF).
Explanation: The Microwave Landing System (MLS) was developed as a precision approach and landing system intended to replace the ILS by addressing its limitations and offering greater flexibility. MLS provides accurate position information (azimuth, elevation, and range) within a wide coverage sector, along with various ground-to-air data.
Operating in the Super High Frequency (SHF) band (5031–5090 MHz, 5.03–5.09 GHz), MLS supported up to 200 channels worldwide. Its higher frequency made it less vulnerable to interference from ground obstacles and enabled advanced features such as curved approaches, something the ILS could not provide.
By comparison, ILS operates using VHF for the localizer and UHF for the glideslope. While MLS was technically superior, its adoption was slow, and the rapid development of RNAV and RNP approaches ultimately rendered it obsolete.
Today, MLS remains in use at only a handful of major airports worldwide.
Question 2. From Mode A to Mode S
Question ID AIR-249935: What will a Mode S transponder reply to?
SSR and ADS-B interrogations
TCAS and ADS-B interrogations
SSR and primary radar interrogations
SSR and TCAS interrogations
Correct Answer: SSR and TCAS interrogations
Explanation: The key part of this question is 'reply to'.
ADS-B is broadcast ADS, so nothing replies to it, and the same is true of primary radar. Mode S transponders will respond (reply) to appropriate Secondary Surveillance Radar interrogations and also to those of TCAS equipped aircraft.
Transponders operate on the interrogation–response principle: SSR (Secondary Surveillance Radar) interrogates, and the transponder replies.
Mode A: Identification. Mode C: Identification + altitude (100 ft increments).
Mode S: Adds more precision, with altitude reported in 25 ft increments, and crucially supports TCAS resolution advisories.
Why not ADS-B?
ADSB = “Broadcast.” It does not reply to interrogations; it simply broadcasts aircraft data continuously, which is why services like Flightradar24 can track aircraft.
Question 3. Understanding ICAO’s Approach Classification
Question ID AIR-249661: Which of the following instrument approach operations are classified as 3D approach operations?
RNP APCH (GNSS and baro VNAV),
GLS,
PAR,
RNP 1,
ILS,
RNP APCH (SBAS)
Correct Answer: 1, 2, 3, 5 and 6
Explanation: A three-dimensional (3D) approach means you have both lateral (horizontal) and vertical navigation guidance. By contrast, a two-dimensional (2D) approach provides only lateral guidance.
Let’s check the options step by step:
RNP APCH (GNSS + Baro-VNAV) → Yes. GNSS gives lateral guidance, Baro-VNAV gives vertical.
GLS (GBAS Landing System) → Yes. Uses GPS corrections from ground stations, provides full lateral and vertical precision guidance.
PAR (Precision Approach Radar) → Yes. Controller gives both lateral and vertical guidance until touchdown.
RNP 1 → No. This is not an approach at all — it’s a navigation specification used for terminal/arrival procedures.
ILS → Yes. Localizer = lateral, glideslope = vertical.
RNP APCH (SBAS / LPV) → Yes. SBAS enhances GNSS for accurate lateral and vertical guidance.
Common trap: RNP1 is not an approach type — it’s a navigation specification for arrivals, not approaches.
Under ICAO’s updated classification:
Type A approaches → Decision height ≥ 250 ft Type B approaches → Decision height < 250 ft
Question 4. How to Read the HSI Correctly
Question ID AIR-250158: The attached image shows a multifunctional display. VOR 1 is displayed, which has been tuned to a nearby VOR station and correctly identified. The aircraft is…
6° left of the outbound course on selected radial 310.
6° left of the inbound course on selected radial 131.
3° left of the inbound course on selected radial 131.
3° right of the outbound course on selected radial 310.
Correct Answer: 6° left of the inbound course on selected radial 131.
Explanation (HSI / VOR interpretation — step by step): The annex shows an EHSI with a selected course of 310°, a “TO” indication, and a deflection just over half-scale to the right.
Quick facts to remember:
A VOR full-scale deflection = 10° (so half-scale ≈ 5°).
“Just over half-scale” therefore corresponds to about 6° off course.
Now read the display logically:
The CDI is deflected to the right by ~6°, so the aircraft is 6° left of the selected track.
The CDI shows a TO indication, so the aircraft is tracking inbound to the VOR (towards the station).
You selected course 310° inbound. Remember: radials radiate from the VOR, so the radial associated with a 310° inbound course is 130° (the reciprocal).
Put together: the aircraft is inbound, about 6° left of the 130° radial (i.e., tracking towards the VOR on the 131°/130° line).
Question 5. When to Go Missed on an RNP Approach
Question ID AIR-249233: When performing an RNP approach, which of the following situations leads to a missed approach unless sufficient visual contact is established?
Communications failure.
TCAS RA.
Position fix differs from the other instruments.
The actual navigation accuracy exceeds the required navigation accuracy.
The lateral deviation exceeds instrument full scale deflection.
Correct Answer: 2, 4, 5
Explanation: During an RNP approach, certain situations require an immediate missed approach unless sufficient visual references are established. Let’s break down the key points:
Communication failure → Not in itself a reason for a go-around. Specific COM-failure procedures exist, and you generally continue the approach as cleared.
TCAS Resolution Advisory (RA) → Always mandatory. Any RA requires an immediate go-around or manoeuvre as instructed.
Position fix differs from other instruments → Not a valid reason for discontinuing. The GNSS source is primary, and RNP systems include accuracy and integrity monitoring to ensure reliability.
Navigation accuracy worse than required → Yes. If the actual navigation performance (ANP) exceeds the required navigation performance (RNP) (e.g., ANP 1.5 when RNP 1.0 required), the approach must be discontinued.
Excessive lateral deviation → Yes. If lateral deviation exceeds half-scale, you must initiate a go-around. Full-scale deflection makes it mandatory.
Key principle: RNP approaches demand strict adherence to accuracy and lateral guidance. If performance falls below the required standard, or if TCAS issues an RA, a missed approach is non-negotiable.
Airhead's Takeaway
These five questions highlight not only facts, but also how EASA examiners like to test your knowledge — by linking definitions to operational consequences.
Keep practising with the Airhead Question Bank, and remember: the exam isn’t just about memorizing answers, but about understanding the principles behind them.
