The NDB Direction Test Explained: Scales NDB in NATS and FEAST

The NDB Direction test — known in the NATS and Eurocontrol FEAST context as the Scales NDB test — is one of the most distinctive aptitude assessments used in ATC selection. It measures your ability to interpret cockpit instruments and determine the spatial relationship between an aircraft and a radio beacon. This guide explains exactly how it works and how to practise effectively.

What Is the NDB Direction Test?

NDB stands for Non-Directional Beacon — a ground-based radio transmitter that aircraft can home in on using onboard equipment. In the test, you are given two cockpit instruments:

**The Heading Indicator (GYRO)** — A directional gyroscope showing the aircraft's current heading (the direction the nose is pointing), displayed as a compass rose with the current heading at the top.

**The Radio Bearing Indicator (RBI)** — A needle that points from the aircraft toward the NDB beacon. The needle is relative to the aircraft: if the needle points to 12 o'clock, the beacon is straight ahead. If it points to 3 o'clock, the beacon is 90° to the right.

Your task is to interpret these two instruments together and determine the aircraft's position relative to the beacon — typically by selecting which of several plan-view diagrams matches the situation shown on the instruments.

Why This Test Is Used

ATC selection tests use the NDB task because it requires genuine spatial reasoning integrated with instrument interpretation. Candidates must:

1. Read the GYRO to establish which direction the aircraft is heading

2. Read the RBI to establish the bearing from the aircraft to the beacon

3. Combine these mentally to determine the absolute bearing from the beacon to the aircraft

4. Translate this into a positional diagram

This chain of mental operations — reading, integrating, rotating, visualising — is precisely the kind of multi-step spatial reasoning that controllers use constantly when interpreting radar data.

The Core Calculation

The key relationship is:

Bearing from beacon to aircraft = Aircraft heading + RBI bearing (modulo 360)

For example: Aircraft heading 090° (due east), RBI shows 270° (needle pointing left, directly behind). The beacon is behind the aircraft. The aircraft is east of the beacon, heading further east.

Working this through consistently — rather than guessing visually — is the most reliable approach. Candidates who learn the formula and practice applying it quickly outperform those who rely purely on spatial intuition.

Common Errors

**Confusing the RBI direction.** The RBI shows the bearing TO the beacon from the aircraft, not FROM the beacon. It is a receiver, not a transmitter indicator. Getting this backwards flips all answers.

**Forgetting to account for heading.** The RBI is relative to the aircraft's heading, not to north. A needle pointing to 12 o'clock means the beacon is ahead — but "ahead" depends on where the aircraft is pointed.

**Overcomplicating the mental rotation.** Systematic calculation (heading + RBI angle) is more reliable than trying to visualise the whole situation at once. Practice the formula until it is automatic.

How to Prepare

The NDB Direction test rewards specific practice more than general spatial reasoning work. The question type is unusual enough that candidates who have seen it before and worked through examples have a significant advantage over those encountering it for the first time in the actual assessment.

Work through examples methodically:

1. Note the GYRO heading

2. Note the RBI bearing

3. Add them together (mod 360) to get the absolute bearing from the beacon to the aircraft

4. Match to the diagram

Speed improves with repetition. Most candidates find that after 30–40 practice questions with feedback, the process becomes semi-automatic and much faster.