# Weather Observations and Navaid Morse Code in Aviation

> Morse code identification for VOR/NDB/ILS and weather communication elements used in operational aviation contexts.

- **Subject:** 090 — Communications
- **Section:** 090-07 — Other Communications
- **Topic code:** 090-07-01
- **Last reviewed:** 2026-04-01
- **Author:** Pablo Asensio Martínez
- **HTML version:** https://pilotsyllabus.com/en/communications/other-communications/weather-observations-morse-code/

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## Morse Code in Aviation
Morse code is used in aviation primarily to identify radio navigation aids (Navaids).

### Navigation Aid Identification
Navaids transmit a continuous Morse code identifier. **A pilot must verify this identifier** to ensure they are tuned to the correct station and that the station is serviceable.
*   **Rule**: If the identifier is not heard, the navaid must **not** be used.
*   **Format**: Identifiers consist of letters from the Latin alphabet.
    *   **VOR**: Typically **3 letters**.
    *   **ILS**: Typically **4 letters**.
    *   **NDB**: Typically **2 or 3 letters**.
*   *Exam Note*: While identifiers can range from 1 to 4 letters in reality, exam questions often cite **"2 or 3 letters"** as the standard configuration for navaids in general.

### Basic Examples
*   **A**: `.-`
*   **T**: `-`
*   **E**: `.`
*   **P**: `.--.`
*   **S**: `...`
*   **L**: `.-..`

## Special Air-Reports (AIREP SPECIAL)
Pilots are required by **ICAO Doc 4444** to generate a "Special Air-Report" whenever specific severe weather conditions are encountered or observed.

### Mandatory Reporting Conditions
A Special Air-Report is required for:
1.  **Turbulence**: Moderate or Severe.
2.  **Icing**: Moderate or Severe.
3.  **Thunderstorms**:
    *   Obscured, Embedded, Widespread, or in Squall Lines.
    *   *Note*: "Embedded" means hidden within other cloud layers.
4.  **Mountain Wave**: Severe.
5.  **Volcanic Activity**: Volcanic Ash Cloud, Eruption, or Pre-eruption activity.
6.  **Surface Visibility**: Heavy duststorm or sandstorm.

For **Transonic and Supersonic** flights, the list is extended to include:
*   Moderate Turbulence.
*   Hail.
*   Cumulonimbus (CB) clouds.

### Reporting Procedure
*   Reports should be made **as soon as practicable**.
*   If a routine position report is due, the Special Air-Report replaces it.

## Turbulence Classifications
The severity of turbulence is defined by the effect on the aircraft and occupants.

| Intensity | Description | G-Load Change |
| :--- | :--- | :--- |
| **Moderate** | Moderate changes in attitude/altitude. **Aircraft remains in positive control**. Loose objects move about. Occupants feel strain against seat belts. | **0.5g – 1.0g** |
| **Severe** | Abrupt changes in attitude/altitude. **Aircraft may be out of control for short periods**. Loose objects tossed about. Occupants forced violently against belts. | **> 1.0g** |

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Free study notes from pilotsyllabus.com. Not a substitute for training at an approved ATO.