Weather Observations and Navaid Morse Code in Aviation

090-07-01Pablo Asensio Martínez2026-04-012 min

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