Weather reaches the cockpit as a fixed sequence of items in fixed units, and this lesson reads that sequence twice: once as the aerodrome report behind the METAR and the ATIS, once as the aircraft's own observations flowing the other way. The measurement physics lives in the meteorology course; here the syllabus wants the report's shape, sources and decoding.
What an aerodrome weather report contains
The report walks the same order every time, each item in its own units:
Wind — direction and speed with any significant variation; the METAR gives direction in degrees true, while the wind spoken by the tower or the ATIS is in degrees magnetic, matching the runway numbers; speed in knots, or metres per second where a State so chooses.
Visibility — metres, as a four-digit group up to 9,000 m, with 9999 meaning 10 km or more.
Present weather — the coded phenomena: rain, snow, fog, thunderstorm and their intensities.
Cloud — amount as FEW, SCT, BKN or OVC (one to two, three to four, five to seven, eight oktas), height in feet, and type only for CB and TCU, the two clouds the report names.
Temperature and dew point — whole degrees Celsius.
Pressure — QNH, and where provided QFE, in whole hectopascals.
Supplementary information — recent weather, wind-shear warnings, runway conditions, aerodrome warnings, restrictions and obstructions.
One word can replace the middle of the report. CAVOK is transmitted when, simultaneously: visibility is 10 km or more; there is no cloud below 5,000 ft or below the highest minimum sector altitude (MSA), whichever is greater, and no CB or TCU at any level; and there is no significant weather. It stands in for the visibility, weather and cloud groups together.
VOLMET and ATIS: where in-flight weather comes from
Two broadcast services carry aerodrome weather to an aircraft in flight, and each has its situation:
VOLMET — meteorological information for aircraft in flight: scheduled or continuous broadcasts of reports for a group of aerodromes, on HF for the long-range routes and VHF regionally. The situation that calls for it: en route, wanting destination and alternate weather without engaging anybody in a dialogue.
ATIS, the automatic terminal information service — the repetitive broadcast of one aerodrome's arrival and departure information: runway in use, transition level, essential operational information and the weather. The situation: approaching or leaving that aerodrome, pulling the routine numbers off the broadcast so the controller need not read them to every aircraft.
D-ATIS — the same ATIS delivered by data link as text, requested and read instead of listened to, with the same content and the same edition letter.
Every ATIS edition carries a phonetic letter, information ALFA, BRAVO and onward through the day, and the pilot reports the letter on first contact, proving which edition was heard; an outdated letter earns the changed items by voice. All three services are broadcasts in the first lesson's exact sense: transmissions addressed to no specific station.
Check you understood
Three questions from this lesson — one straightforward, one that applies it, one that pushes a little further. Nothing is recorded, and you can draw a new set as often as you like.
1. Warm-up
In an aerodrome weather report, cloud amount is given as:
2. Applying it
An ATIS broadcast ends: 'acknowledge information OSCAR on first contact.' The pilot complies by:
3. Pushing it
Routine air-reports are required from an aircraft when:
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What you are looking at: one ATIS broadcast, line by line, with the items a crew acts on called out. The edition letter opens the broadcast and is reported on first contact; the runway in use and transition level set up the arrival; the wind is magnetic, unlike the METAR's true reference, so it maps straight onto the runway numbers; and the QNH sits on the always-read-back list of the read-back lesson once a controller passes it by voice. Decoding a D-ATIS is the same exercise with the ear swapped for the eye.
The aircraft reports back: AIREPs
Observation also flows out of the cockpit. Routine air-reports are made when reporting by data link, en route, at the times position reports are required and ADS-C is not doing the job automatically. The form has three sections: position information, which is obligatory (only its next-position elements may be omitted, by regional agreement); operational information, the estimated arrival time and endurance, sent only when the operator asks or the commander judges it necessary; and the meteorological section, wind, temperature, and turbulence and humidity when available.
Special air-reports are different: they are made by all aircraft, whenever the conditions are met, voice or data link alike. The trigger list:
Moderate or severe turbulence, moderate or severe icing, or severe mountain wave — note where the thresholds sit: turbulence and icing trigger at moderate, mountain wave only at severe.
Thunderstorms, with or without hail, when obscured, embedded, widespread or in squall lines.
Heavy duststorm or sandstorm, volcanic ash cloud, or pre-eruption volcanic activity and eruptions — the atmosphere's own hazards to everyone behind you.
Runway braking action not as good as reported — the one trigger observed on the ground roll rather than in the air.
Transonic and supersonic flight adds three of its own: moderate turbulence, hail, and cumulonimbus clouds.
What the exam asks
The report's item-by-item contents, the CAVOK conditions, the two broadcast services and the special-report trigger list carry the marks. The overview, following the learning objectives:
List the contents and units of aerodrome weather reports, including CAVOK