4.1 Direction, Wind Velocity and Aviation Time

Why Direction and Time Are Unit 1 Material

RBAK — Basic aviation knowledge for RPAS — opens with two topics that look trivial and are examined anyway: how aviation states direction and how it states time. Both are conventions rather than concepts, and both appear in every NOTAM, forecast, chart and radio call you will read as a remote pilot. Getting them wrong does not just cost a mark; it causes a pilot to plan a flight for the wrong hour or fly into a wind they misread.

Expressing Direction

Aviation states direction three ways, and Schedule 4 lists all three.

As a three-figure group. Every bearing, heading and wind direction is written and spoken as three digits, padded with leading zeros. North is 360 (spoken "three six zero"), not 0. East is 090, not 90. A wind from 070 degrees is written 070. Dropping a leading zero is the classic error — 70 is not a valid direction group.

In the clock code. Relative direction from the aircraft is given as a clock position, with the nose at 12 o'clock, the right wingtip at 3, the tail at 6, and the left wingtip at 9. "Traffic at 2 o'clock" means ahead and to the right. For a remote pilot the clock code is most useful when briefing an observer: "aircraft at your 10 o'clock, low" is faster and less ambiguous than a bearing.

As compass points. The four cardinal points are N, E, S and W; the four ordinal (intercardinal) points are NE, SE, SW and NW. Public weather forecasts and site briefings use these; aeronautical products use three-figure groups.

Heading Versus Track

Heading is the direction the aircraft's nose is pointing. Track is the path the aircraft actually makes over the ground. In still air they are the same. In wind they are not, and the angular difference between them is drift.

This matters more than most new remote pilots expect. A fixed-wing RPA flying a survey line in a crosswind must be crabbed — nose angled into the wind — to hold the line. Its heading might be 085 while its track is 090. A multirotor in position-hold mode does the same thing automatically: watch a hovering multirotor in a 15-knot breeze and you will see it tilted into the wind while its position over the ground stays fixed. The tilt is the drift correction, and the power the aircraft spends producing it is power it is not spending on endurance.

Wind Velocity

Wind velocity in aviation always means two numbers together: a direction and a speed. The direction is the one the wind is blowing from, not toward — a "westerly" blows from the west, on a heading of 270. Speed for aviation purposes is in knots.

Written as a group, 27015KT means wind from 270 degrees at 15 knots. Add a gust and it becomes 27015G25KT — mean 15 knots, gusting 25.

The trap here is the reference datum:

• Forecast winds — area forecasts, TAFs, and the wind and temperature forecasts you read in a briefing — are given in degrees TRUE.
• Reported surface winds — the ATIS, a tower or AFIS transmission, and the wind reported on a CTAF — are given in degrees MAGNETIC.

So a TAF wind of 270 and a tower-reported wind of 270 at the same aerodrome are not quite the same direction on the ground. In eastern Australia the magnetic variation is around 11 to 13 degrees east; in the west it is several degrees west. It is a small effect for a drone flying a 200-metre transect, but it is exactly the kind of distinction Schedule 4 topic 1(d) — the relationship between true and magnetic heading — is written to test.

Time: UTC and the Four-, Six- and Eight-Figure Groups

All aeronautical information is timed in Coordinated Universal Time (UTC), written with a trailing Z and spoken as "Zulu". This is deliberate: Australia spans three standard time zones and only some states observe daylight saving, so a single global reference is the only workable option for NOTAMs, forecasts and flight plans.

Schedule 4 asks you to recognise time as a four-, six- and eight-figure group:

A METAR header such as METAR YSSY 250230Z is a six-figure group: Sydney, the 25th of the month, 02:30 UTC.

Converting to and from local time

Add the offset to convert UTC to local; subtract it to convert local to UTC.

Worked example. A NOTAM activates a restricted area from 250600Z to 250900Z. You plan to fly near it at 5:00 pm on the 25th, local time, in Melbourne in January (UTC +11). Convert your flight time to UTC: 17:00 minus 11 hours = 0600Z on the 25th. Your flight starts exactly when the restricted area becomes active. Convert in the direction that puts both numbers in the same reference before you compare them — mixing local and Zulu is how pilots end up inside an active area.

A second example runs the other way. A TAF is valid 2500/2524Z. In Perth (UTC +8, no daylight saving) that period runs from 8:00 am on the 25th local to 8:00 am on the 26th local. A first-light flight at 5:30 am local on the 26th sits at 2521Z — inside the validity window, so the forecast still applies.