3.2 Time and Date

3.2 Time and Date

Quick Answer: RIC-21 §5.2 requires the 24-hour clock with time as four figures (HHMM). Prefer UTC (also called GMT or Zulu). Use local time only if operations stay in one zone. When date and time are both required, send a six-figure group DDHHMM, often with a zone letter (for example, 161200 E).

Time groups appear in flight plans, weather, position reports, and almost every ATC or flight-service exchange. The ROC-A exam expects you to convert 12-hour clock times into four-figure form, know midnight options, prefer UTC, and build six-figure date-time groups.

Twenty-four hour clock and the four-figure group

The twenty-four hour clock system should be used to express time during radiocommunications. Time should be expressed and transmitted by means of four figures:

• The first two figures denote the hour past midnight (00–24 conventions as below).
• The last two figures denote the minutes past the hour (00–59).

There is no “a.m.” or “p.m.” on the air. Ambiguity between 1:45 a.m. and 1:45 p.m. is removed by writing 0130 vs 1345.

Official conversion table (RIC-21 examples)

Memorize these exact official examples—they are classic exam material:

Midnight note: RIC-21 explicitly allows both 2400 and 0000 for midnight. Do not invent a third form. In continuous logging, operators often treat the end of a day as 2400 and the start of the next day as 0000; for the exam, either official form is correct when the circular lists both.

Leading zeros: Early morning hours keep the leading zero (0045, 0130). On the radio you will later pronounce those digits under §5.4 (for example, zero zero four five / zero niner two zero zulu)—but the written/time-group structure is always four figures for time alone.

How to convert any 12-hour time

1. If the time is a.m. and not 12:xx, keep the hour as-is with a leading zero if needed: 9:05 a.m. → 0905.
2. If the time is 12:xx a.m. (midnight hour), the hour is 00: 12:20 a.m. → 0020.
3. If the time is p.m. and not 12:xx, add 12 to the hour: 4:30 p.m. → 16:30 → 1630; 11:45 p.m. → 2345.
4. If the time is 12:xx p.m. (noon hour), the hour is 12: 12:00 noon → 1200; 12:15 p.m. → 1215.

Practice until conversion is automatic—examiners often mix a.m./p.m. traps with the official example set.

Prefer UTC (GMT / Zulu)

RIC-21 states that time is usually referenced to one standard time zone, Coordinated Universal Time (UTC), often referred to as:

• Greenwich Mean Time (GMT), or
• Zulu time (Z)

The purpose is explicit: to avoid confusion between different time zones. Canadian aviation routinely crosses provincial boundaries and operates with aircraft and ground stations that may sit in different offsets (and daylight-saving shifts). UTC is the common reference.

On the air and in written groups, a trailing Z marks Zulu/UTC (for example, 0920Z, spoken under number rules as “zero niner two zero zulu”—see §5.4). The letter Z is the ITU zone designator for UTC; other letters mark other zones when local or named civil zones are used.

When local time is allowed

Local time may be used when operations are conducted solely in one time zone. If every station in the exchange shares the same zone and there is no risk of cross-zone confusion, local civil time expressed in 24-hour four-figure form is acceptable under RIC-21. The moment operations span zones—or you are preparing for standard aeronautical practice—prefer UTC.

Exam trap: “Local time is always preferred in Canada” is false. The guide prefers a single standard (UTC) and only carves out the single-zone exception.

Date and time: the six-figure group

Where the date as well as the time of day is required, use a six-figure group:

Optionally, a zone letter follows the six figures to show which time standard the HHMM portion uses.

Official RIC-21 examples

Break them down:

• 161200 E → day 16, time 1200 (noon), zone letter E (Eastern Standard Time in the example).
• 240245 P → day 24, time 0245 (2:45 a.m.), zone letter P (Pacific Standard Time in the example).

The day is always the calendar day of the month in the six-figure construction shown by the guide; the zone letter qualifies the clock standard of the time portion. Do not insert separators on the air—speak the digits (and zone word/letter as required by procedure), but for study remember the compact written form DDHHMM + zone.

Building your own six-figure groups

Example practice:

• 3:15 p.m. UTC on the 9th → time 1515 UTC → 091515 Z (if marking Zulu).
• 7:00 a.m. local on the 1st in a single-zone local operation → 010700 plus the appropriate local zone letter if required by the message format.

If only time is needed, stay with four figures. Use six figures when the date is required as well.

Time spoken on the frequency (preview of §5.4)

Section 5.2 defines the numeric group. Section 5.4 shows how those digits are spoken. For study continuity:

You will also see times embedded in larger transmissions (for example, “OVER OTTAWA AT TWO EIGHT”). Always map spoken digit strings back to the four- or six-figure structure from §5.2.

Common exam traps

Operational mindset

Using one time standard prevents the classic safety error: two stations acting on the “same” clock reading that actually differs by three hours. UTC is the aeronautical lingua franca. When your examiner asks why Zulu is preferred, answer with the circular’s own words: to avoid confusion between different time zones.

Official source

RIC-21 Issue 3, section 5.2 Time and Date, ISED / Industry Canada study guide for the ROC-A. Confirm any future amendments on the ISED RIC-21 page before exam day if your training materials are old.