We're moving into the SNOWTAM now — Page 360, Lesson 483

We're moving into the SNOWTAM now. This is the specific message format for winter operations, and it's a big one for your exams. Let's start with the description. A SNOWTAM is the message used to report information concerning snow, ice, and standing water on aerodrome pavement areas. So, any time you have those contaminants on the runway, this is the format that carries that information. And here's a critical limitation to remember: its validity is a maximum of 24 hours. After that, it's no longer current, and a new one needs to be issued if conditions persist. Now, the contents. The full requirements are detailed in Appendix 2 to Annex 15, but I'll walk you through the fields you need to know. There's a key rule first: if a field is not applicable, it's left blank and nothing is transmitted. So you only send the fields that actually apply. Let's go through them letter by letter. Field A is the ICAO aerodrome locator code. For example, EGLL for Heathrow. That's the four-letter ICAO identifier. Field B is the date and time of observation, given in UTC. Always UTC, never local time. Field C is the runway designators. For example, 27R. That tells you which runway the report is for. Field D is the cleared runway length, but only if it's less than the published length. It's given in metres. So if the full runway is published as 3,000 metres but only 2,500 metres are cleared, you'd report 2,500. Field E is the cleared runway width, again only if it's less than the published width, in metres. And there's a special note here: if the cleared width is offset, you add an L or an R to indicate which side it's offset to. Field F is the deposits over the total runway length. This is a list of possible conditions, and you report which one applies. Let me read them all out: Nil, which means clear and dry; Damp; Wet or water patches; Rime or frost covered; Dry snow; Wet snow; Slush; Ice; Compacted or rolled snow; and finally, Frozen ruts or ridges. Each of these is a distinct state, and you need to know them all. Field G is the mean depth, in millimetres, for each third of the total runway length. So you split the runway into three equal sections, and you report the mean depth of the contaminant for each third. Field H is the friction measurement on each third of the runway, along with the friction measuring device used. And this is where Figure 18.1 comes in — the surface friction reporting codes. Let me walk you through that table, because you need to know these codes cold. The friction coefficient is measured, and it maps to an estimated surface friction description and a code number. If the friction coefficient is 0.4 and above, the estimated surface friction is Good, and the code is 5. If it's 0.39 to 0.36, that's Medium to good, code 4. If it's 0.35 to 0.3, that's Medium, code 3. If it's 0.29 to 0.26, that's Medium to poor, code 2. If it's 0.25 and below, that's Poor, code 1. And there's one more special case: if the reading is unreliable, you don't assign a number from that scale — you use code 9, and the description is simply Unreliable. So the code is what actually gets transmitted in the SNOWTAM. The friction coefficient range tells you which code to send. Now, before we go further, let me tie this back to the earlier part of the chapter, because the SNOWTAM is part of the broader NOTAM system. Remember, a NOTAM is for information that's operational in nature. And there's a rule I want to make sure you have: when a NOTAM concerns unserviceability of navigation aids, facilities, or communication services, it should give an estimate of the period of unserviceability, or the time at which restoration of service is expected. So you're always telling the recipient when things will be back. There's also the excluded matter rule. A NOTAM should not include information of non-operational importance. That includes partial failures of lighting or ground systems, routine maintenance, any work in progress on runways not in use, or if the equipment can be rapidly removed from the duty runway. Also excluded: temporary obstructions, local area parachuting, and the lack of apron marshalling services and road traffic control. So if it's not operationally significant, it doesn't go in a NOTAM. On distribution: NOTAMs are distributed to addressees for whom the information is of direct operational significance, and who would not otherwise have at least seven days prior notification. So the seven-day rule is key — if they'd already know from another source at least a week ahead, they don't need a NOTAM. The aeronautical fixed telecommunication network, or AFTN, which is the teleprinter network, is used for NOTAM distribution whenever practicable. And when NOTAMs are sent by means other than the AFTN, a six-digit date-time group is used, indicating the date and time of filing the NOTAM, plus the identification of the originator, and that goes preceding the text. Then there are NOTAM checklists. A checklist of current NOTAM is issued at intervals of not more than one month. And that checklist must refer to the latest AIP amendment, AIP supplement, and the internationally distributed AICs — those are Aeronautical Information Circulars. On errors: when errors occur in a NOTAM, a NOTAM with a new number is issued to replace the erroneous one, or the erroneous NOTAM is cancelled and a new NOTAM is issued. So you never just edit the old one — you replace or cancel and reissue. And finally, the summary. A monthly printed plain-language summary of NOTAM in force is to be sent by the most expeditious means to recipients of the IAIP — that's the Integrated Aeronautical Information Package. This summary includes the indications of the latest AIP amendments, the checklist of AIP supplements, and the AICs issued. So to bring it all together: the SNOWTAM is your winter-specific message, valid for a maximum of 24 hours, with those lettered fields A through H covering location, time, runway, cleared dimensions, deposit type, depth per third, and friction codes. And the friction codes from Figure 18.1 are what you'll be tested on — make sure you can map each coefficient range to its code and description.