Recently when I pulled up the TAFs on my computer I had a surprise. Тhe format of the coded aviation forecast was a little different.
TAF CYUL 020238Z 0203/0224 21010KT P6SM BKN025 BKN040 TEMPO 0205/0209 6SM -SHRA BKN020
BECMG 0208/0209 22017KT
FM020900 22017KT P6SM BKN025 BKN040 TEMPO 0209/0212 3SM -SHSNRA
FM021200 24020G35KT P6SM OVC015 TEMPO 0212/0218 3SM -SHSN SCT015 BKN030
FM021800 25020G30KT P6SM BKN030
RMK NXT FCST BY 020600Z=
I'm used to subtle changes from region to region. Even though there is a nationwide standard, itself a subset of the international standard, individual stations and centres develop quirks based on the preference of the old guy that the newbies copy. For example, many places in Canada have variable direction winds, but there's only one place I can think of that frequently uses the codes to show the amount of variation. But this TAF change is a big difference, not a little quirk. I suspected a nationwide change.
Previously that would have been coded like this:
TAF CYUL 020238Z 020324 21010KT P6SM BKN025 BKN040 TEMPO 0509 6SM -SHRA BKN020
BECMG 0809 22017KT
FM0900 22017KT P6SM BKN025 BKN040 TEMPO 0912 3SM -SHSNRA
FM1200 24020G35KT P6SM OVC015 TEMPO 1218 3SM -SHSN SCT015 BKN030
FM1800 25020G30KT P6SM BKN030
RMK NXT FCST BY 06Z=
Those who don't know how to read TAFs are probably laughing at me calling it a big difference. But there's a meaning to standard and that is that one guy doesn't get to use a slash when someone else isn't. I checked other regions to see if the change was everywhere. And it is. Here's Winnipeg.
TAF AMD CYWG 020428Z 0204/0224 19020G30KT P6SM BKN050 OVC070 TEMPO 0204/0207 1SM -SNPL VV006
FM020700 20020G30KT P6SM SCT070 TEMPO 0207/0212 P6SM -SN BKN040
FM021200 28020KT P6SM OVC030 TEMPO 0212/0224 3SM -SHSN OVC015
BECMG 0216/0218 32025G35KT
RMK NXT FCST BY 020600Z=
I could see the difference of course: the old validity block 020324, meaning valid beginning the 2nd day of the month at 0300z up until the 2nd of the month at 2400Z was being made more explicit with the day of the month specified for both the beginning and ending time: 0203/0224. Up until now pilots have been considered smart enough to figure out that a validity of 022206 meant that the first time was in on the 2nd day and the second time on the following day. It's kind of like if you're told "we're having a party on the 2nd of March, from 8 pm to at least 2 am, so drop in any time." You know not to turn up at 2 am on the 2nd of March. Clearly the 2 am being referenced is very early on the 3rd.
But why were they changing it? If anyone believed that people were having accidents because they couldn't tell what day the TAF was for, either they or the accident-prone people were probably attending 2 am parties before making decisions. And if they were going to change that for clarity, then why not make other obscure parts of the TAF clearer? And how do you offset the risk to people who are used to the old codes and make errors because things are being rearranged on them?
I checked the amendments in the latest AIM issue and sure enough it tells me:
Effective November 5, 2008, the format of the Canadian TAF will be modified in accordance with Amendment 74 to ICAO Annex 3, to extend the validity period to a maximum of 30-hr. To accommodate this extended validity period, a two-digit date will be added to all times in the TAF.
So TAFs might someday cover thirty hours instead of the twelve or twenty-four they cover now. That makes sense. Curiously, Vancouver seems to already have a longer TAF. The last two issued have begun:
TAF CYVR 020240Z 0203/0306
TAF CYVR 020538Z 0206/0312
That's twenty-seven and thirty hours, respectively. I suppose that's for flight planning in long flights from Australia and New Zealand. Recent accidents for Qantas and Air New Zealand have nothing to do with trans-Pacific weather, but the latter is shocking enough to be worth mentioning even on such a poor segue. The NZ articles contain some of the most ridiculous aviation speculation ever written, but some basic facts are there, and a picture. I'll probably do a post on it when more information is available.