Shallow Fog

[Toecutter747]

I have a vague memory that a TAF with MIFG doesn't impose an alternate requirement - does anyone have an AIP (or other) reference to support this?

I have searched both the AIP and Pprune to no avail.

Thanks for your input.

[Capt Claret]

Toecutter747

Can't find a reference either, but the definitions of Fog & Mist from the BOM site are:

Fog: Suspension of very small water droplets in the air, reducing visibility at ground level to less than a kilometre.

Mist: Similar to fog, but visibility remains more than a kilometre.

I would have thought that its the reduced visibility, as opposed to fog, as such, that requires the alternate.

As an example, a DRW ATIS earlier this year had a component, "cloud base 1500, visibility 1500m in fog"
Couldn't have been fog if the vis was 1500m. If the vis was 1500m then the aerodrome was open for landings and an alternate wasn't required.

[Keg]

If I recall correctly, the MET part of the Jepp World Wide Text defines shallow fog as 'less than six feet in height'. I'd have to look it up again to be sure.

[Toecutter747]

Thanks guys - that make sense now. As you say it's low vis that creates the alternate requirement, not the presence of any particular weather phenomenon.

[Dookie on Drums]

Yes, no alternate requirement with shallow fog. Don't have the reference at hand sorry.

[Transition Layer]

Personally, I think you'd have to be pretty game not to carry some sort of alternate or contingency fuel based on a forecast of shallow fog only. How many times have we all seen the shallow fog become not so shallow in a matter of minutes?

Sure, rules are rules but there's no subsitute for common sense.

TL

[karrank]

AIP ENR 1.1 - 88 says it is all about the visibility. If unforecast MIFG appears on a SPECI I treat it as a hazard alert coz it will probably develop into something else they didn't forecast either! If the standard issue TAF says MIFG you can supposedly ignore it if the VIS is OK. Not sure I would.

[Dookie on Drums]

All well and good carrying a bit extra juice as I would as well but the operative word is "requirement".