John Carr

Like I said before, I don't EVER go 3585 without having my FOM open in front of me, which I don't right now.

I'll have to look, but I believe that the language of enough fuel to reach the most distant alternate + reserves still applies. Not necessarily the second alternate. I know, that sounds kind of confusing and counter intuitive. But also as mentioned, this is stuff about being able to legally dispatch flights under more extreme circumstances.

Fly Boy Knight

Since it's part of my recurrent studying, here it goes.

3585 Exemption Spark Notes:

Before 3585, flights would not be able to depart for an airport if the weather is forecast to be below landing mins. This is particularly annoying when the main forecast says it'll be fine but a little CONDITIONAL part of the forecast (TEMPO/PROB) says it MIGHT be below mins. Although not likely, this conditional forecast was still limiting because it is part of the TAF.

Example: Required Landing Visibility = 1/2 SM Vis
TAF FM forecast = 1 SM
TAF TEMPO line = 1/4 SM
Without 3585, you'd not be able to depart for this airport

As posted before, People's Express got tired of this crap and pushed exemption 3585.

Exemption 3585 allows you to depart for an airport even though conditional language in the forecast says it'll be below landing mins as long as...

1. The Main Body forecast (FM line... not conditional line) is above required minimums and,

2. The conditional part of the forecast that IS below landing minimums (TEMPO / PROB) is not less than ONE HALF of the required mins (See examples below) and,

3. You file a SECOND IFR Alternate.

Example 1 (from above):
Required Landing Visibility = 1/2 SM Vis
TAF FM forecast = 1 SM
TAF TEMPO line = 1/4 SM
- You can depart for this airport using 3585 as long as you have a 2nd alternate. In this case, HALF of the required 1/2 SM visibility would be 1/4 SM visibility and since the conditional line is not LESS than 1/4 SM, you are good to go.

Example 2: Required Landing Visibility = 1 SM Vis
TAF FM forecast = 1 SM
TAF TEMPO line = 1/4 SM
- You would NOT be able to depart even with 3585 because the tempo forecast is less than 1/2 of the required visibility (half of 1 SM is 1/2 SM and since the tempo is below 1/2, 3585 cannot help you)

If you do use 3585 to depart for an airport, you must have a SECOND alternate. Your second alternate must meet the same IFR Alternate Filing mins as usual ("400 : 1" or "200 : 1/2" Rules as applicable)

When determining a DESTINATION's required weather, all that is controlling is VISIBILITY. You don't have to look at ceiling when using 3585 for your destination.

That said, you can also use 3585 when filing a (FIRST) IFR Alternate. The same conditional language/second alternate requirements apply except, since BOTH ceiling and visibility are controlling when deriving alternate minimums, you must now evaluate both ceiling and visibility.

Example 1:
Derived alternate mins for your 1st Alt: 600ft Ceiling / 2 SM Vis
TAF FM Line: 700ft / 3 SM
TAF TEMPO Line: 400ft / 1 SM
- You may use this airport as an IFR alternate using 3585 as long as you file a second alternate.

Example 2:
Derived alternate mins for your 1st Alt: 600ft Ceiling / 2 SM Vis
TAF FM Line: 700ft / 3 SM
TAF TEMPO Line: 200ft / 1/2 SM
- You may NOT use this airport as an IFR Alternate even using 3585 because the TEMPO ceiling and vis are too low (less than half of 600ft and 2 SM)

You may NOT use 3585 when trying to find a 2nd Alternate. You must find a 2nd alternate without using 3585. All elements of the forecast must be above the required alternate filing minimums.

highalt41

Fly boy pretty much nailed it just remember to use half vis and half ceiling at first alt, and always have a fom handy when and if you are dispatched 3585

Airmedpilot

Exemption 3585 = Can dispatch to destination below minimums, only if not less than 1/2 lowest visibility in a CONDITIONAL statement in a TAF.

First Alternate, not less than half of the alternate minimum ceiling and visibility.

Second Alternate, METAR or TAF or any combination in main body, must be above alternate minimums for ceiling and visibility.