Exemption 3585 allows 121 carriers (and perhaps others) to dispatch to destinations in certain cases with weather below minimums.
What are the forecast weather minimums to be dispatched under exemption 3585? When is it required to have a second alternate listed on the release? What are the forecast weather requirements at the two alternates? What is the regulatory basis for this exemption?
Exemption 3585 is an exemption to 14 CFR 121 dispatch requirements for weather originally requested by Peoples Express. Lots of airlines have requested similar approval, and here is an example on regulations.gov for Air Transportation International.
The exemption that they asked and were approved for was:
...an exemption from §§ 121.613, 121.619(a), and 121.625 of Title 14, Code of Federal Regulations (14 CFR) to the extent necessary to dispatch airplanes under instrument flight rules when conditional language in a one-time increment of the weather forecast states that the weather at the destination, alternate airport, or both airports could be below the authorized weather minimums when other time increments of the weather forecast state the weather conditions will be at or above the authorized weather minimums.
In other words, if there is a conditional or temporary weather condition that is below minimums at the destination or the alternate airport at the flight's ETA1,2, where the flight could not normally be released, they can depart under the 3585 exemption as long as a second alternate that is above required minimums3 is filed in the flight plan and enough fuel is carried to reach the furthest alternate plus the required 45 minute reserve. There are a few other requirements too (training, manual and OpSpec revisions, etc.) but you can take a look at the letter to see them.
The exemption must be requested of and approved by the FAA for each air carrier that wants to use it.
1 The forecast weather conditions at the destination airport must not be less than one-half of the lowest weather minimum visibility value established for the instrument approach procedure expected to be used at the destination
2 The forecast weather conditions at the first alternate airport must not be less than one-half of the alternate weather minimum ceiling and visibility values specified in ATI’s operations specifications for that airport
3 With respect to the second alternate airport listed in the flight release pursuant to this exemption, the METAR, the appropriate time increment of the TAF, or any combination thereof for that airport must indicate in the main body and remarks section of the METAR or TAF that the forecast weather conditions will be at or above the alternate airport weather minimum ceiling and visibility values specified in ATI’s operations specifications for that airport
