Filing Alternate w/changing minimums..?

[Mr. Irrelevant]

When filing an alternate, if the alternate airport is 900-2 but will be temporarily 500-1 during the period of your ETA it seems that this should prevent that airport from being eligible as an alternate. FAR 91.169 appears to spell this out pretty clearly.

A 121 captain has mentioned to me he believes that they've filed to airports with these TEMPO forecasts as long as the predominating forecast at the alternate is still 900-2. Anyone have any dissenting ideas about this? Feedback would be appreciated. Thank you.


Mr. I.

 

[regionalcap]

His 121 company has a specific exemption in their Ops Specs that allows them to do that.

 

[nosehair]

Alternate wx

Prevailing opinion is that the alternate must be forcasting the 600+2/800+2 "at the time of arrival at the alternate." a lower tempo during the eta would void the use as an alternate. That is what I remember and use in training, but honestly, I can't remember any reference. I also know that airline people get into their own routine based on old regs or individual POI's, and/or OpsSpecs, and sometimes don't conform to some of the rules+regs that we in GA have to comply with.

 

[vclean]

Part 121 OpsSpecs determine alternate mins differently. The 1 nav, 2 nav rule adds 400' & 1 mile to the approach mins at an airport served with one navaid. Add 200' & 1/2 mile for airports served by 2 (or more) navaids (navaids usually = ils). Example, airport served by 2 ils approaches, 200 & 1/2 each, alternate minimums for filing are 400 & 1. Unless otherwise stated 91 ops require 600 & 1 for a precision, 800 & 1 for non-precision.

Exemption 3585 is a method of dispatching when conditional language places airport below mins.

 

[igneousy2]

Part 121 OpsSpecs determine alternate mins differently. The 1 nav, 2 nav rule adds 400' & 1 mile to the approach mins at an airport served with one navaid. Add 200' & 1/2 mile for airports served by 2 (or more) navaids (navaids usually = ils). Example, airport served by 2 ils approaches, 200 & 1/2 each, alternate minimums for filing are 400 & 1. Unless otherwise stated 91 ops require 600 & 1 for a precision, 800 & 1 for non-precision.

Exemption 3585 is a method of dispatching when conditional language places airport below mins.

There are actually at least two possible exemptions, 3585 is probably the one your friend is citing, if main body of TAF is good, and you file a 2nd alternate, blast off.

Another, I forget the number, allows you to ignore the TAF for short duration flights if current conditions indicate that the weather will be okay at your time of arrival (you can't just look at the METAR, you've got to look at the trend in the METAR)

Later

 

[dispatchguy]

When I am dispatching off the METAR for 121, I have to consider the TAF - I cant just ignore it as if its not there. If the TAF sez TEMPO 1/2 SM, and the METAR is severe clear - he'll still get an alternate listed. If its determining whether we can launch - I'll look at other things to determine how much faith I have in the TAF and METAR - and still add an alternate, then go if I like the trend.

There is no sicker feeling then blasting off for an airport off the METAR alone, no alternate, and your destination starts reporting visibility in fractions....