Conditional Weather

[Lindy]

Had a "discussion" the other night about CONDITIONAL Weather and whether or not legal to fly:

Forecast had a TEMP Condition at the ETA of 1/4 mile vis (the approaches required 1800RVR) and the current conditions were 1/4 vis. Was it legal to launch?

The discussion centered around whether Conditional weather was controlling.

This is 135 OPS, so we don't have the "Second Alternate" Rule and/or Exemption. (That was a good discussion btw...).

 

[cvsfly]

Yes, it is controlling, but you can use a "combination" of reports.

 

[501261]

Nope, you can't launch.

Here's what the Aviation Inspector's Handbook says about conditional weather:

1407. POLICY ON CONDITIONAL PHRASES IN REMARKS PORTION OF WEATHER FORECAST.
A. Weather forecasts provided by the National Weather Service (NWS) and other sources often have conditional phrases such as "occasional," "intermittently," "chance of," or "tempo" in the remarks portions of the forecasts. These phrases supplement the main body of the forecast by indicating the probability of changing conditions during the forecast period. These modifying phrases, used in the remarks portion of a terminal forecast (FT), indicate the weather conditions for an area within 5 nautical miles of a runway complex. Certain regulations concerning the selection of destination and alternate airports require that "weather reports or forecasts, or any combination thereof, indicate that the weather conditions will be at or above..." the minimum weather conditions specified in those regulations. The FAAs Office of Chief Counsel has consistently interpreted these regulations to mean that the worst weather condition in any of the reports or forecasts used to control a flight movement is the controlling factor. These interpretations make the remarks portion of a forecast as operationally significant as the main body of the forecast. Therefore, it is FAA policy that the worst weather condition in the main body or the remarks portion of a terminal forecast, as well as any weather report used, is the controlling factor when selecting a destination or alternate airport.
B. This policy must be applied when determining compliance with the following regulations:
* FAR 121.613 - Dispatch or flight release under IFR or over the top
* FAR 121.615 - Dispatch or flight release over water: Flag and supplemental air carriers and commercial operators
* FAR 121.619 - Alternate airport for destination: IFR or over the top: Domestic air carriers
* FAR 121.621 - Alternate airport for destination: Flag air carriers
* FAR 121.623 - Alternate airport for destination; IFR or over the top: Supplemental air carriers and commercial operators
* FAR 121.625 - Alternate airport weather minimums
* FAR 135.219 - IFR: Destination airport weather minimums
* FAR 135.223(b) - IFR: Alternate airport requirements

 

[Lindy]

Thanks!!

I didn't have access to the handbook and couldn't find a cite regarding the rule.