Using a TEMPO to determine if altrn is required

[JET1977]

Hello

Based on the TAF below, I am wondering if a destination alternate would be required based on the 1-2-3 Rule. I have heard both sides make the case. Any Dispatchers out there that can provide information regarding using the TEMPO portion of the TAF to decide whether or not to place an alternate in the flight plan.

For this scenario, the aircraft would be arriving at 01Z

TAF AMD Kxxx 212050Z 2121/2224 27014G21KT P6SM BKN010
TEMPO 2123/2203 SCT010
FM220400 27015KT P6SM BKN010
FM220900 26009KT P6SM OVC010
FM222100 26015KT P6SM OVC010

 

[brokedash]

CYA and go with most restrictive. In this case the main body is what is forecast during the valid hours, the tempo is indicating a change that might occur during the hours stated. Put the alt on, remember 1-2-3 is an exemption, not a rule, 121 states all flights will have an alternante, unless 1-2-3 applies, in this example it doesn't.

 

[CA1900]

Short answer is no, you don't need an alternate. The arrival is during the TEMPO window, which is controlling during that time period it indicates. It's only in the TEMPO group because it will last less than half of the time period of the main body. It carries every bit as much weight as the main body, and any conditions listed supersede it during the time window.


I can't find an FAA source, but here's an NOAA one:
http://www.crh.noaa.gov/lot/aviation/tafcode.php


The TEMPO group is used for any conditions in wind, visibility, weather, or sky condition which are expected to last for generally less than an hour at a time (occasional), and are expected to occur during less than half the time period. The TEMPO indicator is followed by a four-digit group giving the beginning hour and ending hour of the time period during which the temporary conditions are expected. Only the changing forecast meteorological conditions are included in TEMPO groups. The omitted conditions are carried over from the previous time group.

 

[Mr. Johnson]

Short answer, yes. Lowest forecasted weather in a time period must be considered.

 

[onewithwings]

CYA and go with most restrictive. In this case the main body is what is forecast during the valid hours, the tempo is indicating a change that might occur during the hours stated. Put the alt on, remember 1-2-3 is an exemption, not a rule, 121 states all flights will have an alternante, unless 1-2-3 applies, in this example it doesn't.

I can't tell you how many times I have to explain exactly that! It's an exemption. The rule is to always carry an alternate to destination under Part 121 rules....unless it meets the exemption.

Yes, go with the most restrictive. If it was the other way around (being in the tempo as opposed to the main body)....still carry an alternate due to "conditional language".

Just My Two Cents

 

[Subpartu]

Short answer is no, you don't need an alternate. The arrival is during the TEMPO window, which is controlling during that time period it indicates. It's only in the TEMPO group because it will last less than half of the time period of the main body. It carries every bit as much weight as the main body, and any conditions listed supersede it during the time window.

Actually you do need an alternate. From 8900.1 Vol 3, Ch 26, Section 1 paragraph 2049:
"...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."

And in this example the ceiling would be 1000' during the entire TAF period, but temporarily between 23 and 03Z there will not be a ceiling. We just don't know when that BKN layer will change to a SCT layer.

If the TAF were to read this: (changed BKN to SCT and SCT to BKN)

TAF AMD Kxxx 212050Z 2121/2224 27014G21KT P6SM SCT010
TEMPO 2123/2203 BKN010
FM220400 27015KT P6SM BKN010
FM220900 26009KT P6SM OVC010
FM222100 26015KT P6SM OVC010

and the arrival time is 0100Z, then the statement of "It carries every bit as much weight as the main body" would apply and an alternate would be required because of the TEMPO ceiling.

 

[OneBadLT123]

The main body of the forecast is controlling. Therefore yes you would need an alternate. (unless your carrier has a 1-1-2 or 1-1-3 opspec exemption)

 

[fltdspx]

decided to delete my post