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GAMEOVER
19th Oct 2010, 20:07
Hi All.

I would like if my point of view is good or not related to some questions about the following METAR and TAF. Please help. REAL METAR and TAF

XXX1 022120Z 33001KT 0100 R04R/0550N R15/0325N R22L/0300N R04L/800N FG VV002 05/05 Q1029 TEMPO 0350

XXX1 022038Z 0221/0321 13002KT 0100 FG BKN001 TEMPO 0221/0305 1000 BCFG BKN002 BECMG 0305/0307 0600 VV002 BCMG 0307/0309 9999 SCT005 SCT025

*Crew, plane(cat C) and aerodrome approved: ILS CAT I-II-III(A)

1. We can take-off and is not necessary a take-off alternate.We can use any RWY

*Aerodrome: U/S ILS CAT II-IIIA

2. We can take-off using RWY 04L but we need a take-off alternate because the prevailing visibility is 100mts and temporary 350mts. (Iīm not sure about it, because visibility along the RWY is 800mts and we could use it for CAT I) What do you think?

3. We could take-off using any RWY between 05:00 and 07:00 on the 3rd day because visibility will be 600mts and we donīt need a take off alternate from this period of time.

Thanks and feel free to consider other situations and considerations: Planning etc.

Regards. :)

cosmo kramer
19th Oct 2010, 21:27
To state the obvious you need a take-off alternate if, at time of the departure, the weather is below the applicable landing minimum.

Since you are probably sitting in the crewroom reading the weather information i would say you can disregard the metar. However, if your depature is within one hour of the issue of the metar you may use the trend of the metar. But since the trend is an improvement it must be disregarded. Hence, for your planning you must assume 100 meter vis = below even CAT3A (200 meter required) = takeoff alternate required.

In this case it make no difference, but if the metar had better values, it would be an advantage to use the trend (provided your take off is within one hour of issue).

If you take-off later than one hour after the issue of the metar, you must use the TAF. In this case you have 100 meter vis untill 7 o'clock, since you have to disregard a temporary improvement and the becoming is not in effect until the end of the interval since it's an improvent too. After 7 you don't need a take-off alternate since you have 600 meters vis = more than 550 meter required for CAT1.

In any case the weather is bad enough untill 7 o'clock that it doesn't matter if CAT3A is unserviceable or not since you will be below minima anyway. To cut it short there is no way around a take-off alternate if your departure is before 7 o'clock.

All of course assuming you have the best minima (no high mountains with consequent higher DA and hence vis requirements) and facilities.

gatbusdriver
19th Oct 2010, 21:32
if airfield is Cat2/3 then we require a Cat1 alternate within 1hr single engine flying time (around 400nm for our fleet).

As long as the airfield minima state that we can, then with the required training, lighting etc, we are allowed to depart with 125m otherwise most airfields we operate into the min RVR required for T/O is 150m.

At the end of the day the TAF means nothing to me,bar a heads up of what the weather might be like (when thinking about departing). Actuals are king!

cosmo kramer
19th Oct 2010, 21:42
This was not the question asked by the original poster, but..
gatbusdriver
if airfield is Cat2/3 then we require a Cat1 alternate within 1hr single engine flying time
...is not true (unless your company has stricter requirement than EU-OPS). Weather just have to be above applicable landing minima at take-off alternate 1 hour after departure. Therefore you may well use the minima for a CAT2/3 approach, if available.

Actuals are king!
Also not true, since the metar is just exactly that an actual. Unless of course you are able to depart at the exact time the meteorologist juts his metar down.

aerobat77
19th Oct 2010, 21:54
when you and the plane are cat IIIa approved just go...

i have flown rightseat Bae146 with CATII and at marginal weather it was always captain decision.

the only thing below catI was that the PIC makes the takeoff and no reduced thrust at takeoff.

now i ride a turbo seneca and cheyenne III leftseat catI and i have to make the decision. at this metar and taf , especially in ambulance missions, we go. not pretty but true. and funny when the doctor in the back tells us he has a hard job with responsibility...

GAMEOVER
19th Oct 2010, 22:50
Thanks for your answers.

-We have to departure within 1 hour of issue. We are in cockpit...slot, passangers on board, etc..

-I understand that we have visibility above the minimums (CAT IIIA) along the RWYs for Take-off and also for landing, havenīt we? No Flex for Take-off, and we can see more than 3 consecutive lights along the RWY centerline.

-The trend in METAR is for a period of 2 hours, (which means that in a metar threre is a forecast, isnīt it) TEMPO 350 mts

If we need an ALTERNATE, What is the use/meaning of TEMPO and visibility along the RWYs for?

Regards.

aerobat77
20th Oct 2010, 08:04
If we need an ALTERNATE, What is the use/meaning of TEMPO and visibility along the RWYs for?

you can legally file an alternate with a TEMPO forecast below your minimums but it may be a risk when you truly have to go there so calculate extra fuel when you have to hold over the alternate. on approach the RVR must be above landing minimums when you,re at the outer marker position. otherwise you have to abort from that position.

if RVR at the outer marker is in limits the final decision to land or go around is of course made at DH regardless what the metar says.

-I understand that we have visibility above the minimums (CAT IIIA) along the RWYs for Take-off and also for landing, havenīt we?

for CATIIIa you are well in the limits .

generally i must say i never saw a weather that lasts for more that a very short period which would exclude a landing with a CATIIIa aircraft and such trained crew.