Prediciting CAT and use of W anti ice

[hifly787]

Hi All
It is said that the Wx radar cant predict CAT but can be expected by referring to Wx charts and pilot reports. My question is how exactly do you use a Wx chart to predict CAT ?
My second question is at night at high altitude cruise how do you determine level of icing is enough to switch on W Anti Ice and for how long do you keep it on ?
Thanks

[BOAC]

8800 hours on 737 and A320, ATPL and you ask?:eek:

[hifly787]

Sorry BOAC I meant apart from the obvious ones . Lost my rating 6 years ago and just wanted to know if anything new has come up.

[BOAC]

Cannot help. 5 years out of touch but not aware of anything "apart from the obvious ones".

Change your 'current aircraft type' perhaps?

[RAT 5]

…..at night at high altitude cruise how do you determine level of icing is enough to switch on W Anti Ice and for how long do you keep it on ?

I'll assume 'high altitude' is >FL300. Up there it is highly unlikely to encounter anything other than very small ice crystals; unless you choose to fly in some horrendous CB. Thus ice accumulation on the upper surface would be unlikely. 2ndly; WAI is more a de-icer than anti-icer. Thus you would allow any ice to build up on the leading edge and then crack it off with a short burst of WAI. Leaving the thing pumping hot air along the LED's could encourage flow back and could lead to severe unwanted consequences.

[Meikleour]

hifly787: I always found that if you keep an eye out for a change in SAT over a short time - this was a good predictor of CAT. And no, I will not give specific figures lest the "PPRUNE experts" jump on me - but 4-5C in less than 5 mins is a good starting point.

[BOAC]

Don't forget the OQ wasMy question is how exactly do you use a Wx chart to predict CAT ? - I cannot think of a suitable answer there apart from basic ATPL Met and the little ^ on the chart?

[hifly787]

BOAC
Basic ATPL MET has changed a lot since when you and I passed those papers
Any Harm in trying to keep learning. There are some real experts here sometimes !

[BOAC]

Agreed, but the chart is a chart. Meikleour has given you a good guide to the well-established 'what is actually happening' routine.

[Lord Spandex Masher]

hifly787: I always found that if you keep an eye out for a change in SAT over a short time - this was a good predictor of CAT. And no, I will not give specific figures lest the "PPRUNE experts" jump on me - but 4-5C in less than 5 mins is a good starting point.

...and also tying in with that if you're approaching a jet stream from the north, or is it the south(?) I can never remember, it's likely that you will encounter CAT.

[BOAC]

if you're approaching a jet stream from the north, or is it the south - neither:) Would give you real problems with a north-south jet...........

My fading memory tells me the CAT is strongest on the 'cold' side of the jet (I'll grant you 'north' for a 'traditional' polar stream in the northern hemisphere:)) next to and just underneath the core of the Jet.

[Lord Spandex Masher]

This is what I meant!

Any CAT is strongest on the cold side of the jet stream

SKYbrary - Clear Air Turbulence (http://www.skybrary.aero/index.php/Clear_Air_Turbulence)

So in the Northern hemisphere approaching from the north and vice versa.

Edit; Roger your edit.

[hvogt]

Although the OP's first question was about charts, the following link might also be of interest:

DLR Portal - News - Greater safety in aviation ? detecting turbulence in advance (http://www.dlr.de/dlr/en/desktopdefault.aspx/tabid-10081/151_read-7615/year-all/#/gallery/11637)

[tom775257]

Regarding RAT 5 and use of WAI. I would suggest this is very type specific, on the A320 the WAI is evaporative and (theoretically at least) will not cause flow back; thus can be used as both de and anti ice.

[despegue]

The Polar side of a Jetstream tends to have more CAT.

Wing Icing can happen at basically any TAT under 5 degrees C, but is most active between -5 en +3 degrees Celcius.
On b737, just checking the wioer bolt is NOT a good practice to detect wing ice by the way! Wing icing occurs much sooner than accretion on the bolt.

[Meikleour]

LSM: The old yardstick used to be:

In the northern hemisphere, when approaching a jet core - watch the SAT
If it is climbing (ie. getting warmer) then the quickest way out of the turbulence is to climb. If it is getting colder then descend.
Reverse for the southern hemisphere.

I personally found the charts to be so vague and non specific as to be almost useless!