ATPL met question 2

[xxRED BARONxx]

Hey guys got another weird question that I got wrong and I dont understand the answer..

An aircraft is experiencing strong westerly winds while tracking 180 degrees at FL370 over continental australia. The TAT is increasing.

To minimise the effects of encountering CAT the pilot should:

a) Descend
b) Climb
c) Alter track to the left
d) Alter track to the right


an explination would be much appreciated!!

thanks

[aviator777]

Relates to CAT near jetstreams. Don't have notes nearby but read up on temp change near core of jetstream for an understanding.

[alphacentauri]

I don't have my ATPL MET book in front of me but do remember this question and can give some guidance on where to look for a more informed answer.

It has to do with the cross section of a jetstream. Jetstreams run from WEST to EAST and so if you are flying towards the south you are probably flying into a jetstream. (hence the increasing westerly wind).

The clue as to where the CAT lies is in the increasing TAT. If I remember correctly increasing TAT means you are near the top of the jetsream and in the southern hemisphere the CAT is encountered on the top southern side of the jetstream. So in this case you would want to descend to avoid the CAT

I know its not the complete answer but hopefully has given you a hint as to the correct answer....I am sure this was covered in my notes so it should be in yours.

Cheers
Alpha

[Capt Fathom]

in the southern hemisphere the CAT is encountered on the top southern side of the jet stream

CAT is generally encountered on the lower, southern side of the jet stream.

The increasing TAT has me stumped. TAT is related to the OAT and your IAS.
But closely follows the OAT up and down. Don't know why it would be increasing whilst heading south?

Simply put, the jet forms where the warm air and the cold air meet, with the warm air to the north, and the cold air to the south (southern hemisphere). It is well depicted on the BoM SigWx Charts. You can see the different heights of the tropopause shown in boxes on the chart.

[alphacentauri]

Indeed it is. Sorry Capt Fathom I stand corrected.

As to the increase in TAT, does OAT increase as you approach the jetstream from the north (warm air), and then decrease as you head further south( cold air)?

[WannaBeBiggles]

OK it's been a little while since I've done AMET but this is what I remember.

There are a number of things to note in this question.



An aircraft is experiencing strong westerly winds while tracking 180 degrees at FL370 over continental australia. The TAT is increasing.

So break the question down. You're up high with a strong westerly, so chances are you are in a JetStream (not associated with a front), more than likely the sub-tropical jetstream.

Where will you find a jetstream? Running perpendicular along the tropopause and stratosphere / upper troposhpere. What does temperature do when you're in the tropopause, stratosphere and troposphere?

What do these do when you are tracking North and what do they do when you're tracking South?

i.e. If I fly in a straight line at the same level to the South, will the jetstream be tropopause be at higher or lower level, thus increasing or decreasing the likelihood of encountering CAT.

Know these things and you'll nail those questions, I had a number of those during my exam.

[xxRED BARONxx]

The answer is (b) climb... I think its the "TAT" that is causing confusion, I think we can all agree in the question we are flying through the tropical jetstream, so when flying through a jetstream the OAT is constant... but does the TAT increase? "To minimise the risk of encountering CAT the pilot should?" I think that we can agree that descending is not an option because the CAT area is on the polar side(where we are tracking) below the jet core... I guess climbing would minimise the risk of encountering the CAT as we would be climbing out above the jetstream above the CAT on the polar side... changing track to left or right wouldnt really do anything I guess so by RTFQ rationale the most logical answer could be climb even tho the scenario is quite strange. But I still dont know why the TAT is increasing while we are maintaining FL370 whilst in the jetstream.. if anyone can answer that Ill take my hat off to them!

[Oktas8]

Not an expert, just an ATPL holder...

It occurred to me that the TAT might be increasing because we are travelling from an area of higher pressure (QNH) towards lower pressure - as we cross the front. At constant flight level, we will therefore be descending, therefore OAT and TAT will be increasing.

[rocket66]

Right, I had this question on my ATPL Met eggs and ham the other day. I chose 'climb' but it did appear in my KDRs.

From what I understand Jetstreams are formed by the fact that the Tropopause above the equator is colder and higher (-70deg 18klms high). At the poles the Tropopause occurs a lot lower and is a lot warmer (-30deg 8klms high).

Above these two points is the isothermal layer. The reletively warm polar air naturally begins to flow toward the equator and the colder air above the equator begins to move south toward the pole. This causes a sort of figure of 8 flow of the winds forming the jetstreams.

So if your flying south and the TAT (TAT=OAT + some of the temp rise due to aircraft froward movement) is rising I would sayyour headed for the jet core. Because CAT occurs on the lower Ploar side of the jet core I would climb??? But like I said I still got the question incorrect who knows what thier logic is :rolleyes:


Rocket

[xxRED BARONxx]

I just did the exam today and got a question similar, something like:

Q: High level jets flow from West to east, you are flying south over aust at FL 300 and the oat is steadily decreasing, where are you in relation to the jetstream?

A: Above/Just below/Significantly below/In the Jet

Put down just below and didnt come up on my KDR...

Some of the icing questions are so absurd.. had one like:

Q: You are flying in light/mod turbulence through a thick altostratus cloud at -3 OAT... what type of ice is most likely?

A: Rime/a combination of rime and clear/clear/none...

I put combination of rime and clear but got icing on my KDR :ugh:

And another one

Q: Which situation would lead to the most rapid build up of ice?

A: Flying through cumulus @ -5deg/Flying through cumulus @ -15deg/stupid answer/stupid answer

I put flying through at -15 because rime ice forms more "rapidly" than clear ice but got icing on my KDR again :ugh:

[Xcel]

Good tip is draw a line with a step. Place a circle at the step. That's your jet stream... Add the temps.

Red baron
Thick alto stratus is clear ice. As is nimbostratus.
Hints are
Thick
Mid level cloud
Temp close to zero.

I always think of ice in bands of temperature... Which then gives me levels to expect them.

what were the 2 stupid answers? Again think of bands of temps.
@-5 your getting clear ice. And at temperatures from 0 to -15 you will accumulate ice fastest. The -15 answer is to far to the extents of major icing problems... If in light stratus at -15 your ice build up is slow as... If in thick nimbo stratus at -5 you'll be looking for a new level pretty quick...

Have a read of the bureau of met book it's gold...

[Xcel]

But I still dont know why the TAT is increasing while we are maintaining FL370 whilst in the jetstream.. if anyone can answer that Ill take my hat off to them!

If your in a jetstream the tat won't change much. If you did want to exit a jetstream, when tracking with it, a turn poleward will be the best course.

But your not in the jet stream... Your approaching it. From the north in this case as your tracking south it is flowing from your right to left.

So the tropopause is stepping down in front of you, and sloping down to the pole. As the worst turbulance is only patches up to 2000' deep either side of the core (yes the poleward lower section is worse) then changing altitude is the best course of action. So which way? When you approach a jetstream you watch the tat. If it is increasing - climb. If it is reducing - descend. Again due to the step up or down as you see it of the tropopause.

http://www.pilotfriend.com/training/flight_training/met/images3/1.jpg