Freezing Level question

Knackers · 20th April 2006, 04:33

I was reading the crash comic last night about icing. Can someone explain to me what role the freezing level in an ARFOR plays in flight planning and flying. Is it just an issue with forecast cloud?

Chadzat · 20th April 2006, 04:50

an a/c without proper de-icing equipment cannot legally plan to fly above the FL. Ie IFR.

HEALY · 20th April 2006, 05:03

Knackers

Fairly broad question which could take pages to explain depending on the type of acft you fly or your experience level however following may help clarify some points (certainly not gospel)

1) Planning a flight above the freezing level with forecast cloud at your planned altitude is asking for trouble. However if the cloud base was such that flight in clear was possible above the freezing level then things are fairly safe provided your climb and descent is not going to put you in it. Flying at night above the freezing level can be hazadous with unseen cloud. It can take a while however if you have picked up some ice on the climb thru the cloud to clear air for it to melt off especially in very cold climates. Certain controls such as trimming devices can become stuck.

2) If you dont have an instrument rating then you should not be anywhere near the cloud in the first place.

3) You will "generally" not get icing if it is a clear and you flying above the freezing level. A clear cold winters day for example.

4) It should be worth noting that just because you have an outside temperature above freezing doesn't mean you wont get icing. ie. High humidity can lead to icing in some engine components (carburettors) under certain conditions.

Again without ascertaining your level of experience its hard to answer fully, hope the points have helped. HOPEFULLY I wont be shot down in flames!

CashKing · 20th April 2006, 10:42

Icing tunnels were developed beginning in the 1940s to study this problem. They are similar to conventional subsonic wind tunnels but are equipped with refrigeration systems that can cool the air to well below freezing. Water droplets are then sprayed into the airflow so that they can freeze on aircraft surfaces. Engineers monitor the buildup of ice on the aircraft. Anti-icing devices such as electric heaters or pipes containing a heated liquid such as alcohol are installed in the parts of aircraft that generate the most ice. When ice begins to build up on a model in the icing tunnel, the heaters are turned on and researchers then study how effective they are at stopping the buildup of ice.
There are many other different kinds of wind tunnels. There are "spin tunnels" that test how aircraft behave when they fly out of control and start spinning, a situation that is commonly referred to by pilots as "departure from controlled flight." These tunnels test whether the pilot can recover in this situation or needs to parachute out of the airplane. There are "free flight" tunnels where models are actually "flown" by remote control by a pilot sitting in a control booth and sending signals to the model through a wire tether. There are also blast-furnace-type tunnels for testing how spacecraft and missiles act in high temperature airflows such as they encounter when reentering the Earth's atmosphere. And there are magnetic tunnels, where the model is held stable inside the tunnel by powerful magnetic fields so that more accurate measurements can be taken.
Before the 1950s, most of the wind tunnels operated in the United States were run by the NACA. But in 1946, a study of American wind tunnels resulted in a recommendation that industry and universities play a greater role in operating wind tunnels. This led to the National Unitary Wind Tunnel Plan Act of 1949. The Act established new supersonic wind tunnels at the three major NACA facilities, but also pushed for the creation of supersonic wind tunnels at universities. The development of a university wind-tunnel base was important both to serve as a check on NACA research and to train new aeronautical engineers. The NACA tunnels were also directed to perform more industry research, symbolizing a decreased emphasis on government-sponsored wind tunnel research.
For years wind tunnels represented a less expensive way of testing an airplane than building the full-size vehicle. But wind tunnel research was and still is expensive. Testing a new airplane design in a wind tunnel costs millions of dollars. As a result, aircraft designers have increasingly shifted to computers and a method called computational fluid dynamics (air, after all, is a fluid, like water), which simulates airflow entirely within a computer. Computing power is relatively cheap, and computer models can be changed much more easily than physical models made of plastic, metal, and wood.
Today, wind tunnels are used less and less and the giant wind tunnels that dominated so many aeronautical research centers starting in the 1930s and 1940s are now often called upon only to serve as backups to the computer simulations, to prove that their predictions are sound. In several important cases, however, aircraft designers have had to use wind tunnels to test their designs after computer simulations have proven inadequate. For example, the Pegasus XL air-launched rocket suffered an in-flight aerodynamic failure that was not predicted by a computer-generated aerodynamic model. But in a matter of years, most of the large NACA-built wind tunnels may become totally silent, their roar replaced by the hum of a supercomputer.

Bomber ARIS · 20th April 2006, 11:03

...and this evening's award for thread drift goes to...

QSK? · 21st April 2006, 03:25

Quote:

Can someone explain to me what role the freezing level in an ARFOR plays in flight planning and flying

Knackers:

I don't mean to be personally critical, mate, but surely this very significant flight operations and safety issue must have been covered in your basic MET training when you did your ab-initio ATC course?

If not, it says something about the quality of ASA's ATC training program.

UnderneathTheRadar · 21st April 2006, 08:39

Quote:

Originally Posted by Chadzat

an a/c without proper de-icing equipment cannot legally plan to fly above the FL. Ie IFR.

Ummmm - not quite true - without proper de-icing equipment you cannot legally fly into 'known icing conditions'. Healy is right when saying that above the FL is fine if you're not in cloud or freezing rain.

The FL helps an IFR pilot decide where 'known icing conditions' will be. Even if there is cloud above the FL, if they can dodge the clouds (isol cb for example) then it's all legal.

UTR.

Knackers · 21st April 2006, 10:59

Thanks for the replies.

QSK, you're right it was, but not from the pilot's perspective. It was all the theory about rime ice, etc, anti icing equipment and so on. I wanted to know, from the pilot's perspective, what he/she does/thinks when receiving the ARFOR and reading the freezing level.

QSK? · 24th April 2006, 02:43

Knackers:

Quote:

I wanted to know, from the pilot's perspective, what he/she does/thinks when receiving the ARFOR and reading the freezing level.

Ok, from MY pilot's perspective, I fly aircraft that are not equipped with anti-icing equipment (typical of most GA aircraft).

CASA regulations dictate that a pilot shall not deliberately fly an aircraft into known icing conditions so the FZL is one of the first, and most significant, items I look for in an ARFOR; particularly during the winter months or when I know I'll be flying over high terrain.

The next thing I look at is the forecast cloud cover. If the cloud cover is BKN or more then, as far as I'm concerned, flight at or above the FZL is out, even if I know the vertical extent of the cloud cover above the FZL is limited and cruising clear of cloud may be possible on top.

The next thing I then consider is the relationship of the FZL to my planned LSALTs. If the FZL is lower than, or very close to, my LSALTs then I look for an alternative route that offers lower LSALTs to put some vertical distance between the FZL and the LSALT. Personally, I like to have a minimum of 2500ft separation between FZL and the LSALT to account for forecasting errors and also to give myself a choice of at least 2 levels going in any direction. If this option is not available at the pre-flight stage, then my flight is not on unless I'm definitely able to confirm that the forecast FZL (ARFOR) is not correct (usually through Airep, other pilot or ATS reports).

Once a decision to go ahead with the flight is made, I constantly monitor the OAT guage throughout the flight to confirm the accuracy or otherwise of the ARFOR's FZL. If I inadvertently experience icing (hasn't really happened to me yet), my escape plan normally involves descending to the LSALT and/or diverting.

Maybe other pilots have got some other good advice for flying in potential icing conditions which I would also welcome.

Hope this helps.

Knackers · 25th April 2006, 03:44

Thanks QSK? - exactly what I was after.

QSK? · 26th April 2006, 02:22

Knackers:

ATC can help IFR pilots by getting other pilot reports to verify the forecast FZL particularly in those areas of your sector where the forecast FZL is very close to the LSALT. The more actual reports the better as it puts pilots ina better position to divert in advance if necessary.

Such reports can also assist ATC in planning your sector operations as you will then know in advance that GA aircraft are most likely to request diversions to lower terrain areas when the FZL is low.

Cheers QSK?

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