julesmusician
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Can I Descend Due To Icing? Says The 737 Pilot

Sat Dec 17, 2005 2:22 am

I heard a pilot asking to descend in the holding stack due to icing? Two questions:

1) What does the warning say in the cockpit for Icing - are there scales of warnings for icing or is it just a general one on modern airliners?

2) Why would a pilot want to descend as I thought that modern jets can cope with icing as they have deicing switches in the cockpit? I would have thought asking to descend in a busy holding stack due to icing would be difficult and never heard anyone else ask it?

J
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undehoulli
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RE: Can I Descend Due To Icing? Says The 737 Pilot

Sat Dec 17, 2005 2:45 am

Ummm...ice can get pretty bad, and even though an airplane might have the capability to deice or anti-ice while airborne, sometime the conditions can be too extreme for the aircraft to rid itself of the ice or keep up with the formation of it. I've always considered that even though an airplane has deicing or anti-icing equipment, the purpose of that equipment is to allow the aircraft to fly to conditions where icing is not present, not to remain in icing conditions.

Also, not every aircraft collects ice the same as a different type. Collection efficiency is how the ice adheres to various surfaces of the aircraft. A surface with a smaller radius of curvature (the horizontal stabilizer, antennas) will collect ice sooner and generally faster than the wing. Next time you drive through an ice storm (not recommended!) look at your antenna - it will be quite glaciated.

Aircraft icing is reported in four levels:

Trace - Ice becomes perceptible. Rate of accumulation is slightly greater than rate of sublimation. It is not hazardous even though deicing/anti-icing is not used unless encountered for an extended period of time (over 1 hour).

Light - The rate of accumulation may create a problem if flight is prolonged in this environment (over 1 hour). Occasional use of deicing/anti-icing equipment removes/prevents accumulation. It does not present a problem is the deicing/anti-icing equipment is used.

Moderate - The rate of accumulation is such that even short encounters become potentially hazardous and use of deicing/anti-icing equipment or diversion is necessary.

Severe - The rate of accumulation is such that deicing/anti-icing equipment fails to reduce or control the hazard. Immediate diversion is necessary.


Enjoy!
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julesmusician
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RE: Can I Descend Due To Icing? Says The 737 Pilot

Sat Dec 17, 2005 2:48 am

That is interesting, I am wondering what the aircraft reports to the captain for Icing warnings - does it get specific like areas and intensity or is it as basic as a car ice warning thermometer?

J
African Civil Aviation Commission president "You don't want to fly out as a passenger and come back as cargo."
 
undehoulli
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RE: Can I Descend Due To Icing? Says The 737 Pilot

Sat Dec 17, 2005 2:50 am

Some airplanes have an ice detector. It vibrates at a certian frequency and when ice forms on it, the vibration frequency changes. This usually causes an annunciator for the pilots informing them that ice has formed, and sometimes even activates the airframe deicing system (including a heater on the ice detector).
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Grbld
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RE: Can I Descend Due To Icing? Says The 737 Pilot

Sat Dec 17, 2005 3:34 am

Well, typically, modern airliners have no problem with flying in icing conditions. I've never had an instance where we couldn't get rid of ice, but you do have to keep your eye on it (as always).

However, there are a few instances in which you'd want to descend in icing conditions:

- If you have a malfunction in a de-ice/anti-ice system

- If you've been flying for a while at high altitude and your fuel is starting to get closer to freezing temperature

- If you're required to slow down to a specific airspeed where you need to extend your flaps—in lots of aircraft you're not allowed to hold in icing conditions with flaps extended (since there are no anti-ice devices on the trailing edge flaps and beyond the slats)

As always, if you get into icing conditions which are too much for you, it can be a good move to descend to a lower altitude, where it's warmer.

Grbld.
 
julesmusician
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RE: Can I Descend Due To Icing? Says The 737 Pilot

Sat Dec 17, 2005 3:44 am

Quoting Grbld (Reply 4):
If you've been flying for a while at high altitude and your fuel is starting to get closer to freezing temperature

What is the typical freezing temp of fuel and what warnings do you get on the systems if it gets there?
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brownbat
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RE: Can I Descend Due To Icing? Says The 737 Pilot

Sat Dec 17, 2005 3:59 am

Aircraft are affected by ice a number of ways, thrust is reduced, drag and weight is increased, and lift is decreased. Basically reduced aircraft performance at the best, at the worst it could cause a plane to go down. It is very serious because it only takes a small amount ice to reduce the lift by significant numbers. The most serious type of ice is formed at temperatures between 0 to minus 10 degrees celcius.
 
AAR90
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RE: Can I Descend Due To Icing? Says The 737 Pilot

Sat Dec 17, 2005 4:04 am

Quoting Julesmusician (Thread starter):
1) What does the warning say in the cockpit for Icing - are there scales of warnings for icing or is it just a general one on modern airliners?

The 737 has no ice warning system. One simply looks at the wipers & other protrusions out the cockpit window. On NG's the pilots can see the wingtips as well.

Quote:
2) Why would a pilot want to descend as I thought that modern jets can cope with icing as they have deicing switches in the cockpit? I would have thought asking to descend in a busy holding stack due to icing would be difficult and never heard anyone else ask it?

Lower is normally warmer...= no/less ice. While modern airliners have anti-ice/de-ice systems, there is no logical reason to remain in icing conditions if one can move to a non-icing condition situation. Most airlines have that as a company policy or requirement.
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HAWK21M
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RE: Can I Descend Due To Icing? Says The 737 Pilot

Sat Dec 17, 2005 4:10 am

Quoting Julesmusician (Thread starter):
What does the warning say in the cockpit for Icing - are there scales of warnings for icing or is it just a general one on modern airliners

On the B737s the Fuel filter Diff Pr Warning illuminates the Filter Icing light necessating providing Fuel heat.

The Front of the Windshield near the Wipers is another Indicator for Icing.
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Starlionblue
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RE: Can I Descend Due To Icing? Says The 737 Pilot

Sat Dec 17, 2005 4:14 am

Quoting Julesmusician (Reply 2):
That is interesting, I am wondering what the aircraft reports to the captain for Icing warnings - does it get specific like areas and intensity or is it as basic as a car ice warning thermometer?

I have this vague memory of a DC-9 or MD-8x jumpseat when the captain used a flashlight on an area just below the windshield.
"There are no stupid questions, but there are a lot of inquisitive idiots."
 
SlamClick
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RE: Can I Descend Due To Icing? Says The 737 Pilot

Sat Dec 17, 2005 4:44 am

Quoting Starlionblue (Reply 9):
I have this vague memory of a DC-9 or MD-8x jumpseat when the captain used a flashlight on an area just below the windshield.

I always looked at the forward side of the cotter pin where the wiper blade attaches to the arm. Very reliable indicator. BTW, how often did they try to stump you on the location of the wet compass?

Quoting Undehoulli (Reply 3):
Some airplanes have an ice detector. It vibrates at a certian frequency and when ice forms on it, the vibration frequency changes.

There is also a type with a rotating wheel and scraper. As ice builds up on the wheel the scraper will remove it. Something measures the effort that requires.

Quoting Grbld (Reply 4):
- If you've been flying for a while at high altitude and your fuel is starting to get closer to freezing temperature

At or near fuel-freeze temperatures (around -49°C rings a bell) it is generally too cold and too dry for structural icing to take place. Wing, intake and windshield ice is usually associated with OATs from just above to well below freezing, but the worst icing is usually from supercooled (and therefore highly unstable) water, which freezes on impact.

Another problem is when the plane has been a long time at very high altitude and is cold-soaked. When you then descend into rain at near-freezing temperatures it will freeze on contact with your sheet metal and windows.

Even in a nice modern turbine airplane, if icing doesn't worry you, it will one day.
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Woodreau
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RE: Can I Descend Due To Icing? Says The 737 Pilot

Sat Dec 17, 2005 4:46 am

Quoting Julesmusician (Reply 5):
What is the typical freezing temp of fuel and what warnings do you get on the systems if it gets there?

Depends on the fuel....  Smile

(I don't remember the exact freezing point of the fuels)
Jet A freezes somewhere around -30C, Jet A-1 has a lower freeze point, continuing on down some Russian fuels which have a freezepoint somewhere lower than -50C.

THe fuel gets routed from the fuel tanks to a heat exchanger where the fuel is used to cool the engine oil (and gets heated up in the process) before it goes into the engine at least on my airplane that's the way it works.
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julesmusician
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RE: Can I Descend Due To Icing? Says The 737 Pilot

Sat Dec 17, 2005 4:49 am

So when you see ice crystals forming on the window out of the passenger windows is that normal or a sign of icing conditions?
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Starlionblue
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RE: Can I Descend Due To Icing? Says The 737 Pilot

Sat Dec 17, 2005 4:54 am

This provides some insight into cold ops:
- Polar Routes article: http://www.boeing.com/commercial/aeromagazine/aero_16/polar.html
- Icing/Deicing article:
http://www.boeing.com/commercial/aeromagazine/aero_08/deice.html
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Grbld
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RE: Can I Descend Due To Icing? Says The 737 Pilot

Sat Dec 17, 2005 7:42 am

Quoting SlamClick (Reply 10):
Even in a nice modern turbine airplane, if icing doesn't worry you, it will one day.

Well, it worried me plenty when I was flying checks at night over the Rockies in an unpressurized Beech 99 sucking on oxygen, avoiding the squall lines and flying at max power to stay in the air.

Scandinavian winter weather is always interesting or a bad day at Innsbruck, but you have so much more margin in modern jets. And if it gets too bad to go, don't go or go somewhere else, as always.

Grbld
 
Alias1024
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RE: Can I Descend Due To Icing? Says The 737 Pilot

Sat Dec 17, 2005 7:51 am

Quoting SlamClick (Reply 10):
how often did they try to stump you on the location of the wet compass?

Of all the strange things Douglas did in their cockpit design, that one takes the cake. The guy that designed that must have been smoking something pretty strong. Either that or he really loved mirrors. Using that in turbulence must be very challenging, if not impossible.
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Stoicescu
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RE: Can I Descend Due To Icing? Says The 737 Pilot

Sat Dec 17, 2005 8:21 am

Quoting Julesmusician (Reply 12):

Yes there ware times I had icing of my windshield so I don't see why you won't be able to see it as a passenger but that doesn't mean it is necessary a serious condition all the time, it depends from case to case.

But as a VFR pilot we don't usually go out in serious weather like the big boys do.
 
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Starlionblue
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RE: Can I Descend Due To Icing? Says The 737 Pilot

Sat Dec 17, 2005 10:39 am

Quoting Alias1024 (Reply 15):
Of all the strange things Douglas did in their cockpit design, that one takes the cake. The guy that designed that must have been smoking something pretty strong.

Well, Douglas was based in the heart of Southern California  Wink Used to live under the flight path for LGB. Loved seeing those MD-11s and Big 10s come in for maintenance!
"There are no stupid questions, but there are a lot of inquisitive idiots."
 
wing
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RE: Can I Descend Due To Icing? Says The 737 Pilot

Sun Dec 18, 2005 5:34 am

On Airbus -as everything else- there is a very easy and logical solution for detection of icing.There is a horn like looking device(ice detector) on the outer center of the windshield.You can see it on this picture.


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Well if you still dont do anything despite the visual cues than the ECAM rings a warning and calls ICE DETECTED.
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