2. I believe some commercial a/c have a point on the nose that's visible that will start picking up ice before any other point on the a/c. It's usually attached to a windshield wiper or something like that. Basically when they notice that they have ice buildup on that, they know that ice is potentially building up somewhere else.
Stratoduck From United States of America, joined Nov 2008, 25 posts, RR: 0
Reply 4, posted (5 years 5 months 3 weeks 2 days 12 hours ago) and read 2355 times:
icing conditions exist when there is visible moisture and temperatures are below 0 and above -40 celsius. below -40, the atmosphere is incapable of holding water (liquid state), so the visible moisture will be ice crystals, and nothing more.
the rule of thumb is that +10 with visible moisture is also considered icing conditions, for two reasons. one, with a reduction in pressure at the air intake on the engine, there will be a corresponding drop in temperature. this may permit the formation of ice on the engine cowl and spinner, if the temperature drop goes below 0. therefore, typical procedure is to turn on the engine heat below +10 degrees on the ground.
the second reason is what happens to air temperature at very high airspeeds (basically in excess of 150ktas, and more like 250+ktas). the air compresses in front of leading edges of the aircraft, and there is a corresponding rise in temperature. at typical cruise speeds of 400ktas, there is about a 20 degree rise in temperature. so while the outside air temperature might be -5, the aircraft's leading edges are bathing in +15 degree air. this temperature of +15 degrees will generally be warm enough to melt the ice and warm the supercooled water to above freezing temperatures, and thus prevent icing. once this ram air temperature falls below +10, there may not be enough heat generated to prevent icing, so the anti-ice is turned on at this point.
the jets have a rosemount probe (aka tat probe) that measure this temperature, which is used for both icing decisions and power settings in older engines. the outside air temperature is calculated from this, and labeled static air temperature (since it is a calculation and not a measurement).
in something like a C-172, the decision is much easier. visible moisture between 0 and -40.
Airbuster From Netherlands, joined Mar 2007, 462 posts, RR: 0
Reply 5, posted (5 years 5 months 3 weeks 2 days 11 hours ago) and read 2339 times:
On the ground with a temperature of between +6C and downto and including -25C and with a temperature dewpoint split of 3 or less.
In the air, same temperature range, but with visible moisture present.
So in theory, you could land on a clear day with a temperature of let's say +3C without anti icing systems on, but once you're on the ground and the dewpoint is for example +2C you'd have to switch it on.
TheGreatChecko From United States of America, joined Mar 2004, 1136 posts, RR: 3
Reply 6, posted (5 years 5 months 3 weeks 2 days 8 hours ago) and read 2302 times:
In addition to our Mark I eyeballs, the aircraft I fly has two icing probes mounted on each side of the nose.
They work on a piezoelectric principal (Wikipedia has a great explanation of exactly how this works: http://en.wikipedia.org/wiki/Piezoelectricity). Basically, when ice begins to accumulate on the probe, an electric field is created and is detected by a sensor. When that field reaches a predetermined point, we get an "Ice Detected" prompt on our Engine Display. That is our cue to turn on all the deice systems (if the ice had not already seen and the systems turned on prior).
More advanced probes found on larger turbine aircraft will also tell you the intensity and type of icing.
It's all pretty cool stuff if you ask me.
"A pilot's plane she is. She will love you if you deserve it, and try to kill you if you don't...She is the Mighty Q400"
Pilotpip From United States of America, joined Sep 2003, 3152 posts, RR: 10
Reply 8, posted (5 years 5 months 3 weeks 2 days 2 hours ago) and read 2234 times:
The wing usually isn't the best place to see it. The best place to see ice is on something sticking out into the airflow right in front of you. Wipers, bolts, and other things like that are good to see it on. Sometimes just seeing it on the unheated part of the windshield is easier.
Modern jets have ice detectors. They vibrate at a specific frequency. If ice starts to build, the frequency changes. The detector in my aircraft will then turn on the wing and engine anti ice (none on the tail of the 170). After 5 minutes, if it's gone it turns the heat off and we move on. These can be deferred so there's a manual override as well.
PGNCS From United States of America, joined Apr 2007, 2884 posts, RR: 49
Reply 9, posted (5 years 5 months 3 weeks 1 day 5 hours ago) and read 2155 times:
Quoting Wardialer (Reply 3): I posted this question because I had been listening to my scanner and on approach/departure, some aircraft are reporting light to moderate icing to the ATC controller.
They are looking at ice build up. On my aircraft (and most I have flown) the most obvious place to see it is on the assembly attaching the windshiled wiper to the aircraft. It is also easy to shine a light on through the windshield at night.
Quoting N901WA (Reply 7): One more HiTech equipment to add. The wing illumination lights That so the Mark 1 eyeball can see the wing from the window. I beleve its MELable in icing conditions but with restrictions.
We can't see the wing at all from the cockpit, and that is an issue on many jet aircraft. Even if we could we couldn't discern much due to the distance from the cockpit unless it's quite pronounced, at which point there are earlier clues.
Quoting Pilotpip (Reply 8): The wing usually isn't the best place to see it. The best place to see ice is on something sticking out into the airflow right in front of you. Wipers, bolts, and other things like that are good to see it on.
N901WA From United States of America, joined Oct 2009, 489 posts, RR: 1
Reply 10, posted (5 years 5 months 3 weeks 1 day 3 hours ago) and read 2121 times:
Sorry I was referring to the Cabin window. I do agree that they are other areas to check for ice, but they are a good aid to check for ice on the Ground and after De-ice. Just like the inboard Wing markings / tuffs on the MD-80's to check for ice.
AAR90 From United States of America, joined Jan 2000, 3525 posts, RR: 45
Reply 11, posted (5 years 5 months 3 weeks 1 day ago) and read 2097 times:
Quoting PGNCS (Reply 9): We can't see the wing at all from the cockpit, and that is an issue on many jet aircraft. Even if we could we couldn't discern much due to the distance from the cockpit unless it's quite pronounced, at which point there are earlier clues.
Of all the airliners I've flown, only the B738 and F100 had portions of the wing visible from the cockpit windows. The F100 had a black stripe painted on it to aide in ice detection. The B738 wingtip/winglet is clearly visible and even "trace" amounts of ice build-up is visible; However, the best indication remains....
Quoting Pilotpip (Reply 8): The wing usually isn't the best place to see it. The best place to see ice is on something sticking out into the airflow right in front of you. Wipers, bolts, and other things like that are good to see it on. Sometimes just seeing it on the unheated part of the windshield is easier.
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