Nick Dobda

Ice Detectors

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Following a FB conversation where a CRJ pilot was talking about icing conditions on a flight today.

The pilot mentioned "ice detectors" and that at higher speeds they can wait until the ice detectors go off before flipping the wing anti - ice switch. At which time it only takes about 5-10 seconds for the wing to heat up enough to melt the ice away.

I looked around and found that this "ice detection" is available in the 737-

Why was it not modeled in the NGX? Limitation of FSX?
 

 

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Hi Nick... I can think of a couple of possible reasons but most likely because those ice detectors are optional equipment and FSX/P3D do not have weather engines that support realistic icing.  PMDG did model icing in the JS41 for FSX, but the effects are entirely by PMDG and do not rely on the wx engine to create the super cooled water droplets as an example.  So even when included as a feature it is more of a game feature than a realistic simulation.

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2 minutes ago, downscc said:

Hi Nick... I can think of a couple of possible reasons but most likely because those ice detectors are optional equipment and FSX/P3D do not have weather engines that support realistic icing.  PMDG did model icing in the JS41 for FSX, but the effects are entirely by PMDG and do not rely on the wx engine to create the super cooled water droplets as an example.  So even when included as a feature it is more of a game feature than a realistic simulation.

Thank you - 

I was thinking that if you were being realistic - you would be on top of whether or not you should be flipping the wing anti-ice switch or not. I wouldn't think it would be proper to be totally reliant on that warning light... although the pilot in the FB post said that it was helpful under certain conditions. 

It was more of a curiosity question. I thought I read somewhere in here that somewhere in the sim (not sure if the origin is the NGX or FSX) that performance/ dynamics is affected by ice conditions in the sim. If correct, there must be some way for the NGX of knowing that icing conditions exist. Also if correct, I would have thought it wouldn't have been hard to have that "ice detector" light pop on if the NGX is modifying its performance based on ice conditions. 

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50 minutes ago, Nick Dobda said:

Why was it not modeled in the NGX? Limitation of FSX?

Although 737s have wing anti-ice and engine anti-ice systems, the ice detection system itself was an optional extra on the 737, so not all 737s have them. You can tell if a 737 has this optional extra by looking at the outside for an additional probe, or on the forward panel on the pilot's side, where there will be a 'push to cancel' button (similar to the master caution button) which illuminates and reads 'ICING P-Cancel' when ice is detected by the probe.

If the optional Ice Detection System is present on the aeroplane, the extra ice detection probe is located on the front left side of the aeroplane, just below where the air bridge connects slightly aft of the angle of attack vane, where there will be two probes instead of the normal one if it has the ice detection system. If I can remember to do it, I'll take a picture of one of them at work tonight, as I know we'll be working on a SAS 737 NG later and I'm pretty sure they have that system on them.

Since PMDG modeled their NG on a real one (I think it was a Southwest Airlines one, but might be wrong about that), I would assume they modeled what that one had (or did not have). There are some limitations of the sim too for icing on the airframe being simulated and it tends to better to have that simulated by a weather add-on such as Active Sky or whatever. 

Many experienced airline pilots will use what is available to them to detect ice, such as watching for an ice buildup on the windscreen in between the wiper and the bottom of the windscreen, or on the bolt and nut which secures the wiper arm. Some airliners have a special little ice detection mast specifically for this purpose; if you ever see an airliner with what looks like a small antenna sticking out of the pillar which is in between the two front windows (look at an A320 and you will see this), that is exactly what the thing it for. It is designed to collect ice in flight when in conditions where wing icing is likely, since it is placed in a specific location in terms of oncoming airflow. It is visible from both the left and right seats, but in the absence of that thing, you can look at the windscreen wipers and get a good indication of if icing is severe, but this method is only good for in flight conditions.

On the ground, a walkaround paying particular attention to the outer wing panels of an NG (where cold soaking is likely) is one of the best indicators for if icing is likely, and it is something we have to look out for at this time of year when doing walkarounds. If it looks like ice is on the underside of the wing near the outboard aileron, it will most likely be advisable to de-ice the aeroplane before departure.

Technically, it's up to the pilots to decide on this, but since we regard it as our responsibility too as ground personnel who want things to be safe, we have in the past (at EGCC) refused to move a vehicle parked behind an airliner (thus preventing it from pushing out) until the crew asked for de-icing (i.e. they were pretty much forced to ask for it by us because they were being cheap in not wanting to pay for de-icing and compromising safety because of it) lol. I bet if you asked the passengers, they'd certainly not have been saying, 'nah, don't bother de-icing us, save the money'.

Edited by Chock
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I think some wx engines such as Active Sky can inject icing conditions but it gets tricky because the only way flight dynamics in icing conditions are modeled in the simulator are by means of artificial changes in aircraft performance and not directly by the impact of say rime ice on leading edges.  The conditions are exactly boundary conditions for the normal flight dynamics formulae and nothing at the edge or beyond is modeled.  Same thing for stalls,  it acts like stalls but they are just cosmetic reactions and not realistic. 

I've never seen icing equipment operate in FSX/P3D when flying in conditions that would absolutely result in icing.  I conclude that it just ain't there (other than the arcade game effects that PMDG added to the FSX JS41).  I've seen implementations such as the PMDG MD11 that provided an indication of icing conditions but it was not a icing detector.

The problem is that if a developer wants to provide a high fidelity simulation including icing effects then one has to go down the difficult path of simulating the flight dynamics of an aircraft with varying icing loads and I just don't think the development time and effort would be cost effective.

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In the case of the CRJ, (and many other aircraft), turning on wing anti-icing puts a substantial load on the engine high-pressure bleed air system, and reduces available engine thrust, so pilots would prefer not to use it unless conditions call for it - when actual ice formation is detected. The ice detectors are very sensitive, and will generate an alert almost immediately if any ice starts forming on the detector probe.

If no ice detectors are installed, pilots will have rely on more traditional methods of detecting ice formation, such as observing ice forming on the wiper blades or window center post, or on the wing leading edges (if visible from the flight deck).

Some Learjets have a small black rubber oval patch glued to the leading edge near the outboard end of the wing. If ice starts forming, it will show up on the patch, and that will be the pilot’s cue to turn on wing anti-ice.

Engine cowl anti-icing does use engine bleed air too, but much less than the wings. The typical SOP with engine anti-ice is to turn it on any time TAT temperature is 10C or below, and visible moisture exists.

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One other point about wing anti-ice is that as Jim says, it is more common to use it as a 'de-icing' system to remove ice which has already built up rather than as an 'anti-icing' system like the engine anti-ice.

This in part is due to the risk of 'runback ice' forming - remember it is only the leading edges (and often indeed only a portion of the leading edges) which are heated, so what you don't want to do is have moisture hitting the heated leading edge, staying liquid, running back over the top surface of the wing and freezing there, where there is no means of removing it.

By waiting for some ice to build up and then turning on the anti-ice system, on the other hand, it is much more likely that the ice that has built up will break away cleanly.

There is one addon which has accurately simulated the aerodynamic effects of icing, incidentally...

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1 hour ago, JRBarrett said:

The ice detectors are very sensitive, and will generate an alert almost immediately if any ice starts forming on the detector probe.

The CRJ pilot said "We entered the cloud and within seconds the ice detectors were going off."

 

 

33 minutes ago, skelsey said:

By waiting for some ice to build up and then turning on the anti-ice system, on the other hand, it is much more likely that the ice that has built up will break away cleanly.

Another good bit of advice that makes sense that I never thought about.

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To be honest, the 737 is not really bothered by ice. Since I've been flying it it's the least of my worries. The Build up on the windscreen wiper is the clue, and on the outer slat if you give the wing system a quick go. Engine Ant-ice is put on if entering cloud as an SOP anyway, until the SAT is -40 then you turn it off.

In descent, the easiest way to get rid or prevent ice buildup is to speed up! 280kts gives a nice Ram buildup so that when you pass -15' SAT , your TAT is well above 0'. 

then as you continue descent, slowly wind the speed back again, keeping TAT above 0' as long as you can. Problem solved usually.

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I flew EMB145s for 15 years.  That plane had multiple ice detectors and a fully automated anti-icing system.  You'd enter icing conditions and within seconds get a blue "ice condition" advisory message on the EICAS.  You'd look up and verify that the engine, wing and tail anti-ice valves had opened.  Done.  When exiting the icing conditions they'd all turn off.  They were definitely all anti-ice; they remained on the whole time the ice detectors were sensing icing conditions.  It was a very dumbed down system that worked well. 

Boeing definitely takes a... more lax approach to airframe icing, at least on the 73.  No ice protection on the outer portion of the wing (I guess we're not using that part lol), and they don't bother with the tail at all.  The aircraft's safety record in ice is very good so this seems to work, but it's an interesting difference in philosophy.  "We'll protect everything because why not?" vs "meh, that's probably good enough."  I think I know which I prefer ;-).

I've never noticed a 737 in the U.S. with ice detectors.  Certainly doesn't mean there aren't any but I don't think they're common here.  It seems kind of pointless if the system isn't going to do anything other than provide a visual indication; you've already got that right outside the window.  It's hard to miss a big collection of ice on that wiper bolt, and that triggers you to take a look at the wing. 

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4 hours ago, skelsey said:

it is more common to use it as a 'de-icing' system to remove ice which has already built up rather than as an 'anti-icing' system like the engine anti-ice. This in part is due to the risk of 'runback ice' forming

Various studies have debunked "ice boot bridging" as a pilot myth and state that you should always fly protected in to icing conditions, indeed the FAA mandate as such https://www.ainonline.com/aviation-news/blogs/ain-blog-faas-new-rule-ice-bridging-not-best-it-could-be. Although it doesn't help that some aircraft manufacturers (e.g. BAe with the JS41) state in their AOMs crews should allow ice to build-up on the boots before inflating them to prevent them being bridged.

In the same vein, is runback icing from early/preventative use of thermal wing anti-ice really a thing? I thought runback was caused by specific types of precipitation such as SLD (super cooled large droplets) or simply severe icing conditions?

Edited by ckyliu

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46 minutes ago, ckyliu said:

Various studies have debunked "ice boot bridging" as a pilot myth

Interesting.  And yet I've had it happen on the Chancellor.  Do you happen to have a reference for "various studies?"

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Had a look at a SAS 737-600 tonight which I was working on, it did not have the optional ice detection gear. Looked at a couple of Jet2 NGs as well and they didn't have it either. You would think if any airline would think it advantageous to have the option it would be SAS, so clearly it isn't that useful to have it if they've not bothered to fit it.

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5 hours ago, downscc said:

Interesting.  And yet I've had it happen on the Chancellor.  Do you happen to have a reference for "various studies?"

Basically, the idea is that older generation deicing boots didn't inflate fast enough to provide a positive fracturing of ice, but this isn't a problem with modern aircraft.  It's thought that pilots of modern aircraft see remnant bits of ice on the boots after a cycle and interpret this as the beginning of bridging, though it's not. 

This is a good article, specifying that both the head of NASA icing research, and all modern deicing boot manufacturers, have no evidence to indicate this phenomenon exists (or even ever did; it seems to trace back to a reference in an Ernest Gann novel.)

"Tom Bond, chief of the icing branch at NASA’s Glenn Research Center in Cleveland, Ohio, has a more detailed definition of ice bridging: “Anecdotally the belief for ice bridging–and it’s called ‘the ice-bridging myth’–is that in the past experience of pneumatic boot operation and their development over decades, the first boots that were put on airplanes had a very slow rise time to break the ice off the surfaces.

“There was the opinion that if you didn’t have enough ice on the boots when you activated them, that if it wasn’t thick enough, if you didn’t have enough threshold of ice built up, that as the boot got out to its outside perimeter or maximum thickness, the ice might stay out in a shell outside of that perimeter and continue to build up and freeze. The boot would [then] retract, and you would have a bridge of ice over the leading edge where the boot could operate inside that shell but not remove it.”

The NTSB doesn’t believe that ice bridging occurs in aircraft equipped with modern de-icer boots. The Board suggests that pilots should turn on the boots as soon as the airplane enters icing conditions and begins accumulating ice. While some residual ice might cling to the boots between inflation cycles, the NTSB conceded, this disappears during subsequent cycles. The Board also said that it has never investigated any accidents that involved ice bridging."

https://www.ainonline.com/aviation-news/aviation-international-news/2007-03-27/ntsb-takes-close-look-ice-bridging#

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6 hours ago, ckyliu said:

...In the same vein, is runback icing from early/preventative use of thermal wing anti-ice really a thing? I thought runback was caused by specific types of precipitation such as SLD (super cooled large droplets) or simply severe icing conditions?

Not in normal conditions.  Reference what I said about the anti-ice systems on the Embraer.  We'd fly with the systems activated for long periods of time without any "runback"; the theory behind thermal anti-icing systems is that the protected surface is warm enough to evaporate most moisture from the layer of air flowing over it.  This could obviously be overcome by severe icing / super-cooled large droplet conditions, but that's not what the systems are designed for anyway.  In normal icing conditions, runback is not really a thing. 

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@downscc in addition to the article link in my post you quoted, I found another article at https://www.aopa.org/news-and-media/all-news/2013/february/pilot/ice-bridging

I haven't found any studies through Google, but there is an official NTSB bulletin on it https://www.ntsb.gov/safety/safety-alerts/Documents/SA_014.pdf

I also found this mentioned in https://www.ntsb.gov/safety/safety-recs/recletters/A07_12_17.pdf which relates to (NTSB) investigation of Comair Flight 3272, EMB120RT N265CA, Monroe MI, USA, January 9,1997:

Quote

AC  25.1419-1A,  “Certification  of  Transport  Category  Airplanes  for  Flight  in  Icing  Conditions,”  dated  May  7,  2004,  states  that,  although  ice  may  not  be  completely  shed  by  one  cycle  of  the  boots,  the  residual  ice  will  usually  be  removed  by  subsequent  cycles  and  does  not  act  as  a  foundation  for  a  bridge  of  ice  to  form.  Further,  information  gathered  at  a  1997  Airplane   Deice   Boot   Bridging   Workshop,   subsequent   icing   tunnel   test s,   and   flight   tests   conducted as part of the Comair nvestigation revealed that ice bridging did not occur on modern airplanes, which are equipped with deice boots that quickly inflate and deflate. The icing tunnel tests also revealed that thin (1/4 inch or less), rough ice accumulations on the wing leading edge deice  boot  surfaces  could  be,  depending  on  distribution,  as  aerodynamically  detrimental  to  an  airplane’s performance as larger ice accumulations. 

 

Edited by ckyliu
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