Practical Application of Anti-Ice?

[Flamin_Squirrel 71]

Hi all. The theory behind anti-ice use is fairly straight forward - on if TAT is +10C or less with visible moisture. However, on descent especially, anti-ice use has to be planned for ahead of time. How is this done? I wouldn't have thought simply looking at your destination's METAR would surfice? Is it based on freezing level forecast? Also, do wing and engine anti-ice get turned on at the same time, or would you sometimes use one without the other? Any input, especially from someone who knows the SOP for 737 anti-ice procedues greatly appreciated, thanks.

[NGXfanatic 85]

This is a nice time to ask these questions, as temps start to creep down all around the globe for us using real world weather. I'm not a pilot, but from what I have gathered, wing anti ice is seldom used, but engine anti ice is common for the aforementioned conditions. I also know that the engine anti-ice is turned off at the higher altitudes when SAT is below -40. From the FCOM: "Anti–Ice, RainEngine TAI must be on when icing conditions exist or are anticipated, except during climb and cruise below -40°C SAT." One of the features in the FMC has me intrigued, which is the Descent Forecast page with the entry of engine TAI altitude. I wonder how the crew choose which altitude to input during the colder months, as if they know exactly what the cloud altitudes are before descent? I figure we can guesstimate in FS, especially if we look at the weather forecast in Active Sky Evolution.

[badderjet 181]

Just recalling observations from memory here -- don't remember anyone use the A/I forecast feature. I doubt you could derive the exact cloud bottoms and tops from forecasts. What they simply did was to switch the system by looking outside and "visually" confirming they are either in or out of clouds, simple as that.Yes engine and wing A/I can be used independently. What I observed was simply, they put engine A/I on (and start switches continuous) when passing cloud layers most of the time. Once in clear air, it would go back to off again, as would the start switches. Never saw them use wing A/I, dunno about its use. Probably only in severe icing or so.

[G550flyer 1,011]

Wing and engine anti ice go hand in hand. Normally if you are using one you will be using the other. You can use them independently if you like. For example, in one type of aircraft i flew(DC-10), if the airport temp was below 6C and the spread between outside temp and dew point was 3 degrees or less....you turn on engine anti-ice. This prevented induction icing in the engine. When the spread is that close, it's very humid or foggy. We also used engine anti-ice at high angle of attack and very slow speeds in the clouds(induction icing again at the intakes). Another time is when your aircraft have performance limited engines. For example, in a G-3, you would turn on engine and wings on the ground in icing conditions. Once the wings reached 100 degrees, the wing warm lights would illuminate. At this point you would turn off the wings and commence the takeoff. We did the same thing when descending through clouds with temps below 10c. Having those engines near idle with engine and wing anti-ice on put so much demand on the engines that the cabin pressure system couldn't keep up causing the cabin to climb. Now days most modern jets all have engines that will provide enough pneumatic pressure during all conditions. In this case , you can turn them both on during icing conditions. In the G-5/550, we turn on both when it's below 10C in visible moisture. We fly in auto also and both system will turn on when the aircraft detects icing conditions. Like stated above, you will anticipate icing. If you are climbing/descending and you notice that the temp is below or will be between 10c and -40 by the time you enter the clouds, you turn them on. while climbing/descending, If I see that the clouds are only a couple of thousand feet thick or I know that i will be in them momentarily, I only turn on the engines. Just remember that they are ant ice systems and should be turned on prior to entering icing. They are not de icing systems which are used after ice build up has occur-ed.

[Spin737 102]

Wing and engine anti ice go hand in hand. Normally if you are using one you will be using the other.

Rick, that's true in some planes, but not in the 737. Wing AI is rarely used.

[DaveCT2003 1,820]

Wing and engine anti ice go hand in hand. Normally if you are using one you will be using the other. You can use them independently if you like. For example, in one type of aircraft i flew(DC-10), if the airport temp was below 6C and the spread between outside temp and dew point was 3 degrees or less....you turn on engine anti-ice. This prevented induction icing in the engine. When the spread is that close, it's very humid or foggy. We also used engine anti-ice at high angle of attack and very slow speeds in the clouds(induction icing again at the intakes). Another time is when your aircraft have performance limited engines. For example, in a G-3, you would turn on engine and wings on the ground in icing conditions. Once the wings reached 100 degrees, the wing warm lights would illuminate. At this point you would turn off the wings and commence the takeoff. We did the same thing when descending through clouds with temps below 10c. Having those engines near idle with engine and wing anti-ice on put so much demand on the engines that the cabin pressure system couldn't keep up causing the cabin to climb. Now days most modern jets all have engines that will provide enough pneumatic pressure during all conditions. In this case , you can turn them both on during icing conditions. In the G-5/550, we turn on both when it's below 10C in visible moisture. We fly in auto also and both system will turn on when the aircraft detects icing conditions. Like stated above, you will anticipate icing. If you are climbing/descending and you notice that the temp is below or will be between 10c and -40 by the time you enter the clouds, you turn them on. while climbing/descending, If I see that the clouds are only a couple of thousand feet thick or I know that i will be in them momentarily, I only turn on the engines. Just remember that they are ant ice systems and should be turned on prior to entering icing. They are not de icing systems which are used after ice build up has occur-ed.

I'd like to thank you for this information! I've known that I needed to learn more about Anti Ice for a while,but given it's been summer, I put it off. It's now time to dig into this, and you gave me a terrific start! Also, had no idea that the start switches should be on when using anti ice (in icing conditions)... nice one!

[JBZ 13]

However, on descent especially, anti-ice use has to be planned for ahead of time. How is this done? I wouldn't have thought simply looking at your destination's METAR would surfice? Is it based on freezing level forecast?

When flying in the United States (lower 48), I use this link http://aviationweather.gov/adds/icing/ and the Supplimentary Icing Information. It's a nice little java tool that shows you where icing is likely to occur and at what altitudes. It will also display any real-world PIREPs that where reported about icing.

[Spin737 102]

Also, had no idea that the start switches should be on when using anti ice (in icing conditions)... nice one!

For more realism: Entering icingStart Switches ONAnti-Ice ON Exiting icingAnti-Ice OFFStart Switches OFF Some airlines have an automatic ignition option that turns on the igniters when you turn on the AI.

[badderjet 181]

I'd like to thank you for this information! I've known that I needed to learn more about Anti Ice for a while,but given it's been summer, I put it off. It's now time to dig into this, and you gave me a terrific start!

Hey sir, I surely hope you didn't mean to say 'summer = no icing' by that, right...!?

[DaveCT2003 1,820]

LOL! Not at all. Just hasn't really been on my mind, until the Maddog's fuel filter freezes up... amazing they modeled that!

[badderjet 181]

Ok good you're up to speed there *sigh*, otherwise we would've had some 'splaining to do!

[Houghton11 12]

To add what JBZ to: up here you can derive the freezing level and icing conditions from these: Dashed lines are the freezing level.

[skysurfer 76]

Rick, that's true in some planes, but not in the 737. Wing AI is rarely used.

Right.In our airline we are not authorized to use Engine and Wing Anti- Ice at the same time.

[G550flyer 1,011]

Rick, that's true in some planes, but not in the 737. Wing AI is rarely used.

Spin737, my post was a general aircraft anti ice post. I did point out the performance limited issues. Seems the 737 falls into this case. take a look at these limitations Engine anti-ice must be on when icing conditions exist or are anticipated, except during climb and cruise below -40°C SAT.Use of wing anti-ice above FL350 may cause bleed trip off and possible loss of cabin pressure. (SP.16.8) The limitations further stated that wing anti-ice must be on, on the ground during icing conditions. Seems some operators leave it off in this situation if de-icing is performed. Interesting that wing anti ice is inhibited with the throttles at takeoff position. I did notice that the stick shaker is adjusted to icing condition speeds when the wing anti ice switch is turned on in flight. Sounds like the penalty on the engines is so large that the wing anti ice is indeed used for de-icing after ice accumulation. This also make some pilots more reluctant to use it. I don't mess around with icing. The airfoil takes a big hit in performance during accumulation. Stall speed creeps up on you in those situations. Here is a interesting read from the FAA safety reporting system. This was from a 737-700 pilot. Icing. Descending into alb out of approximately 12000 ft, captain turned on engine anti-ice prior to descending into clouds. Shortly thereafter, I noticed rime ice building up on the windshield and wiper bolt. I advised the captain. He acknowledged, but did not elect to turn on wing heat. I turned on wing inspection light to look for ice. I could not determine visually. I asked the captain if he could see any ice? He said that he could not tell. In my mind, I am thinking, if I was the PF, I would turn on the wing heat. There is ice buildup on the windshield, but we can't see anything on the wing. Descending below approximately 5000 ft, we were below clouds. Landed uneventfully. On postflt, I found light rime ice buildup on the wing and tail leading edges just as I had suspected. I should have acted on that little voice inside and suggested more strongly to turn on the wing heat. Our procedure for wing heat is listed in fom. Primary procedure is to use wing heat as a deice procedure. The problem is, that this is based on being able to see from the cockpit if there is ice on the wing. In my previous experience on boeing aircraft, our procedure was to turn wing heat on, if there was ice accumulation on the windshield. The action was automatic, if ice was accumulating on windshield. Most pilots that I fly with are reluctant to turn wing heat on unless there are large visible chunks of ice on the wing. There have been numerous times that I have been the PNF, and the same scenario with ice on the windshield, but the captain looks and decides not to turn on wing heat. Based on this event, I suggest that maybe there could be improvement in our procedure. We were in compliance with the 'primary method' of wing anti-ice usage suggested in our fom. If it may be required, then the only way we can determine if it is required is to look. We looked, and we didn't see anything. The secondary method of using wing heat as anti-ice would have covered us in this situation, but the captain elected not to do that procedure. In my experience, this procedure is rarely followed. I would like to see our procedure changed so that if there is ice buildup on the windshield, etc, then we automatically turn on the wing heat. In the future, I will also more strongly suggest that the wing heat be turned on.

[skysurfer 76]

Hi all. However, on descent especially, anti-ice use has to be planned for ahead of time. How is this done? I wouldn't have thought simply looking at your destination's METAR would surfice? Is it based on freezing level forecast? Hi.For enroute phase of flight we use many FAA approved tools like one of those: http://www.aviationweather.gov/adds/icing/ http://aviationweather.gov/adds/flight_path/ Select Icing, AIRMET and SIGMET. It will show you all areas affected and detailed descriptions at what altitude you can expect icing en route and how bed is that. Some airlines turn anti ice on anytime when T < 10C and ceiling at or below 2000 ft because they considered it as a moisture as well.We don't use this in order not to over penalize airplane performance. Also enroute prog charts may help http://www.aviationweather.gov/products/swh/ Any input, especially from someone who knows the SOP for 737 anti-ice procedues greatly appreciated, thanks.