b-732 original, engine anti ice use
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b-732 original, engine anti ice use
I want to know why if a crossing a front line at 350 near a cb , st elmos fire and all that stuff , i have to be with the engine anti ice off , due to the limitation of " engine tai must be on when icing conditions exist or anticipated , exept during climb and cruise below - 40Cº sat." Some pilots told they never turn them off in those contodions , others say that at those temperatures ice never forms and if you turn it on you get the temperature higher and you induced to form ice . God please hepl me
best regads , safe flights.
B732 The last of the romantics
best regads , safe flights.
B732 The last of the romantics
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Proper Use of Engine A/I
Gentlemen:
Please, read the SOP. Stop listening to all the nonsense (feel free to substitute another eight-letter word).
The following applies to P/W JT8D as well as CFM as well as IAE2500: (Please, please, please...in the words of James Brown...read the book to confirm the following.)
Engine anti-ice is to be used when icing conditions exist or are anticipated. (Note...the term is "anti-Ice", not "de-ice". I'll refer to this notion, again, in a moment.)
Now, since we pilots are basically stupid idiots, 'icing conditions' are defined for us, since the engineers doubt we know what that means.
If you're on the ground AND the temperature is +10 or below (+50F)...(note, it's not 'below' +10...it's +10 or below.) AND you're in visible moisture (which is defined as 1 statute mile or less visibility in the case of fog/mist, if not actual precip falling) OR you're taxiing over moisture (like packed snow, water puddles, ice, etc)...THEN you must have the Engine A/I on.
To simplify the above paragraph, consider ANY moisture a threat when the temp is +10 or below. (This includes temps at -40 and below, too, by the way!)
This covers the 'on-ground' situations.
Now, let's talk about in flight. Again, the engine anti-ice is to be on when icing conditions exist or are anticipated. This means when you're in precip (or inflight visibility is 1 statute mile or less...or any kind of visible moisture, for that matter) AND the TAT is +10 or below. This includes if the SAT is -40 or below. (Yes, really, it does!!!)
There is an exception to this inflight rule. If you are climbing or cruising AND the SAT is below -40 (If you're exactly at -40, then you can't use this exception. It's gotta be colder than -40 SAT!), AND you're not in, around, amongst CBs, then you can turn off the engine A/I.
To clarify...you're cruising at FL 350 at a TAT of -42 but
you're picking your way through CBs, THEN YOU HAVE TO HAVE THE ENGINE A/I ON!!!
If you're cruising at FL350 with a TAT of -42 and you're in cirrus...no need for engine Anti-ice. HOWEVER, once you begin your descent out of FL350 (assuming you're still in the cirrus, you need engine anti-ice (because you no longer can take advantage of the climb/cruise exception...you're now descending)!
Now, the difference between anti-ice and de-ice: I can't tell you how many times I've flown with well-intending, good-natured pilots who look out the window...maybe looking at the windshield wiper nuts or Ice Probe or whatever...and say, "Gosh, we're not picking up any ice. No need for engine anti-ice. We'll wait a bit to see if any builds up before turning on the engine anti-ice."
Their logic is that the windshield and probe are at a 'low'pressure' station of the fuselage. Thus, those areas will be the first to pick up ice.
Ok...well, the engine inlets are low pressure stations, too. (Duh!!!!)
Most SOPs explicitly warn against waiting to turn on the engine anti-ice until ice accretion becomes evident. To do so is a very dangerous practice.
Please don't listen to these well-intentioned pilots. I know, they're trying to save fuel...which is a big consideration these days. But, instead read, re-read, understand when and how to use engine anti-ice. It's all very simply-stated in the book.
Safe flying!!!
PantLoad
Please, read the SOP. Stop listening to all the nonsense (feel free to substitute another eight-letter word).
The following applies to P/W JT8D as well as CFM as well as IAE2500: (Please, please, please...in the words of James Brown...read the book to confirm the following.)
Engine anti-ice is to be used when icing conditions exist or are anticipated. (Note...the term is "anti-Ice", not "de-ice". I'll refer to this notion, again, in a moment.)
Now, since we pilots are basically stupid idiots, 'icing conditions' are defined for us, since the engineers doubt we know what that means.
If you're on the ground AND the temperature is +10 or below (+50F)...(note, it's not 'below' +10...it's +10 or below.) AND you're in visible moisture (which is defined as 1 statute mile or less visibility in the case of fog/mist, if not actual precip falling) OR you're taxiing over moisture (like packed snow, water puddles, ice, etc)...THEN you must have the Engine A/I on.
To simplify the above paragraph, consider ANY moisture a threat when the temp is +10 or below. (This includes temps at -40 and below, too, by the way!)
This covers the 'on-ground' situations.
Now, let's talk about in flight. Again, the engine anti-ice is to be on when icing conditions exist or are anticipated. This means when you're in precip (or inflight visibility is 1 statute mile or less...or any kind of visible moisture, for that matter) AND the TAT is +10 or below. This includes if the SAT is -40 or below. (Yes, really, it does!!!)
There is an exception to this inflight rule. If you are climbing or cruising AND the SAT is below -40 (If you're exactly at -40, then you can't use this exception. It's gotta be colder than -40 SAT!), AND you're not in, around, amongst CBs, then you can turn off the engine A/I.
To clarify...you're cruising at FL 350 at a TAT of -42 but
you're picking your way through CBs, THEN YOU HAVE TO HAVE THE ENGINE A/I ON!!!
If you're cruising at FL350 with a TAT of -42 and you're in cirrus...no need for engine Anti-ice. HOWEVER, once you begin your descent out of FL350 (assuming you're still in the cirrus, you need engine anti-ice (because you no longer can take advantage of the climb/cruise exception...you're now descending)!
Now, the difference between anti-ice and de-ice: I can't tell you how many times I've flown with well-intending, good-natured pilots who look out the window...maybe looking at the windshield wiper nuts or Ice Probe or whatever...and say, "Gosh, we're not picking up any ice. No need for engine anti-ice. We'll wait a bit to see if any builds up before turning on the engine anti-ice."
Their logic is that the windshield and probe are at a 'low'pressure' station of the fuselage. Thus, those areas will be the first to pick up ice.
Ok...well, the engine inlets are low pressure stations, too. (Duh!!!!)
Most SOPs explicitly warn against waiting to turn on the engine anti-ice until ice accretion becomes evident. To do so is a very dangerous practice.
Please don't listen to these well-intentioned pilots. I know, they're trying to save fuel...which is a big consideration these days. But, instead read, re-read, understand when and how to use engine anti-ice. It's all very simply-stated in the book.
Safe flying!!!
PantLoad
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NB It only says 'must be on' etc etc. It does not say 'must be off'. It is yet another example of 'Captain's discretion' in my book. On some of the rare occasions I have been forced to fly through a significant convective or orographic cloud at such levels I have ?'discressed'?
The 'theory' as I understand it is that at -40 and below the amount of water vapour that can be present in an air mass is so insignificant as to cause no 'threat'. That is why with convective rising air, even at that temperature, I would consider the use of a/ice as it may be carrying vapour upwards from lower levels.
You will not fall out of the sky or 'cook' the engine if you use it!
The 'theory' as I understand it is that at -40 and below the amount of water vapour that can be present in an air mass is so insignificant as to cause no 'threat'. That is why with convective rising air, even at that temperature, I would consider the use of a/ice as it may be carrying vapour upwards from lower levels.
You will not fall out of the sky or 'cook' the engine if you use it!
It's gotta be colder than -40 SAT!), AND you're not in, around, amongst CBs, then you can turn off the engine A/I.
The most relevant definition of icing conditions is that given by the aircraft / engine manufacturer – follow the SOPs. Each aircraft / engine type will have different icing characteristics and thus may have different limitations / operating procedures.
The generic ‘no ice below -40C’ has been shown to be incorrect on several occasions, and the threat of icing, particularly near Cbs (up to 15nm) is even more relevant with modern engines with their refined aerodynamics and close tolerances. Remember that ice can adhere to thin leading edges of fan blades before the thicker airframe surfaces, this is apart from any temperature / pressure changes in the intake.
Cbs can have high concentrations of water vapor at the top and in the anvil; think of this as the dirty smoke from the Cb ‘chimney’ funneling particles upward. Below the anvil, ‘the soot from the smoke’ falls out; this is often soft hail – ‘grauple’ which can represent large quantities of moisture. Hail passing through an engine will at some point melt, if this is in ‘the wrong’ place it might refreeze or stick other particles together.
Most engine types have anti-icing systems; if this is not used and the engine suffers icing then even if you do have the option for additional de-icing it might not clear the ice. Another consideration is the intake lip. Although the engine may not suffer icing, the intake could do. If the intake anti-icing is selected on late and any significant accumulation of ice is shed from the intake then it could go into the engine – shed ice lumps can be larger and denser than any bird.
The generic ‘no ice below -40C’ has been shown to be incorrect on several occasions, and the threat of icing, particularly near Cbs (up to 15nm) is even more relevant with modern engines with their refined aerodynamics and close tolerances. Remember that ice can adhere to thin leading edges of fan blades before the thicker airframe surfaces, this is apart from any temperature / pressure changes in the intake.
Cbs can have high concentrations of water vapor at the top and in the anvil; think of this as the dirty smoke from the Cb ‘chimney’ funneling particles upward. Below the anvil, ‘the soot from the smoke’ falls out; this is often soft hail – ‘grauple’ which can represent large quantities of moisture. Hail passing through an engine will at some point melt, if this is in ‘the wrong’ place it might refreeze or stick other particles together.
Most engine types have anti-icing systems; if this is not used and the engine suffers icing then even if you do have the option for additional de-icing it might not clear the ice. Another consideration is the intake lip. Although the engine may not suffer icing, the intake could do. If the intake anti-icing is selected on late and any significant accumulation of ice is shed from the intake then it could go into the engine – shed ice lumps can be larger and denser than any bird.
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My understanding is that below 40 degrees most clouds are made up of ice crystals and therefore pose no engine icing hazard with climb or cruise power set. I'm not sure why this changes in descent. It may have something to do with idle thrust, slower airflow through the engine, etc. Any thoughts?
On the CFM and the JT8Ds only the cowl is heated. We have no way of protecting or anti icing the fan blades (other than increasing thrust) but I would be amazed if you could get fan blade icing at the power settings used during flight. The fan speed and centrafugal forces are just to great to allow ice to form. The only time I have ever encountered it is during prolonged taxi or ground holding in fog at low ambient temperatures.
I do remember some hoary old captain remarking that the definition of icing conditions wasn't always +10/-40 and so it is possible that these figures are quite conservative.
On the 732 EAI is quite a fuel penalty. I doesn't appear to be so significant on the CFM so I suppose it's the usual. If there is doubt there is no doubt! Switch it on.
Just my thoughts!
On the CFM and the JT8Ds only the cowl is heated. We have no way of protecting or anti icing the fan blades (other than increasing thrust) but I would be amazed if you could get fan blade icing at the power settings used during flight. The fan speed and centrafugal forces are just to great to allow ice to form. The only time I have ever encountered it is during prolonged taxi or ground holding in fog at low ambient temperatures.
I do remember some hoary old captain remarking that the definition of icing conditions wasn't always +10/-40 and so it is possible that these figures are quite conservative.
On the 732 EAI is quite a fuel penalty. I doesn't appear to be so significant on the CFM so I suppose it's the usual. If there is doubt there is no doubt! Switch it on.
Just my thoughts!
Cbs can have high concentrations of water vapor at the top and in the anvil
I am not saying you are wrong - far from it. Perhaps it is only tropical storms where tops are invisible to radar due lack of moisture at the higher levels of 35,000 ft plus, while European CB's do have considerable moisture in tops and anvils (?) which are generally at much lower altitudes than their Pacific counterparts.
Centaurus – “… how come weather radar is often unable to pick anvils and CB tops.”
My description could have included ice particles and ‘mixed phase’ water/water-ice crystals with the water vapor.
Weather radars only see a restricted range of water particle size, and generally do not see ice crystals or small droplets e.g. WXR does not paint cloud or fog, only larger water droplets, e.g. rain.
I am more familiar with the older radars which covered a reasonable range of conditions; I suspect that the newer radars might require greater interpretation in non standard conditions. I recall that the large Cb anvils that I ‘experienced’ painted yellow/green. Hereby is a problem, in that some crew’s consider these conditions acceptable for hazard-free flight. This is not the case for Cbs; the yellow/green areas contain water / ice particles or vapor (small particles), which could lead to various forms of icing (and may involve turbulence).
Re “… while European CB's do have considerable moisture in tops and anvils (?) which are generally at much lower altitudes than their Pacific counterparts.”
I wonder if this has more to do with droplet size. Does WXR paint the European CBs more readily due to larger droplets, whereas tropical CBs, in colder air consist more of ice crystals? In my experience of both Cb types, engine icing problems occurred at the tropopause, and / or just below zero OAT, and particularly just over the top of a developing storm.
My description could have included ice particles and ‘mixed phase’ water/water-ice crystals with the water vapor.
Weather radars only see a restricted range of water particle size, and generally do not see ice crystals or small droplets e.g. WXR does not paint cloud or fog, only larger water droplets, e.g. rain.
I am more familiar with the older radars which covered a reasonable range of conditions; I suspect that the newer radars might require greater interpretation in non standard conditions. I recall that the large Cb anvils that I ‘experienced’ painted yellow/green. Hereby is a problem, in that some crew’s consider these conditions acceptable for hazard-free flight. This is not the case for Cbs; the yellow/green areas contain water / ice particles or vapor (small particles), which could lead to various forms of icing (and may involve turbulence).
Re “… while European CB's do have considerable moisture in tops and anvils (?) which are generally at much lower altitudes than their Pacific counterparts.”
I wonder if this has more to do with droplet size. Does WXR paint the European CBs more readily due to larger droplets, whereas tropical CBs, in colder air consist more of ice crystals? In my experience of both Cb types, engine icing problems occurred at the tropopause, and / or just below zero OAT, and particularly just over the top of a developing storm.
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Centaurus - most of these 'events' you describe are due to the 'tops' (which do indeed not generally have free water in them) containing rapidly rising air from the clouds below. Hence the importance of looking well down with the scanner during peak activity to see what is 'happening' below.
This is why you can also get a significant 'bump' in clear air near a CB top. There are many and varied significant air currents around a CB.
This is why you can also get a significant 'bump' in clear air near a CB top. There are many and varied significant air currents around a CB.
disclaimer: when in doubt read the manual
Just to add some background.
Typical multispool by-pass Engines have a nasty effect on precipitation when operating at low power (taxi on the ground, descent and approach and yes even at crusie). They depress the temperature of the ingested airstream in the front section of the engine, (inlets, fan, and yes even the front spool stages of the compressor) This of course makes much more likely that the engine will acrete ice somewhere before the aircraft does at these conditions.
Most engines are tested to handle the acretion and shedding cycles of ice in actual flight operations as long as you are at or above flight idle. However engines are not tested to handle icing at ground idle conditions or at depressed idle conditions in the air.
And the of course there are the ringers where even in cruise the engines may acrete enough ice over time behind the fan in the front compressor spool which when shed may cause some serious surprises. These type of problems are often what are addressed by subsequent airworthiness directives aimed at operating condition avoidance.
As far as different procedures for different engines. This has a tendancy to get combined with rumor and compound misunderstanding of ice and the powerplant. As such all the engine and airframe manufacturers were urged to maintain the same wording in their operating manuals relative to the conditions of when to expect icing. I haven't personallly reviewed all the various manufacturer's manuals, but I would be disappointed if there was any variance between engines in this regard. Of course what get's rewitten later by individual operators is another story.
Just to add some background.
Typical multispool by-pass Engines have a nasty effect on precipitation when operating at low power (taxi on the ground, descent and approach and yes even at crusie). They depress the temperature of the ingested airstream in the front section of the engine, (inlets, fan, and yes even the front spool stages of the compressor) This of course makes much more likely that the engine will acrete ice somewhere before the aircraft does at these conditions.
Most engines are tested to handle the acretion and shedding cycles of ice in actual flight operations as long as you are at or above flight idle. However engines are not tested to handle icing at ground idle conditions or at depressed idle conditions in the air.
And the of course there are the ringers where even in cruise the engines may acrete enough ice over time behind the fan in the front compressor spool which when shed may cause some serious surprises. These type of problems are often what are addressed by subsequent airworthiness directives aimed at operating condition avoidance.
As far as different procedures for different engines. This has a tendancy to get combined with rumor and compound misunderstanding of ice and the powerplant. As such all the engine and airframe manufacturers were urged to maintain the same wording in their operating manuals relative to the conditions of when to expect icing. I haven't personallly reviewed all the various manufacturer's manuals, but I would be disappointed if there was any variance between engines in this regard. Of course what get's rewitten later by individual operators is another story.
