Fan Blade Icing / Deicing on the 737
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Fan Blade Icing / Deicing on the 737
Hey chaps, since that time of the year is fast approaching I have a question regarding fan ice on the 737 (possibly that would apply to other types, too).
Last year I had an argument with the deicing handler who initially refused to deice the fuselage, wings and tail unless we would first perform fan blade deicing. Taxiing in with TAI we collected some ice on the fan blades - during the walkaround I made sure the fan was free to rotate, the cowl was free of ice. The ops frequency at this point was already overloaded, every flight was requesting fan blade deicing (and everyone sounded similarly surprised) - the waiting time estimate went up to three hours until a heater unit would be available. To cut a long story short we finally deiced, pushed back, performed an ice shedding run up and finally flew home. My outfit does not have any regulation covering fan ice in addition to the OM and I could not find anything else which would indicate that a clean fan is mandatory for startup. Obviously leaving the airplane out overnight in freezing rain or similar conditions would necessitate hot air deicing of the engines, especially if the cowl and spinner are affected, too - but what would be your call in this situation? LEOS and other service providers happily state in their promotional documents that "it is prohibited to start the engine when fan blade icing occurs" - is there any truth to this? On that day at least it seemed like someone wanted to cash in on the conditions and suggested putting the pilots under pressure...
Cheers!
Edit: Even found a picture taken that day:
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FCOM: (Cold Weather Operations - External Inspection)
and
EASA SIN 2008-29
Last year I had an argument with the deicing handler who initially refused to deice the fuselage, wings and tail unless we would first perform fan blade deicing. Taxiing in with TAI we collected some ice on the fan blades - during the walkaround I made sure the fan was free to rotate, the cowl was free of ice. The ops frequency at this point was already overloaded, every flight was requesting fan blade deicing (and everyone sounded similarly surprised) - the waiting time estimate went up to three hours until a heater unit would be available. To cut a long story short we finally deiced, pushed back, performed an ice shedding run up and finally flew home. My outfit does not have any regulation covering fan ice in addition to the OM and I could not find anything else which would indicate that a clean fan is mandatory for startup. Obviously leaving the airplane out overnight in freezing rain or similar conditions would necessitate hot air deicing of the engines, especially if the cowl and spinner are affected, too - but what would be your call in this situation? LEOS and other service providers happily state in their promotional documents that "it is prohibited to start the engine when fan blade icing occurs" - is there any truth to this? On that day at least it seemed like someone wanted to cash in on the conditions and suggested putting the pilots under pressure...
Cheers!
Edit: Even found a picture taken that day:
Uploaded with ImageShack.us
FCOM: (Cold Weather Operations - External Inspection)
Engine inlets ............................................................ ...................... Check
Verify that the inlet cowling is free of snow and ice.
Verify that the fan is free to rotate.
Verify that the inlet cowling is free of snow and ice.
Verify that the fan is free to rotate.
SP.16.3 - Deleted the requirement to verify that the fan blades are free of snow
and ice. The is a maintenance function and is accomplished on the first flight
of the day. The flight crew should still verify that the fan is free to rotate. Any
accumulation of ice and snow on the spinner and fan blades should be
removed using the ice shedding procedure during taxi-out and prior to setting
takeoff thrust.
and ice. The is a maintenance function and is accomplished on the first flight
of the day. The flight crew should still verify that the fan is free to rotate. Any
accumulation of ice and snow on the spinner and fan blades should be
removed using the ice shedding procedure during taxi-out and prior to setting
takeoff thrust.
GUIDANCE MATERIAL
1. Intake and Fanblade Icing
a. During extended ground operations/taxiing prior to flight in conditions of moderate to
heavy freezing precipitation, it is possible for snow and slush to accumulate within the
engine intake ducting and/or on the rear surfaces of engine compressor/ fan blades.
Such accumulation(s) may not be visible to the crew, nor prevented by the use of
engine anti-icing, especially when engines are operated at or close to ground idle rpm.
Intake duct deposits and engine blade deposits may detach and be ingested by the
engine(s) during the subsequent application of high power settings for takeoff, with
consequential adverse effects on engine operation, and possible flameout.
Ice accumulation on the surfaces of engine compressor/fan blades may severely affect
the aerodynamic characteristics of the blade(s) and cause compressor stall, leading to
surging and engine malfunctioning and/or reduced thrust.
Several accidents have already occurred due to these phenomena.
Paragraph 2 gives detailed information on general de- / anti-icing precautions for
aeroplane operations on the ground.
b. Intake icing. This is, in part, caused by the design of engine intake / ducting on certain
aircraft, whereby accumulations of snow and/or slush can occur in the engine air
intake(s) during low power engine operations, such as taxiing after landing and also
prior to takeoff, in certain meteorological conditions. Relatively long/curved intake
ducts/tracts are particularly prone to this phenomenon.
This phenomenon is most likely in occur to susceptible aircraft during precipitation of
heavy snow or rain at temperatures close to 0°c before and after engine start. In such
cases, the use of engine anti ice system may be ineffective in preventing accumulations
forming in engine intakes.
It is also likely that such deposits may not be visible or apparent to pilots and ground
staff, particularly so in the case of high-mounted engines. Also, in some cases,
accumulation will not take place until after engine start. This situation may be masked
by the fact that the de/anti-icing treatment of the rest of the airframe is still effective,
with frozen deposits not yet forming on the treated areas.
The consequences of unrecognised intake icing will only become evident during high
power engine running (i.e. during takeoff), when it can be too late to take precautionary
actions.
c. Ice accumulation on the rear face of engine compressor / fan blades. This phenomenon
is most likely to occur in susceptible engines during precipitation of heavy snow or rain
precipitation at temperatures close to 0°c before and after engine start. In such cases,
the use of engine anti-ice system may be ineffective in preventing accumulations
forming on the rear faces of blades.
4 of 12
It is also likely that such deposits may not be visible or apparent to pilots and ground
staff, particularly so in the case of high-mounted engines. Also, in some cases,
accumulation will not take place until after engine start (rotating parts striking supercooled
droplets).
Note: Compressor/fan blade icing may have occurred during the previous approach/taxi
in. In this case, such accumulations may be detected during a subsequent pre-flight
inspection (PFI). The potential for re-occurrence during any subsequent operation of
engine(s) must be recognised and precautionary measures taken.
Alternatively, accumulations may occur after engine-start on previously inspected and
“clean” blades. Such occurrences will therefore not be detected during PFI, nor during
normal idle/low power running of engines during ground manoeuvring.
In such cases, it is vital that the potential for blade icing is fully understood by
responsible staff and appropriate countermeasures are employed, as recommended by
the aircraft manufacturer.
The consequences of unrecognised blade icing will only become evident during high
power engine running (i.e. during takeoff), when it can be too late to take precautionary
actions.
d. Recommendation. In the first instance, manufacturers’ recommendations, where given,
should be followed.
In cases where guidance is not provided, operators should liaise with manufacturers
and other qualified entities to obtain advice in order to develop suitable procedures.
It is recommended that operators take appropriate action to recognise and address
these phenomena in their Operations Manuals and to give suitable advice, guidance
and training to pilots and ground staff. Good coordination between Operations and
Maintenance is essential, in particular with regard to maintenance inspections (in
conjunction with the maintenance programme and manufacturer’s recommendations).
Although these phenomena are known to affect certain turbine powered aircraft, it
should be borne in mind that certain piston-engine powered aircraft could be susceptible
to these phenomena, too.
1. Intake and Fanblade Icing
a. During extended ground operations/taxiing prior to flight in conditions of moderate to
heavy freezing precipitation, it is possible for snow and slush to accumulate within the
engine intake ducting and/or on the rear surfaces of engine compressor/ fan blades.
Such accumulation(s) may not be visible to the crew, nor prevented by the use of
engine anti-icing, especially when engines are operated at or close to ground idle rpm.
Intake duct deposits and engine blade deposits may detach and be ingested by the
engine(s) during the subsequent application of high power settings for takeoff, with
consequential adverse effects on engine operation, and possible flameout.
Ice accumulation on the surfaces of engine compressor/fan blades may severely affect
the aerodynamic characteristics of the blade(s) and cause compressor stall, leading to
surging and engine malfunctioning and/or reduced thrust.
Several accidents have already occurred due to these phenomena.
Paragraph 2 gives detailed information on general de- / anti-icing precautions for
aeroplane operations on the ground.
b. Intake icing. This is, in part, caused by the design of engine intake / ducting on certain
aircraft, whereby accumulations of snow and/or slush can occur in the engine air
intake(s) during low power engine operations, such as taxiing after landing and also
prior to takeoff, in certain meteorological conditions. Relatively long/curved intake
ducts/tracts are particularly prone to this phenomenon.
This phenomenon is most likely in occur to susceptible aircraft during precipitation of
heavy snow or rain at temperatures close to 0°c before and after engine start. In such
cases, the use of engine anti ice system may be ineffective in preventing accumulations
forming in engine intakes.
It is also likely that such deposits may not be visible or apparent to pilots and ground
staff, particularly so in the case of high-mounted engines. Also, in some cases,
accumulation will not take place until after engine start. This situation may be masked
by the fact that the de/anti-icing treatment of the rest of the airframe is still effective,
with frozen deposits not yet forming on the treated areas.
The consequences of unrecognised intake icing will only become evident during high
power engine running (i.e. during takeoff), when it can be too late to take precautionary
actions.
c. Ice accumulation on the rear face of engine compressor / fan blades. This phenomenon
is most likely to occur in susceptible engines during precipitation of heavy snow or rain
precipitation at temperatures close to 0°c before and after engine start. In such cases,
the use of engine anti-ice system may be ineffective in preventing accumulations
forming on the rear faces of blades.
4 of 12
It is also likely that such deposits may not be visible or apparent to pilots and ground
staff, particularly so in the case of high-mounted engines. Also, in some cases,
accumulation will not take place until after engine start (rotating parts striking supercooled
droplets).
Note: Compressor/fan blade icing may have occurred during the previous approach/taxi
in. In this case, such accumulations may be detected during a subsequent pre-flight
inspection (PFI). The potential for re-occurrence during any subsequent operation of
engine(s) must be recognised and precautionary measures taken.
Alternatively, accumulations may occur after engine-start on previously inspected and
“clean” blades. Such occurrences will therefore not be detected during PFI, nor during
normal idle/low power running of engines during ground manoeuvring.
In such cases, it is vital that the potential for blade icing is fully understood by
responsible staff and appropriate countermeasures are employed, as recommended by
the aircraft manufacturer.
The consequences of unrecognised blade icing will only become evident during high
power engine running (i.e. during takeoff), when it can be too late to take precautionary
actions.
d. Recommendation. In the first instance, manufacturers’ recommendations, where given,
should be followed.
In cases where guidance is not provided, operators should liaise with manufacturers
and other qualified entities to obtain advice in order to develop suitable procedures.
It is recommended that operators take appropriate action to recognise and address
these phenomena in their Operations Manuals and to give suitable advice, guidance
and training to pilots and ground staff. Good coordination between Operations and
Maintenance is essential, in particular with regard to maintenance inspections (in
conjunction with the maintenance programme and manufacturer’s recommendations).
Although these phenomena are known to affect certain turbine powered aircraft, it
should be borne in mind that certain piston-engine powered aircraft could be susceptible
to these phenomena, too.
Last edited by STBYRUD; 4th Nov 2011 at 10:20.
I'm afraid your de-icing provider was correct - quotes from my airline winter ops guide material:
In conjunction with the contamination check, prior to engine start, the engines must be inspected. Only hoar frost is permitted on the exterior of the engine. However, engine inlets, inlet lips, fans (check for rotation), spinners, fan exhaust ducts, must be checked free of frost, ice, snow and slush.
Engine anti-ice should be ON whenever ground-icing conditions exist or anticipated. High bypass ratio engines are particularly vulnerable to the formation of ice on and in the engine during low power ground operations. With engine anti-ice selected to ON, the leading edge of the inlet lip and inlet sensor systems are anti-iced, but the spinner, fan blades, and low-pressure compressor inlet stator are not.
Engine ice build-up can occur during taxi and ground holding even without visible moisture present. Industry events involving severe engine damage point to increased risk when the OAT is in the range from +5°C to -5°C and visibility is reduced in drizzle, rain, freezing drizzle or freezing rain.
When operating in this range,
Flightcrew should take the following precautions:
Engine nacelle inlet and fan blades should be carefully inspected as close to departure time as practicable to ensure that the face and backs of the fan blades are free of ice, as well as of snow or frost, that the fan is clear and free to rotate and no pooling of moisture is present. This is to avoid any engine damage, e.g. due to the ingestion of ice or to the accretion of snow that might block the fan. Manufacturers provide a ground run-up ice-shedding procedure to avoid engine damage. All such procedures presume that the engine was free of contamination when it was started. The engine warm-up time of at least 2 minutes (in order to avoid thermal shock) must additionally be respected, with the thermal shock risk being higher in icing. Refer to the QRH for static run-up procedures.
Engine ice build-up can occur during taxi and ground holding even without visible moisture present. Industry events involving severe engine damage point to increased risk when the OAT is in the range from +5°C to -5°C and visibility is reduced in drizzle, rain, freezing drizzle or freezing rain.
When operating in this range,
Flightcrew should take the following precautions:
Engine nacelle inlet and fan blades should be carefully inspected as close to departure time as practicable to ensure that the face and backs of the fan blades are free of ice, as well as of snow or frost, that the fan is clear and free to rotate and no pooling of moisture is present. This is to avoid any engine damage, e.g. due to the ingestion of ice or to the accretion of snow that might block the fan. Manufacturers provide a ground run-up ice-shedding procedure to avoid engine damage. All such procedures presume that the engine was free of contamination when it was started. The engine warm-up time of at least 2 minutes (in order to avoid thermal shock) must additionally be respected, with the thermal shock risk being higher in icing. Refer to the QRH for static run-up procedures.
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I'm afraid your de-icing provider was correct
Yes, it is sensible. Yes it needs to be properly enforced, and not just 'here and there'.
STBYRUD - I'm not sure where you start from when you go holding over PSA, but I think some sort of notification to your company would be in order, and if it is not a 'mandatory' under your regulator, maybe an ASR?
Or if you suspect fan icing on taxi in, perform an ice shedding procedure as close to shut down as possible (given jet blast problems behind, of course). If that gives you a clean engine for the turn around, problem solved 
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Different companies have different procedures. In our supplementary normal procedures there is something about fan blade icing and according to that it is allowed as long as you can get rid of it with a normal ice shedding procedure.
Engine inlets...................................................... ...................................CHECK
Verify that the inlet cowling is free of snow and ice.
Verify that the fan is free to rotate.
Snow or ice that accumulates on the fan spinner or fan blades during extended shutdown periods must be removed by maintenance or other means before engine start.
Snow or ice that accumulates on the fan spinner or fan blades as a result of operation in icing conditions, such as during approach or taxi in, is allowed if the fan is free to rotate and the snow or ice is removed using the ice shedding procedure during taxi out and before setting takeoff thrust.
Verify that the inlet cowling is free of snow and ice.
Verify that the fan is free to rotate.
Snow or ice that accumulates on the fan spinner or fan blades during extended shutdown periods must be removed by maintenance or other means before engine start.
Snow or ice that accumulates on the fan spinner or fan blades as a result of operation in icing conditions, such as during approach or taxi in, is allowed if the fan is free to rotate and the snow or ice is removed using the ice shedding procedure during taxi out and before setting takeoff thrust.
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Thanks for the replies so far, that section Denti posted reads strangely familiar, thats also in my book The one I posted above is the bog standard Boeing FCOM. So where does that leave us? When I reported the event to the company last year I got a confused reply that 'its all in the book' and they could not understand why I would wonder about it... Lets say that there is no such thing like the 'clean wing policy' that ICAO would advocate for engines, would I be right in saying that? Boeing seems to think its not a big deal as long as the fan can spin and you shed the ice before TO, obviously ground service companies want to sell their services AND cover their asses... Hm.
The one I posted above is the bog standard Boeing FCOM. So where does that leave us? When I reported the event to the company last year I got a confused reply that 'its all in the book' and they could not understand why I would wonder about it... Lets say that there is no such thing like the 'clean wing policy' that ICAO would advocate for engines, would I be right in saying that? Boeing seems to think its not a big deal as long as the fan can spin and you shed the ice before TO, obviously ground service companies want to sell their services AND cover their asses... Hm.
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I have to say i was kinda surprised when i discovered this little gem in our manuals, in my previous company fan blade ice had to be removed before engine start, no exceptions. The company owned the necessary equipment and we used it quite often.
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CFM Flight Operations Newsletter №3 Fall 2010
One of the most frequently asked questions from flight crews
is, “How much ice accumulation on the spinner and fan blades
is acceptable before deicing is required prior to dispatch?”
Unfortunately, due to various environmental conditions,
airport operations, airline policies and procedures, etc., there
is no single recommendation that encompasses all situations.
Typically, operators task the ground maintenance crews with
engine deicing as required. During preflight, the flight crew
verifies that the engine cowl and inlet are free of contaminants
and that the fan rotates freely.
Figures 1, 2, and 3 show various spinner/fan blade ice
conditions that can be encountered during operations in
icing conditions.
Figures 1 and 2 show that ice has accumulated only on the
spinner cone and that no ice is visible on the fan blades,
booster splitter or booster inlet guide vanes. In these
situations, even if a thin layer of ice/snow were present on
the fan blades, performing the ground ice shed procedure
per the FCOM (Flight Crew Operating Manual) would be
sufficient.
Figure 3 shows the spinner completely ice-covered and ice
accumulated on the fan blade leading edge and pressure
surface, with the heaviest concentration at the root and
decreasing towards the fan blade tip. This phenomenon is
due to centrifugal forces preventing ice build-up near the
tip. In this case, as well as situations where ice accumulation
is visible on the booster splitter and inlet guide vanes, it is
advisable to discuss the situation with maintenance prior to
dispatch, particularly if moderate to severe icing conditions
are forecast for taxi and takeoff. If deicing the engine prior
to push back or delaying the flight is not an option, then
perform the FCOM ice shed procedure as soon as possible
during taxi-out.
Important: The information, opinions and recommendations presented in this article are those of the engine manufacturer. The
policies, documents and operating procedures specified by the airplane manufacturers and your airline take precedence.
All Document: http://aviacom.ucoz.ru/CFM_Flight_Op..._Fall_2010.pdf
One of the most frequently asked questions from flight crews
is, “How much ice accumulation on the spinner and fan blades
is acceptable before deicing is required prior to dispatch?”
Unfortunately, due to various environmental conditions,
airport operations, airline policies and procedures, etc., there
is no single recommendation that encompasses all situations.
Typically, operators task the ground maintenance crews with
engine deicing as required. During preflight, the flight crew
verifies that the engine cowl and inlet are free of contaminants
and that the fan rotates freely.
Figures 1, 2, and 3 show various spinner/fan blade ice
conditions that can be encountered during operations in
icing conditions.
Figures 1 and 2 show that ice has accumulated only on the
spinner cone and that no ice is visible on the fan blades,
booster splitter or booster inlet guide vanes. In these
situations, even if a thin layer of ice/snow were present on
the fan blades, performing the ground ice shed procedure
per the FCOM (Flight Crew Operating Manual) would be
sufficient.
Figure 3 shows the spinner completely ice-covered and ice
accumulated on the fan blade leading edge and pressure
surface, with the heaviest concentration at the root and
decreasing towards the fan blade tip. This phenomenon is
due to centrifugal forces preventing ice build-up near the
tip. In this case, as well as situations where ice accumulation
is visible on the booster splitter and inlet guide vanes, it is
advisable to discuss the situation with maintenance prior to
dispatch, particularly if moderate to severe icing conditions
are forecast for taxi and takeoff. If deicing the engine prior
to push back or delaying the flight is not an option, then
perform the FCOM ice shed procedure as soon as possible
during taxi-out.
Important: The information, opinions and recommendations presented in this article are those of the engine manufacturer. The
policies, documents and operating procedures specified by the airplane manufacturers and your airline take precedence.
All Document: http://aviacom.ucoz.ru/CFM_Flight_Op..._Fall_2010.pdf
All above seem to cover the question.
However some situations do require interpretation and judgements, best left to the manufacturer and company procedures.
It sounds to me like this is outside the purvey of a ground deicing company (you better have the procedures available to display
It's impractical for a ground deicing company to perform an operating function or maintenance function on an aircraft which is what would be required to get rid of ice inside an engine pod.
The safety of flight must always be paramount, and this is often assured by ground operating procedures before starting the takeoff roll (runups at prescribe conditions to shed the ice when its small enough not to cause damage to the engine parts.
Aerodynamic issues are not significant (for the engines) since by the time you have got the engines anywhere near its stall line, the ground-idle ice has shed (its the possibilty of mechanical dmg from the ice shed that is to be avoided)
Lots of room for more discussion on this e.g. what do you do when there is way too much ice buildup to safely shed
However some situations do require interpretation and judgements, best left to the manufacturer and company procedures.
It sounds to me like this is outside the purvey of a ground deicing company (you better have the procedures available to display
It's impractical for a ground deicing company to perform an operating function or maintenance function on an aircraft which is what would be required to get rid of ice inside an engine pod.
The safety of flight must always be paramount, and this is often assured by ground operating procedures before starting the takeoff roll (runups at prescribe conditions to shed the ice when its small enough not to cause damage to the engine parts.
Aerodynamic issues are not significant (for the engines) since by the time you have got the engines anywhere near its stall line, the ground-idle ice has shed (its the possibilty of mechanical dmg from the ice shed that is to be avoided)
Lots of room for more discussion on this e.g. what do you do when there is way too much ice buildup to safely shed
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It's impractical for a ground deicing company to perform an operating function or maintenance function on an aircraft which is what would be required to get rid of ice inside an engine pod.
I think this is interesting. We are required to remove fan blade ice that accumulates during taxi-in during freezing fog type weather. I think that usually this is silly, as it will accumulate again during taxi-out, and needs removing with a run-up at the take off hold.
I am going to send some of this to the deicing chief.
Sweedish Steve
Interesting
Some risk in somebody getting into your engine unless under the control of maintenance. I suppose with training and some oversight it's OK.
Just keep the dirty boots and loose change/FOD out and of course no frayed electrical wires that touch the fan blade.
Not always. Here in ARN the deicing company performs fan blade deicing with hot air. When they are called out for deicing, they will always inspect the fan blades. The ice forms on the back of the blades, and is not always visible.
Some risk in somebody getting into your engine unless under the control of maintenance. I suppose with training and some oversight it's OK.
Just keep the dirty boots and loose change/FOD out and of course no frayed electrical wires that touch the fan blade.
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After shut down, spin the fan in the backwards direction? Hot core air now defrosts the ice (on inboard fan section - where it usually forms). Watch out for refreeze. If you have a tail wind on stand, you have auto deice, no tail wind, you have manual deice. As you sit spinning the fan, think of what you are gonna tell the few pax know ask if you were trying to start the thing up ;-)
Ice shed run up before shutdown preferable, careful of the taxiway fiction capability as well as the efflux.
Mr L
Ice shed run up before shutdown preferable, careful of the taxiway fiction capability as well as the efflux.
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Fan De-icing
I am very new to this so please forgive this question.
I read an article where de-icing on the ground of the fan blades and core is normally done using hot air pumped forward from the rear of the engine. There were certain specific limitations regarding max pressure and temperature of the de-icing air used. It also mentioned the fact that the details were given in the Maintenance Manual.
However my question is why can't you use normal de-icing fluid as you would on the wings etc?
I read an article where de-icing on the ground of the fan blades and core is normally done using hot air pumped forward from the rear of the engine. There were certain specific limitations regarding max pressure and temperature of the de-icing air used. It also mentioned the fact that the details were given in the Maintenance Manual.
However my question is why can't you use normal de-icing fluid as you would on the wings etc?
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That would gunk up the engine, get into tiny holes, would cause all kinds of problems - sticky glycol and precision mechanics dont mix...
By the way, I like what LEOS came up with and is now testing in FRA - A contraption that channels pack cooling exhaust into the engines - no need for an A/C cart or frost fighter - good stuff! Hope they make more of them and have them ready soon...
By the way, I like what LEOS came up with and is now testing in FRA - A contraption that channels pack cooling exhaust into the engines - no need for an A/C cart or frost fighter - good stuff! Hope they make more of them and have them ready soon...
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I have a doubt : the supplementary procedures say icing condition exist when oat is below 10C and there is -visibible moisture with visibility less than 1statute mile or -ice,snow etc. So if we have for example -20 degrees with clear sky , high visibility and very low humidity, how to behave? In the preflight we should put the PROBE HEAT ON? Put anti-ice? Etc....???
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I'd had this scenario many times on the 73 and 320s where ice would be lodged at the back the turbines blades in the front section only. Heater available in 2 hrs stuff. A good pair of leather gloves I individually removed the ice from each blade....pain in ars@, hands frozen but job done plus a run up prior to t/o.....
