Anti Ice questions
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Anti Ice questions
Hi,
I'm prepping for my TR on the NG and I have a few q's:
Let's assume it's snowing, OAT = -5°C
After being deiced, would you take off using
a) Engine A/I
b) Wing A/I
c) Both
d) None?
And why?
And what about landing:
during descent, as SAT increases above -40°, you turn on Engine A/I and as you enter clouds and you see freezing, you turn on Wing A/I.
TAT never reaches +10°C
Would you land with both Engine A/I and Wing A/I?
Thanks!
I'm prepping for my TR on the NG and I have a few q's:
Let's assume it's snowing, OAT = -5°C
After being deiced, would you take off using
a) Engine A/I
b) Wing A/I
c) Both
d) None?
And why?
And what about landing:
during descent, as SAT increases above -40°, you turn on Engine A/I and as you enter clouds and you see freezing, you turn on Wing A/I.
TAT never reaches +10°C
Would you land with both Engine A/I and Wing A/I?
Thanks!
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I do not fly the 737 but see no reason why it should differ significantly from any other jet type. That said, I would answer;
a) Yes. OAT less than plus ten degrees and visible moisture present.
b) Yes. OAT less than plus three degrees and same conditions as above.
c) Yes. See a and b above.
d) No, both. See a,b and c above.
In the descent your first concern will be engine anti ice once the SAT has increased to minus 40C, but only if there is visible moisture present. If there is no visible moisture you need not concern yourself. Regarding airframe ice, this is generally likely to be of concern later in the descent when the SAT warms to minus 20C, but again only if there is something in the atmosphere to freeze. On a clear day with no moisture present you need not worry about engine or airframe icing however cold it gets.
a) Yes. OAT less than plus ten degrees and visible moisture present.
b) Yes. OAT less than plus three degrees and same conditions as above.
c) Yes. See a and b above.
d) No, both. See a,b and c above.
In the descent your first concern will be engine anti ice once the SAT has increased to minus 40C, but only if there is visible moisture present. If there is no visible moisture you need not concern yourself. Regarding airframe ice, this is generally likely to be of concern later in the descent when the SAT warms to minus 20C, but again only if there is something in the atmosphere to freeze. On a clear day with no moisture present you need not worry about engine or airframe icing however cold it gets.
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Anti ice
There is a lot of misunderstanding out there about anti-ice and de-ice procedures. I have not flown the B737 NG but have flown a lot of Boeings as well as L1011 and BAC 1-11.
On the ground de-icing fluid is applied to clear the aircraft of contamination and then protect it to the end of the 4th segment (1500 feet). You should not use wing de-ice (heat) as this can cause 2 problems.
1. Bake the fluid onto the leading edges.
2. If you loose an engine after V1 you will not have enough thrust to complete the take-off segments.
Engine anti-ice does not affect the thrust as all you are doing is giving a bit more throttle to make up the difference, so it stays on if the temp is +10 or below and there is visible moisture. The reason for the +10 and not 0 is due to the pressure drop at the intake and hence temperature drop.
Remember that your holdover time for fluid starts when the application is finished not when it is started.
On go around the wing anti-ice should be switched off if you have a single engine go-around for the reasons cited above.
On the ground de-icing fluid is applied to clear the aircraft of contamination and then protect it to the end of the 4th segment (1500 feet). You should not use wing de-ice (heat) as this can cause 2 problems.
1. Bake the fluid onto the leading edges.
2. If you loose an engine after V1 you will not have enough thrust to complete the take-off segments.
Engine anti-ice does not affect the thrust as all you are doing is giving a bit more throttle to make up the difference, so it stays on if the temp is +10 or below and there is visible moisture. The reason for the +10 and not 0 is due to the pressure drop at the intake and hence temperature drop.
Remember that your holdover time for fluid starts when the application is finished not when it is started.
On go around the wing anti-ice should be switched off if you have a single engine go-around for the reasons cited above.
Remember that your holdover time for fluid starts when the application is finished not when it is started
Not sure if this is a US vs EU difference but the FAA defines holdover times in FAR 121.629
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Cold weather ops
I fly the NG and our procedures are as follow,
We differentiate icing conditions (visible moisture, 10 deg celcius or less) and freezing conditions (visible moisture, 3 degrees or less).
In your scenario -5 deg and snow it would be freezing conditions.
ENGINE Anti Ice (TAI) on in icing conditions, during taxi, climb and level flight with SAT above -40 deg. TAI on always during descent when in icing conditions, also with temp below -40 deg.
WING Anti Ice (WAI) on the ground during taxi in icing conditions, but not if de-iced with type 2 or 4 fluid. As mentioned above, it will bake the fluid to the wing. If de-iced with type 1 fluid you would select WAI on. However WAI will trip off when selecting T/O thrust.
WAI on descent only as needed when encountering actual airframe icing, good indication is ice forming on the windshield near the centre post, or on the windshield wipers. Its recommended by boeing to use WAI as a de-icer, so you
would let a thin layer of ice build up on the wings and then select WAI on to clear it of, when you visually confirmed the leading edge is clean, you swith WAI off again.
HOT starts at start of the application of anti-ice fluid (second step if two step procedure).
good luck with the type rating
We differentiate icing conditions (visible moisture, 10 deg celcius or less) and freezing conditions (visible moisture, 3 degrees or less).
In your scenario -5 deg and snow it would be freezing conditions.
ENGINE Anti Ice (TAI) on in icing conditions, during taxi, climb and level flight with SAT above -40 deg. TAI on always during descent when in icing conditions, also with temp below -40 deg.
WING Anti Ice (WAI) on the ground during taxi in icing conditions, but not if de-iced with type 2 or 4 fluid. As mentioned above, it will bake the fluid to the wing. If de-iced with type 1 fluid you would select WAI on. However WAI will trip off when selecting T/O thrust.
WAI on descent only as needed when encountering actual airframe icing, good indication is ice forming on the windshield near the centre post, or on the windshield wipers. Its recommended by boeing to use WAI as a de-icer, so you
would let a thin layer of ice build up on the wings and then select WAI on to clear it of, when you visually confirmed the leading edge is clean, you swith WAI off again.
HOT starts at start of the application of anti-ice fluid (second step if two step procedure).
good luck with the type rating
Last edited by Ditched; 8th Feb 2012 at 19:17.
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The FCOM is quite clear about engine and wing anti ice on the ground. Any time engine anti ice is used, wing anti ice must also be selected (with the only exception being after a type II or IV fluid has been applied). therefore one temp is below +10 with visible moisture then you will be using both.
As above, when in flight WAI is only used when ice build is observed.
Kenny is quite right, no differnces here - HOT begins at the start of the application of the anti ice procedure.
As above, when in flight WAI is only used when ice build is observed.
Kenny is quite right, no differnces here - HOT begins at the start of the application of the anti ice procedure.
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Anti ice
Hold Over Times
Some interesting replies re HOT
There was an iccident in Oslo many years ago with a B737 operated by BA on charter. De icing fluid was applied but halfway through the applicator ran out and had to be refilled (took about 30 mins). The other side of the aircraft was de-iced and the time was started at the finish of application. As the aircraft got airborne it rolled to 90 degrees and only through the quick action of the crew holding top rudder did they survive. When the aircraft got to 210 kts (or thereabouts) the ice came off the stalled wing and a normal landing ensued. I believe as a result of this incident UK rules were changed that HOT starts at the end of the procedure.
I can understand if this has been changed due to financial reasons, but I would be vary careful on the amount of time from start to finish.
If you take off with the wing de-ice bleeds on and loose an engine (I realise you would be having a very bad day and the chances of that happening at MTOW on a limiting climbout are probably nil) then you will not have enough thrust to complete the 4 segments. Certification is based on no wing AI blleds on.
Also if you taxi with the WAI on then you are going to really heat up the leading edges (no airflow over them) leading to all kinds of problems. On the B727 it was definately a no do and the result was invaribly led indication malfuntions. We had an AD from Boeing telling us not to do it. On most aircraft the WAI is inhibted on the ground by the squat switch. However picture what is going on when you lift off, the bleeds open and you loose a fair chunk of thrust right at the time you call for wheels up and the gear doors open increasing your drag. If this is your procedure I would ask your managment to re-look at your procedures.
Some interesting replies re HOT
There was an iccident in Oslo many years ago with a B737 operated by BA on charter. De icing fluid was applied but halfway through the applicator ran out and had to be refilled (took about 30 mins). The other side of the aircraft was de-iced and the time was started at the finish of application. As the aircraft got airborne it rolled to 90 degrees and only through the quick action of the crew holding top rudder did they survive. When the aircraft got to 210 kts (or thereabouts) the ice came off the stalled wing and a normal landing ensued. I believe as a result of this incident UK rules were changed that HOT starts at the end of the procedure.
I can understand if this has been changed due to financial reasons, but I would be vary careful on the amount of time from start to finish.
If you take off with the wing de-ice bleeds on and loose an engine (I realise you would be having a very bad day and the chances of that happening at MTOW on a limiting climbout are probably nil) then you will not have enough thrust to complete the 4 segments. Certification is based on no wing AI blleds on.
Also if you taxi with the WAI on then you are going to really heat up the leading edges (no airflow over them) leading to all kinds of problems. On the B727 it was definately a no do and the result was invaribly led indication malfuntions. We had an AD from Boeing telling us not to do it. On most aircraft the WAI is inhibted on the ground by the squat switch. However picture what is going on when you lift off, the bleeds open and you loose a fair chunk of thrust right at the time you call for wheels up and the gear doors open increasing your drag. If this is your procedure I would ask your managment to re-look at your procedures.
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Anti Ice
Sorry I made a mistake in my first post. HOT is of course started at the start of final application.
FODCOM 19/2006
2.1 Holdover Times
2.1.1 The holdover time for de-icing/anti-icing fluids is determined by thorough scientific investigation using a standard series of tests. The resulting holdover timetable provides an estimated time that the de-icing/anti-icing fluid will prevent the formation of frost or ice and the accumulation of snow on the protected surfaces of the aircraft whilst on the ground. The guidelines do not imply icing protection when airborne.
2.1.2 Holdover time begins when the final application of anti-icing fluid commences, and expires when the anti-icing fluid loses its effectiveness. It is essential therefore that flight crew understand how holdover times are derived and what constitutes a failed anti-icing fluid.
2.1.3 Holdover times are published on the AEA website at AEA - Home and the AEA reference document is “Recommendations for De-icing/Anti-icing of Aircraft on the Ground”. Holdover times may also be provided by de-icing/anti-icing fluid manufacturers. These times have been derived from standard tests specified in the Society of Automotive Engineers (SAE) documents. As these tests could not fully simulate the number of variables existing, information has been included with the holdover timetables that indicate factors that may cause the fluid to fail earlier than the published holdover time.
2.1.4 Flight crew should use the published holdover time, plus their judgement of the actual conditions as guided by their company procedures and training, to decide whether the fluid is likely to have.
pre-take-off check or pre-take-off contamination check as defined below.
a) Pre-take-off Check. The commander should continually monitor the environmental situation after the performed de-icing/ant-icing treatment. Prior to take-off he should assess whether the applied holdover time is still appropriate. This check is normally performed from inside the flight deck.
b) Pre-take-off Contamination Check. A check of the critical surfaces for contamination should be completed. This check should be performed when the condition of the critical surfaces of the aircraft cannot be effectively assessed by a pre-take-off check or when the applied holdover time has been exceeded. This check is normally performed from outside the aircraft. The alternate means of compliance to a pre-take-off contamination check is a complete de-icing/anti-icing re-treatment of the aircraft.
2.1.5 It has come to the notice of the CAA that some operators have procedures which allow the published holdover times to be varied by not starting the holdover time when the fluid is applied but when precipitation starts, or by starting and stopping the holdover time as precipitation starts and stops. Both these methods are untested and, from a technical viewpoint, are considered non-conservative and may well give flight crew misleading information on which to base their take-off decision. Once the published holdover time is exceeded the probability of fluid failure is increased.
2.2 Flight Crew Awareness
2.2.1 Operators should remind flight crew of the need to keep the aircraft surfaces free from frost, ice, slush and snow unless otherwise permitted in the aircraft flight manual.
2.2.2 Flight crew training should include information on the construction and use of holdover timetables, and on how to recognise the point at which the duration of holdover protection is reduced and a fluid is deemed to have failed. This can be recognised when frozen deposits start to form or accumulate on treated aeroplane surfaces.
2.2.3 As previously stated, the holdover time starts when the anti-icing fluid layer starts to be applied and runs continuously until the lower or upper limit is reached, at which point the holdover time is exceeded. The Commander should use his judgement, backed up with appropriate checks as detailed above, to establish whether it is still safe to depart when the holdover time has been exceeded.
2.3 Operators’ Responsibility
2.3.1 Operators are reminded that it is their responsibility to have in place robust procedures for the operation of aircraft in icing conditions; these include detailed ground de-icing/anti-icing holdover time procedures.
2.4 Recommendation
2.4.1 Operators should review their de-icing/anti-icing holdover time procedures and training in the light of the above, amending their Operations Manuals where necessary.
Hope this clears it up
FODCOM 19/2006
2.1 Holdover Times
2.1.1 The holdover time for de-icing/anti-icing fluids is determined by thorough scientific investigation using a standard series of tests. The resulting holdover timetable provides an estimated time that the de-icing/anti-icing fluid will prevent the formation of frost or ice and the accumulation of snow on the protected surfaces of the aircraft whilst on the ground. The guidelines do not imply icing protection when airborne.
2.1.2 Holdover time begins when the final application of anti-icing fluid commences, and expires when the anti-icing fluid loses its effectiveness. It is essential therefore that flight crew understand how holdover times are derived and what constitutes a failed anti-icing fluid.
2.1.3 Holdover times are published on the AEA website at AEA - Home and the AEA reference document is “Recommendations for De-icing/Anti-icing of Aircraft on the Ground”. Holdover times may also be provided by de-icing/anti-icing fluid manufacturers. These times have been derived from standard tests specified in the Society of Automotive Engineers (SAE) documents. As these tests could not fully simulate the number of variables existing, information has been included with the holdover timetables that indicate factors that may cause the fluid to fail earlier than the published holdover time.
2.1.4 Flight crew should use the published holdover time, plus their judgement of the actual conditions as guided by their company procedures and training, to decide whether the fluid is likely to have.
pre-take-off check or pre-take-off contamination check as defined below.
a) Pre-take-off Check. The commander should continually monitor the environmental situation after the performed de-icing/ant-icing treatment. Prior to take-off he should assess whether the applied holdover time is still appropriate. This check is normally performed from inside the flight deck.
b) Pre-take-off Contamination Check. A check of the critical surfaces for contamination should be completed. This check should be performed when the condition of the critical surfaces of the aircraft cannot be effectively assessed by a pre-take-off check or when the applied holdover time has been exceeded. This check is normally performed from outside the aircraft. The alternate means of compliance to a pre-take-off contamination check is a complete de-icing/anti-icing re-treatment of the aircraft.
2.1.5 It has come to the notice of the CAA that some operators have procedures which allow the published holdover times to be varied by not starting the holdover time when the fluid is applied but when precipitation starts, or by starting and stopping the holdover time as precipitation starts and stops. Both these methods are untested and, from a technical viewpoint, are considered non-conservative and may well give flight crew misleading information on which to base their take-off decision. Once the published holdover time is exceeded the probability of fluid failure is increased.
2.2 Flight Crew Awareness
2.2.1 Operators should remind flight crew of the need to keep the aircraft surfaces free from frost, ice, slush and snow unless otherwise permitted in the aircraft flight manual.
2.2.2 Flight crew training should include information on the construction and use of holdover timetables, and on how to recognise the point at which the duration of holdover protection is reduced and a fluid is deemed to have failed. This can be recognised when frozen deposits start to form or accumulate on treated aeroplane surfaces.
2.2.3 As previously stated, the holdover time starts when the anti-icing fluid layer starts to be applied and runs continuously until the lower or upper limit is reached, at which point the holdover time is exceeded. The Commander should use his judgement, backed up with appropriate checks as detailed above, to establish whether it is still safe to depart when the holdover time has been exceeded.
2.3 Operators’ Responsibility
2.3.1 Operators are reminded that it is their responsibility to have in place robust procedures for the operation of aircraft in icing conditions; these include detailed ground de-icing/anti-icing holdover time procedures.
2.4 Recommendation
2.4.1 Operators should review their de-icing/anti-icing holdover time procedures and training in the light of the above, amending their Operations Manuals where necessary.
Hope this clears it up
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On the NG with wing anti ice on the ground the valves will close when take off thrust is set, this takes care of the lack of thrust issue. At lift off the wing anti ice switch trips off. Using wing anti ice on the gnd with 8 degrees and rain feels very uneccessary and agreed, simply over heats the leading edge. I believe it's boeing's own supp procedure to be used in icing conditions (10 degrees or below with visible moisture). If our company wanted this added to the FCOM then Boeing would have to issue a NTO (No technical objection) first so one way or another it is Boeing approved. Below is the FCOM text:
Wing Anti-ice Operation - On the Ground
Use wing anti-ice during all ground operations between engine start and takeoff when icing conditions exist or are anticipated, unless the airplane is, or will be protected by the application of Type II or Type IV fluid in compliance with an approved ground de-icing program.
Wing Anti-ice Operation - On the Ground
Use wing anti-ice during all ground operations between engine start and takeoff when icing conditions exist or are anticipated, unless the airplane is, or will be protected by the application of Type II or Type IV fluid in compliance with an approved ground de-icing program.
