News:

Precision Simulator update 10.173 (24 February 2024) is now available.
Navburo update 13 (23 November 2022) is now available.
NG FMC and More is released.

Main Menu

Anti-Ice - utilization

Started by andrej, Mon, 22 Mar 2021 09:40

andrej

Hello all,

I am in need of a little guidance on how to use the anti-ice. For the record, I prefer the Anti-Ice system with with automatic control.

On a ground -> in icing conditions (temp. <=10*C, visible moisture)

After startup, and after de-icing, I turn on WAI, NAI. Then once doing my after-take off flow, I move both to Auto.

In the air -> in icing conditions
I leave it in Auto

On an approach -> in icing conditions
I turn on EAI and NAI  during the approach phase and move back to auto after I do my after landing flows.

Now, I noticed that, if left up to my co-pilot, NAI seems to have more priority than WAI. Why is that? Most importantly, what I am doing wrong / have missed?

Thank you for any guidance.
Best!
Andrej

United744

Hi,

From what I understand of the systems, the wing "anti-ice" isn't...it's DE-ICE. Why does this matter?

An anti-ice system is pre-emptive. It's switched on BEFORE the problem starts, as to prevent the problem occurring (within limits).

A de-ice system is reactionary. The situation must have occurred before it can be used (for example, de-ice boots are used AFTER ice has already started to form on the leading edges, otherwise far from removing ice, they can actually help the build-up then become completely ineffective).

The rule-of-thumb for any anti-ice or de-ice system is "freezing conditions exist and visible moisture present".

In the case of nacelle anti-ice, the engines are sucking air, reducing the local air pressure around the nacelles cooling the intake air, and subsequently the intakes, and thus ice can accumulate in conditions as warm as +10 deg. C TAT.

In the case of wing anti-ice, withOUT auto-mode, the ice-detector will accrue icing until such time as it conducts electricity, at which moment the "WING ICING" alert will appear. This is the time to switch on wing anti-ice.

If the auto mode is fitted, the auto system will activate in place of the alert, and then will switch off some time after the condition is cleared.

With nacelle anti-ice, a similar ice detection system exists, and will switch the system on/off more frequently.

Personally, while auto mode is OK for nacelle anti-ice, I prefer to override the system and switch it on if conditions exist and I'm flying through cloud. It may not be required (and the auto system may not switch it on) but it is preventative and ensures the intakes/fan are clear of ice.

Once I'm clear of the top of cloud, I give the system a minute, then I switch it off.

In summary:

Engine anti-ice ON when:

TAT <= +10 deg. C and visible moisture present (mist/fog, cloud).

Wing anti-ice ON when:

* Alert message
* Visible icing (not possible in the sim)
* Switch it OFF once clear of icing conditions

Do NOT use wing anti-ice after de-icing the airframe. The fluids are NOT designed for use with wing anti-ice on the ground prior to takeoff.

If you use wing anti-ice too early in the icing conditions, what happens is the precipitation hits the warm surface, runs backwards towards the unheated part of the wing, and freezes there instead.

It works by allowing some ice accumulation, then heating the underside enough for the airflow to rip the ice blocks off the wing surface and away from the wing.

Hardy Heinlin

Quote from: United744 on Mon, 22 Mar 2021 19:36
From what I understand of the systems, [...]

If you use wing anti-ice too early in the icing conditions, what happens is the precipitation hits the warm surface, runs backwards towards the unheated part of the wing, and freezes there instead.

Is that your understanding or is this info from a 744 related source?

Actually, the ice sensors detect icing conditions very early (at the sensor locations near the nose). The wing and nacelles won't be significantly iced at the time of the first sensor trigger.

The 744 anti-ice can do both anti-ice and de-ice. It can prevent ice accumulation and, when activated later, can remove ice as well -- while a plain de-ice system can only remove but not prevent.

A typcial de-ice system, for example, may be an expandable rubber body along the wing leading edge. It can only work when a good amount of ice is accumulated. The rubber body will get inflated, its volume increases, and the ice breaks off. Thereafter the rubber body volume decreases to the normal size to be ready for the next cycle. If it remains at max volume and ice accumulates again, the system will be inoperative. That's why it's important to distinguish such plain de-ice systems from anti-ice systems. The 744 has an anti-ice system, not a plain de-ice system.

This rubber body cycle logic is not to be confused with the cycle logic in the 744 ice sensor system -- see Aerowinx manual, page 473, search for "vibrates at 40 kHz by magnetostrictive effects".

United744

It was my understanding of it.

I wasn't sure if the vibration of the detect probe was also on this aircraft or another aircraft.

andrej

Thank you both for clarification. This was very helpful. :)

Best!
Andrej

Britjet

#5
Wing anti-ice (yes, that's what it's called!) on the 747 can have both manual and auto modes depending on the aircraft spec, as we know. I've never used the auto system but I do know that for both, the wing system is "ineffective" whenever the leading edge flaps are deployed, because the hot air just gets blasted overboard instead of heating the inner surfaces of the LE flaps.
They are activated and effective (either in auto or manual) whenever the aircraft is airborne with the LE flaps extended retracted. The method we used (in manual) was to switch it on for a minute or so, every time an EICAS message appeared. This mainly happened in the sim, which was a royal PITA. On the actual aircraft it was seen rarely, and if so it was usually at holding speeds in freezing cloud.
I'm reminded that the 707 had no wing ant-ice at all - it didn't need it due to the wing sweep/camber etc..
Peter

Avi

Quote from: Britjet on Tue, 23 Mar 2021 13:37
They are activated and effective (either in auto or manual) whenever the aircraft is airborne with the LE flaps extended.
You meant retracted, right?
Avi Adin
LLBG

John H Watson

Quotethe ice-detector will accrue icing until such time as it conducts electricity,

Not quite technically correct. The ice detector has a small filament which is made to vibrate at a specific frequency. When ice builds up on the filament, the frequency changes. The change in frequency is sensed and the probe is heated in timed cycles to keep the filament free of ice.

If the heat is required for a certain time period to clear the ice on the filament, the anti-ice system is activated. the anti-ice system.

QuoteThe heater cycle counter keeps track of the number
of cycles. Usually, the heater can melt the ice in approximately ten
seconds. But in severe icing, the heater is on for a longer time. If the
heater stays on for 15 to 25 seconds, the detector counts that as two
cycles. At the count of two, the detector closes the ICE COWL
switch. At the count of ten, it closes the ICE WING switch.

Britjet

@ Avi

Yes, sorry - I mean retracted...thanks..
Peter

dhob

Airplanes with the Manual anti-ice system have one ice detector installed on the left side.

The system functions as follows:

Manual
As ice builds up on the ice detector sensor element during flight, the resonant frequency of the sensing element decreases. When a 0.02 ±0.005 inch ice layer accumulates, the heater turns on to melt the ice. When the resonant frequency returns to its initial value, the heater turns off, normally 7-8 seconds after it turns on. This process is repeated as long as icing conditions exist.

When a probe icing/de-icing cycle occurs, the detector outputs an icing signal to the EIU's for 60 seconds. If an additional icing/de-icing cycle occurs during this time interval, the 60-second icing signal is begun again.

The EICAS advisory message >ICING is displayed when the ice detector output indicates icing.
(a) The EICAS advisory message >NO ICING is displayed when the ice detector output no longer indicates icing.

For airplanes with the Auto Anti-ice system installed, there are two ice detectors installed on each side. The Auto system functions as follows:

Auto
As ice builds up on the ice detector sensor element during flight, the resonant frequency of the sensing element decreases. When a 0.02 ±0.005 inch ice layer accumulates, the heater turns on to melt the ice. When the resonant frequency returns to its initial value, the heater turns off, normally 7-8 seconds after it turns on. This process is repeated as long as icing conditions exist. The ice detector keeps count of the number of icing/de-icing cycles of the sensor element.

When 2 consecutive probe icing/de-icing cycles are counted, the detector outputs a signal to activate the engine anti-ice system for 180 ±10 seconds. If an additional icing/de-icing cycle occurs during this time interval, the 180-second engine anti-ice activation period is begun again.

(a) If it takes more than 15 seconds to melt the ice on the first icing/de-icing cycle, the ice detector will activate the engine anti-ice system for 180 ±10 seconds without waiting for a second cycle.

When 10 consecutive probe icing/de-icing cycles are counted, the detector outputs a signal to activate the wing anti-ice system for 180 ±10 seconds. If an additional icing/de-icing cycle occurs during this time interval, the 180-second wing anti-ice activation period is begun again.

The Boeing FCOM, Supplemental Procedures provides the following guidance for Wing anti-ice use:

Wing Anti-ice Operation - In flight
Ice accumulation on the flight deck window frames, windshield center post, or windshield wiper arm, or side windows may be used as an indication of structural icing conditions and the need to turn on wing anti-ice.

Manual System
The wing anti-ice system may be used as a de-icer or anti-icer in flight only. The primary method is to use it as a de-icer by allowing ice to accumulate before turning wing anti-ice on. This procedure provides the cleanest airfoil surface, the least possible runback ice formation, and the least thrust and fuel penalty. Normally, it is not necessary to shed ice periodically unless extended flight through icing conditions is necessary (holding).

Auto System
The wing anti-ice system may be used as a de-icer or anti-icer in flight only. The primary method is to use the automatic ice detection system which acts as a de-icer by allowing ice to accumulate before turning wing anti-ice on. This procedure provides the cleanest airfoil surface, the least possible runback ice formation, and the least thrust and fuel penalty.

The secondary method is to use wing anti-ice before ice accumulation. Operate the wing anti-ice system as an anti-icer only during extended operations in moderate or severe icing conditions.

Operationally, on the ground after engine start, for both Manual and Auto systems, Nacelle anti-ice must be selected ON immediately after all engines are started and remain on during all ground operations when icing conditions exist or are anticipated except when OAT is less than -40°C.

Inflight, for the Manual system:
Nacelle anti-ice must be ON during all flight operations when icing conditions exist or are anticipated, except when SAT is below -40°C. When using the nacelle anti-ice system manually in areas of possible icing, activate nacelle anti-ice before entering icing conditions.
Wing anti-ice should be turned on when the >ICING EICAS message displays, or visible ice buildup on the windshield, wipers, etc. When the >NO ICING message displays, turn of the Wing anti-ice. Note, the Wing anti-ice is inhibited on the ground (valves do not open), and is ineffective inflight with the flaps out of up.

Inflight for the Auto anti-ice system:
If Nacelle switches were ON for takeoff, place them to the AUTO position during the After Takeoff checklist. The Wing Anti-ice switch remains in AUTO at all times under normal conditions.
Per Boeing procedure, the Wing anti-ice switch stays in the AUTO position throughout the flight- preflight through secure checklist. The Nacelle Anti-ice switches are in AUTO in preflight, selected to ON after engine start (if needed), set to AUTO during After Takeoff checklist, and remain in AUTO unless needed for taxi in. During shutdown checklist, they are placed back to the AUTO position.

The only time inflight the Auto anti-ice switches are placed to ON is if a NNC requires it, such as a EICAS valve message or Ice Crystal Icing.


Hardy Heinlin

Quote from: dhob on Wed, 24 Mar 2021 23:06
(a) The EICAS advisory message >NO ICING is displayed when the ice detector output no longer indicates icing.

In some older manuals, the >NO ICING message is excluded. Was that a general upgrade or is it airline specific? Does anybody know? I haven't implemented this message, and nobody asked for it in the past 10 years.


Regards,

|-|ardy

Jeroen Hoppenbrouwers

When does >NO ICING extinghuish?

Hardy Heinlin

Perhaps when anti-ice is deactivated and a certain unlatch-time-delay is passed.

dhob

#13
The >ICING and >NO ICING EICAS messages do not extinguish, they must be canceled. However, once canceled they cannot be recalled.

Hardy Heinlin

These two messages also inform about "no icing":

>ANTI-ICE WING
>ANTI-ICE NAC

They appear when no icing conditions exist and TAT > 12°C and the related anti-ice is active.

Are these also included on aircraft that have the >NO ICING message?

Maybe the former two are only enabled for dual ice dectors with auto activation systems, while the >NO ICING message is for manual systems with a single ice dector?

Will

#15
QuoteWhen does >NO ICING extinguish?

When you take your bourbon on the rocks.
Will /Chicago /USA

dhob

The >ANTI-ICE WING and >ANTI-ICE NAC are only on airplanes with the Auto anti-ice system installed. Further, they only display if the switches are in the ON position, and the TAT is > 12C and icing conditions no longer exist. If operating the system as designed, and the switches are in the AUTO position during flight, then there will not be any EICAS messages displayed. Only a non-normal condition displays an EICAS message on the auto system if the switches are in AUTO.

The >ICING and >NO ICING EICAS messages are only on the airplanes with the manual anti ice system. My best guess is these messages were added by an IDS software update quite awhile ago.

Hardy Heinlin

Thanks. That makes sense.

I'll try to implement those ICING messages in the next PSX update (for models with manual control).

Britjet

In BA with the manual system we didn't have a NO ICING message.

Jeroen Hoppenbrouwers

Quote from: Will on Thu, 25 Mar 2021 01:07
QuoteWhen does >NO ICING extinguish?

When you take your bourbon on the rocks.

That's a bug. That should have been >NO CLUE.