fabristunt

Automatic Anti-Ice Operation

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Hi everyone,

 

I've been reading the FCOM that comes with the 747 and also some others I found online, but none of them include an explaination of the automatic anti-ice, it's just mentioned as an option. On smartcockpit I found something on the automatic Ice protection system, something about the number of sensors that need to detect ice in order to get the NAI and WAI to turn on. 3 detectors for the NAI, 10 for the WAI.

 

I'd like to know more, like if I'll get the WAI and NAI green indications on the EICAS when it automatically turns on. I'm asking because when I took of from UNNT, Novosibirsk a couple of hours ago I didn't get any indication at all. The weather was definitely what one would call Icing condition:

UNNT 201300Z 22008MPS 1300 1000SE SHSN DRSN SCT013 OVC025CB M06/M08 Q1012 R16/490150 R25/490150 NOSIG RMK QFE749/0999=

 

How do I know if the Automatic NAI kicked in? Is there some sort of feedback? If so, why didn't I get any on my takeoff and climbout through the soup? I've been sitting for about an hour at the cargo ramp before taking off and the weather was like that all along. Manually forcing the NAI to on gave me some warnings on the EICAS, I guess due to the engines sitting at idle thus making the duct pressure too low for it to work. I flipped it back to auto and took off without any problems.

 

I've seen someone get an Ice Detected warning in another topic, but I think he had manual anti-ice with detectors. It means that the simulated aircraft can recognise icing conditions then.

 

Regards,

Fabrizio

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Hi Fabrizio, great weather you found!

 

I did some research and found technical notes for a Saudi operator I think, stating that the aircraft needed to be airborne for auto AI to work. This would imply a need to turn it on after start (NAI anyway) so it's ready when the time comes to depart in icing conditions. It doesn't answer why it didn't activate once airborne, but I'll go through the notes again and share them if I can find them.

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From what I believe this could have several problems. I don't know how PMDG detects icing in FSX/P3D, maybe internally there was no report of icing. I use icing detection + manual mode, and I've seen the icing light illuminating a few times while ascending/descending, I use ASN and it did actually report icing during these times.

 

I did find this while browsing around, they're talking about a B767/757  but the last post is interesting:

http://www.airliners.net/forum/viewtopic.php?t=749773

 

I doubt that's what actually happens in FSX/P3D, as it's either icing or no icing. I guess if the simulator doesn't actually report any icing there won't be any icing. Then again, I find icing a useless feature as it's not properly simulated. X-Plane does a better job at it, still not perfect, but not as bad as both FSX and P3D.

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  I find icing a useless feature as it's not properly simulated. X-Plane does a better job at it, still not perfect, but not as bad as both FSX and P3D.

Icing is properly simulated in the sim. It's up to the developer to incorporate the correct airfile tables and create the gauges/anti-ice panels specific to the aircraft.

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Surface as M08 C and by the time you got into the overcast above 2500 I'm sure the temps were below -10 C.  Icing can occur below -10 C but it's unlikely.  Also, didn't mention what your TAT was while in the visible moisture.

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Hi,

 

If the automatic anti ice option on the 744 works like the automatic anti ice of the T7, then yes the aircraft must be in the air so that the system activates. On the ground, the engine anti-ice must be manually set to on to work.

The wing anti ice cannot be used on the ground as the condition to activate them is the aircraft in the air and the leading edge flaps retracted.

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On smartcockpit I found something on the automatic Ice protection system, something about the number of sensors that need to detect ice in order to get the NAI and WAI to turn on. 3 detectors for the NAI, 10 for the WAI.

 

 

Whaaaaaaa? There are a maximum of two detectors on the 744 for detecting ice. They are located below the pitot probes on the side of the fuselage (nose area). Both are used for wing and nacelle anti-ice. Two detectors are required for automatic operation. Some aircraft have manual operation with a single detector (which gives EICAS advisories). Some aircraft have no detectors at all.

 

The wing anti ice cannot be used on the ground as the condition to activate them is the aircraft in the air and the leading edge flaps retracted.

 

 

 

Not all aircraft have the LE flap inhibit (The manual type may not have it). Note that the LE flaps position themselves in front of the leading edge when deployed, so the LE flaps themselves become potential surfaces for ice accumulation.

 

Cheers

JHW

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@All

 

Thanks for your help, I use the NAI manually when on ground and when I think I need it in flight.

However, can anybody confirm that I'll get NAI and WAI indications in green on the EICAS also when the system kicks in automatically? I guess I would, but didn't find anything on that.

 

@Qavion2

Hi John, here's my source

http://www.smartcockpit.com/aircraft-ressources/B747_Symposium_(2002).html

 

Note that if auto anti-ice installed, three hits on detector turns on NAI, ten hits on detector turns on WAI.

 

 

You can find it at the beginning of page 2. Maybe I was wrong when thinking that 3 hit on detectors meant 3 detectors detecting ice.

 

Regards,

Fabrizio

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Not all aircraft have the LE flap inhibit (The manual type may not have it). Note that the LE flaps position themselves in front of the leading edge when deployed, so the LE flaps themselves become potential surfaces for ice accumulation.

 

Ok. I'll take that. Ma reference was the FCOM provided with the 744v3 which doesn't specify the type of anti ice system.

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You can find it at the beginning of page 2. Maybe I was wrong when thinking that 3 hit on detectors meant 3 detectors detecting ice.

 

 

Thanks for the reference, Fabrizio.

 

It's hard to explain, but the two ice detectors have heaters. "Hits" are the number of times the heater on an ice detector goes through a heating cycle. The expression "counts" is more commonly used in Boeing documents.

 

Basic operation: An ice detector has a metal probe sticking out into the airstream (Sorry, no non-copyrighted pictures available). The probe is (electromagnetically) made to vibrate at a certain frequency. If ice builds up on the probe, it changes the vibrational frequency (simply through the weight of the ice). When this happens, the ice detector system senses the frequency change and heat is applied to the probe to remove the ice. If this heating is required 3 (?) times in succession to remove the ice, the aircraft knows that there is an icing issue sufficient to activate the Nacelle Anti Ice system. Note that all my books say 2 times (including the Boeing Maintenance Manual).

 

Ice accumulation on wings is less likely. Some big Boeing pilots say they have been through their entire careers without using it. This is why it takes 10 heating cycles (hits) to activate the wing anti-ice system.

 

On the real aircraft, you can simulate ice by grabbing the probe with your fingers (not recommended! :Tounge: ). It will then heat up very rapidly.

 

 

Ok. I'll take that. My reference was the FCOM provided with the 744v3 which doesn't specify the type of anti ice system.

 

 

Thanks, Romain. I'll keep that in mind.

 

Cheers

JHW

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Thanks John for your detailed explanation. The document I linked does also mention pilots who never used WAI as you say :) It's just under the part I quoted here.

 

So manual NAI on ground it is then. I'll keep an eye on the EICAS when I think it should turn on in flight and see if it works.

 

Regards,

Fabrizio

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So manual NAI on ground it is then.

 

 

I forgot to mention that even though I can burn my fingers on the ice detector probes on the ground, when the aircraft is on the ground, the system doesn't count the probe heating cycles. So, basically, no auto-NAI on the ground.

 

That link you provided has some interesting stuff in it.... although some of it went over my head :Tounge:  I think some of it applies to the Classic 747. The document was created 14 years ago... so I don't know if some of the stuff still applies.

 

However, can anybody confirm that I'll get NAI and WAI indications in green on the EICAS also when the system kicks in automatically? I guess I would, but didn't find anything on that.

 

 

Yes, the indications are based on valve positions and/or pressure sensors. The green flow bar logic can get a bit tricky at times though. The Aerowinx forum recently had some interesting conversations on flow bar indications during EXT AIR application :fool:

 

Cheers

JHW

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