COLD WEATHER OPERATION.
 

Hello to you.
I have two questions:
1-Why should the extended flight with slats extended,in icing conditions be avoided?
2-Why should we avoid remaining in a holding for a long time in icing conditions?

My total non pilot guesses.

1. Slats extended could expose areas that are more likely to allow ice build up?
2. Something to do with the frequent same direction turning? E.g would the reduction in static pressure on the lower wing allow slightly more ice build up on opppsite wings i.e a slight imbalance?

Thats as good as i can summise.

1. Wing anti-ice does not work with slats exrended.

2. Prolonged flight in known icing will simply build up more ice. Also, more ice may build faster at higher angles of attack and slower airspeeds.

Hello.
Thanks.your answers seem to be right and logical.about question 1,I thought the same as you do but I was not sure.

Hello.
Thanks for your answers.but about question 1,your answer depends on the A/C type.I fly A300-600 and with slats extended,wing anti ice operates.

Wing anti-ice may operate but it wouldn't be effective.

It does on the B737.
It is also effective.

Because you may ice up mechanical areas inside the flap which may need maintenance to inspect after landing,hence the requirement to maintain flaps 15 or more after landing until shutdown.

Because eventhough the aircraft you operate is certified in icing condition,it is not in severe icing and more than 40 minutes in moderate i believe.
The protection on maneuvring(vref) is demontrated with icing accumulated on non deiced area of your aircraft(stabiliser,some slats..)up to 3 a certain limit,i believe around 2-3 inches.(40 minutes in mod icing).
If you are staying in icing longer than that you are on your own....

This is incorrect, on some aircraft there is no wing anti-ice for extended leading edge devices such as the 747 while others like the 727 and 737 range from mostly heated to partially heated while extended. Whether the heated device have as effective anti-icing capabilities when extended, I am not sure but would not be surprised if it is less effective.

If you want an airplane-specific answer, then specify the airplane in the question.

It does on the Falcon 50 and 900 series aircraft, in fact leaving the wing heat on after landing will cause major damage to the slats, requiring their replacement, a rather expensive mistake.

The 727 also had some heat on the LEDs when extended. I've landed enough times with ice everywhere else that was not heated.

in addition

1 You could get into a situation where the slats could not be retracted due to build up or asymmetric slat if only one retracted

2 You should always be thinking about leaving icing conditions rather than sitting in them. Severe icing of which no a/c is certified for continuous flight in, can be caused by exposure time. EG climbing through a layer of icing may present light icing but continued exposure at the same level may cause severe icing build up

Some aircraft types are very prone to ice build up on the lower fuselage.
At holding airspeed with a high body angle it can become quite serious, so the last place to be in ice is stuck in a holding pattern.

I am quite sure ATRs dont like icing with flaps extended:\

ATR's don't like icing with flaps retracted! :}

Just a couple months ago an ATR-72 and my humble DHC-8-102 were climbing for FL240, in moderate icing for just a little over 20 min. We still had a stable climb rate right up to the top, while the ATR ended up descending because they could not maintain altitude at 17,000. Much different wing between the two (same basic weight as talked with the crew an hour later) resulted in different characteristics. As a crew we discussed that the second we saw a trend towards a level (+200 fpm or less) or negative climb rate, we were going to descend for warmer air, and we had already changed our heading to try and get out of the icing. Prudent discussions anytime you find the white crap on the plane.

As it is, no icing is good icing and many competent (and not so competent) pilots have not reached home base because of staying in icing conditions.

NASA has a great icing training series found here: Aircraft Icing Training - Courses

It's a great series for those of you who don't encounter icing on a regular basis, and a great refresher for those of us who do.

Hi
some mistakes about anti ice on 737 or misunderstanding.

1- WAI and/or E/I work slats extended, but not on the flaps of course, not on the elevator and others parts of the airplane. That the reason why, it's not recommended to hold at "low speed" in icing conditions.

2- Vref ice : if WAI was used during flight, is only due because the computed Stall warning logic adjusts stick shaker and minimum manoeuvre speed bars on the airspeed indicator on the NG.
But on the CL, Boeing says in App and Landing :If ice formation are observed on the airplane surfaces, VREF ADD 10kts this ensure maneuvering capability. Not the same logic.

The starting point is icing conditions should be avoided at all times if possible, as should holding. Both are a waste of fuel. Icing conditions and holding together are the greatest waste of time and money. Furthermore, there are list of failures you would prefer not to occur whilst in icing conditions, hence the very reasonable advice of avoiding extended holding in icing conditions.

Regarding to holding with flaps extended in icing conditions I think you'll find that it is aircraft specific. Many aircraft have functioning ice protection systems in all configurations, some don't. This is aircraft specific. But the important thing to know is that ice builds up everywhere, even where the manufacturer does not expect it - in spite of extensive flight testing. Therefore common sense suggests that this is best avoided. Additionally, you are now exposed to additional failure scenarios, some of which may not have been flight tested.

Yes, do a little bit if you have to. But try not to. If you are forced to do so, you will find that changing your level by 2,000 feet will drastically change your ice accumulation rate.

I hope this helps.

PM

Also, as many of you will be aware, lift can be increased by slotting the leading edge of an aerofoil. Slats do this by creating a slot/gap between themselves and the remainder of the wing. The leading edge slot provides additional lift by delaying the upper surface separation until higher angles of attack.
Should flight in icing conditions cause build up in this slot then it negates the purpose.

As for holding in icing conditions, I would prefer to avoid than lengthily test the limits.

Also, the A380 WAI works when slats extended. As with other Airbus and Boeing aircraft previously operated.

NB - When you have flap extended, its possible to get icing on the leading edges of the flap aerofoils as well. Seen this after landing in icing conditions many times on both Boeing and Airbus aircraft.

Bottom line - If your slats/flaps ice up, your high lift devices may jam making landing or even diverting limiting. Hence the recommendation to not hold in a config other than clean (in icing conditions)

ps. What jets don't have leading edge deice with the slats extended? Are there any??

747-400/8 FCOM Vol. 1 says it "is inhibited", Vol. 2 just says "ineffective."

Our FCOM for the -400 says ineffective in both sys description and supplementary procedures... But it doesn't say it doesn't have it!!

(Reason I ask - I've had new to the company F/O's on both A320 and 737 who have stated that there is no point as it doesn't work when I've gone to put it on during the approach. Then been amazed when the ice disappears...Where does this come from??)