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Approach in heavy ice condition

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Approach in heavy ice condition

Old 5th Nov 2006, 23:50
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Approach in heavy ice condition

What would you do if you have to fly an approach in heavy ice conditions. Are the wing anti ice, engine anti ice, etc enough or would you prefer to fly the initial phase of the approach at a faster than normal speed to increase the TAT? ( Do you think that faster than 250 ias could be necessary? )
And what happens when we have to slow down to the final approach speed ?
If we fly the approach with AP and AT on, what would you do if the pitot tube dont give us "the true" because of ice formation. What I think : AT disconnect and flying with nomal engine indications. I want to know from the pros whats the procedure.
If we are on a descend with FLCH mode, and that happens, I think we have to disconnect as fast as possible the AP to avoid pitching down or up do to false ias indication or going to CWS mode. ( again, whats the procedure here )

Thank you very much
Alejandro from Argentina
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Old 6th Nov 2006, 00:00
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My plan would be to avoid that kind of icing if at all possible. If unavoidable then I doubt that the small increase in TAT through a higher airspeed would make any significant difference to your airframe icing and would bring with it the downside of possible flying outside your turbulence or normal manouvering speeds. If wing and engine anti-ice are insufficient to deal with the problem then you must really ask what you are doing there and consider going elsewhere. If your pitot tubes are all iced up (and that serious icing on 3 heated pitots) then you fly whatever your QRH says you fly for unreliable airspeed indications.
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Old 6th Nov 2006, 09:33
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I think that this is another one of those occasions where I would wimp out (and hold or divert). If my anti-ice/de-ice systems are unable to cope at normal landing speeds then we are dealing with something outside the certification of the aircraft and I'm not a test pilot. If my ice and rain protection system are U/S, well that's another matter and I'd hope that this would be covered in the Abnormal Checklist.

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Old 6th Nov 2006, 10:01
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Some airplane flight manuals specify a higher approach speed - in the order of 10 knots added to the additive for wind gusts etc when in moderate to heavy ice or with ice on the airframe. Also it may advise to add 10 knots to all holding and approach speeds, up to the flap limit speed for any flap setting.
Some manuals may recommend less landing flap. This may be to reduce the risk of the tailplane stalling, i.e. the less pitch down tendency the tail has to counter the better for all who find themselves in such an unenviable situation.
While it is all very well to say you shouldn't be there in the first place, fact is if you fly in certain parts of the world you will go there sometime and may not have the fuel to go somewhere better.
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Old 9th Nov 2006, 20:25
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delay flaps extension, as ice can build up.
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Old 9th Nov 2006, 21:20
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‘Heavy Ice’

Standard Definitions (UK AIP 8.3.2 ‘Airframe Icing’):-
It should be noted that the following icing intensity criteria are reporting definitions; they are not necessarily the same as forecasting definitions because reporting definitions are related to aircraft type and to the ice protection equipment installed and do no involve cloud characteristics. For similar reason, aircraft icing certification criteria might differ from reporting and/or forecasting criteria.
Trace - Ice becomes perceptible. Rate of accumulation slightly greater than rate of sublimation. It is not hazardous even though de-icing/anti-icing equipment is not utilized, unless encountered for more than one hour.

Light - The rate of accumulation might create a problem if flight in this environment exceeds 1 hour. Occasional use of de-icing/anti-icing equipment removes/prevents accumulation. It does not present a problem if de-icing/anti-icing equipment is used.

Moderate - The rate of accumulation is such that even short encounters become potentially hazardous and use of de-icing/anti-icing equipment, or diversion is necessary.

Severe - The rate of accumulation is such that de-icing/anti-icing equipment fails to reduce or control the hazard. Immediate diversion is necessary.

It appears that the thread is discussing severe icing conditions and therefore these should be avoided, or if already in the conditions, leave them as soon as possible (diversion from route/altitude).

If the approach is being flown in less than severe conditions then follow the manufacturer’s recommendations; do not change procedures on myth or mistaken belief, i.e. “delay flaps extension, as ice can build up”.
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Old 10th Nov 2006, 03:36
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Completely with you "Piltdown man",always try to avoid those situations check your weather briefing , however if you find yourself in such conditions I would say fly faster to ensure lift,avoid iddle setting on your engines to avoid flame out ,do anything you might consider to improve you chances to survival ,you are already in a very dangerous situation,know your aircraft and feel how is flying ,some airfoils are more sensible and tend to build up ice quicker than others,check your NNC,QRH.
For unreliable Air speed at least in jets for a determinate Weight ,ALT there is a determinate THR setting and pitch angle for every stage CLB,DES or CRZ get familiar with them ,monitor always as if was your first flt, and if you see and/or hear unusual indications and warnings,crosscheck instruments check pitch att and THR setting and go to your QRH.
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Old 10th Nov 2006, 06:59
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Everybody has stated that at all costs, such heavy or severe icing conditions are to be avoided. These aircraft are not certificated for them.
And an extra warning in our manual is to avoid using speedbrakes in icing, if possible. If you fly the 757, it is normally difficult to comply with ATC's normal altitude/speed (energy level) demands.

Just tell them in serious icing conditions that you have a problem and more distance to descend/slow down is required.
If necessary to avoid very bad conditions, tell them what you require. If the controller is new, then state that your only other option is to declare an emergency, and make a "PIREP" or such, which should require ATC to warn all other pilots about the problems.

Don't even takeoff into such conditions-and if FO, tell the Captain, if he or she is strictly "mission-oriented" (for example, he says "..now look, my job is to get this plane and its people over to airport ABC, not to sit here...") , that such a flight exceeds the aircraft's design limits.

In our older jets, wings which have not been de-iced before takeoff can have a stall speed about 150% compared to the normal speed!
During approach, planes with icing on the tail leading edge, have been known to cause a severe pith-over, requiring about 100 pounds of force to pull the nose back up! This has happened to transport jets, not just to turboprops such as King-Airs.
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Old 10th Nov 2006, 08:58
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Originally Posted by alistomalibu
( again, whats the procedure here )
Thank you very much
Alejandro from Argentina
Hi Alejandro,

in these kind of situations a good thing is to anticipate the problem and avoiding to be directly involved in the situation From your weather folder you can determine what is going to bring that severe icing condition and therefore make a plan to get out of it if things will start to go bad. Monitor your preceeding aircrafts and check what kind of approach they are flying and if they are starting to have troubles due to ice formation, because if they do you will probably be in the same condition in a while. Don't mess around with freezing rain as long as possible.

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