Do, or Don't you, select anti icing in advance?
 

Can anyone enlighten me on Airbus and Boeing requirements re having anti icing on prior to entering icing conditions. Is there any direction on how far in advance, for example, 2 minutes? Or do the manufacturers just require it selected on "prior" to entering icing conditions without specifying a time constraint?

The Flight manuals are part of this answer (others to comment)

The manfacturers recommend guidelines regarding visible moisture and below what temp (hopefully consistent).

The regulation presumes some variation or judgement delay by the flight crew in recognition and thus some aircraft tolerance is to be demonstrated.

As always in environmental encounters a degree of avoidance plus a degree of tolerance is expected to keep things safely in balance

The only thing you lose is efficency, burn the fuel, fly safe.

Would say some of these turbo props have it on most of the time during descents..yes or no? Or is the C152 different ahem...:suspect:

To answer your question directly: TAI (as per the books) prior to entering clouds within the magic icing window between 10°C TAT and -40°C SAT, WAI usually only after accumulating a bit of ice on the leading edge, or if its just a short icing encounter shortly after exiting the icing conditions to clear the wing... Thats on the 737NG.

we are talking degrees celcius here...right? Not seeking to be pedantic but USA works diff than me.

Yeah, Celsius... a physicist should know to declare his units. :oh:

Yes, it's not a turbo-prop :}
(unless you readers know different :O)

No manufacturer that I am aware of specifies a "pre-heat" time. In fact, if the system is certificated as a primary automatic system, it will be activated by an ice detector, which, obviously, has to detect ice first.

That said, it can take a finite period of time to heat the wing to a fully evaporative state, perhaps a couple of minutes ( assuming it was designed to be fully evaporative). This would completely depend on the hi-stage air temperature and volume flow, size of the wing, wing temperature, RAT, and mass of liquid water being encountered.

When I flew the MD-80, I would routinely heat up the main wing while being vectored above the clouds if I expected ice during the approach. This was simply because the tail had to be cycled before beginning the approach, during which time the main wing would not be getting any heat...so I wanted the wing hot to begin with. I really don't know if that worked the way I thought it would or not, since I have no idea how fast the wing cooled once the air was shut off, but it seemed like it was a good plan.

what about the Tristar
 

does it not a a super safe system, that can predict the ice formation, and select ON, just in time.

(sorry)

In my beast, I would select On, even with the super auto system mode.

glf

All very interesting....thanks to all...

Gulfstreamaviator,
do I understand that the gulfstreams have an auto anti ice on system, and that's all that's required by the manufacturer?

Mansfield,
the MD80 would cycle between tail anti ice and wing anti ice, is that correct?

STBYRUD,
737NG does not require wing anti ice before entering icing conditions, is that what Boeing says? Turn in on after entering conditions, or exiting??

Anyone with Airbus requirements?

Use of Anti-ice systems
 

Some aircraft use anti-ice systems as de-icers, so it is not possible to give a 'one size fits all' answer. In the case of the B747Classic Engine Anti-ice should be ON during ground or inflight operations whenever icing conditions exist or are anticipated. On the other hand Wing Anti-ice should be turned on following an icing encounter. Also, if icing exists it is important to use wing anti-ice before extending any flap so that the LE devices are cleared before extension. (due no anti-icing action for LE devices available after extension). Some aircraft have an auto detection/activation of anti-ice system and manual de-ice operation. (Prop & Engine anti-ice Auto - Wing Leading edge de-icer manual)

Hawk37: the DC-9 and MD-80 family use bleed air to heat the wing leading edges and the horizontal stabilizer leading edges, but the system cannot do both at the same time. Later versions of the airplane had an auto-cycling feature, but the earlier versions required a manual cycle of the tail every ten or fifteen minutes (can't remember the precise number...might have been twenty). In any case, a tail cycle is required prior to commencing the approach, as the airplane is prone to ice contaminated tailplane stall issues.

OldFella: I'm not sure about older jet transports, but the airplanes that I have flown, that are equipped with thermal wing ice protection, can heat the slats in any position. The slat, if heated, is always protected...however the inner leading edge of the main wing that is exposed by an extended slat is not. Theoretically, certification should have evaluated each configuration to make sure that the requirements for icing certification were met.

The de-ice vs. anti-ice question, by itself, almost defines the ambiguity in this issue. The terms get interchanged through various publications, manuals, etc. Boeing says the primary method of operating the wing "anti-" ice system is as a "de-"icer, etc., etc.

Notwithstanding the terminology, any system that cannot function properly until ice has accreted on the surface is a de-icer. Boots are obviously the prime example, but there are other technologies that function in a mechanical manner. On the other hand, any system that is capable of preventing the ice from forming is an anti-icer. An anti-icing design may (depending on design) work as a de-icer, but a de-icing system can never work as an anti-icer. Any ice protection system that is automatically operated by an ice detector is, necessarily, functioning in a de-ice mode, regardless of capability.

On the 744 with GE engines, nacelle anti-ice is now used in the descent whenever the temp is <10C and visible moisture or other icing conditions exist or "are anticipated." There is no requirement for a specific time before entering those conditions, but if descending through multiple cloud layers, it is smart to turn it on at TOD and adjust the VNAV Descent page prior to that time so the correct TOD is calculated for the higher idle N1.

Anti-icing
 

Hi Mansfield. The B747 Classic LE devices are not provided with any heat source when extended. I don't know about later models.

I believe that the 737-200 says to wait for an accumulation prior to heating wings.

On the 727, it seemed better to do it earlier as ice could blow back into engines.

Opinions anyone?

ok thanks all for the information. Appreciated.