For Professional Pilots
 

Excuse my ignorance, but...........
It seems a recurring theme in aircraft accidents is failure to turn on the de-icing system in icing conditions, with occasionally disastrous results.
Why is de-icing not permanently "on"? Does the de-icing system cause problems if used in non-icing conditions? Obviously I'm missing something here, what is it?

Couple reasons....

Deice is a huge electrical consumer on the airplane. So the crew must have the ability to shed it in the event of a fault or because of some loss of the supply. Another reason to turn it off is on the ground, the deice (pitot, AOA indicators, static ports, ADC sensors fuel vents, engine intake lip ice, heated props, windshields etc) will get really hot....and with no airflow it will cause damage to it or something else.

I'm sure there a couple of more reasons.

Hope that helps

a lot of the newer airplanes, this system is completely automated. when ice is detected, AI turns on. on these planes, the pitot, drains, etc are built to withstand these temperatures continuously.

don't confuse de-ice with anti-ice

Don't you have to wait for the ice to build up some before you try to crack it off? or am I thinking old systems?

anti ice = used before entering icing conditions
deice = used after ice has accumulated usually done on the ground and on the leading edges of the pneumatic system

4 different types of systems

Bleed air used to heat the leading edges of the the wings and engine nacelles and horizontal stabilizer also used to heat the wheel brakes and windshield this is generally used in a turbine powered aircraft ,
some turbine aircraft also have inertia doors to reduce the chance of ice ingestion PT6

Electrically powered heated blankets used for leading edges and propeller roots, electrically powered pitot tubes, electrically powered heated windshields

Pneumatic systems used to fill rubber bladders that are glued to the leading edges they fill up like a balloon and crack off the ice, can be powered by a vacuum pump and or bleed air from a turbine

TKS systems a fine mesh screen placed on the leading edges of the wings and tail that bleed deicing fluid,
Also an alcohol system that may be installed to clear the windshield and radome.

As previously posted there is a big draw on elex power if the heaters are used
Also there is a reduction in power available if the bleed air system is employed, and or reduced climb power available.

So the anti ice systems are not in use unless visible moisture is seen and the OAT is 10 C degrees or less

Though on just about every aircraft the pitot heaters are turned on on takeoff, this may also include the angle of attack indicators and the static ports

NOTE for the the smaller single engine aircraft these are generally kept off till icing conditions are encountered and generally they only have pitot heat.
Plus usually driven off the exhaust manifold a windshield defrost and and carb heat

on the jets i taught on, ice never accreted on critical areas. the system used ultra-sonically vibrating probes that would detect changes in frequency (the slightest amount of ice buildup) to control the heat system. the wings, tail, and engine inlets were heated when necessary. the drains were heated when the engines were running. however, icing that is intense enough that the AI or DI systems cannot cope with it is the definition of "severe icing"

that being said, turbo-props, older planes, etc all follow the rules that the avi8torny mentioned. i flew turbo props that had boots, and yes...we would have to wait for the ice to build before we busted it off. the pax would get frightened when they heard the ice flying off the wings and smashing into the side of the fuselage. for me, that was a comforting sound.

I fly a Boeing 727. Below 10 degrees C/ 50F, we are required to open the engine anti-ice, which pumps hot air from the compressor sections of the engines into the the round intake which prevents ice.

-Why?

Turbine engines are VERY sensitive to air flow. This engine works the same as the Otto cycle on the motor that drives my 928. If a small ridge of ice manages to exist on a significant section of the Pratt & Whitney JT8D-15, the resultant "squirrely" airflow could lead to what is known as a compressor stall.

-This is why turbine engines are NOT in the hands of the average person. These things are SENSITIVE! They burn up in seconds; You cannot talk on the phone and run a turbine- You WILL eventually fry the thing!

I fly Boeing 727's for a small cargo company out of Memphis, Tennessee, and I don't know why anyone would take off in a modern transport category jet airplane without the wings and tail being de-iced.

In any case, when I open the engine anti-ice, i'm pumping 700 degree air inside the front edge of the cowling; I sometimes have to ask my captain to open up the engine heat. This stuff is important! A small ridge of ice on a JT8D-17 intake can TOTALLY screw up the engine! it will start coughing and belching.

N!

the jt8-d isnt exactly the epitome of modern turbine technology. ive got a couple hundred hours sitting side-saddle in a 72...obviously not your level of expertise. great airplane, but the systems were 1960's design. the modern engines of today are basically impervious to compressor stalls....FADEC and CVG's take care of it. the CF-34's and AE3007's on my jungle busses were pretty tech.

We primarily dont use it until we have to because it severly inhibits available power in certain phases of flight. If you're descending, or at altitude, then no big deal, but on take off or trying to climb, we always wait as long as possible. (turbine, bleed air system)

SOP when I flew cargo was all deice on (prop heat, pitot heat, windshield heat, etc.) in any visible moisture below 10C or at the PIC's discretion other times.

Anti-ice was leading edge boots and the most unnerving thing is letting the ice build up before you use 'em. If you get an itchy trigger finger you can pop the boots too early and now the ice won't break away and it just provides a nice icy surface for new ice to cling to that the boots can't/won't remove. You have to wait until it's about 3/4"-1" thick.

The PA31 can carry a TON of ice (maybe literally - MGW was 7,000 and I swear I've landed with at least 1,000-1,500 pounds of ice packed on one) as can the Be99 turboprop, both of which I flew.

Never did like flying ice, but having some degree of anti/de protection is HUGELY comforting.

Supposedly the Challenger 602 is actually certified for flight in known SEVERE icing - this is from a guy I know that is Captain on one. I find that almost unfathomable since the defintion of "severe" is a rate of accumulation in excess of control systems ability to keep up with it - so I'm assuming this is "severe" as reported by PIREP in other, "lesser" aircraft types since by definition if it's YOU saing "severe" you're basically saying "our systems can't keep up with it", which would never be allowed - at least I wouldn't think so...

The definitions are very weird when it comes to icing anyway. We were always told that for it to be "known icing" you actually had to be the one in it. Even with a PIREP in hand along your intended route we'd be asked to "go take a look and if it's bad, you can always turn around or divert". So "known" isn't really "known" unless it's you - something to keep in mind if you're flying an aircraft not certified for flight in known icing conditions and you ever have to request an altitude change (be careful what you say on the radio) or declare an emergency due to icing conditions. You can shoot yourself in the foot easily. Keep a stack of ASRS forms in your bag - I always did and still do!

The more modern engines have loads of bleed and while it does cost you a bit of performance and raises the temps on the engine, you never run out of hot air to get the ice taken care of.

The one thing that has not been mentioned is if you get ice on your belly or someplace that you cannot get rid of it. That makes the airplane heavier and this can be a handful. At that point you need to get to a lower altitude and get it melted off or if its freezing at all altitudes, time to get on the ground or get out of icing conditions.

just as an aside, the CL65 (CRJ) does not have any anti ice on the complete tail section. Bombardier says it doesnt need it because not enough ice can form there to affect performance!! I have some pictures of huge amounts of ice on the horizontal stab that i forwarded to them. They said "normal". lol..!

same thing on the ERJ-170, 175, 190. It has a cold tail section....Embraer claims that aerodynamically, it's impossible for ice to form on the tail. :/ The -145 series has a heated tail.

Thanks for everyone's input.

The other thing to remember is that everyone should take a look at a fighter jet. None of them (that I know of) have any airframe de-icing on them at all. Engines yes, but not airframe.

Reason is that they go through the air fast enough that the ice simply will not stay on the surfaces.

isn't a T38 not certified to fly in any known icing?

The wings on the F-5/T-38 are so thin that they do not do well with ANYTHING on them.

The J-85 engine does have de-icing on the IGV's (inlet guide vanes) so the engines should stay running. As well the old F-5/T-38 has more than enough power (even on single engine) to get out of the icing if needed.