Wow. All I can say is "not true". Not all ice is known ice.
I have picked up ice where non was forecast, reported, or expected. In fact the scariest ice I ever encountered was in the form of light freezing rain in good VMC conditions. The rain was not visible coming out of a high overcast, and in moments the windshield was completely obscured and the airframe covered in clear ice. This was many years ago flight instructing in a 172. My student was on his first orientation flight!
If you are flying in conditions forecast to contain ice, or forecast to be conditions conducive to the formation of ice (even if it isn't forecast), you're in known ice.
If you're flying in conditions known to cause ice (visible moisture, freezing temps, or temps just above freezing), you're in known icing conditions.
If you're flying in conditions from which PIREPs have been produced of icing, even though none was forecast or shown on current weather reports, you're in known icing conditions.
If you're flying in conditions in which PIREPs have been received stating "negative icing," but are in conditions conducive to the formation of ice, you are flying in known icing conditions.
If you are flying in conditions in which PIREPs have been received stating "negative icing," but ice is foreast or weather conditions indicate potential icing conditions, you are in known icing conditions. And you might be a redneck. (had to throw that in there)
Having said this, from a strictly legal point of view, current official weather observations negating the presence of ice, in certain circumstances, may be a lawful basis for flight in conditions otherwise conducive to icing. Bearing in mind that merely being legal does not make one safe nor form a solid foundation beneath one's wheels or wings...one should not seek loopholes when dealing with ice. Particularly in aircraft not certificated for operations in ice.
If one is in the clear well away from visible moisture and enounters ice (rare, but possible as descrbed above), one may consider one's self in emergency conditions, and act appropriate to the conditions encountered. Remaining in such conditions can be particularly hazardous.
In the case of the encounter with clear ice outside clouds and presumably in temperatures above freezing, removing one's self to a safer position (eg, where one was prior to encountering the freezing rain) is a wise choice, One should consider landing with reduced or no flaps, and carefully consider the ramifications of reducing power or increasing it, along with airspeed changes and the effects of tailplane stall and/or a traditional aerodynamic wing stall, as well as changes in approach speeds, etc.
If in such conditions freezing rain was in the forecast, legally on hasn't much of a leg to stand upon, as one is in known icing conditions. Encountering such conditions, even when well clear of visible moisture, may indeed be an emergency, but may not provide justification for being there...one has flown into forecast icing, and therefore into known ice.
Arguements regarding failures of turbine engines in Transport Category Part 25 airplanes, in comparison to single engine piston airplanes, are ludicruous. Why, certainly a turbine engine may shed a part, fail, operate on redued power, or otherwise become impaired in some way. However, a turbine powered multi engien airplane capable of a required climb gradient on one engien being compared to loss of power in a single engine piston powered airplane is nonsensical, as clearly the piston single is going down.
Defenders of the single engine piston faith tend to spout off that a piston twin might not be able to maintain altitude with an engine loss, as though the engine loss is the issue...it is not. It is one of many issues, but regarding that one point, the piston twin will go a lot farther on one than will the single in most cases.
Far more likely, and far more frequent, is the loss of a generator, alternator, instrument, gyro, radio, vacum source, etc. Generally even the piston twin has double redundancy of most componts, including the vacum sources, electrical sources, and often instruments.
Not discussed thus far is the wisdom of using radar when flying IMC, both for precipitation mapping and ground mapping. Handy-dandy gollyl-gee-whiz-bang xm weather and the latest terrain GPS database don't make up for the ability to see weather with weather radar in real time, particularly in the case of convective activity.
Many pilots have been killed flying partial panel with fully functioning airplanes. I've seen countless gyro instruments over the years fail, but by far the majority of them have been in less expensive self-contained gyro instruments, particularly vacum powered instruments. These have been a combination of failure of vacum pumps in vacum powered instruments (common in carbon vane dry pumps), pneumatic contamination (including air leaks), and instrument failure. I've had a number of cases over the years of failed pitot-static instruments, most commonly from system contamination (very small insects in the lines swelling with exposure to moisture in flight more than any other cause).
While I've certainly encountered such problems in multi engine airplanes too, including turbine powered airplanes, system redundency and improved quality of instrumentation and appliances has generally made this a non-issue.
Over the past week, I've watched a catastrauphic engine failure in a large turbojet multi engine airplane, experienced an attitude gyro failure, an electrical inverter failure, and several other miscellaneous system failures of a non-critical (but occasionally very annoying) nature.
The turbojet failure occured as I watched a B777 depart. It produced fire and smoke and loud bangs and sounds. I watched it climb ahead uneventfully, enter a downwind, base, and final, and land equally uneventfully. Try that in a single engine airplane.
The attitude gyro failure was a primary gyro failure in a turbine airplane. The gyro began indicating a turn, then a roll to the left, and then began spinning right. This failure occured at night over unlighted terrain. Reference to a second gyro and turning over control of the flight to a second pilot with a perfectly good gyro in front of him solved the problem. System redundancy not common to piston singles proved particularly useful. The electrical failure was also a non-event. A secondary inverter went offline when something occured for which the system removed the inverter and illuminated an annunciator telling me of the change. The only signs I had were an autopilot disconnect with the AC transient, and the light. My corrective action? Check the aux inverter attached to the failed bus, re-engage the autopilot, and call for the checklist.
Electrical failures of most any kind in a single piston in instrument conditions are seldom so uneventful. Particularly considering single piston airplanes are often flown single pilot, and single pilot IFR already produces one of the highest workloads a cockpit can have.
Several weeks ago during a simulator checkride, I was given an unusual attitude condition. Per SOP, I was to close my eyes and look down, while the sim examiner worked his magic. When I looked up, I saw only brown on the attitude indicator. I began to try rolling as I reduced power, but the results were confusing, as I didn't see what I expected on the attitude display indicator (ADI). A quick glance at the standby gyro and copilot attitude gyro confirmed that I had been given two conditions at once; I had been rolled inverted and nose low, and at that point the instructor had frozen and failed my attitude gyro. I recovered glancing at the copilot attitude gyro, and then handed the airplane to the copilot while I re-oriented myself. I suspect I would have been in more dire circumstances in a single piston in the clouds in such a situation. In this case, the presence of two additional attitude gyros was particularly helpful in determining exactly what I had before me...as only one additional gyro still left me trying to guess which was which. The standby attitude gyro was the tie breaker, and made my actions and decisions simple.
Engine failure is one point of concern, but again, only one. Most who make these arguements have never had an engine failure, and perhaps don't appreciate it beyond a book-learning level...may not appreciate the reality of what it means to be without power, especially in a single engine airplane. Most pilots are plagued with the it-can't-happen-to-me syndrome until it does, and then become loud preachers of caution much like myself...I see it occasionally here and on other boards as pilots are awakened to the light of day...often rudely. Once you've had that experience, you may well rethink the wisdom of trying to land a single engine piston airplane with failing instruments and no power out of a cloud. Especially with terrain below.
As I said before, generally inexperience speaks in favor of single engine IMC, whereas those who counter that concept generally speak from a background of experience...and generally from a wiser place. When someone with a lot of hours or numbers or letters following their flying name, find out when their last engine failure, instrument failure, or forced landing was...and see if they're talking from the basis of many hours of point to point ho-hum existance in a dream world, or if they have a comparative dose of reality from which to speak.
