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From Implausible to Probable
In aviation, there is something more menacing than the mob. It starts at 32 Fahrenheit and only ceases to be dan- gerous once a decreasing thermom- eter throttles moisture from the at- mosphere. It ruins airflow over wings and disrupts the ability of propellers to produce thrust. It has caused innumer- able accidents throughout the history of aviation. Icing can be remarkably dangerous. We are forced to deal with it while living on the shivering side of the equinox.
The pilot of the charter flight was Don Jonz (feeling that “Don Jones” was too bland, he had opted for a more singular surname). Jonz was the presi- dent, chief pilot and sole shareholder of Pan Alaska Airways. Jonz possessed substantial experience in icing condi- tions (unsurprising for an Alaskan bush pilot). With tragic irony, he had written a magazine article about ice just prior to the accident. The article was published in Flying Magazine two weeks after N1812H had vanished. It was pithy with some good pointers: icing encounters occur predominantly around 0 Celsius; a change of a few thousand feet is generally enough to exit icing conditions; never accept a hold at an altitude where ice is accu- mulating, etc. Unfortunately, Jonz also drifted into bravado: “Be wary of pilots
Though the specifics may vary, compo- nents protected against ice are generally uniform across different aircraft types.
who say [that flying into ice] can’t be done. They can’t...If you don’t like ice, stay the hell out of IFR.”
The chartered Cessna 310C was sparsely equipped. Only the pitot tube was protected against ice. Certification rules were an odd animal in the early 1970s. Part 135 regulations had been around for less than a decade, and they did not yet provide guidance for operation into known icing conditions (rules pertaining to the aircraft were nonetheless still applicable). Within a year of the crash, new regulations were developed for light aircraft operated under Part 135.
Jonz’s f light plan took him through Portage Pass, a valley bounded by mountains. V-317 traced a line through the area with a MOCA of 8,000 feet. Two hours before Jonz was due to traverse Portage Pass, an Air Force helicopter turned back due to low ceil- ings and severe turbulence. Terminal and area forecasts indicated moderate rime ice between 6,000 and 15,000 MSL. Jonz bragged multiple times in his posthumous article about success- fully traversing areas of ice without the need for deice equipment. A good guess is that Jonz set off towards Por- tage to take a peek. Facing bad turbu- lence and deteriorating visibility (with a couple congressmen in the back), a climb to a safe IFR altitude had to have sounded like a good idea.
The Right Tools for the Job
Ice protection is a multi-system affair on modern aircraft Flight
In the event of equipment failure, do not fear. Maintain sufficient airspeed and establish an exit strategy.
into Known Icing (FIKI) equipment provides protection for the windshield, leading edge of the wings, engine in- take, and pitot-static system. Propeller- driven aircraft are generally equipped with heated propeller boots as well. There is a good argument that this is the most important piece of equip- ment on a turboprop. A fouled prop does a poor job transferring power into torque.
Props are generally heated via a brush block and slip ring. An amp gauge indicates proper operation of the system. If the amps drop, at least one propeller boot has failed (this can generate an imbalance on the affected side as ice causes one blade to weigh more than the others). If the amp gauge indicates zero, the brush block is no longer in contact with the slip ring (none of the props will be heated). On most twin-engine aircraft, the sys- tem cycles between different propeller pairs to reduce total electrical load requirements. The amp gauge must be monitored over a period of time in order to ensure that the different sequences of heaters are working.
In general, turning on prop heat is better done earlier than later. If you wait until a quarter of an inch is on the prop before activating the system, you will inevitably startle passengers with the iterant thuds of shed ice slap- ping the fuselage (applicable to wing- mounted engines). Before long, the paint perpendicular to the prop arc will be sanded down to bare metal. More concerning is the fact that even
10 • TWIN & TURBINE / November 2021