Icing effects in even the most sophisticated flight simulators are simple models that do little more than increase aircraft weight to simulate in-flight icing.
Currently, pilots only experience the effects of an ice protection system failure for the first time in a real flight situation.
Snow
Normally snow is not a hazard with respect to icing, unless it begins to adhere to aircraft surfaces. If snow does begin to stick, it should then be treated as an icing encounter because ice may begin to form under this accumulation of snow. This is a rare situation for which no aircraft is evaluated in the icing-certification process. If it occurs, the aircraft should exit the conditions as quickly as possible, coordinating with ATC as necessary.
AIRCRAFT ICING CONDITIONS
Nearly all aircraft icing occurs in supercooled clouds. These are clouds in which liquid droplets are present at temperatures below 0 ºC (32 ºF). At temperatures close to 0 C (32 ºF), the cloud may consist entirely of such droplets, with few or no ice particles present. At decreasing temperatures, the probability increases that ice particles will be found in significant numbers along with the liquid droplets. In fact, as the ice water content increases, the liquid water content tends to decrease, since the ice particles grow at the expense of the water particles. At temperatures below about -20 ºC (-4 ºF), most clouds are made up entirely of ice particles.
SUBLIMATION. A process where ice turns directly into water vapor without passing through a liquid state.
SUPERCOOLED DRIZZLE DROP (SCDD). Drizzle drops aloft within supercooled clouds. The term currently is not in wide use.
SUPERCOOLED LARGE DROP (SLD). A supercooled droplet with a diameter greater than 50 micrometers (0.05 mm). SLD conditions include freezing drizzle drops and freezing raindrops.
SUPERCOOLED LIQUID WATER (SLW). Liquid water at temperatures below 0 °C. SLW is found in clouds, freezing drizzle, and freezing rain in the atmosphere. This water freezes on aircraft surfaces. Most aircraft icing occurs in supercooled clouds, which consist of SLW, sometimes with ice crystals.
LIGHT ICING. The rate of accumulation may create a problem if flight is prolonged in this environment. Occasional use of deicing/anti-icing equipment removes/prevents accumulation.
ICING ENVELOPES. These icing envelopes, found in 14 CFR part 25, appendix C, are used for the certification of aircraft for flight in icing conditions. They specify atmospheric icing conditions in terms of altitude, temperature, liquid water content (LWC), and droplet size represented by the median volume diameter (MVD). (The envelopes use the term mean effective diameter (MED), but this equates to the median volume diameter for the instrumentation and assumptions current at the time the envelopes were established.) There are two classes of icing envelopes: continuous maximum and intermittent maximum. The continuous maximum is for stratus-type clouds, and the intermittent maximum is for cumulus-type clouds.
FREEZING RAIN. Freezing rain consists of supercooled liquid water drops with diameters of 500 micrometers (0.5 mm) or greater, and a typical representative diameter of 2 mm. The droplets tend to break up if their size exceeds approximately 6 mm. When encountered by an aircraft in flight, freezing rain can cause a dangerous accretion of icing.
FREEZING DRIZZLE. Freezing drizzle consists of supercooled liquid water drops with diameters smaller than 500 micrometers (0.5 mm) and greater than 50 micrometers (0.05 mm).
CLEAR ICE. A glossy, clear, or translucent ice formed by the relatively slow freezing of large supercooled water droplets. The terms “clear” and “glaze” have been used for essentially the same type of ice accretion, although some reserve “clear” for thinner accretions which lack horns and conform to the airfoil.
MIXED ICE. Simultaneous appearance of rime and clear ice or an ice formation that has the characteristics of both rime and clear ice.
MODERATE ICING. The rate of accumulation is such that even short encounters become potentially hazardous and use of deicing/anti-icing equipment or flight diversion is necessary.
RIME ICE. A rough, milky, opaque ice formed by the instantaneous freezing of small, supercooled water droplets.
SEVERE ICING. The rate of accumulation is such that deicing/anti-icing equipment fails to reduce or control the hazard. Immediate flight diversion is necessary.
Structural Icing
Ice forms on aircraft structures and surfaces when supercooled droplets impinge on them and freeze. Small and/or narrow objects are the best collectors of droplets and ice up most rapidly. This is why a small protuberance within sight of the pilot can be used as an “ice evidence probe.” It will generally be one of the first parts of the airplane on which an appreciable amount of ice will form. An aircraft’s tailplane will be a better collector than its wings, because the tailplane presents a thinner surface to the airstream.
The type of ice that forms can be classified as clear, rime, or mixed, based on the structure and appearance of the ice. The type of ice that forms varies depending on the atmospheric and flight conditions in which it forms.
Condições de Formação de Gelo em Aeronave
Aproximadamente todas formações de gelo em aeronave ocorre em nuvens super resfriadas. Estas são nuvens nas quais gotículas estão presentes em temperaturas abaixo de 0ºC (32ºF).
Em temperaturas perto de 0ºC, a nuvem pode consistir inteiramnete de tais gotículas, com pouca ou nenhuma partícula de gelo presente. Em temperaturas mais baixas, a probabilidade aumenta de modo que partículas de gelo serão encontradas em significantes números acompanhadas de gotículas líquidas. De fato, quando o conteúdo de água gelada aumenta, o conteúdo de água líquida tende a diminuir, desde que as partículas de gelo crescem às custas das partículas de água. Em temperaturas abaixo de -20ºC (-4ºF), muistas núvens são formadas inteiramente de partículas de gelo.
A regra geral é que quanto mais partículas de gelo e menos gotículas líquidas que estão presentes, MENOS acúmulo de gelo na estrutura.
Isto é porque as partículas de gelo tendem a quicar para fora da superfície da aeronave, enquanto as gotículas super resfriadas congelam e aderem à superfície. Como resultado, o acúmulo de gelo é frenquentemente maior em temperaturas NÃO muito distante de ZERO Celcius (0ºC), onde o conteúdo da água líquida pode ser abundante, e é usualmente desprezível em temperaturas abaixo de -20ºC.
Uma excessão à regra geral é também declarada que pode ser feita para superfícies aquecidas por um sistema te´rmico de proteção contra gelo ( ou por aquecimento aerodinâmico perto do ponto de estagnação de um componente da aeronave em velocidades em excesso de talvez 250 Knots). Para tais superfícies, partículas de gelo podem derreter sob impacto e depois retroceder para regiões traseiras mais frias e congelar.
Avião algumas vezes acumula pouco ou nenhum gelo mesmo quando voando dentro de nuvens em temperaturas NÃO muito abaixo de 0ºC. Um explicação é que embora tais nuvens sejam usualmente compostas predominantemente de gotículas de água líquida, elas algumas vezes consistem unicamente de partículas de gelo, e neste caso o acúmulo de gelo será mínimo.
Quanto maior o conteúdo de água líquida da nuvem, mais rapidamente é acumulado gelo nas superfícies da aeronave.
O tamanho das gotículas também é importante. Goticulas maiores têm maior inércia e são menos influenciadas pelo fluxo de ar em volta da aeronave do que as gotículas menores. O resultado pe que gotículas maiores colide sobre mais superfície da aeronave do que as gotículas menores.
ICING CONSIDERATIONS FOR THE PHASES OF FLIGHT
PREFLIGHT
Freezing level. Pilots should locate freezing levels on forecast maps. This will assist in developing a contingency plan in the event icing is encountered.
TAXI
While taxiing in snow or ice, leave extra space around your aircraft and taxi at a slower rate.
TAKEOFF AND CLIMBOUT
Verify that the airspeed indicator is working properly and that the pitot heat is on.
CRUISE
It is possible to exit the icing conditions by a change in altitude or a minor change in flightpath, this is certainly advisable.
DESCENT
Pilots may consider periodically disengaging the autopilot and hand flying the airplane when operating in icing conditions. If this is not desirable because of cockpit workload levels, pilots should monitor the autopilot closely for abnormal trim, trim rate, or airplane attitude.
Pilots should try to stay on top of a cloud layer as long as possible before descending into the clouds. This may not be possible for an aircraft that uses bleed air for anti-icing systems because an increase in thrust may be required to provide sufficient bleed air. If configuration changes are made during this phase of flight, they should be made with care in icing conditions.
HOLDING
During holding, an airplane may be more vulnerable to ice accumulation because of the slower speeds and lower altitudes during this phase of flight.
Caution concerning the use of the autopilot, as described above, is also applicable to holding during or after flight in icing conditions.
If the aircraft reacts adversely to a change of configuration, the pilot should return the aircraft to its original configuration.
APPROACH AND LANDING
During or after flight in icing conditions, when configuring the airplane for landing, the pilot should be alert for sudden aircraft movements.
Extension of landing gear may create excessive amounts of drag when coupled with ice. Flaps and slats should be deployed in stages, carefully noting the aircraft’s behavior at each stage.
Before beginning the approach, deicing boots should be cycled because they may increase stall speed and it is preferable not to use these systems while landing.
Once on the runway, pilots also should be prepared for possible loss of directional control caused by ice buildup on landing gear.
Windshield anti-icing and deicing systems can be overwhelmed by some icing encounters or may malfunction. Pilots have been known to look out side windows or, on small GA aircraft, attempt to remove ice accumulations with some type of tool (plotter, credit card).
Wing Stall
The wing, when contaminated with ice, will ordinarily stall at a lower AOA, and thus at a higher airspeed. Even small amounts of ice, particularly if rough, may have some effect. An increase in approach speeds may be advisable if any ice remains on the wings.
The stall characteristics of an aircraft with ice-contaminated wings may be markedly degraded, and serious roll control problems are not unusual.
Você pode notar no gráfico abaixo que há suficiente tempo para recuperar a atitude normal do voo entre o "Alerta de Stall" e o "Coeficiente Máximo de Sustentação".
Pode ser notado também o "Angulo de Ataque" [AOA] bem menor quando as asas contém gelo o que fará o STALL ocorrer em ângulos de ataque bem menores aos ângulos quando as asas não contém gelo.
Fidelidade do Simulador de Voo para Treinamento de Stall
Infrared Deicing Systems
Infrared (IR) deicing technology involves melting frost, ice, and snow from aircraft surface with infrared energy. IR energy systems are based on natural gas- or propane-fired emitters that are used to melt frost, ice, and snow. Infrared energy does not heat up the surrounding air and tests have shown that it has negligible effect on the aircraft cabin temperature [13].
[13] Environmental Protection Agency. Preliminary Data Summary Airport Deicing Operations (Revised). August 2000.
Two main manufacturers are leading the way in developing infrared-based deicing systems: Radiant Energy Corporation with the InfraTek™ system and Infra-Red Technologies with the Ice Cat™ system. The Ice Cat™ system uses IR emitters fueled by natural gas or propane mounted on booms that are fitted to specially designed trucks. Thebooms are then positioned above the aircraft surface and the IR emitters are used to remove frost, ice, and snow. Currently there is no commercial application of this system.
The InfraTek™ system consists of infrared generators, called Energy Processing Units (EPUs), located in an open-ended, hangar-type structure. The EPUs are fueled by natural gas and generate IR energy waves to melt and evaporate frost, ice, and snow. If the aircraft surface is dry, the IR waves are reflected away. A diagram of this process is shown below (figure taken from [17]):
The InfraTek™ system is designed to be operated by only one person and is mainly controlled by a computer. Before deicing can begin, the floor of the InfraTek™ system facility is heated in order to facilitate the deicing process of aircraft lower parts such as the landing gear. Depending on the type of aircraft and the severity of ice and snow build up, the energy and wavelength generated by the EPUs are adjusted. In March of 1996, InfraTek™ technology was shown to deice a Boeing 727 in six minutes, which is about the same amount of time it would take to achieve deicing results using conventional ADFs [13].
There are currently three InfraTek™ Deicing System facilities in the US (December 2009) and one in Oslo, Norway. The largest by volume is the one installed at JFK International Airport in March 2006. The facility was operating during the 2006-2007 deicing season. The system is designed to provide deicing services for up to a 747-300 size aircraft [18]. The following performance benefits have been documented:
- Approximately 90% reduction of glycol use per aircraft under snow and ice conditions.
- No glycol use for defrosting operations.
Furthermore, in terms of budget management, using the InfraTek™ system allows more accurate winter operations budgets for customers since the system charges a fixed fee based on the size of the aircraft. Conventional deicing methods are priced based on the volume of fluid applied, which varies based on the severity of winter weather conditions. However, cost data is currently limited by the number and scale of facilities using the InfraTek™ system.
The JFK InfraTek™ facility is reported to have cost $9.5 million [18]. With such infrastructure costs, there needs to be a commitment by airlines to make use of the facility.
Effective Training for Flight in Icing Conditions
Billy P. Barnhart
Bihrle Applied Research, Inc.
Jericho, New York 11753
Thomas P. Ratvasky
National Aeronautics and Space Administration
Glenn Research Center
Cleveland, Ohio 44135
How ice contamination affects aircraft handling so they may apply that knowledge to the operations of other aircraft undergoing testing and development. Participant feedback on the ICEFTD was very positive.
A safe way to explore the flight envelope.
University of Tennessee Space Institute
Billy P. Barnhart engineer in the development of NASA’s ICEFTD.
Thomas P. Ratvasky is an aerospace engineer at the NASA Glenn Research Center’s Icing Branch. he also served as the on-board flight test engineer during the icing flights of the Twin Otter Icing Research Aircraft.
ICEFTD Training Sessions
Four formal demonstrations of the ICEFTD took place between October 2004 and November 2005. In total, eighty-four pilots and flight test engineers from the industry, regulatory and military communities received practical lessons on an iced airplane’s reduced performance and handling qualities.
The first two demonstrations were held in October 2004 and May 2005 at the University of Tennessee Space Institute in Tullahoma, Tennessee.
Twenty-four pilots and flight test engineers from Bombardier, Cessna, Raytheon, U.S. Army, U.S.
Forestry Service, the FAA, and Canada’s Transportation Safety Board participated in the In-Flight Icing and Its Effects on Aircraft Handling Qualities short course. This short course consisted of lectures, a flight in the UTSI Navion variable stability airplane, and a simulator session in NASA’s ICEFTD.
The capability for including icing effects into flight training simulators used for initial and recurrent training will allow pilots to experience representative icing-induced aircraft handling characteristics,especially in failure case training scenarios. Presently, icing effects in even the most sophisticated flight simulators are simple models that do little more than increase aircraft weight to simulate in-flight icing.
Realistic icing simulator models however, based on aerodynamic effects of airframe icing, will enhance safety by allowing pilots to recognize important visual and tactile cues associated with an icing event.
Currently, pilots only experience the effects of an ice protection system failure for the first time in a real flight situation. As in stall and windshear training, improved icing flight simulation will better equip pilots to employ the correct procedures and techniques to effect a recovery to a safe flight condition.
The airplane chosen for this activity was a DeHavilland DHC–6 Twin Otter since NASA had extensive operational experience in icing conditions with this airplane and the Twin Otter has a known sensitivity to ice contaminated tailplane stall.
Icing Effects
These exercises demonstrated stark differences in handling characteristics and pitch control between the non-iced Twin Otter and the Twin Otter with failure case ice shapes. For example, no abrupt pitch or roll tendencies occurred during stalls with the non-iced Twin Otter. However, during stalls with failure ice, pilots experienced and commented on the “roll-off” tendency, especially with flaps set at 20°. These rolloffs resulted in steep bank angles, sometimes reaching or exceeding 90°. Figure 6 contains plots from one of the flap 20° stalls. The first 100 sec shown is a stall maneuver for the No-Ice configuration. Note that there were no strong roll off or pitch down tendencies at 70 sec when the stall angle was achieved. After 100 sec, the All-Ice switch was enabled, and the stall maneuver with ice was performed. Observe at about 170 sec the abrupt stall with large sideslip and roll the pitch angle achieved a 50° nose down attitude during the recovery.
During flap transitions with failure ice, pilots noted flap position in relation to the first signs of controllability problems. Many pilots expressed some surprise when encountering the very high control forces associated with wing flap extension, and discovered the difficulty in maintaining good pitch attitude control. All pilots experienced large pull forces to maintain 85 knots as flaps transitioned beyond 20°, and when the column force also became oscillatory, most were unable to maintain good airspeed control.
As power was added, the forces increased and when power was set to idle, the forces decreased. Likewise, as airspeed increased, the pull forces increased and were more oscillatory and when airspeed was decreased, the forces and oscillations were reduced.
When flaps were raised, all noted that the forces and oscillations went away when flaps were less than 15°.
This introduction provided a necessary practice and orientation for the more difficult approach tasks that followed.
Operational Scenarios
These exercises were developed to provide realistic pilot task with the iced aircraft. Since icing issues often arise during the approach and landing phases, it was appropriate to look at these phases for the exercise.
Performing the approach using basic instrument displays required a higher pilot workload to perform the task. From the outset it was apparent that for some pilots, the workload was high in order to fly the basic IMC approach task using the raw data glide slope and localizer presentation. This was the reason for changing the training profile during the second week, so pilots could get a feel for the basic task workload with no compensation for ice, and comparisons on the pilot performance and HQR’s could be made between the No-Ice and All-Ice configurations.
No-Ice Approach and Landing
This first IMC task allowed the pilots an opportunity to understand the workload of the basic task, while developing their instrument scan. Pilot performance and ratings indicated good flying qualities with relatively low levels of pilot compensation required to meet the desired performance of the task. This exercise was initiated in the clouds, and the pilot was given heading and altitude instructions to intercept the localizer. The flaps were transitioned from dF = 0° to dF = 30° by the final approach fix, and the pilot was to maintain 85 knots on final approach. The pilot made power changes and trim changes accordingly as flaps and speed were set to maintain descent rate along the glide slope. All pilots were able to trim the airplane and fly with one hand on the yoke, and one hand on the throttle.
Data from one of these approaches are shown in figures 7 and 8. This pilot felt the workload was fine; he could make radio frequency changes, read maps, etc. It took him some time to get established on airspeed and had some lateral overshoots on the localizer. Overall, he rated the task with an HQR = 3 (aircraft characteristics were fair with some mildly unpleasant deficiencies, but desired performance was achieved without improvement).
All-Iced Approach and Landing
Pilot performance and HQR’s for the approach and landing in the All-Ice configurations generally indicated a much more challenging airplane to fly.
The second and third approaches were made with All-Ice and dF = 20° and dF = 30°, respectively. When the flaps were lowered, the control anomaliesexperienced during the flap transition were revisited.
With dF = 20°, a slight pull force was required even with full-nose up trim in order to maintain the 85 knot target approach speed. With dF = 30°, a significant pull force (15 lb) was required to maintain 85 knots. Force oscillations occurred on top of these steady pull forces, making speed and attitude control difficult. Most pilots used two hands on the yoke to control the airplane.
Many pilots found that the workload associated with flying an approach to CAT I minimums with the failure case icing condition was in many cases at the limits of their abilities. Handling problems were caused by horizontal tail ice, but the task was further complicated the failure ice on the wing, which resulted in lateral handling problems made it difficult to control airspeed.
In some cases, wing stall recoveries were difficult due to the high induced drag at high angle of attack and low altitude. Increased power was not enough to break the stall, and there was not much altitude to exchange for airspeed. These cases would sometimes result in a crash. All experienced pilots found that most of their attention had to be devoted to controlling pitch to achieve vertical path performance. This element of the task consumed most of their attention because of icing related instability, high control forces, inability to trim, and related pitch control anomalies. Although not sensed by the pilot, during the pitch excursions, the Gmeter would often cycle between 0 to 2.5 G. Because of the intense amount of attention required for pitch control using a basic attitude indicator, lateral path performance and airspeed control usually suffered.
This pilot had difficulty throughout the approach. Airspeed was consistently high, which made the pitch control more difficult. Power changes were large and abrupt, which degraded handling further.
Concentrating on the longitudinal problems, he failed to intercept the localizer initially and had multiple lateral overshoots throughout the approach. Towards the middle of the approach, the large pitch oscillations caused multiple stall warnings as G was increased and airspeed decreased. Since it was clear that the pilot was task saturated, the instructor suggested raising the flaps to 10° to finish the approach. The workload was considerably deceased with this configuration, and the pilot was able to successfully land the airplane. Note in figure when flaps reached 10°, the oscillations in angle of attack, pitch angle, and longitudinal input were greatly reduced. This pilot rated the iced airplane with dF = 30° as an HQR = 10 (aircraft characteristics have major deficiencies, and that control would be lost during some point of the operation).
Handling Quality Ratings
After each approach and landing, pilots familiar with HQR’s were asked to use the Cooper-Harper rating system to rate their ability to complete the approach and landing tasks within specific adequate and desired performance metrics. The HQR’s from sixteen pilots who performed the approaches in the No-Ice/ dF = 30°,
All-Ice/dF = 20°, and All-Ice/dF = 30° configurations were compiled into figure.
For the No-Ice, dF = 30° configuration, pilots rated the approach and landing between an HQR = 2 to HQR = 4. Many pilots commented on the lack of practice as contributing to the higher rating, and this point should be considered in using the actual HQR number. Even without much practice, the general rating was that desired performance was achieved and aircraft characteristics were good to fair with some deficiencies.
For the All-Ice, dF = 20° configuration, pilot ratings ranged from an HQR = 4 to HQR = 9. The increase in the ratings was certainly due to the reduced stabilityand controllability as well as the handling anomalies associated with icing. The increased spread in the numbers reflected to some degree the skill level and experience of the individual pilot receiving the training. Additionally, the spread could have been influenced by the “learning curve” or proficiencygained as the training progressed and pilots became more familiar with the displays and aircraft characteristics. This was an expected result as pilot task performance generally improved with practice and it did affect pilot ratings. In a more rigorous pilot evaluation setting, a certain amount of time would be given to pilots to develop a baseline level of proficiency and familiarization before rating a task.
For the All-Ice, dF = 30° configuration, pilot ratings ranged from an HQR = 7 to HQR = 10. This increase in the ratings reflects the increased workload associated with the greater amount of pilot compensation at the higher flap setting. In this configuration, none of the pilots were able to meet the adequate performance metrics of the approach due to the inability to trim, the large and oscillating column forces, large pitch excursions when making power changes (one-handed operation), and loss of situational awareness on the lateral position. As stated above, some pilots encountered wing stalls and were unable to recover in this configuration due to increased drag and limited altitude. Although most pilots rated the dF = 30° approach the worst case condition, a few rated this task slightly better (lower compensation) than the dF = 20° approach. These pilots felt that the proficiency acquired on the dF = 20° approach, which was flown before they flew the technically more difficult dF = 30° approach, was the reason. Overall, pilot ratings accurately reflected the inability of meeting performance requirements with flaps extended. Most pilots exited the training device perspiring freely and commenting that no additional workout was needed for the rest of the day. These comments confirmed the physical effort and intense concentration required to perform the training tasks.
Pilot Comments on ICEFTD Training Sessions
All pilots commented very favorably on their training experience and the applicability it had to their present occupations. Pilots who had participated in development programs for aircraft with reversible controls identified strongly with the characteristics shown by the ICEFTD. Others who had not had this experience were in general surprised by the amount of effort it took to perform the given tasks. None had ever encountered the levels of control forces or feedback activity as was demonstrated during this simulation.
One pilot commented that he recently completed an extensive icing development and certification program on a Part 25 business jet with a major aerospace company. During the development phase with 22.5 min ice shapes on the horizontal tail leading edge, he observed large, uncommanded stick pumping and pitch transients when flaps were moved to the landing configuration. He also noted that the aircraft could not be trimmed at the approach speed. Stick pumping developed and strengthened as the aircraft accelerated with increase power setting. The simple procedure of raising the flaps to the last setting completely eliminated the problem. This pilot was pleasantly surprised to observe that the ICEFTD accurately simulated the same phenomenon that he had experienced, even though the two aircraft were radically different in design, tailplane configuration, and powerplant. The lectures and the ICEFTD demonstration gave him a clear understanding of what he had experienced during their icing program. He strongly recommend the ICEFTD to any flight test crew (test pilots and flight test engineers) who are in the process of preparing for an icing development or certification program. He considered this training a“must have”.
REFERENCE
Barnhart, B., Dickes, E., Gingras, D., Ratvasky, T., Simulation Model Development for Icing Effects Flight Training, SAE 2002–01–1527, April 2002.
Gingras, D.R., Dickes, E.G., Ratvasky, T.P., and Barnhart, B.P., Modeling of In-Flight Icing Effects for Pilot Training, AIAA Modeling and Simulation Technologies Conference and Exhibit, Aug. 5–8, 2002, Monterey, CA, AIAA Paper 2002–4605.
Icing for General Aviation, NASA Glenn, 2001, http://iceboxesn.grc.nasa.gov/ext/education/video/video.html
Papadakis, M., Gile Laflin, B.E., Youssef, G.M., and Ratvasky, T.P., Aerodynamic Scaling Experiments with Simulated Ice Accretions, AIAA 39th Aerospace Sciences Meeting and Exhibits, Jan. 8–11, 2001, Reno, NV, AIAA Paper 2001–0833.
Ratvasky, T., Blankenship, K., Rieke, W., Brinker, D., Iced Aircraft Flight Data for Flight Simulator Validation, SAE–2002–01–1528, April 2002.
Ratvasky, T.P., Ranaudo, R.J., Barnhart, B.P., Dickes, E.G., and Gingras, D.R., Development and Utility of a Piloted Flight Simulator for Icing Effects Training, AIAA 41st Aerospace Sciences Meeting and Exhibit, Jan. 6–9, 2003, Reno, NV, AIAA Paper 2003–0022.
Russell, P., Pardee, J., Joint Safety Analysis Team-CAST Approved Final Report Loss of Control JSAT Results and Analysis, December 2000. Tailplane Icing, NASA Glenn, 1998, http://iceboxesn.grc.nasa.gov/ext/education/video/video.html
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