9.2 Weather Hazards

 





The weather hazard most detrimental to safe flying is icing. For years, airframe icing has been recognized as a significant aviation hazard. Icing encounters can lead to increased aerodynamic drag and weight, along with a reduction in lift and thrust. Together, these factors result in a higher stall speed and degradation in overall aircraft performance. To maintain altitude and counter the effects of drag during flight in icing conditions, the angle of attack is generally increased, and power is applied to the engine(s). This can further expose unprotected regions of the aircraft to ice accretions. If exposure is prolonged, the aircraft will lose the ability to continue stable flight Freezing temps and visible moisture are the two ingredients you need to get structural icing.

The severity of aircraft icing depends on the rate of accumulation, effectiveness of available de-icing equipment and actions a pilot must take to avoid or combat accumulation of ice. The pilot determines severity through an assessment of how well the aircraft can handle the accreted ice. Moderate or severe icing reported by a small aircraft carries a different meaning than the same severity reported by a large aircraft. Due to inexperience in ice identification (and because the differences among icing types are often small), ice type is often inaccurately reported.

Trace icing" refers to a rate of ice accumulation just slightly greater than the rate of ice loss due to sublimation. This category of icing is not hazardous, and no action is normally necessary when this category is encountered for one hour or more. "Light icing" indicates that the rate of ice accumulation may create a problem if the aircraft remains in this environment for one hour or more. The occasional use of de-icing or anti-icing equipment may be necessary to remove or prevent accumulation. "Moderate icing" indicates a rate of accumulation so great that even a short encounter can become hazardous. The use of de-icing or anti-icing equipment – along with a heading or altitude change – is usually necessary. In the case of "severe icing," the rate of accumulation is such that de-icing or anti-icing equipment cannot adequately control or reduce the hazard. An immediate heading and/or altitude change is typically necessary. Rime ice favors colder temperatures, lower liquid water content and small droplets. Clear ice forms when only a small portion of the drop freezes immediately, while the remaining water smears over the aircraft surface and gradually freezes

One early symptom of airframe icing is decreased air speed. Clear icing can be especially hazardous because it tends to form "horns" near the top and bottom of the leading edge, greatly affecting airflow. Wind tunnel and flight tests have shown that frost, snow and ice accumulations on leading edge or upper surface of the wing no thicker than a piece of course sandpaper can reduce lift by 30% and increase drag up to 40%.

It’s important to plan and check the weather the night before your flight to determine if snow, freezing rain or frost is in the forecast. When it comes to avoiding ice, pilot reports (PIREPS) as well as SIGMETS and AIRMETS, are among the best tools at your disposal. Always ask your 3rd-party provider for those during a preflight briefing and keep the "big picture" in mind when operating around potential icing conditions.

Referneces 

Howard’s. (n.d.). Seven Types of Ice (& When to Use Them). Blog - Howard’s | Howard’s. Retrieved October 5, 2022, from https://www.howards.com/blog/seven-types-of-ice-when-to-use-them/

Go/No-Go Decision Making And How To Use It In Business. (2021, September 21). FourWeekMBA. Retrieved October 5, 2022, from https://fourweekmba.com/go-no-go-decision-making/

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