Chapter 5: Weather Hazards of Turbulence, Icing, Ceilings, Visibility, and Ash Clouds

CHAPTER FIVE

Weather Hazards of Turbulence, Icing, Ceilings, Visibility, and Ash Clouds

500.

INTRODUCTION

This chapter will cover the causes of turbulence, classification of the various categories of

turbulence, conditions under which turbulence exists, and recommend flying procedures used

when turbulence is encountered. Additionally, it covers the requirements for icing formation,

types of icing, and their effects on aircraft flight and aircraft components, including techniques

that should be followed for safe flight. Finally, this chapter introduces the student to ceilings and

visibility, sky coverage terminology, and the requirements for fog formation and dissipation, plus

a synopsis of the aviation hazards of volcanic ash clouds.

Turbulence is one of the most unexpected aviation hazards to fly through and also one of the

most difficult hazards to forecast. Severe and extreme turbulence has been known to cause

extensive structural damage to military aircraft, with lesser intensities resulting in compressor

stalls, flameouts, and injury to crewmembers and passengers. From minor bumps to severe

mountain wave turbulence, turbulence comes in many forms and is usually worst during the

winter months. Turbulence causes an estimated $30 million in annual aviation assets damage.

Aircraft icing is another aviation weather hazard. Many aircraft accidents and incidents have

been attributed to aircraft icing. In fact, many ice-related mishaps have occurred when the

aircraft was not deiced before attempting takeoff. Most of the time, ground deicing and anti-

icing procedures adequately handle icing formation. However, there are times when pilots are

caught unaware of dangerous ice buildup.

Historically, low ceilings and poor visibilities have contributed to many aircraft accidents. Fog,

heavy snow, heavy rain, blowing sand, and blowing dust all restrict visibility and can result in

low ceilings. Adverse weather conditions causing widespread low ceilings and visibilities can

restrict flying operations for days. Since ceiling and visibility is so important to operational

flying, it is imperative a pilot understands the strict meanings of the two terms. There are many

different kinds of "visibility," but pilots are usually more concerned with "prevailing visibility."

Ash clouds from volcanic eruptions present a unique hazard to aviation. Though most prudent

aviators would choose to keep well clear of any active volcano, certain situations such as

evacuations may require the military to operate in close proximity to ash clouds. The

corresponding causes of aircraft damage are discussed in the last portion of the chapter.

501.

LESSON TOPIC LEARNING OBJECTIVES

Terminal Objective: Partially supported by this lesson topic:

2.0

Upon completion of this unit of instruction, student aviators and flight officers will

demonstrate knowledge of meteorological theory enabling them to make intelligent

decisions when confronted with various weather phenomena and hazards.

Weather Hazards of Turbulence, Icing, Ceilings, Visibility, and Ash Clouds

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