Turbulence
Use reports and forecasts to determine areas of potential turbulence during flight planning. Tools that could be used for this purpose include the area forecast, pilot reports, AIRMETs, SIGMETs, convective SIGMETs, center weather advisories, severe weather warnings, and the severe weather outlook.
Clear air turbulence can be expected near jet streams, fast moving cold fronts, and where there are strong winds over rough terrain.
Standing lenticular clouds are an indicator of mountain wave turbulence.
Clouds with vertical development are indicators of turbulence. Many hazards are present in thunderstorms, one if which is turbulence. Stay at least 20 miles away from thunderstorms to avoid strong turbulence. If a thunderstorm is accidentally penetrated, however, it is better to stay on course and go on through. Turing around would probably increase time spend in the thunderstorm. Additionally, the bank angle increases load factor and so increases stress experienced by the aircraft. Many pilots will also turn on de-ice or anti-ice equipment and carburetor heat if inside a thunderstorm, since icing conditions are common.
In addition to turbulence and icing, thunderstorms also contain rain, lightning, and possibly hail. Do not takeoff in the face of an approaching thunderstorm. Do not fly an aircraft that is not equipped with thunderstorm detection in clouds or at night in areas of suspected thunderstorm activity. All thunderstorms should be considered hazardous, and those with tops above 35,000 feet should be considered extremely hazardous.
If moderate or severe turbulence is encountered, reduce airspeed to the airplane's recommended turbulence penetration speed. Do not try to strictly maintain altitude as this will place a lot of aerodynamic stress on the airplane. Instead, allow some altitude fluctuations up and down. If necessary, request a block altitude from air traffic control. You might also need to disengage the autopilot's altitude hold.
In flight awareness of turbulence areas can be maintained by monitoring HIWAS or contacting flight watch or the flight service station.
Icing
Ice will accumulate on the aircraft when in visible moisture and the collecting surface is below freezing. This means icing can occur at slightly warmer than freezing ambient temperatures, since many parts of the aircraft are cooled aerodynamically. This temperature drop is a result of the lower pressure areas generated by the airplane's various airfoils as it flies.
Icing is described as being either rime, clear, or mixed. Rime is forms when small supercooled water droplets contact the collecting surface. Because the droplets are small, they freeze immediately on contact. This results in a rough, milky looking layer of ice forming on the leading edges of wings, struts, unheated probes, and windshield. When larger droplets are encountered, they take a second to freeze, running along the collecting surface as a liquid during the freezing process. This produces a hard, clear accumulation of ice called clear ice. Mixed ice is a combination of rime and clear, having the negative characteristics of both.
Icing can be expected when in visible moisture with an ambient temperature between plus 2 and minus 10 degrees Celsius. Accumulation of ice increases aircraft weight, degrades performance, and results in unpredictable aerodynamic characteristics. Regardless of the deice or anti-ice equipment installed on the airplane, or what great claims may have been made about these systems by their manufacturer or on the internet, icing conditions must always be avoided. Early recognition and prompt action are the keys to avoiding a hazardous situation.
You should be aware of temperatures aloft and any available reports of cloud bases and tops. If you encounter icing conditions, request and altitude change to exit the icing. This might involve a climb or descent to warmer temperatures or VFR weather conditions. Icing conditions are often confined to a few thousand feet of altitude and can many times be exited by climbing. Light rime icing is common near the tops of a cloud layer when it is clear above, as a result of the sunshine.
In order to make pilot reports of icing usable, standard descriptors are used for icing intensity. Icing is described as trace when icing becomes perceptible. In trace ice, the use of deicing or anti-icing equipment is not utilized unless the pilot stays in those conditions for more than an hour. Icing is described as light if it might create a problem if stuck in it for over an hour. Occasional deice or anti-ice use is required. Moderate means even short encounters become potentially hazardous. The use of deice or anti-ice or flight diversion is necessary. Finally, a report of severe icing indicates the deice or anti-ice equipment on the airplane fails to control the icing and immediate flight diversion is necessary.
When interpreting reports of icing, it is important to taking the reporting aircraft type into consideration. If a 757 reports light rime icing, that same icing might be severe icing for you.
Consider a no flap or reduced flap landing if icing is suspected on the tail. The increased downwash over the tail from flap extension could result in an excessive horizontal stabilizer angle of attack. This could result in a sudden, uncontrollable pitch over caused by the tail stalling.
Frost as thick as medium sandpaper can decrease wing lift by as much as 30-40%.