Types of Icing on Aircraft

This is not the kind of icing on your favorite chocolate cake. This is far more dangerous. Icing on the surfaces of wings, elevators and rudders can completely ruin a pilots day, if not his or her entire life. Here are the three types of icing that can occur:

• Rime - Milky, rough and opaque ice. It is usually caused by supercooled water droplets freezing when they contact the aircraft.
• Clear - Clear (duh) and typically smooth ice . It is generally caused by larger drops of supercooled water freezing when they contact the aircraft.
  
• Mix - A mix of rime and clear icing.
  

Back to Studying - More Weather Acronyms

Back from Mexico, it is time for more studying. What better thing is there for me to study than flying and weather? Well, maybe reading about motorcycling, but that's about it.

Some terms for today:

• AIRMET (from wikipedia) - Airmen's Meteorological Information, is a weather advisory issued by a meteorological watch office for aircraft that is potentially hazardous to low-level aircraft /aircraft with limited capability. Compared to SIGMETs, AIRMETs cover less severe weather: moderate turbulence and icing, surface winds of 30 knots, or widespread restricted visibility.
  
  AIRMETs are broadcast on the ATIS at ATC facilities, and are referred to as Weather Advisories. AIRMETs are valid for six hours.
  
  There are three types of AIRMET, all identified by a phonetic letter: S (Sierra), T (Tango), and Z (Zulu).
  
  AIRMET SIERRA (Mountain Obscuration or IFR) ceilings less than 1000 feet and/or visibility less than 3 miles affecting over 50% of the area at one time. Extensive mountain obscuration.
  
  AIRMET TANGO (Turbulence) Moderate Turbulence, sustained surface winds of 30 knots or more.
  
  AIRMET ZULU (Icing) Moderate icing, freezing levels
• SIGMET (Also from wikipedia) - Significant Meteorological Information, is a weather advisory that contains meteorological information concerning the safety of all aircraft. There are two types of SIGMETs, convective and non-convective. The criteria for a non-convective SIGMET to be issued are severe or greater turbulence over a 3,000-square-mile (7,800 km2) area, or severe or greater icing over a 3,000-square-mile (7,800 km2) area or IMC conditions over a 3,000-square-mile (7,800 km2) area due to dust, sand, or volcanic ash.
  
  This information is usually broadcast on the ATIS at ATC facilities. A SIGMET is a forecast valid for up to four hours. They are assigned an alphabetic designator from N (November) through Y (Yankee), excluding S and T.
  
  A Convective SIGMET is issued for convection over the Continental U.S. Convective SIGMETs are issued for an area of thunderstorms affecting an area of 3,000 square miles (7,800 km2) or greater, a line of thunderstorms at least 60 nm long, and/or severe or embedded thunderstorms affecting any area that are expected to last 30 minutes or longer.
• PIREP - A Pilot Report is typically a report of actual weather conditions to a ground station from a craft in flight. Loosely, the term PIREP is given to many types of pilot reports from traffic conditions to how good the food is at everybody's favorite little airport grill.
  

Glossary Term of the Day - ATIS

What is ATIS? ATIS is an acronym for Automatic Terminal Information Service.

What REALLY is ATIS and why do I need to know? ATIS is a continuous broadcast of current weather and airport information at busy airports. It typically contains information like current NOTAMs, active runways, weather (including the all-important wind and barometer information), available aproaches, etc... The broadcast message is updated as weather and other information dictate. Each unique message is associated with a letter. Each day, ATIS broadcasts start with 'A' or 'alpha.' The end of each broadcast will announce its letter designation, like "End of information Echo."

The information from an ATIS broadcast is important. DO NOT IGNORE it! The barometer is used to set the altimiter before take off and before approach; wind and active runway information let you know if you will need to do cross wind takeoff or landing and the NOTAMS should inform you about things like runway and taxiway repairs, obstructions, etc...

What's with the letter designation? Well, before taxing to take-off and before landing (usually on initial contact with the control tower where you want to land), the pilot should let the tower know they have listened to ATIS. Here's an example...

"North Las Vegas ground, Cessna 12345. Taxiing from terminal to run-up area runway 07 with Echo." This identifies me, where I am headed and lets the ground controller know that I listened to the most recent ATIS broadcast.

ATIS information is non-control. Just because ATIS says the active runway is 07 doesn't mean 12R can't be used. ATIS is advisory, not control.

Other info: Wikipedia

ATIS frequencies in and around Las Vegas:
132.4 - KLAS - Mc Carran International Airport
118.05 - KVGT- North Las Vegas Airport
270.1 - KLSV - Nellis Air Force Base
322.375 - KNID - China Lake, CA

Many ATIS broadcasts can be accessed from a phone. You call the number and just listen.

Glossary Term of the Day - OAT

OAT - Outside Air Temperature
The Outside Air Temperature (OAT) is important to a pilot, especially when it is very cold. According to the AOPA's Air Safety Foundation's Safety Advisor (Weather No. 2)...

Icing is most likely to occur when:

• The outside air temperature (OAT) is between 0ºC and -20ºC, but the worst icing will usually occur between 0ºC and -10ºC.

• If the temperature dew point spread is fewer than 2ºC and the temperatures are between 0ºC and -20ºC be especially vigilant for ice.

• The worst icing is common in the top 1,000 feet of cumulus clouds when the temperature is 0ºC or lower.

• Keep a sharp eye on the OAT gauge and if visible moisture (clouds) is encountered when the OAT is between these temperatures, be prepared to change altitude if ice begins to accumulate.

...Many aircraft I have flown in has no OAT Gauge...