Air Line Pilot, April 2005, p.29

ALPA's Aviation Weather Project Team has, for many years, supported the use of pilot reports of weather conditions as the most up-to-date and accurate communication of current flight conditions. Despite modern technology designed to detect, model, and present weather conditions to those aviation users who need this information, PIREPs are still our most accurate real-time inflight weather reports. 

The National Weather Service (NWS) and airline weather departments use the observations of flight crews who report conditions of turbulence, ceilings and cloud tops, thunderstorms, tornadoes, airframe icing conditions, actual winds aloft, and/or volcanic ash to verify (or not) actual conditions. From these reports, the NWS modifies weather forecasts and/or generates SIGMETs and AIRMETs. 

Weather is a dynamic phenomenon, and change is constant. Despite various methods of observing, recording, and categorizing weather data, large sections of Earth are not included in ground-based observations, weather balloon samples, satellite "eye in the sky" images, or infrared data. 

The Pacific Ocean is the largest single geographic area on the globe, with minimum ground-based observation stations and minimum air traffic to report existing conditions. Through individual position reports and/or PIREPs, the NWS updates its database with current conditions. However, because of the time and distance between some waypoints, in some cases more than 60 minutes, significant weather conditions may exist between these waypoints at which flight crews transmit position reports. 

Satellites have become weather observers' single greatest tool-because they can "see" the weather. With satellite-based infrared sensing, meteorologists can reliably measure temperature and moisture content. However, weather balloons launched from Hawaii, Guam, Samoa, Japan, China, and Russia track only a narrow section of the expansive Pacific region and at only 12-hour intervals recording winds, pressure, and temperature. 

These resources provide valuable information and are wonderful tools for developing weather forecasts. However, forecasting areas of turbulence is not quite a science. Turbulence is extremely difficult to forecast, and some types of turbulence, such as "clear air turbulence" or CAT, are impossible to predict. 

Because of the continued problems of turbulence causing serious inflight injuries to flight attendants and passengers, pilots who fly the Pacific are encouraged to report actual weather conditions, volcanic activity, and turbulence via PIREPs. PIREPs can then be used for timely notification to other flights and for updating our NWS data system. 

While the flight crews of many U.S. and Canadian airlines use "blind transmissions" on frequencies 123.45 or 121.5 MHz to inform other flight crews about enroute turbulence encounters, the flight crews of many foreign carriers do not. While this air-to-air communication is very helpful to nearby flight crews, if these transmissions are not forwarded as PIREPs via voice or ACARS, that information does not become part of the NWS reporting database. 

If a flight is the first flight of the day on a specific track, it is the verification and discovery flight--i.e., the first to encounter any turbulence or other adverse conditions (or discover that what was forecast isn't there!). These "first flights" are particularly important in reporting weather conditions, thereby updating the NWS database and providing valuable information needed for planning later flights. 

While the Pacific is unique because of its size and infrequent air traffic, the PIREP is equally important over areas such as the contiguous 48 United States. Flight crews who are actually flying through or observing the weather are the best reporters to document current conditions. 

Having accurate weather information with known or documented areas of turbulence--from both position reports and PIREPs--will help the NWS generate its forecasts, SIGMETs, AIRMETs, and other weather products. With actual up-to-date information, the airline can select tracks based on the best information available for optimum fuel economy and passenger safety and comfort. With PIREP information in hand, flight crews can prevent many injuries relating to turbulence encounters by notifying the cabin crew early enough to give them time to prepare the cabin for riding through the turbulence. 

Until electronic equipment that will alert the crew within minutes of possible turbulence encounters ahead is installed on the airplane, flight crews will continue to bump into choppy air. For now, PIREPs are the real thing and the best information available to us--if flight crews use them properly. 

PIREPs about turbulence should contain aircraft location, time of occurrence in UTC, turbulence intensity ("light," "moderate," "severe," or "extreme"), whether the turbulence occurred in or near clouds, aircraft altitude or flight level, and duration of turbulence.

--First Officer Phyllis Cleveland (United), B-747 and Pacific Safety Coordinator for the United MEC Central Air Safety Committee.