Story ID: 
FAA Revises Real-time Weather Analysis Guidance
By: Amy Wilder
Caption: System provides backup when automated sensors fail
Word Count: 192
The FAA revised its guidance on using National Weather Service real-time mesoscale analysis (RTMA) weather data when automated sensors fail to report temperature or altimeter settings at airports. Last week, the agency issued a revision of Information for Operators (INFO) 24001 that follows operator feedback on temperature mitigation procedures related to performance, winter operations, and instrument approaches at cold-temperature-restricted airports.
RTMA provides hourly temperature and altimeter reports for approximately 540 airports when automated weather observation systems experience sensor failures. The data is available through the FAA Weather Camera website.
Operators may use RTMA data with certificate management office approval and must implement mitigation procedures to account for latency and variability. When the temperature is missing, operators must use the mitigated temperature for takeoff and landing calculations. When the altimeter setting is missing, operators must use RTMA mitigated pressure and increase minimum weather ceiling values by 100 feet and visibility by half a mile.
The FAA researched the RTMA system through the NWS Environmental Modeling Center, concluding that altimeter setting and temperature data can be used in lieu of missing metar information with proper mitigation strategies.