Number 240
June 1999
Weather ASOS-ciations
Automated Surface Observing System (ASOS) is the current weather reporting equipment at many airports. However, some pilots and controllers believe that this equipment occasionally provides inconsistent or unreliable weather information to users. Our first report, from a General Aviation pilot, illustrates:
A Matter of Conscience
In an old Walt Disney movie, Jiminy Cricket sang a song that ended, “…and always let your conscience be your guide.” A Tower Controller did just that, stating in his ASRS report that, “the only valid information the pilot had in this case was my notably unauthorized remark.”
s Weather at XYZ was reported as clear, visibility 7-10
miles, no remarks. I checked the ATIS repeatedly during the last 45 minutes of the flight. No change from clear and 8 miles. There was frequent lightning ahead with indications of storm activity on the [aircraft’s] weather avoidance equipment. The ASOS at XYZ is supposed to be attended and augmented as necessary. In this case, a thunderstorm was close enough to the airport to be seen and heard, but there was no mention of it on the official weather. Another reporter, an experienced weather observer, explains how the ASOS can arrive at these apparently inconsistent weather reports.
s The [small] aircraft had just turned base to final to
Runway 16, having been cleared to land while it was on downwind. [At that time, I issued] the ASOS wind at 100 degrees at 8 knots. A thunderstorm was about three miles west of the field. I felt the Tower buffeted by the wind. I issued to the pilot, based on observation of [current] ASOS and the parking lot, “ASOS wind variable at 4 knots, in reality it’s bending the trees.” The aircraft required 3,200 feet of runway to land. On touchdown, the ASOS still read variable at 4 knots. As the aircraft exited the runway, ASOS updated the wind to 250 degrees at 9 knots gusting to 16 knots, then 270 degrees at 15 knots gusting to 21 knots. The originally reported wind was 170 degrees different from the actual wind at the time of landing, and 2.5 times the velocity and approaching the aircraft’s demonstrated crosswind landing capability. Controllers may not transmit specific values (such as the ceiling, visibility, or, in this case, wind), other than those listed in the current ASOS. The exceptions include airports at which an official weather observer is on site, or at which the weather report has been composed or verified by the weather station. Pilots must therefore rely on their basic piloting skills (for example, observation of a wind sock or comparison of ground speed vs. airspeed) for final determination of safe landing conditions. To read more about a Controller’s role in disseminating weather information, refer to the Air Traffic Control Handbook (7110.65L, Paragraph 2-6-7).
s The ceilometer only sees clouds directly over its sensor.
This means on a dreary overcast day, if there is one small break in the clouds over the sensor, it calls the sky clear. Furthermore, the visibility sensors…generally show the visibility to be much greater than it actually is. Some technical advances have improved the accuracy of ASOS readings and increased the frequency of broadcast updates. However, the equipment is programmed to update ASOS and ATIS broadcasts only when a significant weather change occurs. For more information, check out the ASOS User’s Guide on the Web at: http://www.nws.noaa.gov/asos/index.html
Location, Location, Location
In another report to ASRS, a Local Controller notes that the location of ASOS sensing devices may generate wind reports that differ from those produced by sensors elsewhere on an airport.
s [ASOS] wind instrument is installed at the south end of
the airport in a partially sheltered location. [The reading] differs by 50 degrees or more during northwest winds when compared to mid-field wind sensors. Additionally, this sensor is 2 miles from the approach end of Runway 19. I believe this instrument does not give a good representation of wind conditions. Tower and Approach have direct-reading instrument from the mid-field sensor. Reports such as this one, sent either directly to airport management or to ASRS, have resulted in the relocation of ASOS sensing equipment at several airports.
The Bottom Line
A final thought from a controller who is also a weather observer charged with trying to update the ASOS report during changing weather conditions:
s I attempted to manually override the system, but it was
so slow, we were still reporting VFR while the storm raged outside. If you are using weather from an automated station, when the weather is changing rapidly, don’t believe what is being reported.
ASRSRecentlyIssuedAlertsOn…
Uncommanded roll in a B737 Metal shaving debris on A320 flight control wiring P-56 (White House airspace) avoidance procedures FOD (Foreign Object Damage) hazard at a Michigan airport BAE-41 engine flameouts during reversal and at steady idle
A Monthly Safety Bulletin from
The Office of the NASA Aviation Safety Reporting System, P.O. Box 189, Moffett Field, CA 94035-0189 http://olias.arc.nasa.gov/asrs
April1999ReportIntake
Air Carrier / Air Taxi Pilots General Aviation Pilots Controllers Cabin/Mechanics/Military/Other 2314 656 56 145
TOTAL
3171
飞行翻译公司 www.aviation.cn 本文链接地址：美国ASRS安全公告CALLBACK cb_240.pdf
June 1999
Weather ASOS-ciations
Automated Surface Observing System (ASOS) is the current weather reporting equipment at many airports. However, some pilots and controllers believe that this equipment occasionally provides inconsistent or unreliable weather information to users. Our first report, from a General Aviation pilot, illustrates:
A Matter of Conscience
In an old Walt Disney movie, Jiminy Cricket sang a song that ended, “…and always let your conscience be your guide.” A Tower Controller did just that, stating in his ASRS report that, “the only valid information the pilot had in this case was my notably unauthorized remark.”
s Weather at XYZ was reported as clear, visibility 7-10
miles, no remarks. I checked the ATIS repeatedly during the last 45 minutes of the flight. No change from clear and 8 miles. There was frequent lightning ahead with indications of storm activity on the [aircraft’s] weather avoidance equipment. The ASOS at XYZ is supposed to be attended and augmented as necessary. In this case, a thunderstorm was close enough to the airport to be seen and heard, but there was no mention of it on the official weather. Another reporter, an experienced weather observer, explains how the ASOS can arrive at these apparently inconsistent weather reports.
s The [small] aircraft had just turned base to final to
Runway 16, having been cleared to land while it was on downwind. [At that time, I issued] the ASOS wind at 100 degrees at 8 knots. A thunderstorm was about three miles west of the field. I felt the Tower buffeted by the wind. I issued to the pilot, based on observation of [current] ASOS and the parking lot, “ASOS wind variable at 4 knots, in reality it’s bending the trees.” The aircraft required 3,200 feet of runway to land. On touchdown, the ASOS still read variable at 4 knots. As the aircraft exited the runway, ASOS updated the wind to 250 degrees at 9 knots gusting to 16 knots, then 270 degrees at 15 knots gusting to 21 knots. The originally reported wind was 170 degrees different from the actual wind at the time of landing, and 2.5 times the velocity and approaching the aircraft’s demonstrated crosswind landing capability. Controllers may not transmit specific values (such as the ceiling, visibility, or, in this case, wind), other than those listed in the current ASOS. The exceptions include airports at which an official weather observer is on site, or at which the weather report has been composed or verified by the weather station. Pilots must therefore rely on their basic piloting skills (for example, observation of a wind sock or comparison of ground speed vs. airspeed) for final determination of safe landing conditions. To read more about a Controller’s role in disseminating weather information, refer to the Air Traffic Control Handbook (7110.65L, Paragraph 2-6-7).
s The ceilometer only sees clouds directly over its sensor.
This means on a dreary overcast day, if there is one small break in the clouds over the sensor, it calls the sky clear. Furthermore, the visibility sensors…generally show the visibility to be much greater than it actually is. Some technical advances have improved the accuracy of ASOS readings and increased the frequency of broadcast updates. However, the equipment is programmed to update ASOS and ATIS broadcasts only when a significant weather change occurs. For more information, check out the ASOS User’s Guide on the Web at: http://www.nws.noaa.gov/asos/index.html
Location, Location, Location
In another report to ASRS, a Local Controller notes that the location of ASOS sensing devices may generate wind reports that differ from those produced by sensors elsewhere on an airport.
s [ASOS] wind instrument is installed at the south end of
the airport in a partially sheltered location. [The reading] differs by 50 degrees or more during northwest winds when compared to mid-field wind sensors. Additionally, this sensor is 2 miles from the approach end of Runway 19. I believe this instrument does not give a good representation of wind conditions. Tower and Approach have direct-reading instrument from the mid-field sensor. Reports such as this one, sent either directly to airport management or to ASRS, have resulted in the relocation of ASOS sensing equipment at several airports.
The Bottom Line
A final thought from a controller who is also a weather observer charged with trying to update the ASOS report during changing weather conditions:
s I attempted to manually override the system, but it was
so slow, we were still reporting VFR while the storm raged outside. If you are using weather from an automated station, when the weather is changing rapidly, don’t believe what is being reported.
ASRSRecentlyIssuedAlertsOn…
Uncommanded roll in a B737 Metal shaving debris on A320 flight control wiring P-56 (White House airspace) avoidance procedures FOD (Foreign Object Damage) hazard at a Michigan airport BAE-41 engine flameouts during reversal and at steady idle
A Monthly Safety Bulletin from
The Office of the NASA Aviation Safety Reporting System, P.O. Box 189, Moffett Field, CA 94035-0189 http://olias.arc.nasa.gov/asrs
April1999ReportIntake
Air Carrier / Air Taxi Pilots General Aviation Pilots Controllers Cabin/Mechanics/Military/Other 2314 656 56 145
TOTAL
3171
飞行翻译公司 www.aviation.cn 本文链接地址：美国ASRS安全公告CALLBACK cb_240.pdf
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