This one appears in an entry under "Additional Services" in the FAA Pilot/Controller Glossary and claims that ATC provides a wide range of additional services to pilots, including "Weather and Chaff" information, which seems like an unusual entry. What does "chaff" mean in this context?

Originally chaff was the remains of a wheat plant cut down and with the grains in the head thrashed out, which is then discarded. It's also a biblical reference to the wicked condemned by God to hell i.e. "the chaff, which the wind driveth away". In modern times, it is associated with a physical countermeasure to radar whereby thousands of metallic strips are ejected out of an aircraft to confuse enemy radars or break the track of radar guided anti aircraft weapons. I though the phrase in the P/CG might have been a reference to some sort of anachronistic term about the environment which was termed "chaff" but I don't know. I did locate this story from NOAA's website where their weather radar in Louisville, KY, was spoofed by military chaff which had been dispersed during nearby training exercises. This gives though to another risk of an aircraft flying through a cloud of chaff and ingesting it into the engines, or causing some other kind of system damage. This would seem to be a remote possibility but who knows. Anybody know what the P/CG meant by chaff in this reference.

  • $\begingroup$ Re "It’s also a biblical reference to the wicked condemned by God to hell i.e. “the chaff, which the wind driveth away”." -- well-- we're living in ominous times-- so, might be some need for a NOTAM-- the FAA must consider all eventualities-- $\endgroup$ – quiet flyer Apr 18 at 14:29
  • $\begingroup$ When chaff was dropped, ATC was required to give an advisory to aircraft, but it was of a general nature. No special separation criteria, unlike fuel dumping. $\endgroup$ – atc_ceedee May 8 at 14:40

In the Pilot/Controller Glossary, this is the definition of "Chaff" and would be its meaning in the context of "Additional Services" referenced in your question.

CHAFF- Thin, narrow metallic reflectors of various lengths and frequency responses, used to reflect radar energy. These reflectors, when dropped from aircraft and allowed to drift downward, result in large targets on the radar display.

On some radar equipment chaff may appear similar to areas of precipitation.

  • $\begingroup$ One presumes that this would be a bad thing to ingest into any kind of engine intake and that the area should be avoided. Also it interferes with radar increasing the possibility someone else is in the area, which is also considered bad. $\endgroup$ – Criggie Apr 19 at 3:44

When KRCA was a B52 base, it was quite common for those aircraft to drop aluminum chaff (think BIG pieces of tinsel) as part of their training. It would spread out very quickly, and you'd see hundreds of strong primary targets in the area of the drop. They'd hang there for a long time, following the wind. Quite annoying, especially if you had a non-transponder aircraft in the area. With the B1s that are now based at KRCA, we don't see this anymore, but we occasionally see ECM jamming. It's very effective, but thankfully, it's of short duration.

When these activities are being conducted, we advise all aircraft in the area, so they know that our radar performance may be degraded. It's not the issue that it once was.

Weather services consist of advising pilots of radar displayed weather, but also of forecast weather along the route(AIRMETs), pilot reports (PIREPs - both solicitation AND dissemination), altimeter settings along the route, destination airport weather, and anything else that may assist the pilot with planning the flight.

Once, during a particularly bad day for thunderstorms, I had an American Airlines aircraft, who had just completed multiple weather deviations around BFF, ask about the weather along his route to KEWR. Poor guy was from KSEA, and had to come 200 miles south of his normal route to get around the squall line. I looked at our overhead display, and saw that there was another line of thunderstorms out east, that went from BRD (Brainerd, Minnesota) all the way down to the Gulf.

On the next screen, I saw that the upper winds were from the southwest, 80 knots at FL330, and turned out of the northwest at BRD. I recommended that he go direct BRD, then SLT (Slate Run), which rejoined his flight plan. He called his dispatch. A minute later, he requested the route I suggested, and informed me that all subsequent aircraft for American going to the east coast would do the same.


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