Yes, it does happen from time to time...a G-AIRMET somehow gets issued that just doesn't make sense. Imagine for a moment that you are flying out of central Michigan at about 0000 UTC. So prior to your departure, you call Flight Services to get a standard briefing. You tell the briefer that your plan is to fly IFR at 7,000 feet and you are not equipped with a certified ice protection system (IPS). The briefer tells you about an AIRMET for moderate airframe ice from 4,000 to 10,000 feet covering most of lower Michigan. The briefer says that he would not recommend an IFR flight at 7,000 feet given the risk of moderate airframe ice along your proposed route. You hang up the phone with the understanding that you are not going to make this flight.
So you get online and start to examine the weather more carefully and you notice the legacy AIRMET the briefer was telling you about.
WAUS43 KKCI 092048 AAA
CHIZ WA 092048 AMD
AIRMET ZULU UPDT 5 FOR ICE AND FRZLVL VALID UNTIL 100300
...SEE SIGMET VICTOR SERIES...UPDT
AIRMET ICE...WI LM MI LH IL IN
FROM 20NNE GRB TO YVV TO 20ESE DXO TO 20WSW GIJ TO 20SW ORD TO
MOD ICE BTN 040 AND 120. CONDS CONTG BYD 03Z ENDG 06-09Z.
Here's the G-AIRMET snapshot valid at 0000 UTC...
Next you look at the freezing level forecast (below) also valid at 0000 UTC. You are surprised to see that the freezing level is forecast to be 8,000 feet cutting through the northern edge of the G-AIRMET.
The freezing level was nearly 11,000 feet along most of your planned route. The Current Icing Product (CIP) and Forecast Icing Product (FIP) showed no chance of airframe ice below 10,000 feet. Something is just not right.
This really did occur and I sent an e-mail out to one of my colleagues at the Aviation Weather Center (AWC) who just happened to be coming on duty that afternoon. Here was his reply...
I apologize for that AIRMET. I canceled it. Normally I QC the previous shift, but I didn't do it today. No excuse. I am going to carry an AIRMET in that area tonight starting at 09Z, but have the bases at 100. Thanks for catching that and again, I apologize for the obvious mistake."
Shortly after I got his reply, he had issued an amendment to the G-AIRMET to cancel it.
WAUS43 KKCI 100127 AAB
CHIZ WA 100127 AMD
AIRMET ZULU UPDT 6 FOR ICE AND FRZLVL VALID UNTIL 100300
...SEE SIGMET VICTOR SERIES...
AIRMET ICE...ND SD MN WI LS MI
FROM 70SE YWG TO 90ESE YQT TO SSM TO 20ESE RHI TO 50S FAR TO 40N
PIR TO 40NW RAP TO 50NNW ISN TO 70SE YWG
MOD ICE BLW FL180. CONDS CONTG BYD 03Z THRU 09Z.
AIRMET ICE...WI LM MI LH IL IN...UPDT
FROM 30NW TVC TO 20NE YVV TO 40E ECK TO 20ESE DXO TO 20WSW GIJ TO
20SW ORD TO 20NNE GRB TO 30NW TVC
Moral of the story...you better strive to learn what you can about aviation weather. Short of that and you are trusting the system to keep you safe. There are way too many other weather products that I use (and teach) that go way beyond what you get during a standard briefing. This case was benign, however, the briefers just don't know enough to keep me out of a bad situation. Just imagine if this was a case where there was widespread structural icing and NO G-AIRMET.
Most pilots are weatherwise, but some are otherwise™
Scott Dennstaedt, PhD
Weather Systems Engineer
CFI & former NWS meteorologist