A Center Controller reported an aircraft encountering icing descended below the Minimum Vectoring Altitude.

ACN 1961141 2022-12 Piper Single Undifferentiated or Other Model Commuter and GA Icing Incidents

CruisePart 91

What is ASRS?

The Aviation Safety Reporting System is NASA's voluntary, confidential, non- punitive incident-reporting system, established 1976. Pilots, controllers, dispatchers, and maintenance technicians file reports describing safety- relevant events. NASA de-identifies every report before adding it to the public database. Reports are not investigated by NASA, the FAA, or the NTSB — they represent the reporter's perspective.

Pilot narrative

Verbatim from the de-identified NASA record. First-person account by the reporter. NASA strips identifying details (names, company, specific time); anonymization placeholders are ZZZ, X, Y.

Aircraft X came to me from ZZZ Approach reporting light icing. I had informed ZZZ approach that due to my MIA's I would not be able to turn or descend this aircraft until the vicinity of ZZZ1. I let the pilot know I would descend them to my lowest usable altitude of 8000 ft. in less than two minutes. Shortly after, Aircraft X showed descending to 8700 ft. in the 9000 ft. MIA block. I asked them to verify level at 9000 ft. and the altimeter, as this commonly happens in this area as they change altimeters. They said they were unable to maintain their altitude due to icing. I called a low altitude alert and told them to maintain 9000 ft. if possible. Once they entered the 8000 ft. block I descended them to 8000 ft. They were supposed to turn south, which would keep them clear of a neighboring 9000 ft. block, but they did not make the turn. I turned them XXR at first, then eventually put them on a 150 heading when they turned too slow to miss the block and called a low altitude alert for the 9000 ft. block they had turned in to. At this point they were still slowly descending and it became clear they needed to land now. I offered them ZZZ2, as it was the closest airport, and they accepted. I called ZZZ3 and told them the situation and coordinated 7000 ft. altitude and 090 heading to get them to ZZZ2. The aircraft was still descending so I asked them to try to maintain 7000 ft. for the next sector and called another low altitude alert. I put them on the 090 heading and eventually changed them to ZZZ3's frequency. The pilot was clearly in distress so I did not ask them the type of icing while I had them, but later called ZZZ3 for a report and was told the icing was severe mixed icing. I put in the PIREP and informed that other aircraft in my sector that may be affected by this. We had no other reports of icing in this area today, so there was no way of knowing it was going to happen. In the future I could inform ZZZ approach perhaps to have the aircraft return to ZZZ if they were getting bad icing at 9000 ft. my lowest usable altitude.

NASA classification — Anomalies

ATC Issue
Deviation - Altitude
Deviation - Track / Heading
Deviation / Discrepancy - Procedural
Ground Event / Encounter
Inflight Event / Encounter

NASA classification — Assessments

Contributing Factors / Situations: Airspace Structure · Chart Or Publication · Human Factors · Weather
Primary Problem: Weather

ASRS reports are voluntarily submitted, de-identified by NASA, and represent the reporter's perspective. The presence of reports on a topic cannot be used to infer prevalence in the National Airspace System. The authoritative source is the NASA ASRS Database Online at asrs.arc.nasa.gov ↗.