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ZSE controller described a below authorized altitude event when an aircraft apparently misunderstood the altitude assignment.
| Attributes | |
| ACN | 980050 |
| Time | |
| Date | 201111 |
| Local Time Of Day | 1801-2400 |
| Place | |
| Locale Reference | YKM.Airport |
| State Reference | WA |
| Environment | |
| Light | Night |
| Aircraft 1 | |
| Make Model Name | Turbo Commander (JetProp) Undifferentiated |
| Operating Under FAR Part | Part 135 |
| Flight Phase | Descent |
| Flight Plan | IFR |
| Person 1 | |
| Function | Enroute |
| Qualification | Air Traffic Control Fully Certified |
| Person 2 | |
| Function | Pilot Flying Captain |
| Qualification | Flight Crew Multiengine Flight Crew Instrument Flight Crew Air Transport Pilot (ATP) |
| Experience | Flight Crew Last 90 Days 40 Flight Crew Total 2900 Flight Crew Type 210 |
| Events | |
| Anomaly | ATC Issue All Types Deviation - Altitude Overshoot Deviation - Procedural Clearance Inflight Event / Encounter CFTT / CFIT |
Narrative:
I was working only 2 aircraft both inbound to ykm. An AC90 was descending to 9;000 ft and had read back the clearance. I issued 6;000 ft to the other aircraft and that aircraft read it back. I noticed that the AC90 had descended below 9;000 ft and I asked him to say altitude. He read back what the mode C was showing 8;300 ft. I immediately issued a climb back to 9;000 ft and told the aircraft my minimum IFR altitude. The AC90 said that he read back a clearance to 6;000 ft. I never heard him read back that clearance and was not busy; so I should have caught it if he did.I am always very focused on read backs and take extra care to listen. We can always listen more closely and try to avoid read back errors.
Original NASA ASRS Text
Title: ZSE Controller described a below authorized altitude event when an aircraft apparently misunderstood the altitude assignment.
Narrative: I was working only 2 aircraft both inbound to YKM. An AC90 was descending to 9;000 FT and had read back the clearance. I issued 6;000 FT to the other aircraft and that aircraft read it back. I noticed that the AC90 had descended below 9;000 FT and I asked him to say altitude. He read back what the Mode C was showing 8;300 FT. I immediately issued a climb back to 9;000 FT and told the aircraft my minimum IFR altitude. The AC90 said that he read back a clearance to 6;000 FT. I never heard him read back that clearance and was not busy; so I should have caught it if he did.I am always very focused on read backs and take extra care to listen. We can always listen more closely and try to avoid read back errors.
Data retrieved from NASA's ASRS site as of April 2012 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.