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Combination of icing conditions and mountain wave cause C208 pilot to descend from 12000 to 10000 ft with takeoff power set. Low altitude alert from ZAB at 10500 ft and VFR at 10000 ft.
| Attributes | |
| ACN | 769294 |
| Time | |
| Date | 200801 |
| Local Time Of Day | 0001 To 0600 |
| Place | |
| Locale Reference | airport : abq.airport |
| State Reference | NM |
| Altitude | msl single value : 12000 |
| Environment | |
| Flight Conditions | IMC |
| Weather Elements | Ice |
| Light | Night |
| Aircraft 1 | |
| Controlling Facilities | tracon : abq.tracon |
| Operator | common carrier : air taxi |
| Make Model Name | Caravan Undifferentiated |
| Operating Under FAR Part | Part 135 |
| Flight Phase | descent other |
| Flight Plan | IFR |
| Person 1 | |
| Affiliation | company : air taxi |
| Function | flight crew : first officer |
| Qualification | pilot : cfi pilot : atp |
| Experience | flight time last 90 days : 300 flight time total : 8000 flight time type : 3800 |
| ASRS Report | 769294 |
| Person 2 | |
| Affiliation | government : faa |
| Function | controller : radar |
| Events | |
| Anomaly | altitude deviation : excursion from assigned altitude inflight encounter : weather inflight encounter : turbulence other anomaly other anomaly other |
| Independent Detector | atc equipment : msaw other flight crewa |
| Resolutory Action | controller : issued alert flight crew : regained aircraft control |
| Supplementary | |
| Problem Areas | Aircraft Flight Crew Human Performance Weather |
| Primary Problem | Weather |
Narrative:
Upon crossing the manzano mountains; we picked up light to moderate icing at 12000 ft MSL. The propeller began to vibrate as the propeller heat dissipated the ice. At that moment we experienced a downdraft which caused the autoplt to disconnect. At that point we added takeoff power which caused the aircraft to continue to descend. Upon reaching 11500 ft; abq approach questioned our altitude. At 10500 ft approach issued a low altitude alert. At 10000 ft we were in VFR conditions and we canceled IFR. Due to icing and mountain wave; we were unable to maintain our assigned altitude of 12000 ft. Using a different route could have prevented icing and mountain wave.
Original NASA ASRS Text
Title: COMBINATION OF ICING CONDITIONS AND MOUNTAIN WAVE CAUSE C208 PILOT TO DESCEND FROM 12000 TO 10000 FT WITH TKOF POWER SET. LOW ALTITUDE ALERT FROM ZAB AT 10500 FT AND VFR AT 10000 FT.
Narrative: UPON XING THE MANZANO MOUNTAINS; WE PICKED UP LIGHT TO MODERATE ICING AT 12000 FT MSL. THE PROP BEGAN TO VIBRATE AS THE PROP HEAT DISSIPATED THE ICE. AT THAT MOMENT WE EXPERIENCED A DOWNDRAFT WHICH CAUSED THE AUTOPLT TO DISCONNECT. AT THAT POINT WE ADDED TKOF PWR WHICH CAUSED THE ACFT TO CONTINUE TO DSND. UPON REACHING 11500 FT; ABQ APCH QUESTIONED OUR ALT. AT 10500 FT APCH ISSUED A LOW ALT ALERT. AT 10000 FT WE WERE IN VFR CONDITIONS AND WE CANCELED IFR. DUE TO ICING AND MOUNTAIN WAVE; WE WERE UNABLE TO MAINTAIN OUR ASSIGNED ALT OF 12000 FT. USING A DIFFERENT RTE COULD HAVE PREVENTED ICING AND MOUNTAIN WAVE.
Data retrieved from NASA's ASRS site as of May 2009 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.