Beech 1900
Flight Crew Air Transport Pilot (ATP); Flight Crew Flight Instructor; Flight Crew Instrument; Flight Crew Multiengine
Flight Crew Last 90 Days 140; Flight Crew Total 7500; Flight Crew Type 700
Workload; Distraction
Aircraft Equipment Problem Critical; Deviation - Altitude Undershoot; Deviation / Discrepancy - Procedural Clearance; Inflight Event / Encounter Weather / Turbulence
Flight Crew Returned To Clearance; Flight Crew Took Evasive Action
Weather; Human Factors; Aircraft
While flying a night cargo flight to SLC; I experienced a possible altitude deviation while descending for approach. I was the single pilot Captain of a BE1900. Weather was IFR with light turbulence and moderate mixed icing in clouds. After departing and climbing to 16;000 FT; airframe ice began to accumulate to the point where the wing leading edge had approximately 3/4 to 1 inch. I cycled the de-ice boots and the ice was shed; and then repeated the process about 5 minutes later. Ice continued to accumulate and when I attempted to activate the boots again; very little ice came off. The boots had become ineffective (though they were; by all indications; operating). I requested a climb to FL180; but was still skirting the cloud tops at this altitude so ice continued to accumulate slowly. Shortly after reaching FL180; I got a red warning light for a right engine bleed air fail. After recycling the bleed air on/off switch; the light remained on; so I concluded that the indication was real and turned the right bleed air system off; and continued the flight. As I got closer to the LHO VOR; ZLC instructed me to hold over LHO at FL180. In fact; they were telling all SLC inbounds to hold due to changing the direction of flow into the airport. After holding one turn at LHO; I was instructed to continue to CARTR Intersection and hold there. Before reaching CARTR; though; I was switched to SLC Approach Control; was given a vector to the localizer; and a descent to 12;000 FT. Passing through approximately 16;000 FT; I got a red cabin altitude warning light; which indicates a cabin altitude in excess of 10;000 FT. Apparently; the single operating bleed from the left engine was not allowing the pressurization system to keep up with the set cabin altitude of 5;000 FT. I was not too concerned about this because I was in descent; and I anticipated being below 10;000 FT MSL shortly anyway. I expedited my descent to greater than 2;000 FPM. At one point in the descent; ATC said to 'maintain 12;000 FT;' and looking at the altimeter; I thought that I had overshot to 11;700 FT; so I quickly corrected back to what I thought was 12;000 FT. Within a minute after that; however; ATC told me to descend to 12;000 FT and that they were showing me at 13;000 FT. I confirmed 13;000 FT on the altimeter and told the controller that I was continuing my descent to 12;000 FT. I don't know if I misread the altimeter and/or misunderstood the Controller. It was a tad confusing. Perhaps I was actually at 12;700 FT; not 11;700 FT; when the Controller said 'maintain 12;000 FT' and erroneously climbed back to 13;000 FT. I think that it's doubtful that I had actually descended to 11;700 FT and then inadvertently climbed back to 13;000 FT. Whatever actually happened; my confusion was fed by the simultaneous distractions of the cockpit altitude warning and my desire to make a fast descent; as well as my concern for the build up of ice that was still on the wings.
BE1900 pilot reports accumulating ice at 16;000 FT that is successfully shed by the boots through several cycles before becoming unable to shed the ice. Climbing to FL180 results in less ice formation and a right engine bleed failure. During descent for landing the cabin altitude warning light comes on but is ignored due to the descent rate as well as an early level off at 13;000 FT vice the cleared altitude of 12;000 FT noted by ATC.