Dash 8-100
Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 160; Flight Crew Total 6200; Flight Crew Type 5500
Workload; Troubleshooting; Confusion; Time Pressure
Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Published Material / Policy
Flight Crew Took Evasive Action; Flight Crew FLC complied w / Automation / Advisory; Flight Crew Overcame Equipment Problem
Aircraft
We were at 4;000 FT just on our descent. In the middle of checking in with Approach we had a Triple Inverter Failure. We lost every instrument on the Captain's side except the airspeed indicator and the HSI. I; the Captain; immediately clicked off the autopilot and hand flew. We asked Approach for a heading and the First Officer pulled out the checklist. I already knew to pull the circuit breaker (behind my head) to isolate all of the inverters; but I waited until the First Officer read it on the Multiple Inverter Emergency Checklist. I then transferred the controls to the First Officer and pulled the 115v Bus Tie circuit breaker. I immediately regained my instruments; but the First Officer lost all of the corresponding instruments on his side. The only lights left on the caution panel were SEC INV; and R26AC. These lights are appropriate for a secondary inverter failure. The First Officer transferred the controls back to me since I had my instruments back online; and he continued the checklist. The checklist calls for the Aux inverter to be switched to the failed side. We complied; switching the Aux Inverter to the Secondary Inverter (failed side); which caused the First Officer to regain all his instruments back except his altimeter. This caused the illumination of the AUX INV caution light; and we still had the SEC INV along with the R26AC caution light as well. I knew right away that something was wrong because these were not the appropriate lights that we should have. My understanding of the system is that the First Officer should have regained ALL of his instruments; with the only the SEC INV caution light illuminated on the caution panel. Instead we had all 3 lights illuminated on the caution panel (SEC INV; AUX INV; R26AC) and no altimeter on the First Officer's side. The First Officer noticed that the Aux inverter and the secondary inverter load were showing only 72v; not 115v like they should. We noted this and continued the checklist. The primary inverter was of course still showing 115v and working correctly. The next thing on the checklist calls for the 115v bus tie Circuit Breaker to be pushed back in. So I transferred the controls back to the First Officer; and pushed the Breaker back in. Unfortunately because the system was malfunctioning; I lost all of my instruments once again. I knew this was likely to happen since the system wasn't responding like it should; and I immediately pulled the breaker back out. The First Officer transferred the controls back to me and I flew the rest of the flight with the breaker popped. This gave me my full panel of instruments; and gave the First Officer all of his with the exception of his altimeter. It was VFR. We were lucky. Please understand that I chose to keep the Aux Inverter selected to the Secondary Inverter; which was the failed side; even though it was 'dragging down' the Aux inverter; simply because it gave us the most instruments possible at the time. And as for defying the checklist and leaving the breaker out for the remainder of the flight; I believed this was the safest thing to do. I of course; ran this by the First Officer and he agreed it was the safest way to continue the flight. By this time we were just about to be cleared for the visual approach; and we landed safely with no further issues. There was no need to notify ATC.Somehow the secondary inverter was causing the whole system to fail. The First Officer and I ran the appropriate Checklist for a Multiple Inverter Failure; and of course had to use our better judgment as to the deviations that we made from the checklist. In our situation; I would wholeheartedly do it the same way again.
A DHC-8-100 Secondary Inverter failed during the approach descent which resulted in an unusual inverter configuration in order to keep all flight instruments powered except the First Officer's altimeter.