Turbo Commander 690 Series
Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine
Flight Crew Last 90 Days 100; Flight Crew Total 11000; Flight Crew Type 1000
Human-Machine Interface; Situational Awareness
Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Published Material / Policy; Ground Event / Encounter Ground Strike - Aircraft; Inflight Event / Encounter Unstabilized Approach
Aircraft Aircraft Damaged; Flight Crew Executed Go Around / Missed Approach
Aircraft; Human Factors
Practicing an ILS approach in VFR conditions; after intercepting the LOC I had to do a 360 to provide spacing for a C-172 who was on an IFR flight plan. Upon re-intercepting the LOC and tracking it inbound I was waiting for the Glide Slope to be one dot above before lowering my landing gear. After continuing inbound a ways more and no Glide Slope flags; but also no Glide Slope movement I discovered that the Captain's side Glide Slope was frozen at 1 1/2 dots above. I verified this with the co-pilots side Glide Slope. After trying to switch frequency and then switch back; identifying again that it was the right frequency the Tower cleared me to land. I failed to check 3 in the green and got low enough to rub some rivets on the belly of the aircraft before initiating a go around and landing. Another contributing factor was the fact that I had been practicing slow flight with gear up and 1/2 flaps and had pulled the landing gear circuit breaker to silence the horn. Doing the before landing check list is usually accomplished upon Glide Slope intercept before the outer marker. The fact that I never got Glide Slope intercept threw me out of sequence on my use of check list. To prevent this in the future I would not continue to trouble shoot a problem on final but would instead go around and re-evaluate; or complete the checklist and land.
AC690 pilot becomes distracted by a malfunctioning glide slope indication during approach and nearly lands gear up before going around. A landing gear circuit breaker had been pulled to silence the warning horn while practicing slow flight and was not reset.