Date: 201910
Local time of day: 1801-2400
Location: ZZZ.Airport, US
Flight conditions: VMC
Light: Night
Aircraft: Bonanza 36
Operator: Personal
Operating under: Part 91
Flight plan: None
Mission: Training
Flight phase: Landing
Airspace: Class G ZZZ
ATC / advisory: CTAF ZZZ
Aircraft component: Gear Lever/Selector
Component problem: Improperly Operated
Reporter organization: Personal
Reporter function: Captain; Pilot Not Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP); Flight Crew Flight Instructor; Flight Crew Instrument; Flight Crew Multiengine
Human factors: Communication Breakdown; Situational Awareness
Anomaly: Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy; Ground Event / Encounter Gear Up Landing
Detector: Person Flight Crew
When detected: In-flight
Result: Aircraft Aircraft Damaged; General Maintenance Action
Contributing factors: Procedure; Human Factors
Primary problem: Human Factors

Narrative: We were on a night training flight for night currency. The pilot flying was planning to update her night currency. I was acting as PIC/CFI/PNF in the right seat.We met at the airport approximately XA:45 pacific time. After preflighting the aircraft we started engines at approximately XB:20. Some engine roughness was noted at startup but was resolved after leaning and runup checklist was completed. Additional time was lost waiting for a transient aircraft who was lost on the airport trying to find his way to a gate for exit. I informed the Pilot flying to hold position until the transient airplane was clear of all runways. We offered assistance via radio to the transient pilot whom we directed to the ramp.We made a normal takeoff on Runway XXL; retracted the landing gear; and entered a normal left traffic pattern. On downwind we extended the landing gear and continued to a normal landing with full stop. We then taxied back for another takeoff and entered the downwind leg. Upon reducing power for the approach we noticed some engine roughness which I attributed to 'pushing the prop' because of our relatively high airspeed and being full rich at minimal power. The pilot flying thought it was an engine malfunction so I attempted to adjust the mixture to no satisfaction to the pilot flying. I directed the Pilot Flying to go to full flaps for landing as we were turning final and speed seemed high. We continued the approach to landing and failed to do a 'GUMP' check for landing gear due to our distraction resulting from the engine issue.We did not get a gear warning alarm even though the MP was at 11 inches. Had that alarm sounded; we would have; if time and altitude allowed; been able to extend the landing gear or otherwise execute a go-around.This is a case of two senior pilots trusting each other to 'Take care of business.' The distraction with the engine caused me to forget the pre-landing checklist which I assumed the PF was managing but was really my responsibility as CFI/PIC.The result was a gear-up landing which resulted as a very smooth landing with minimal damage to the aircraft and no injuries to personnel.




Synopsis: Bonanza pilot reported that distraction and failure to follow the checklist resulted in a gear-up landing.