Aero Commander 500 Series
Flight Crew Flight Instructor; Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Commercial
Flight Crew Last 90 Days 120; Flight Crew Total 3200; Flight Crew Type 250
Situational Awareness; Workload; Troubleshooting; Physiological - Other
Deviation - Altitude Excursion From Assigned Altitude; Deviation - Altitude Overshoot; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Clearance; Flight Deck / Cabin / Aircraft Event Other / Unknown; Inflight Event / Encounter Weather / Turbulence
Air Traffic Control Provided Assistance; Air Traffic Control Issued New Clearance; Flight Crew Overcame Equipment Problem; Flight Crew Requested ATC Assistance / Clarification; Flight Crew Returned To Clearance
Human Factors; Environment - Non Weather Related
While climbing to complete a fire mapping mission; I was cleared to 17;000 ft. MSL. I asked for a block altitude of 17;000 ft. - FL190 due to the presence of a smoke column that would likely cause me to deviate from my assigned altitude. As I got closer to the column; my altitude shot up to 17;500 ft. before I received further clearance. At some point I was cleared to FL210. I became so task saturated managing piston engines during the climb; attempting to complete the mapping mission with two camera operators in the backseat; avoiding the smoke column and negotiating block altitudes with ATC that I failed to change my nose cannula to a full face mask above FL180. I started to have extreme difficulty processing information in a timely manner; as well as making decisions and communicating effectively. After asking for a lower altitude; 17;000 ft.; I was able to think clearly and manage tasks and communication appropriately.
AC500 pilot reported deviating from assigned altitude and neglecting oxygen face mask requirements.