Cessna Aircraft Undifferentiated or Other Model
Flight Crew Air Transport Pilot (ATP); Flight Crew Flight Instructor; Flight Crew Instrument; Flight Crew Multiengine
Flight Crew Last 90 Days 60; Flight Crew Total 19000; Flight Crew Type 2500
Workload; Distraction
Conflict Airborne Conflict; Deviation - Altitude Excursion From Assigned Altitude; Inflight Event / Encounter Weather / Turbulence
Air Traffic Control Provided Assistance; Flight Crew Became Reoriented
Weather; Human Factors
I remember the event; just not sure on which flight. I was flying a Cessna 340 or a Cessna 210. Both flights were from Denver Centennial (APA) flying north. Same route; same altitude and same moderate or greater turbulence from APA to north of the Wyoming state line. The turbulence was too rough to use the autopilot; it gets behind making matters worse. I was cruising north of BJC at 8000 ft. Between keeping an eye on an aircraft at 9 o'clock low flying the same direction as I was; my class B chart; other traffic; and dealing with the turbulence (up to 100 ft deviations) I was pretty busy. My map and other stuff was thrown off the co-pilot seat. At the time of the deviation; I was trying to pick it up off the floor to verify the border of Class B airspace. I'd lost a couple hundred feet and was correcting when the controller called an altitude alert. Apparently the aircraft was at 7000 ft. The airspace between BJC and Fort Collins/Loveland is usually congested with VFR traffic. I feel I need to have eyes outside as much as possible when I am under; or just outside of Class B airspace where most of the VFR traffic is. When the turbulence is light or smooth I often use the autopilot so I can spend more time looking for the little airplanes that are so hard to see. I will continue to be vigilant and attempt to comply with ATC instructions.
Cessna pilot reported he accidentally descended while trying to retrieve his chart off the aircraft floor. ATC issued an altitude alert.