Pilot reported a pressurization problem and advised ATC.

Attributes
ACN	1750279
Time
Date	202007
Local Time Of Day	0601-1200
Place
Locale Reference	ZZZ.ARTCC
State Reference	US
Environment
Flight Conditions	Mixed
Light	Daylight
Aircraft 1
Make Model Name	Duke 60
Operating Under FAR Part	Part 91
Flight Phase	Cruise
Route In Use	Direct
Flight Plan	IFR
Component
Aircraft Component	Pressurization System
Person 1
Function	Single Pilot Pilot Flying Captain
Qualification	Flight Crew Multiengine Flight Crew Instrument Flight Crew Commercial
Experience	Flight Crew Last 90 Days 200 Flight Crew Total 1700 Flight Crew Type 40
Events
Anomaly	Aircraft Equipment Problem Critical

Narrative:

Upon reaching FL210; I noticed a hissing noise from the back of the cabin near the door. The cabin pressure was decreasing so I immediately initiated a descent and notified ATC. I was asked if I wanted to [request priority handling] and at that time; the cabin pressure was beginning to correct itself; so I said no. I just asked to continue the flight at 11;000 ft. To be safe just in case it happened again.

Original NASA ASRS Text

Title: Pilot reported a pressurization problem and advised ATC.

Narrative: Upon reaching FL210; I noticed a hissing noise from the back of the cabin near the door. The cabin pressure was decreasing so I immediately initiated a descent and notified ATC. I was asked if I wanted to [request priority handling] and at that time; the cabin pressure was beginning to correct itself; so I said no. I just asked to continue the flight at 11;000 ft. to be safe just in case it happened again.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.