GA pilot reported inadvertently starting descent on localizer without clearance resulting in an air ...

Attributes
ACN	1655531
Time
Date	201906
Local Time Of Day	0601-1200
Place
Locale Reference	DAL.Airport
State Reference	TX
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Make Model Name	Small Aircraft
Operating Under FAR Part	Part 91
Flight Phase	Final Approach Landing
Route In Use	Vectors
Flight Plan	IFR
Person 1
Function	Pilot Flying Single Pilot
Qualification	Flight Crew Instrument Flight Crew Multiengine Flight Crew Private
Experience	Flight Crew Last 90 Days 42 Flight Crew Total 623 Flight Crew Type 100
Events
Anomaly	Conflict NMAC Deviation - Altitude Excursion From Assigned Altitude Deviation - Procedural Clearance
Miss Distance	Vertical 300

Narrative:

I was flying to dallas love field (dal) under an IFR flight plan. While approaching dal; I was following vectors from the regional ATC for runway 31R at dal. I was instructed to maintain 4;000 feet and intercept the localizer for runway 31R. Upon intercepting the localizer (while in clouds) my plane; via the autopilot; began to descend along the glide slope. The controller then gave instructions for me to turn right. After following additional vectors; I again intercepted the localizer for 31R. The ATC or tower person asked me to call a phone number upon landing. I then landed without incident and called the number. The person I talked with reported that another plane; which I could not see because of clouds; was under and close to my plane on the first approach. It would have been helpful if the controller pointed out the traffic. It is also common to follow the glide slope upon intercepting the localizer as my autopilot in programmed to do. Specific instructions not to descend would also be helpful.

Original NASA ASRS Text

Title: GA pilot reported inadvertently starting descent on localizer without clearance resulting in an air conflict.

Narrative: I was flying to Dallas Love Field (DAL) under an IFR flight plan. While approaching DAL; I was following vectors from the regional ATC for runway 31R at DAL. I was instructed to maintain 4;000 feet and intercept the localizer for Runway 31R. Upon intercepting the localizer (while in clouds) my plane; via the autopilot; began to descend along the glide slope. The controller then gave instructions for me to turn right. After following additional vectors; I again intercepted the localizer for 31R. The ATC or tower person asked me to call a phone number upon landing. I then landed without incident and called the number. The person I talked with reported that another plane; which I could not see because of clouds; was under and close to my plane on the first approach. It would have been helpful if the Controller pointed out the traffic. It is also common to follow the glide slope upon intercepting the localizer as my autopilot in programmed to do. Specific instructions not to descend would also be helpful.

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.