Air carrier aircraft in IMC on the sfo ILS prm runway 28L stopped its descent at 3;000 ft because an...

Narrative:

We were being vectored for the sfo ILS prm runway 28L approach; and in the vicinity and south of rokme; we were first cleared to 3;000 ft; and then while descending and just south of heman; we were cleared to 2;000 ft and instructed to intercept the localizer and cleared for the approach. When descending through about 3;200 ft; we received a 'traffic alert' from ATC who re-cleared us to stop our descent at 2;500 ft; as ATC had an unknown transponder indicating 2;000 ft in the 'no transgression zone.' we had the target on TCAS with an indicated climb. I stopped my descent at 3;000 ft. The target was heading east and climbing through about 2;200 ft. Through breaks in the clouds; I acquired the light; single-engine aircraft at my 11:00 o'clock position a couple of hundred yards away. We passed directly overhead the aircraft while it showed 2;300 ft on TCAS. We got two traffic advisory (TA) callouts but no resolution advisory (RA) calls or indications. We continued our ILS prm runway 28L approach without further disruption.

Original NASA ASRS Text

Title: Air Carrier aircraft in IMC on the SFO ILS PRM Runway 28L stopped its descent at 3;000 FT because an unknown aircraft was climbing to 2;300 FT inside the No Transgression Zone and TCAS alerted two TA's.

Narrative: We were being vectored for the SFO ILS PRM Runway 28L approach; and in the vicinity and south of ROKME; we were first cleared to 3;000 FT; and then while descending and just south of HEMAN; we were cleared to 2;000 FT and instructed to intercept the localizer and cleared for the approach. When descending through about 3;200 FT; we received a 'TRAFFIC ALERT' from ATC who re-cleared us to stop our descent at 2;500 FT; as ATC had an unknown transponder indicating 2;000 FT in the 'NO TRANSGRESSION ZONE.' We had the target on TCAS with an indicated climb. I stopped my descent at 3;000 FT. The target was heading east and climbing through about 2;200 FT. Through breaks in the clouds; I acquired the light; single-engine aircraft at my 11:00 o'clock position a couple of hundred yards away. We passed directly overhead the aircraft while it showed 2;300 FT on TCAS. We got two Traffic Advisory (TA) callouts but no Resolution Advisory (RA) calls or indications. We continued our ILS PRM Runway 28L approach without further disruption.

Data retrieved from NASA's ASRS site as of April 2012 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.

Attributes
ACN	969074
Time
Date	201109
Local Time Of Day	0601-1200
Place
Locale Reference	NCT.TRACON
State Reference	CA
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Make Model Name	Widebody Low Wing 4 Turbojet Eng
Operating Under FAR Part	Part 121
Flight Phase	Initial Approach
Route In Use	Vectors
Flight Plan	IFR
Aircraft 2
Make Model Name	Small Aircraft
Flight Phase	Climb
Flight Plan	VFR
Person 1
Function	Captain Pilot Flying
Qualification	Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Last 90 Days 200 Flight Crew Total 21000 Flight Crew Type 13000
Events
Anomaly	Conflict Airborne Conflict

Air carrier aircraft in IMC on the sfo ILS prm runway 28L stopped its descent at 3;000 ft because an unknown aircraft was climbing to 2;300 ft inside the no transgression zone and TCAS alerted two TA's.