An aircraft on approach to sfo received incorrect glideslope information and descended below the gli...

Attributes
ACN	1324271
Time
Date	201601
Local Time Of Day	1201-1800
Place
Locale Reference	NCT.TRACON
State Reference	CA
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Make Model Name	A320
Operating Under FAR Part	Part 121
Flight Phase	Final Approach
Flight Plan	IFR
Person 1
Function	Approach
Qualification	Air Traffic Control Fully Certified
Experience	Air Traffic Control Time Certified In Pos 1 (yrs) 2.5
Person 2
Function	First Officer Pilot Flying
Experience	Flight Crew Last 90 Days 169 Flight Crew Total 12403 Flight Crew Type 11482
Events
Anomaly	ATC Issue All Types Deviation - Altitude Crossing Restriction Not Met Deviation - Procedural Clearance Deviation - Procedural Published Material / Policy

Narrative:

I was vectoring to final for the approach. Aircraft X was on a vector to intercept the localizer. I issued a crossing instruction for the final approach fix. This protects for the adjacent airport arrivals below them on their approach. Aircraft X read it back and I verified the read back. I was dealing with another aircraft for the approach and when I looked back aircraft X was at 2000 feet at the final approach fix. About 800 feet low. I then saw conflicting traffic on final (for the adjacent airport) at 1600 feet about a mile west of aircraft X and eastbound. I asked aircraft X if he was crossing the fix at 2800 feet and he responded there was a glideslope issue. I instructed them to climb and asked if he had the airport in sight. He said yes so I cleared him for a visual approach. The loss already happened and there was divergence now.we had a similar situation last week with a descent prior to the final approach fix where they should have. So the new procedure came out yesterday to change how we clear aircraft. Before I always instructed aircraft to maintain an altitude until established on the localizer. Management instructed us to give a crossing restriction at the final approach fix to fix this problem. I started doing that today which is not what I'm used to. I believe the pilots also were confused which led to this loss.

Original NASA ASRS Text

Title: An aircraft on approach to SFO received incorrect glideslope information and descended below the glideslope and a crossing restriction into conflict with crossing traffic below it.

Narrative: I was vectoring to final for the approach. Aircraft X was on a vector to intercept the localizer. I issued a crossing instruction for the final approach fix. This protects for the adjacent airport arrivals below them on their approach. Aircraft X read it back and I verified the read back. I was dealing with another aircraft for the approach and when I looked back Aircraft X was at 2000 feet at the Final Approach Fix. About 800 feet low. I then saw conflicting traffic on final (for the adjacent airport) at 1600 feet about a mile west of Aircraft X and eastbound. I asked Aircraft X if he was crossing the fix at 2800 feet and he responded there was a glideslope issue. I instructed them to climb and asked if he had the airport in sight. He said yes so I cleared him for a Visual Approach. The LOSS already happened and there was divergence now.We had a similar situation last week with a descent prior to the final approach fix where they should have. So the new procedure came out yesterday to change how we clear aircraft. Before I always instructed aircraft to maintain an altitude until established on the localizer. Management instructed us to give a crossing restriction at the Final Approach Fix to fix this problem. I started doing that today which is not what I'm used to. I believe the pilots also were confused which led to this LOSS.

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.

An aircraft on approach to sfo received incorrect glideslope information and descended below the glideslope and a crossing restriction into conflict with crossing traffic below it.