Air Traffic Control Fully Certified
Air Traffic Control Time Certified In Pos 1 (yrs) 2.5
Workload; Situational Awareness; Human-Machine Interface
ATC Issue All Types; Deviation - Altitude Crossing Restriction Not Met; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Air Traffic Control Provided Assistance; Air Traffic Control Separated Traffic; Air Traffic Control Issued Advisory / Alert; Air Traffic Control Issued New Clearance; Flight Crew Overcame Equipment Problem; Flight Crew Requested ATC Assistance / Clarification; Flight Crew Became Reoriented
Airspace Structure; Chart Or Publication; Procedure; Aircraft
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.
I was pilot flying on an ILS Approach. Received very late turn onto final and clearance for approach from Approach Control while descending through approximately 4000 feet. Clearance was Maintain 2800 until SHAKE; Cleared ILS approach. ILS Identifier WAS verified. Approximately 2-3 miles outside of SHAKE; Glideslope captured and descended on glideslope. We then got a gradual but FULL SCALE deflection showing us ABOVE glideslope. While cross checking the approach plate and the altitude of the preceding aircraft 5 miles ahead of us; it became apparent that something didn't make sense. The preceding aircraft altitude was almost the same as ours. Simultaneously; we got a call from Approach Control to State Altitude. We were at 2000 feet over SHAKE. At this time; we also got a FULL SCALE deflection below glideslope.We were in VMC conditions with the preceding aircraft in sight. The glideslope finally stabilized throughout the remainder of the approach. We reported the issue to ATC. Throughout the Approach the ILS Frequency showed Identified. When we arrived at the gate; we talked to both the Tower and Approach control Supervisors. He explained the sequence of events. They mentioned that a similar event occurred with another aircraft not long after our event.
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.