Date: 201706
Local time of day: 0001-0600
Location: SCT.TRACON, CA
Aircraft: Widebody Transport
Operator: Air Carrier
Flight plan: IFR
Flight phase: Final Approach
Airspace: Class B SCT
ATC / advisory: TRACON SCT
Second aircraft: A321
Reporter organization: Government
Reporter function: Approach
Reporter qualification: Air Traffic Control Fully Certified
Human factors: Workload; Time Pressure; Situational Awareness; Communication Breakdown; Confusion; Distraction
Second reporter function: Approach
Anomaly: ATC Issue All Types; Conflict Airborne Conflict; Deviation - Speed All Types; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Air Traffic Control
When detected: In-flight
Result: Air Traffic Control Issued New Clearance
Contributing factors: Human Factors; Procedure; Staffing
Primary problem: Human Factors

Narrative: Working Downey Sector; Aircraft X was on final for Runway 25L at 170knots. Aircraft Y was about 8 miles in trail; I instructed Aircraft Y to slow to 210knots; and there was no reply; reached out for Aircraft Y again no answer. I then asked Feeder to try the aircraft again. A plane who I thought was Aircraft Y checks in slowing to 180knots. I next slowed the aircraft to 150 knots; canceled the approach clearance to maintain separation.  When it was obviously not going to work I turned the aircraft and instructed them to climb to 4000.  At that point the pilot asked if that instruction is for Aircraft Z. I stayed negative; Aircraft Y. I reached out for Aircraft Y again; no reply. I was also using our traffic situation display to look for Aircraft Y. I noticed the plane was in feeder's airspace and switched them to their frequency. Within seconds Aircraft Y was found on Stadium sectors frequency. I then broke the Aircraft X off the approach and Aircraft Y continued with the approach.  After reviewing all of the sectors voice and the replay; this situation was 'The Perfect Storm.' It was a complex puzzle and once we figured out all the pieces; we took all the steps to establish separation and get every plane safely in position. It always sounds easy; expect a bad read back; you'll catch it. Always try to make yourself aware of similar sounding call signs.


Second narrative: Aircraft Y (Air Carrier XY) was a 25L arrival from my sector (EAFR) 124.05 to Downey (DNYR) 124.9. I inadvertently switched comm of Aircraft Y to Stadium (STAR) 128.5.This minor and normally inconsequential error snow balled into the perfect storm that highlighted everyone's expectations on hearing what they expected to hear. Myself; the Downey controller; and just as significant the pilots of both Aircraft Y and Aircraft Z.I switched Aircraft Y to the incorrect frequencies 128.5. Normally this error is corrected by the pilot checking in; the STAR controller hearing the aircraft on the wrong frequencies; but seeing the aircraft; since he sees these aircraft; and switching it to the correct frequencies. In this instance the aircraft (Aircraft Y) did not check in; but instead stayed silent for approx. 30 miles! Only when Aircraft Y was 3 miles from the FAF; LIMMA and had already lost separation with Aircraft Z; did he make his initial transmission on 128.5 by asking about his speed. When DNYR hadn't talked to Aircraft Y and he was 25 miles from the airport; he verbally called EAFR across the room to switch Aircraft Y. At the exact same time; Aircraft Z about 40 miles behind Aircraft Y; but not on the frequencies at the same time was asking for clarification of his approach clearance. I heard an Aircraft asking for clarification; and 'assumed' that it must have been Aircraft Y concerned seeing the [aircraft] ahead turning final. I re-iterated to Aircraft Y his ILS 25L approach clearance; issued a speed reduction to 200kts; issued traffic a [type aircraft] he was slowing for and behind; and switched his frequencies to DNYR 124.9. I expected to hear Aircraft Y acknowledge. Aircraft Z did acknowledge; because he was expecting to hear his call sign; when in fact the instructions were for Aircraft Y.Aircraft Z checks in to 124.9 DNYR was expecting Aircraft Y; so he responds with instructions for him to slow further; since he is not seeing him slow from EAFR's 200kt speed reduction. In hind sight; of course Aircraft Y isn't slowing; because he is sitting on 128.5 having not checked in. DNYR cancels Aircraft Y's approach clearance with an altitude paper stop; and a further speed reduction; hoping to salvage the longitudinal spacing. Aircraft Z acknowledges for Aircraft Y on each and every one of the transmissions for Aircraft Y.At approx 5-3 miles from the FAF; the picture gets resolved in a series of further errors. DNYR realizes that Aircraft Y is not responding but Aircraft Z is; and switched Aircraft Z back to EAFR. EAFR is still trying to get a hold of Aircraft Y because he hears the controllers and the supervisor saying they still do not have comms with Aircraft Y. So I attempted to have a [air carrier] pilot transmit to Aircraft Y because there was the possibility that due to Aircraft Y's low altitude he could not hear me from my transmitter sight. Just by chance; as [air carrier] was transmitting to Aircraft Y... Aircraft Z was coming back on frequencies from the 124.9 DNYR controller's last instructions. Aircraft Z thinking this was for him talks to [air carrier] acknowledging for the Aircraft Y transmission; but using Aircraft Z; which [air carrier] heard but did not correlate either. On a second transmission to have Aircraft Y cancel his approach clearance; I heard Aircraft Z use his Aircraft Z call sign and understood the similar sounding call sign confusion and error; and rectified the remainder of Aircraft Z's flight to LAX.Meanwhile 8-9 miles from the LAX; Aircraft Y was calling STAR asking to slow. This was his first transmission since I had switched him in error 30 miles. STAR took action with Aircraft Y once they figured out the DNYR's traffic. DNYR descended Aircraft Y towards the heavy aircraft. DNYR was climbing the heavy because he was not sure any other way to 'get away' from the trailing Aircraft Y catching up so quickly at this late stage clarity that aircraft that he though was separated; were not. Aircraft Y saw the heavy; saw the airport and made a visual approach. the heavy was taken around for another approach.The errors in this sequence of events are noteworthy.I see the following breakdowns or errors as contributory to this scenario.1. EAFR switching Aircraft Y to STAR; and not hearing Aircraft Z's read back for the 124.9 frequencies change.2. Aircraft Y not checking in on STAR for 30 miles.3. DNYR transmitting to Aircraft Y but not understanding Aircraft Z was responding.4. Aircraft Z acknowledging to Aircraft Y's transmissions on multiple occasions.5. STAR descending Aircraft Y into Aircraft Z instead of climbing away from the conflict.6. DNYR not taking action to break someone out earlier; even though apparent vertical separation had been maintained (or so he thought).I have been a controller for years. I never thought that I would get tangled up in; or be the first contributory factor for such an event. I hope this event can be a learning tool for others; because only after seeing and hearing all the contributory ATC and Pilot factors; can a 'perfect storm' scenario play out to this degree.I feel; correction; I know; that the amount of staffing; or lack there is a contributing factor. On this shift there a staffing number of 11 or 12 bodies. This number changes from new Operations Manager (OM) to OM and Area rep and their negotiated staffing level. We started this shift with 8 bodies. One (1) of those was incapacitated due to medications; therefore could not work control positions; leaving 7 bodies. One more of these 7 was 'half room' certified; leaving 6 bodies to rotate through the radar sectors.Last I checked if 11 bodies is the staffing number that means we had 63% of our required staffing to work this shift. If 12 bodies is the number then that further degrades what we had available to work that night to a 58% level.This staffing inadequacy is normal! This bears repeating......WE ARE UNDERSTAFFED TO WHAT IS BECOMING A DANGEROUS LEVEL. If we were a [Heavy aircraft] that requires 2 pilots; we are metaphorically flying our RADAR sectors with one (1) controller 63% of the time. It's actually worse than that.....we almost never staff our 'hand offs'; because of staffing. So we are 'flying' our radar sectors solo 100% of the time; however because we have been in this reduced staffing situation for so many years; it has become the 'norm'. Now we only have 63% of the staffing that it takes to fly the sectors solo; and people wonder why controllers are having errors.The amount of overtime (OT) being used is extraordinary. In the situation of this event 3 of the 7 usable controllers were on OT. 2 out of the 3 controllers involved in this situation were on OT. Most controllers in this area (LA Arrivals) are being scheduled for [many] day weeks; every week. You have controllers that request for extensions sitting on the table; yet no effort is made in the current administration to supplement staffing by approving the voluntary requests; which will also reduce OT expenditures.I sit here and type this report for 2 hours; trying to make it make sense to the reader. You the reader; will read and discuss; and make a determination of what can we do with the tools that we have available to help. Meanwhile there are controllers working 6 day weeks; with a lot of 10 hour days; hearing bad read backs and correcting the errors; and every once in a great while; not catching the error; and a situation like this unfolds. We are working our tails off every day to keep the system safe; and I feel 'dis-heartened' that I did not catch the hear back of the wrong frequencies change I issued; that led to so many subsequent other controller/pilot errors.We need more staffing. We need to work less OT but still have full staffing.


Synopsis: Two SoCal TRACON Controllers reported a situation when similar sounding callsigns resulted in a loss of separation on final.