Medium Large Transport; Low Wing; 2 Turbojet Eng
Air Traffic Control Fully Certified
Air Traffic Control Time Certified In Pos 1 (yrs) 22
Situational Awareness; Distraction; Communication Breakdown
ATC Issue All Types; Deviation / Discrepancy - Procedural Clearance; Inflight Event / Encounter CFTT / CFIT
Air Traffic Control Issued New Clearance; Flight Crew Returned To Clearance
Human Factors; Procedure
I was assigned NORR; (Norton Sector). Aircraft X was an IFR arrival into ONT from over DAWNA. After initial approach information; the aircraft was assigned a heading; (190) and a descent to 10;000. (MVA 9;700) The pilot responded; 'Aircraft X; say again.' I issued; 'Aircraft X; fly heading 1-9-0; descend and maintain eight thousand. During this time; I believe I 'tagged up' a VFR 1200 code that was a potential conflict for arrivals as well as issued an approach clearance for another ONT arrival. Furthermore; at no time did the LA (Low Altitude) alarm sound. A few moments later; I observed the Mode C indicating 8;500. I said; 'Aircraft X; assigned altitude one -zero- thousand.' I believe the pilot responded that he was assigned eight thousand; and began a climb. I'm writing this from home; so I do not have the Falcon and/or transcript available.What led to the event and why it happened:Although the MVA in that area has changed from time to time; the lowest altitude I assign is 10;000. This has been my habit for decades. When I watched the Falcon; I was shocked to hear '8;000.' It is not an altitude I have ever issued in that area; nor is it one I would ever consider. How that number entered my mind has me at a loss. What is more; when the pilot responded correctly; it still did not register as 'eight thousand.' This is why I'm so bewildered. Hear back/read back is part and parcel to our work. When I try and analyze this; I feel as if I'm left with 'excuses' rather than sound reasons why this occurred.The following are the possibilities that I believe led to the event: 1. At SCT; particularly in those areas where we work a majority of inexperienced VFR/IFR; we spend a lot of time correcting read back errors from pilots. This can be frustrating because when one is busy and a correction has to be made it is as if we have additional airplanes on frequency. Having to say things twice to one airplane is similar to having to say things once for two airplanes. This unsettles our flow and can cause interruptions to service for other customers. That frustration; an emotion; may get heated and cause us to miss other read backs. 2. It was suggested to me that because the call sign was read back; 'Aircraft X;' and because I used 'Aircraft X' while issuing the instruction; that the number eight was somehow what I was thinking; rather than ten or one zero thousand.3. When I scan; I ask myself four questions for each airplane:Are there any conflicts?Is separation ensured?Is there anything I need to do for the pilot?Is the data block complete?As the scan continues; it gets refined and reduced to:Are there any conflicts?Because it never occurred to me that I issued 8;000 as an altitude assignment; I was only scanning for conflicts for Aircraft X. Seeing no conflicts; I passed over his Mode C to scan the other airplanes on frequency. It was only as the airplane approached an area where a lower altitude could be assigned; thus is there anything I need to do for the pilot; that I first observed the 8;500 Mode-C. Hearing no LA alarm; I had no reason to think that altitude was an issue.4. SCT; it seems; has been in continuous motion for several years. By that I mean we have had several changes; large and small; that collectively; that have caused controllers to have to think more with less traffic. Working backwards; we've had: Climb/Descend via implemented; numerous new approaches; airspace changes; transitioning from ARTS to STARS; NIDS; and numerous other procedural changes to our everyday work. But it seems as one change is about to settle; another one surfaces. We've had little time to let these things settle and allow the foundation to become firm. This can; and does cause; distraction.5. SCT has been under tight scrutiny for some time now. While I do believe controllers must be held to a high standard; take pride in their work; and strive for excellence; continuous discussion about our failures over against the thousands of good and unreported work can cause a sense of paranoia.All these are not mentioned to explain the 'why' but perhaps; in part; they are enough to cause distraction and thus my failure to issue the correct altitude. I think this issue goes slightly deeper than read back / hear back. It's one thing to miss a read back; it is quite another to issue the wrong altitude. It should be remembered that on initial contact; the correct altitude was issued. So what caused a derailment from that thought; and how can it be avoided?1. Modify my scan to regularly include Mode C and compare that value to the MVA. This has a twofold benefit of not relying on what was written on the strip; (regardless of what I think I issued;) or relying on the 'L/A' alarm which might not sound. Any descent into; or suspected based on descent rate; and the controller can immediately issue an altitude corresponding to the MVA.Are there any conflicts?Is separation ensured?MVA?Is there anything I need to do for the pilot?Is the data block complete?
SCT TRACON Controller reported issuing an incorrect altitude to an aircraft that brought it below the MVA.