Narrative:

I approached lvk from altamont pass (vpalt) where I began my descent from 4;500 feet MSL. I had been in contact with norcal approach most of my flight from jaq. Just before this point approach informed me of IFR traffic in the vicinity of lvk and to stay clear of it. I asked if an alternate route was advised; approach did not suggest one. I don't remember exactly what they said. I feel it worthy to note that 1-3 miles before reaching vpalt the aircraft magnetic compass started rotating wildly in both directions while my attitude of flight was level and unaccelerated. The bluetooth GPS (dual) for my tablet; located in full view of the sky on the dash that I was using for navigation; had also lost its signal. At this point I maintained my heading and used the headings on my flight log and landmarks that I was already familiar with on previous flights to livermore. The compass regained its sanity a minute or two later; the GPS regained its signal roughly 7-10 miles from lvk. I remember having to force the app (iflight planner) on my ipad to close and re-open it. About 10 miles out from lvk I was advised by approach to contact livermore tower. I promptly did so. Tower instructed me to make a right base entry for a 2-mile final to runway 25R. I had the airport in sight. Being aware of IFR traffic on the approach path I stayed north of highway 580 until I was two miles out and proceeded to turn base (heading 160 roughly). Tower then proceeded to advise me saying 'what I'm going to have you do is..' or something to that effect and gave me a list of at least three instructions that were difficult to make out due to noise and the rapidity he gave them. I made out 'left turn' and 'follow cessna' and couldn't understand why I would be directed to turn head-on into approaching traffic so I missed the rest of the details and I informed tower that I didn't understand; I was also occupied with planning my turn to final and seeing and avoiding traffic. Tower then immediately asked me to turn east and I promptly did so. Soon after tower asked me if I saw the cessna. I saw it at my 10 o-clock on the approach to 25R in roughly 300 feet at my altitude. Fortunately the approaching cessna was descending on final while I maintained the tpa of 1;400 feet. It was under me by the time our ground paths intersected at which point I reported that it was under me. I was then instructed to follow it. At this point I had to make a 160 degree right turn to make final and I was already past the approach path for 25R. I made a hard right turn lowering the nose. Tower informed me that I had crossed the approach path of 25L inappropriately. I was able to recover to a proper approach path and I had the cessna in sight on final ahead and below me. Tower informed the cessna that I was close behind on final. The cessna announced a go-around. I continued my approach and landed uneventfully. Contributing factors: I was in a critical phase of flight nearly needing to turn final when tower advised me of his plans. I may have understood incorrectly but what I heard seemed inconsistent with safety and normal pattern procedures when on right-base. I was fully expecting to turn right not left or east first. Flying east on a 250 approach (160 right turn) made the turn to final dangerous and avoidance of the 25L approach path impossible. I figure a 45 degree angle ideal and 90 degrees the maximum. I'm not certain but it's possible that tower instructed me to 'report 2-mile base for 25R' but I didn't hear the report part and that; while I was still on the same transponder code assigned by approach and not instructed to squawk VFR; lvk tower may not be equipped with radar making them unaware of my position unless I reported it. I assumed tower was aware of my position. I may have missed the report instruction because of the compass and GPS events but I do recall the controller speaking too quickly and in a muffled tone. It's not the first time that I've heard controllers sound likethey have marbles in their mouths. No offense but for those that don't hear this muffled fast language every day it may as well be greek at times. My past two experiences at livermore several months ago were very easy approaches. Tower instructed me to make straight-in approaches and the worst that was unexpected was a last-minute runway change which I handled just fine. So the different VFR approach and IFR traffic definitely tested my metal and I think the controller's as well. I also didn't have much recent flying time within the last 90 days; though I had last flown a local flight at jaq just over two months prior. I give the tower controller credit for staying with me; queuing me to look for the cessna I was supposed to follow.

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Original NASA ASRS Text

Title: A pilot reported a near miss in the LVK traffic pattern after he became confused by ATC's instructions to establish him in the traffic pattern and he could not get timely clarification.

Narrative: I approached LVK from Altamont Pass (VPALT) where I began my descent from 4;500 feet MSL. I had been in contact with Norcal Approach most of my flight from JAQ. Just before this point approach informed me of IFR traffic in the vicinity of LVK and to stay clear of it. I asked if an alternate route was advised; approach did not suggest one. I don't remember exactly what they said. I feel it worthy to note that 1-3 miles before reaching VPALT the aircraft magnetic compass started rotating wildly in both directions while my attitude of flight was level and unaccelerated. The Bluetooth GPS (Dual) for my tablet; located in full view of the sky on the dash that I was using for navigation; had also lost its signal. At this point I maintained my heading and used the headings on my flight log and landmarks that I was already familiar with on previous flights to Livermore. The compass regained its sanity a minute or two later; the GPS regained its signal roughly 7-10 miles from LVK. I remember having to force the app (iFlight Planner) on my iPad to close and re-open it. About 10 miles out from LVK I was advised by Approach to contact Livermore Tower. I promptly did so. Tower instructed me to make a right base entry for a 2-mile final to Runway 25R. I had the airport in sight. Being aware of IFR traffic on the approach path I stayed north of Highway 580 until I was two miles out and proceeded to turn base (heading 160 roughly). Tower then proceeded to advise me saying 'what I'm going to have you do is..' or something to that effect and gave me a list of at least three instructions that were difficult to make out due to noise and the rapidity he gave them. I made out 'left turn' and 'follow Cessna' and couldn't understand why I would be directed to turn head-on into approaching traffic so I missed the rest of the details and I informed Tower that I didn't understand; I was also occupied with planning my turn to final and seeing and avoiding traffic. Tower then immediately asked me to turn east and I promptly did so. Soon after Tower asked me if I saw the Cessna. I saw it at my 10 o-clock on the approach to 25R in roughly 300 feet at my altitude. Fortunately the approaching Cessna was descending on final while I maintained the TPA of 1;400 feet. It was under me by the time our ground paths intersected at which point I reported that it was under me. I was then instructed to follow it. At this point I had to make a 160 degree right turn to make final and I was already past the approach path for 25R. I made a hard right turn lowering the nose. Tower informed me that I had crossed the approach path of 25L inappropriately. I was able to recover to a proper approach path and I had the Cessna in sight on final ahead and below me. Tower informed the Cessna that I was close behind on final. The Cessna announced a go-around. I continued my approach and landed uneventfully. Contributing Factors: I was in a critical phase of flight nearly needing to turn final when Tower advised me of his plans. I may have understood incorrectly but what I heard seemed inconsistent with safety and normal pattern procedures when on right-base. I was fully expecting to turn right not left or east first. Flying east on a 250 approach (160 R turn) made the turn to final dangerous and avoidance of the 25L approach path impossible. I figure a 45 degree angle ideal and 90 degrees the maximum. I'm not certain but it's possible that Tower instructed me to 'REPORT 2-mile base for 25R' but I didn't hear the report part and that; while I was still on the same transponder code assigned by Approach and not instructed to squawk VFR; LVK Tower may not be equipped with radar making them unaware of my position unless I reported it. I assumed Tower was aware of my position. I may have missed the report instruction because of the compass and GPS events but I do recall the Controller speaking too quickly and in a muffled tone. It's not the first time that I've heard controllers sound likethey have marbles in their mouths. No offense but for those that don't hear this muffled fast language every day it may as well be Greek at times. My past two experiences at Livermore several months ago were very easy approaches. Tower instructed me to make straight-in approaches and the worst that was unexpected was a last-minute runway change which I handled just fine. So the different VFR approach and IFR traffic definitely tested my metal and I think the Controller's as well. I also didn't have much recent flying time within the last 90 days; though I had last flown a local flight at JAQ just over two months prior. I give the Tower Controller credit for staying with me; queuing me to look for the Cessna I was supposed to follow.

Data retrieved from NASA's ASRS site as of July 2013 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.