Narrative:

I was the pilot monitoring during this flight. We were initially cleared for the ILS 25L approach and after we acknowledged we had the airport and the traffic in front of us in sight we were subsequently cleared for the visual to 25L to follow a B767 7 miles in front of us. ATC provided us the requisite caution wake turbulence following the heavy alert information. ATC also instructed us to contact tower at limma. Shortly after the automated '2500 ft' audio call we experienced our first wake turbulence related roll. The pilot flying was already flying ½ dot to one dot high on the glideslope to risk mitigate the wake turbulence. Winds were calm at altitude and remained below 5 KTS and aligned with the runway throughout the approach and landing. The pilot flying and I discussed the winds and I advised him to go-around at any point in the approach during which his comfort level was exceeded. By the time we discussed all this we had passed limma and I did not make the directed call to tower. Shortly after passing limma we experienced our second; much more pronounced and persistent roll associated with the heavy's wake turbulence. That event prompted much more discussion between the pilot flying and me. We had finished the mechanical checklist items and we were both attending to the heavy's flight path and our returning to the desired flight plan for our approach through the last round of wake turbulence. I focused on our vertical path and the heavy's position in relation to us in the exclusion of overlooking completing my technique of checking that my taxi light was now on in response to 'cleared to land' clearances by the tower. When I make one more check of the mechanical checklist items being completed at the automated '1000 ft' call; that is also the time I double check a landing clearance by looking at my taxi light switch position. If the switch is in the 'on' position; then I know we've received and acknowledged the landing clearance. I failed to respond to that normal habit pattern because of my focus on the B767 in front of us and our flight path in relation to the heavy's. Consequently we landed without acknowledging ATC's 'cleared to land' call and I didn't realize it until we rolled out onto the high speed taxiway and I didn't have a taxi light illuminating the path in front of me. We checked in with tower and received our hold short instructions. I acknowledged the hold short instructions and added that I would give him a call on the landline as soon as able. After securing the aircraft for our all-night turnaround return flight; I called the ATC tower supervisor; identified myself and the flight over which I had command. I apologized for not having acknowledged the tower calls and he told me we had clearance to land and that we presented no conflict or significant problem. However; he reminded me that we needed to make contact with tower as soon as quickly as possible after landing to ensure we were both on the same page for holding short of the parallel runway. Retrospectively; it's clear that both the pilot monitoring and pilot flying attended to the wake turbulence event to the exclusion of ensuring we acknowledged our clearance to land. The mechanical checklist affords the pilot a very tangible item which provides both tactile and visual feedback of completing a required task. For whatever reason my completing the mechanical checklist registered a note of being done with everything prior to landing to include my personal mnemonic of using the taxi light switch in the 'on' position as verification we received and acknowledged landing clearance. While we routinely receive instructions from ATC to contact another ATC agency at some point later than the time when the instruction is provided; it does require the pilots to add to their to-do list at the appropriate time. Distractions always offer the opportunity for normal habit patterns and actions to be disrupted and this is certainly the case here. The second wake turbulence event; I believe; defined the upper limit of both the pilot monitoring and pilot flying tolerance levels to continue with the approach. Had we encountered any further flight path disruptions on the order of the second event; I knew in my mind we were going around. That series of decisions drew my focus to the remainder of the approach and I believe was the critical event which distracted me to the point my clearance to land mnemonic wasn't accomplished and consequently the ATC clearance not acknowledged. Fatigue considerations: this was an all-night turnaround for me after several days of not flying. Therefore I had fully acclimated to a daytime rhythm. I attempted to get a nap during the late afternoon prior to the flight and had successfully encountered a 'sinker' that I thought would help me settle into some quality sleep. I had fallen asleep and believe that I was in a deep sleep when I was awakened by the phone ringing. My response was one of those adrenaline rush responses one encounters when suddenly awakened from a deep sleep. After handling the call I attempted to go back to sleep but unsuccessfully so. Therefore this event occurred at the approximate 19 hour point of my waking day with probably about 20 minutes or so of quality sleep captured during the one attempted nap. I did not feel overly tired to start the trip and have encountered this same circumstance many times before flying intentionally or other all-night turnarounds. Therefore I did not call 'fatigued' prior to the start of the sequence. As I reviewed the events I do believe; however; that fatigue did play a part in my ability to continue to check and double check my work when faced with a distraction. Normally I will check the taxi light switch at least twice prior to landing to reconfirm the landing clearance. However; that didn't occur and I believe fatigue impacted my usual series of scans during an approach; scans which normally encompasses the taxi light switch. I do believe I had an opportunity to help avert this oversight. Had I verbalized to the pilot flying that my decision was we were going around should we encounter wake turbulence on the order we had previously; I think that collective affirmation would have provided both of us a joint; non-verbal acknowledgement that this encounter defined the boundaries of our tolerance levels. Verbalizing that pre-determined decision would have provided a clear course of action we both agreed to should another encounter ensue. As odd as it sounds; I think those two factors would have instilled a sense of relief that would have freed up some preoccupation with the wake turbulence event and afforded me the opportunity to return to normal habit patterns and consequently catch the taxi light position proactively and the fact I had not acknowledged our landing clearance.

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Original NASA ASRS Text

Title: A B737 Flight Crew reported a wake vortex encounter on final approach at LAX that was enough of a distraction they failed to call the Tower at LIMMA.

Narrative: I was the pilot monitoring during this flight. We were initially cleared for the ILS 25L approach and after we acknowledged we had the airport and the traffic in front of us in sight we were subsequently cleared for the visual to 25L to follow a B767 7 miles in front of us. ATC provided us the requisite caution wake turbulence following the heavy alert information. ATC also instructed us to contact Tower at LIMMA. Shortly after the automated '2500 FT' audio call we experienced our first wake turbulence related roll. The pilot flying was already flying ½ dot to one dot high on the glideslope to risk mitigate the wake turbulence. Winds were calm at altitude and remained below 5 KTS and aligned with the runway throughout the approach and landing. The pilot flying and I discussed the winds and I advised him to go-around at any point in the approach during which his comfort level was exceeded. By the time we discussed all this we had passed LIMMA and I did not make the directed call to Tower. Shortly after passing LIMMA we experienced our second; much more pronounced and persistent roll associated with the heavy's wake turbulence. That event prompted much more discussion between the pilot flying and me. We had finished the mechanical checklist items and we were both attending to the heavy's flight path and our returning to the desired flight plan for our approach through the last round of wake turbulence. I focused on our vertical path and the heavy's position in relation to us in the exclusion of overlooking completing my technique of checking that my taxi light was now on in response to 'cleared to land' clearances by the Tower. When I make one more check of the mechanical checklist items being completed at the automated '1000 FT' call; that is also the time I double check a landing clearance by looking at my taxi light switch position. If the switch is in the 'on' position; then I know we've received and acknowledged the landing clearance. I failed to respond to that normal habit pattern because of my focus on the B767 in front of us and our flight path in relation to the heavy's. Consequently we landed without acknowledging ATC's 'cleared to land' call and I didn't realize it until we rolled out onto the high speed taxiway and I didn't have a taxi light illuminating the path in front of me. We checked in with Tower and received our hold short instructions. I acknowledged the hold short instructions and added that I would give him a call on the landline as soon as able. After securing the aircraft for our all-night turnaround return flight; I called the ATC Tower Supervisor; identified myself and the flight over which I had command. I apologized for not having acknowledged the Tower calls and he told me we had clearance to land and that we presented no conflict or significant problem. However; he reminded me that we needed to make contact with Tower as soon as quickly as possible after landing to ensure we were both on the same page for holding short of the parallel runway. Retrospectively; it's clear that both the pilot monitoring and pilot flying attended to the wake turbulence event to the exclusion of ensuring we acknowledged our clearance to land. The mechanical checklist affords the pilot a very tangible item which provides both tactile and visual feedback of completing a required task. For whatever reason my completing the mechanical checklist registered a note of being done with everything prior to landing to include my personal mnemonic of using the taxi light switch in the 'on' position as verification we received and acknowledged landing clearance. While we routinely receive instructions from ATC to contact another ATC agency at some point later than the time when the instruction is provided; it does require the pilots to add to their to-do list at the appropriate time. Distractions always offer the opportunity for normal habit patterns and actions to be disrupted and this is certainly the case here. The second wake turbulence event; I believe; defined the upper limit of both the pilot monitoring and pilot flying tolerance levels to continue with the approach. Had we encountered any further flight path disruptions on the order of the second event; I knew in my mind we were going around. That series of decisions drew my focus to the remainder of the approach and I believe was the critical event which distracted me to the point my clearance to land mnemonic wasn't accomplished and consequently the ATC clearance not acknowledged. Fatigue Considerations: This was an all-night turnaround for me after several days of not flying. Therefore I had fully acclimated to a daytime rhythm. I attempted to get a nap during the late afternoon prior to the flight and had successfully encountered a 'sinker' that I thought would help me settle into some quality sleep. I had fallen asleep and believe that I was in a deep sleep when I was awakened by the phone ringing. My response was one of those adrenaline rush responses one encounters when suddenly awakened from a deep sleep. After handling the call I attempted to go back to sleep but unsuccessfully so. Therefore this event occurred at the approximate 19 hour point of my waking day with probably about 20 minutes or so of quality sleep captured during the one attempted nap. I did not feel overly tired to start the trip and have encountered this same circumstance many times before flying intentionally or other all-night turnarounds. Therefore I did not call 'fatigued' prior to the start of the sequence. As I reviewed the events I do believe; however; that fatigue did play a part in my ability to continue to check and double check my work when faced with a distraction. Normally I will check the taxi light switch at least twice prior to landing to reconfirm the landing clearance. However; that didn't occur and I believe fatigue impacted my usual series of scans during an approach; scans which normally encompasses the taxi light switch. I do believe I had an opportunity to help avert this oversight. Had I verbalized to the pilot flying that my decision was we were going around should we encounter wake turbulence on the order we had previously; I think that collective affirmation would have provided both of us a joint; non-verbal acknowledgement that this encounter defined the boundaries of our tolerance levels. Verbalizing that pre-determined decision would have provided a clear course of action we both agreed to should another encounter ensue. As odd as it sounds; I think those two factors would have instilled a sense of relief that would have freed up some preoccupation with the wake turbulence event and afforded me the opportunity to return to normal habit patterns and consequently catch the taxi light position proactively and the fact I had not acknowledged our landing clearance.

Data retrieved from NASA's ASRS site as of April 2012 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.