An air carrier crew on the LAX RIIVR Arrival began deviating around thunderstorms without ATC clearance because the TRACON Controller was task saturated; but eventually cleared them.
Synopsis
An air carrier crew on the LAX RIIVR Arrival began deviating around thunderstorms without ATC clearance because the TRACON Controller was task saturated; but eventually cleared them.
Narrative
Descending on the RIIVR TWO Arrival into LAX we were navigating to GRAMM intersection as we were deviating around an area of weather to the east. There were numerous cells in the area that would need to be navigated around. At altitude; we could visually see a clear route from our present position to GRAMM. However; when the Controller issued a descent to us; it became evident that our descent path would potentially take us through an area of weather between our present position and GRAMM. Due to the weather in the area and the amount of traffic descending into the LA basin; the Controller was task saturated and the radio frequency was experiencing numerous blocked calls associated with the large number of clearances issued and the requests for deviation around the weather by arrival aircraft. As it became apparent that we would need to deviate to the left of course; we tried to get clearance from the Controller; but with no luck. At one point the Controller asked all aircraft to suspend their transmission in order that he could control the situation. Unfortunately; we needed his ear immediately. As we neared the cell; I told the Controller that we needed an immediate left turn. With no response; we started a left turn and I announced to the Controller that we were turning left. Upon hearing my intention; he advised us not to turn left yet to which I responded that doing so would put us through the cell. At that point we stopped the turn. We had a TCAS target to our left that was not at our altitude to which we presume the Controller immediately gave an altitude clearance; followed immediately with a clearance for us to turn left and increase our descent rate. We were able to miss the cell and since we had no TCAS warning; we presume that the Controller had maintained proper separation. Although this was a stressful situation for the Controller and us; the Controller kept his cool and performed his duties in a professional manner. His quick recognition of the potential conflict resulted in a positive resolution of the situation. I think that the dynamic nature of developing weather and high-density traffic conditions makes incidents such as this one; to be quite stressful and have a very real potential for compromising safety.
Second reporter narrative
[We were] descending from FL210 to 17;000 FT; RIIVR Arrival; direct GRAMM. [There was a] line of thunderstorms [and we] requested left turn around weather. [We were] unable to get through to ATC due to several aircraft calling at once. Unable to wait any longer; we started to deviate around weather. Approximately 5 seconds later; we were able to advise ATC of our turn for weather. ATC responds they are unable. We stop our turn and explain severe weather ahead. ATC clears a turn left of course for weather. We comply and continue to LAX.
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.