Narrative:

Aircraft Y; vtu dept; was appreq'd as a crossover with LC2. LC2 advised that they were launching a casta (aircraft X); and last to the beach visual. We rolled aircraft Y; and aircraft Y reached the beach first. The LC1 team observed that aircraft Y was ahead and above the aircraft X casta departure off the north side. Aircraft Y was advised of the traffic and told that aircraft X would maintain visual separation; then switched to departure. About 3 miles offshore; I observed the conflict alert go off. Aircraft X had caught up to and climbed several hundred feet above aircraft Y; lateral separation was less than two miles.the 'last to the beach visual' technique assumes aircraft with like performance; which was not really the case in this situation. The usual way that the LC1 and LC2 controllers apply this technique makes it a race to the beach: which ever departure is second has to get visual separation with the other one; which is in the lead (and expected to stay there). The local control with the aircraft in the lead is expected to advise his aircraft that there is another departure close in trail off the other side who will maintain visual separation. The controller with the lagging aircraft is responsible for obtaining the visual separation or; if that doesn't work; build separation via some alternative technique. Personally; I do not like this technique because there is no guarantee of positive separation between the two aircraft. Depending on the performance characteristics of the aircraft involved; the leading aircraft may not be able to maintain its lead; or the succeeding aircraft may out-climb the lead aircraft. In either of these situations; it is not likely that the trailing aircraft will be able to maintain visual contact (and separation) with the one that was originally in the lead. When faced with a 'last to the beach visual' situation as a local control controller; my personal technique is to deliberately ensure that my aircraft is the second one to the shoreline. This places the separation responsibility on me; and gives me more control over the situation. If I feel that the visual separation is uncertain or likely to be lost; I will either turn my aircraft or stop it at an intermediate altitude to create positive separation. Either of these techniques would have kept the aircraft y-aircraft X situation from developing.

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Original NASA ASRS Text

Title: LAX Tower Controller describes an operational error caused by a technique employed at LAX. A faster aircraft is told to maintain visual separation from a slower aircraft and passes the slower aircraft causing the loss of separation.

Narrative: Aircraft Y; VTU dept; was appreq'd as a crossover with LC2. LC2 advised that they were launching a CASTA (Aircraft X); and last to the beach visual. We rolled Aircraft Y; and Aircraft Y reached the beach first. The LC1 team observed that Aircraft Y was ahead and above the Aircraft X CASTA departure off the north side. Aircraft Y was advised of the traffic and told that Aircraft X would maintain visual separation; then switched to departure. About 3 miles offshore; I observed the Conflict Alert go off. Aircraft X had caught up to and climbed several hundred feet above Aircraft Y; lateral separation was less than two miles.The 'Last to the beach visual' technique assumes aircraft with like performance; which was not really the case in this situation. The usual way that the LC1 and LC2 controllers apply this technique makes it a race to the beach: Which ever departure is second has to get visual separation with the other one; which is in the lead (and expected to stay there). The LC with the aircraft in the lead is expected to advise his aircraft that there is another departure close in trail off the other side who will maintain visual separation. The controller with the lagging aircraft is responsible for obtaining the visual separation or; if that doesn't work; build separation via some alternative technique. Personally; I do not like this technique because there is no guarantee of positive separation between the two aircraft. Depending on the performance characteristics of the aircraft involved; the leading aircraft may not be able to maintain its lead; or the succeeding aircraft may out-climb the lead aircraft. In either of these situations; it is not likely that the trailing aircraft will be able to maintain visual contact (and separation) with the one that was originally in the lead. When faced with a 'Last to the beach visual' situation as a LC controller; my personal technique is to deliberately ensure that my aircraft is the second one to the shoreline. This places the separation responsibility on me; and gives me more control over the situation. If I feel that the visual separation is uncertain or likely to be lost; I will either turn my aircraft or stop it at an intermediate altitude to create positive separation. Either of these techniques would have kept the Aircraft Y-Aircraft X situation from developing.

Data retrieved from NASA's ASRS site 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.