Narrative:

While crossing the mountains (which were approximately 5;000 feet MSL) at 6;600 feet assigned; and on the KEFFR3; near jward; just east of elb; we received a TA/RA alert and were directed to maintain vertical speed. We had heard sct direct a bonanza to climb 300 feet which probably put him at 7;000 ft. We didn't realize he was on a crossing vector with us.when we received the TA/RA alert he was crossing from right to left at an angle and came approximately 2 miles and 400 feet from us. We advised sct that we had received the TA/RA alert but that was not answered. Instead; about 10 seconds later sct 'sort of' asked if we were descending to 4;000 ft. (As if he were suggesting he had assigned that altitude before). I am certain he had not given that altitude before because if he had that would have put us in the mountains we had just crossed. We advised we were then going to 4;000 feet.I know the la valley is very active and the controllers are very busy; but in this case I feel it was a simple case of too close. The controller seemed to have seen the event coming on by giving the bonanza a short climb of 300 feet but that was just not enough. Had the TCAS directed a descent; [it] would have been impossible due to the mountains below us.

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Original NASA ASRS Text

Title: A widebody transport crew inbound to LGB responded to a TCAS/RA advisory to 'maintain vertical descent.' The crew saw a Bonanza crossing left to right. According to the report no traffic information was issued to the crew.

Narrative: While crossing the mountains (which were approximately 5;000 feet MSL) at 6;600 feet assigned; and on the KEFFR3; near JWARD; just east of ELB; we received a TA/RA alert and were directed to maintain vertical speed. We had heard SCT direct a Bonanza to climb 300 feet which probably put him at 7;000 ft. We didn't realize he was on a crossing vector with us.When we received the TA/RA alert he was crossing from right to left at an angle and came approximately 2 miles and 400 feet from us. We advised SCT that we had received the TA/RA alert but that was not answered. Instead; about 10 seconds later SCT 'sort of' asked if we were descending to 4;000 ft. (as if he were suggesting he had assigned that altitude before). I am certain he had not given that altitude before because if he had that would have put us in the mountains we had just crossed. We advised we were then going to 4;000 feet.I know the LA Valley is very active and the controllers are very busy; but in this case I feel it was a simple case of too close. The controller seemed to have seen the event coming on by giving the Bonanza a short climb of 300 feet but that was just not enough. Had the TCAS directed a descent; [it] would have been impossible due to the mountains below us.

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.