Near midair collision after altitude deviation altitude overshot.

Attributes
ACN	267478
Time
Date	199404
Day	Mon
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : lhs airport : lax
State Reference	CA
Altitude	msl bound lower : 6000 msl bound upper : 7000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Operator	common carrier : air carrier
Make Model Name	Jetstream 31
Operating Under FAR Part	Part 135
Flight Phase	descent other
Route In Use	enroute airway : bur
Flight Plan	IFR
Aircraft 2
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Operating Under FAR Part	Part 91
Flight Phase	cruise other
Flight Plan	VFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : instrument pilot : flight engineer pilot : commercial pilot : atp
Experience	flight time last 90 days : 90 flight time total : 4700 flight time type : 1500
ASRS Report	267478
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : commercial pilot : instrument
Events
Anomaly	altitude deviation : overshoot conflict : nmac non adherence : clearance other anomaly other
Independent Detector	other controllera
Resolutory Action	controller : issued new clearance none taken : unable
Consequence	faa : reviewed incident with flight crew
Miss Distance	vertical : 450
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation Operational Error

Narrative:

Inbound to lax, while talking to bur approach we were told to descend and maintain 6000 ft. I replied that we were going down to 6000 ft. We noticed a GA aircraft coming the opposite direction, same heading but no traffic call from the controller. The controller called out 'air carrier X stop,' then stopped talking, I replied that we had the aircraft in sight, he then gave us a heading and turned us over to lax (so-cal) approach. Upon landing we were asked to call burbank approach control, where the supervisor advised me the altitude. We had been assigned was 7000 ft not 6000 ft. He advised me to be more careful, I explained that I had asked my partner (first officer) and he also recalls being assigned 6000 ft. The supervisor said he had listened to the tape and his controller had said 7000 ft and I replied with 6000 ft. However the controller did not catch the readback and failed to notice us go below 7000 ft. We believe what caused the problem was another aircraft that was having radio problems and kept 'stepping on' other xmissions. I am not sure if the controller was distraction by this problem, but we both were sure we had been assigned 6000 ft. I believe a little more attention to detail on both parties might have alleviated this problem.

Original NASA ASRS Text

Title: NMAC AFTER ALT DEV ALT OVERSHOT.

Narrative: INBOUND TO LAX, WHILE TALKING TO BUR APCH WE WERE TOLD TO DSND AND MAINTAIN 6000 FT. I REPLIED THAT WE WERE GOING DOWN TO 6000 FT. WE NOTICED A GA ACFT COMING THE OPPOSITE DIRECTION, SAME HDG BUT NO TFC CALL FROM THE CTLR. THE CTLR CALLED OUT 'ACR X STOP,' THEN STOPPED TALKING, I REPLIED THAT WE HAD THE ACFT IN SIGHT, HE THEN GAVE US A HDG AND TURNED US OVER TO LAX (SO-CAL) APCH. UPON LNDG WE WERE ASKED TO CALL BURBANK APCH CTL, WHERE THE SUPVR ADVISED ME THE ALT. WE HAD BEEN ASSIGNED WAS 7000 FT NOT 6000 FT. HE ADVISED ME TO BE MORE CAREFUL, I EXPLAINED THAT I HAD ASKED MY PARTNER (FO) AND HE ALSO RECALLS BEING ASSIGNED 6000 FT. THE SUPVR SAID HE HAD LISTENED TO THE TAPE AND HIS CTLR HAD SAID 7000 FT AND I REPLIED WITH 6000 FT. HOWEVER THE CTLR DID NOT CATCH THE READBACK AND FAILED TO NOTICE US GO BELOW 7000 FT. WE BELIEVE WHAT CAUSED THE PROB WAS ANOTHER ACFT THAT WAS HAVING RADIO PROBS AND KEPT 'STEPPING ON' OTHER XMISSIONS. I AM NOT SURE IF THE CTLR WAS DISTR BY THIS PROB, BUT WE BOTH WERE SURE WE HAD BEEN ASSIGNED 6000 FT. I BELIEVE A LITTLE MORE ATTN TO DETAIL ON BOTH PARTIES MIGHT HAVE ALLEVIATED THIS PROB.

Data retrieved from NASA's ASRS site as of July 2007 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.