<< >> NASA ASRS Report 201856, February 1992

Operational error occurs when ARTCC radar controller fails to hear clearance acknowledged with an improper controller induced clearance uncoord descent to occupied altitude in a potential conflict with opposite direction traffic.

Attributes
ACN	201856
Time
Date	199202
Day	Sat
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : hec
State Reference	CA
Altitude	msl bound lower : 34300 msl bound upper : 35000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zla
Operator	common carrier : air carrier
Make Model Name	Large Transport, Low Wing, 2 Turbojet Eng
Navigation In Use	Other Other
Flight Phase	descent other
Flight Plan	IFR
Aircraft 2
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Flight Phase	cruise other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 200 flight time total : 12000 flight time type : 2000
ASRS Report	201856
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Experience	flight time last 90 days : 209 flight time total : 7980 flight time type : 525
ASRS Report	201885
Events
Anomaly	conflict : airborne less severe non adherence : required legal separation non adherence other other anomaly other
Independent Detector	other controllera
Resolutory Action	controller : issued new clearance other
Consequence	faa : reviewed incident with flight crew faa : investigated Other
Miss Distance	horizontal : 24000 vertical : 1300
Supplementary
Primary Problem	ATC Human Performance
Air Traffic Incident	Operational Error
Situations
ATC Facility	procedure or policy : unspecified

Narrative:

I believe that our flight, an large transport, was cleared to descend and maintain fl-330. As we were descending through FL345, los angeles center asked if we were going to maintain FL350 'he showed us low.' we immediately climbed back to FL350 and visually saw an medium large transport type aircraft pass, going the opposite direction. Upon landing at la international airport, I phoned la center as instructed by la center on the VHF radio. I spoke with mr xy and we discussed the situation. I phoned la center approximately 3 hours later that afternoon and found out that a read-out of the center tapes confirmed that we had, in fact, been cleared to FL330. Supplemental information from acn 201855. The low altitude reached was 34300 ft. I said we were cleared to FL330. The center controller said no. We were cleared only to FL350. The medium large transport passed us low to our left at about 3-4 mi. It is clear that there was a mis-communication about what was said, heard or read- back.

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Original NASA ASRS Text

Title: OPERROR OCCURS WHEN ARTCC RADAR CTLR FAILS TO HEAR CLRNC ACKNOWLEDGED WITH AN IMPROPER CTLR INDUCED CLRNC UNCOORD DSCNT TO OCCUPIED ALT IN A POTENTIAL CONFLICT WITH OPPOSITE DIRECTION TFC.

Narrative: I BELIEVE THAT OUR FLT, AN LGT, WAS CLRED TO DSND AND MAINTAIN FL-330. AS WE WERE DSNDING THROUGH FL345, LOS ANGELES CTR ASKED IF WE WERE GOING TO MAINTAIN FL350 'HE SHOWED US LOW.' WE IMMEDIATELY CLBED BACK TO FL350 AND VISUALLY SAW AN MLG TYPE ACFT PASS, GOING THE OPPOSITE DIRECTION. UPON LNDG AT LA INTL ARPT, I PHONED LA CTR AS INSTRUCTED BY LA CTR ON THE VHF RADIO. I SPOKE WITH MR XY AND WE DISCUSSED THE SITUATION. I PHONED LA CTR APPROX 3 HRS LATER THAT AFTERNOON AND FOUND OUT THAT A READ-OUT OF THE CTR TAPES CONFIRMED THAT WE HAD, IN FACT, BEEN CLRED TO FL330. SUPPLEMENTAL INFO FROM ACN 201855. THE LOW ALT REACHED WAS 34300 FT. I SAID WE WERE CLRED TO FL330. THE CTR CTLR SAID NO. WE WERE CLRED ONLY TO FL350. THE MLG PASSED US LOW TO OUR L AT ABOUT 3-4 MI. IT IS CLR THAT THERE WAS A MIS-COM ABOUT WHAT WAS SAID, HEARD OR READ- BACK.

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.