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ZLA controller experienced operational error at approximately FL310 when misinterpreting flight crew's clearance readback; separation was lost.
| Attributes | |
| ACN | 703270 |
| Time | |
| Date | 200809 |
| Local Time Of Day | 1201 To 1800 |
| Place | |
| Locale Reference | navaid : ave.vortac |
| State Reference | CA |
| Altitude | msl bound lower : 25000 msl bound upper : 31000 |
| Environment | |
| Flight Conditions | VMC |
| Light | Daylight |
| Aircraft 1 | |
| Controlling Facilities | artcc : zoa.artcc |
| Operator | common carrier : air taxi |
| Make Model Name | Citation I/SP |
| Operating Under FAR Part | Part 135 |
| Flight Phase | descent : vacating altitude |
| Flight Plan | IFR |
| Aircraft 2 | |
| Controlling Facilities | artcc : zoa.artcc |
| Operator | common carrier : air carrier |
| Make Model Name | Regional Jet 200 ER&LR |
| Operating Under FAR Part | Part 121 |
| Flight Phase | cruise : level |
| Flight Plan | IFR |
| Person 1 | |
| Affiliation | government : faa |
| Function | controller : radar |
| Qualification | controller : radar |
| Experience | controller radar : 1 |
| ASRS Report | 803270 |
| Events | |
| Anomaly | conflict : airborne less severe non adherence : required legal separation |
| Independent Detector | atc equipment : conflict alert other controllera |
| Resolutory Action | controller : issued alert controller : issued new clearance |
| Miss Distance | horizontal : 25800 vertical : 800 |
| Supplementary | |
| Problem Areas | ATC Human Performance |
| Primary Problem | ATC Human Performance |
| Air Traffic Incident | Operational Error |
Narrative:
Aircraft X at FL350 issued descent to FL310 because of converging traffic; air carrier Y at FL300. Later; aircraft X was issued 'turn 20 degrees right; reduce speed to 250 KTS.' pilot read back 'down to 250; 20 degrees right.' never did pilot say descent or flight level; pilot thought he was cleared to FL250. I took his readback as 'slowing down 250.'
Original NASA ASRS Text
Title: ZLA CTLR EXPERIENCED OPERROR AT APPROX FL310 WHEN MISINTERPRETING FLT CREW'S CLRNC READBACK; SEPARATION WAS LOST.
Narrative: ACFT X AT FL350 ISSUED DSCNT TO FL310 BECAUSE OF CONVERGING TFC; ACR Y AT FL300. LATER; ACFT X WAS ISSUED 'TURN 20 DEGS R; REDUCE SPD TO 250 KTS.' PLT READ BACK 'DOWN TO 250; 20 DEGS R.' NEVER DID PLT SAY DSCNT OR FLT LEVEL; PLT THOUGHT HE WAS CLRED TO FL250. I TOOK HIS READBACK AS 'SLOWING DOWN 250.'
Data retrieved from NASA's ASRS site as of May 2009 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.