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37000 Feet | Browse and search NASA's Aviation Safety Reporting System |
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An ARTCC radar controller cleared an air carrier B737 to descend to FL250, however, the flight crew thought the assigned altitude was descend to FL240, and read back the entire clearance. The B737 received a TCASII alarm and spotted an MD88 800 ft below them as they were passing FL243. The controller asked the B737 flight crew if they were level at FL250 and they responded that they were leveling at FL240.
| Attributes | |
| ACN | 362054 |
| Time | |
| Date | 199703 |
| Day | Mon |
| Local Time Of Day | 0601 To 1200 |
| Place | |
| Locale Reference | atc facility : atl |
| State Reference | GA |
| Altitude | msl bound lower : 24000 msl bound upper : 25000 |
| Environment | |
| Flight Conditions | VMC |
| Light | Daylight |
| Aircraft 1 | |
| Controlling Facilities | artcc : ztl |
| Operator | common carrier : air carrier |
| Make Model Name | B737 Undifferentiated or Other Model |
| Operating Under FAR Part | Part 121 |
| Flight Phase | descent other |
| Route In Use | enroute : on vectors |
| Flight Plan | IFR |
| Aircraft 2 | |
| Operator | common carrier : air carrier |
| Make Model Name | MD-88 |
| Operating Under FAR Part | Part 121 |
| Navigation In Use | Other |
| Flight Phase | cruise other |
| Flight Plan | IFR |
| Person 1 | |
| Affiliation | company : air carrier |
| Function | flight crew : first officer |
| Qualification | pilot : flight engineer pilot : atp |
| Experience | flight time last 90 days : 160 flight time total : 6500 flight time type : 1580 |
| ASRS Report | 362054 |
| Person 2 | |
| Affiliation | company : air carrier |
| Function | flight crew : captain oversight : pic |
| Qualification | pilot : atp |
| Experience | flight time last 90 days : 100 flight time total : 11000 flight time type : 6000 |
| ASRS Report | 362612 |
| Events | |
| Anomaly | conflict : airborne less severe non adherence : published procedure non adherence : required legal separation |
| Independent Detector | aircraft equipment other aircraft equipment : unspecified other controllera other flight crewa |
| Resolutory Action | none taken : detected after the fact |
| Consequence | Other |
| Miss Distance | horizontal : 0 vertical : 800 |
| Supplementary | |
| Primary Problem | ATC Human Performance |
| Air Traffic Incident | Operational Error |
Narrative:
ATC was very busy as many aircraft were on arrival to atl. Holding instructions were given to many. We were cleared to atl via radar vectors, fly heading 270 degrees, descend and maintain FL240 (from FL270). I read back the entire clearance. As we descended through FL245, we noticed an aircraft passing right to left very close to our position (coming towards us from about 1:30 - 2 O'clock position). We slowed the descent as TCASII went from 'traffic, traffic' to 'monitor vertical speed.' the aircraft passed under our nose as we were going through FL243 -- TCASII showed -800 ft. Then ATC calls the traffic out to us and we respond 'we saw him.' then ATC says 'confirm assigned altitude FL250.' we said 'no, we were cleared to FL240, we're leveling at FL240.' nothing more was said. We think the controller simply made a mistake clearing us to FL240 because he was busy. We're also glad it was VFR and we could see the traffic.
Original NASA ASRS Text
Title: AN ARTCC RADAR CTLR CLRED AN ACR B737 TO DSND TO FL250, HOWEVER, THE FLC THOUGHT THE ASSIGNED ALT WAS DSND TO FL240, AND READ BACK THE ENTIRE CLRNC. THE B737 RECEIVED A TCASII ALARM AND SPOTTED AN MD88 800 FT BELOW THEM AS THEY WERE PASSING FL243. THE CTLR ASKED THE B737 FLC IF THEY WERE LEVEL AT FL250 AND THEY RESPONDED THAT THEY WERE LEVELING AT FL240.
Narrative: ATC WAS VERY BUSY AS MANY ACFT WERE ON ARR TO ATL. HOLDING INSTRUCTIONS WERE GIVEN TO MANY. WE WERE CLRED TO ATL VIA RADAR VECTORS, FLY HDG 270 DEGS, DSND AND MAINTAIN FL240 (FROM FL270). I READ BACK THE ENTIRE CLRNC. AS WE DSNDED THROUGH FL245, WE NOTICED AN ACFT PASSING R TO L VERY CLOSE TO OUR POS (COMING TOWARDS US FROM ABOUT 1:30 - 2 O'CLOCK POS). WE SLOWED THE DSCNT AS TCASII WENT FROM 'TFC, TFC' TO 'MONITOR VERT SPD.' THE ACFT PASSED UNDER OUR NOSE AS WE WERE GOING THROUGH FL243 -- TCASII SHOWED -800 FT. THEN ATC CALLS THE TFC OUT TO US AND WE RESPOND 'WE SAW HIM.' THEN ATC SAYS 'CONFIRM ASSIGNED ALT FL250.' WE SAID 'NO, WE WERE CLRED TO FL240, WE'RE LEVELING AT FL240.' NOTHING MORE WAS SAID. WE THINK THE CTLR SIMPLY MADE A MISTAKE CLRING US TO FL240 BECAUSE HE WAS BUSY. WE'RE ALSO GLAD IT WAS VFR AND WE COULD SEE THE TFC.
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.