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Air carrier large transport descended below assigned altitude while conflicting small aircraft climbed above assigned altitude due to updraft.
| Attributes | |
| ACN | 103847 |
| Time | |
| Date | 198902 |
| Day | Sat |
| Local Time Of Day | 0601 To 1200 |
| Place | |
| Locale Reference | atc facility : ipl |
| State Reference | CA |
| Altitude | msl bound lower : 11000 msl bound upper : 12000 |
| Environment | |
| Light | Daylight |
| Aircraft 1 | |
| Operator | common carrier : air carrier |
| Make Model Name | Large Transport, Low Wing, 3 Turbojet Eng |
| Flight Phase | descent other |
| Route In Use | enroute : direct enroute airway : zla |
| Flight Plan | IFR |
| Aircraft 2 | |
| Operator | general aviation : personal |
| Make Model Name | Small Aircraft, Low Wing, 1 Eng, Retractable Gear |
| Flight Phase | cruise other |
| Route In Use | enroute : direct |
| Flight Plan | IFR |
| Person 1 | |
| Affiliation | government : faa |
| Function | controller : radar |
| Qualification | controller : radar |
| Experience | controller non radar : 15 controller radar : 15 |
| ASRS Report | 103847 |
| Person 2 | |
| Affiliation | company : air carrier |
| Function | flight crew : captain oversight : pic |
| Qualification | pilot : atp |
| Events | |
| Anomaly | altitude deviation : overshoot non adherence : clearance non adherence : published procedure non adherence : required legal separation other spatial deviation |
| Independent Detector | other controllera |
| Resolutory Action | other |
| Consequence | faa : investigated |
| Miss Distance | horizontal : 15000 vertical : 0 |
| Supplementary | |
| Primary Problem | ATC Human Performance |
| Air Traffic Incident | Pilot Deviation Operational Error |
Narrative:
Large transport was issued 'cross 40 mi east of mzb at 12000', descend and maintain 10000.' (he was wbound, landing at san.) he read the clearance back correctly. Small aircraft was sebnd on V458 at 11000' traffic was called to both aircraft. Large transport descended below 12000' through 11000' in confliction with small aircraft. He said his clearance was to cross 40 mi east of mzb at or below 12000' to maintain 10000'. At the same time, small aircraft encountered a strong updraft that took him to 11700'. There was no vertical sep at 2-3 mi. The normal/standard clearance is to cross 40 mi east of mzb at or below 12000', descend and maintain 10000', but this time sep was needed from small aircraft, so 'at or below' was changed slightly to 'at.' perhaps a change in phraseology to stress or clarify the restriction is necessary. Also, I believe the pilot merely dials in the final assigned altitude. Perhaps he should dial in the interim assigned altitude until it is obsolete or cancelled.
Original NASA ASRS Text
Title: ACR LGT DESCENDED BELOW ASSIGNED ALT WHILE CONFLICTING SMA CLIMBED ABOVE ASSIGNED ALT DUE TO UPDRAFT.
Narrative: LGT WAS ISSUED 'CROSS 40 MI E OF MZB AT 12000', DSND AND MAINTAIN 10000.' (HE WAS WBOUND, LNDG AT SAN.) HE READ THE CLRNC BACK CORRECTLY. SMA WAS SEBND ON V458 AT 11000' TFC WAS CALLED TO BOTH ACFT. LGT DSNDED BELOW 12000' THROUGH 11000' IN CONFLICTION WITH SMA. HE SAID HIS CLRNC WAS TO CROSS 40 MI E OF MZB AT OR BELOW 12000' TO MAINTAIN 10000'. AT THE SAME TIME, SMA ENCOUNTERED A STRONG UPDRAFT THAT TOOK HIM TO 11700'. THERE WAS NO VERT SEP AT 2-3 MI. THE NORMAL/STANDARD CLRNC IS TO CROSS 40 MI E OF MZB AT OR BELOW 12000', DSND AND MAINTAIN 10000', BUT THIS TIME SEP WAS NEEDED FROM SMA, SO 'AT OR BELOW' WAS CHANGED SLIGHTLY TO 'AT.' PERHAPS A CHANGE IN PHRASEOLOGY TO STRESS OR CLARIFY THE RESTRICTION IS NECESSARY. ALSO, I BELIEVE THE PLT MERELY DIALS IN THE FINAL ASSIGNED ALT. PERHAPS HE SHOULD DIAL IN THE INTERIM ASSIGNED ALT UNTIL IT IS OBSOLETE OR CANCELLED.
Data retrieved from NASA's ASRS site as of August 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.