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An LJ35 flight crew experienced a pressurization problem climbing out of 38700 ft. They misunderstood their clearance to a lower altitude and descended below clearance limit.
| Attributes | |
| ACN | 809022 |
| Time | |
| Date | 200810 |
| Local Time Of Day | 0001 To 0600 |
| Place | |
| Locale Reference | navaid : zzz.vortac |
| State Reference | US |
| Altitude | msl single value : 24000 |
| Environment | |
| Flight Conditions | VMC |
| Light | Night |
| Aircraft 1 | |
| Controlling Facilities | artcc : zzz.artcc tower : dfw.tower |
| Operator | common carrier : air carrier |
| Make Model Name | Learjet 35 |
| Operating Under FAR Part | Part 121 |
| Flight Phase | climbout : vacating altitude |
| Flight Plan | IFR |
| Person 1 | |
| Affiliation | company : air carrier |
| Function | flight crew : captain oversight : pic |
| Qualification | pilot : atp |
| Experience | flight time last 90 days : 240 flight time total : 10000 flight time type : 8000 |
| ASRS Report | 809022 |
| Person 2 | |
| Affiliation | company : air carrier |
| Function | flight crew : first officer |
| Qualification | pilot : atp pilot : cfi pilot : commercial pilot : instrument pilot : multi engine |
| Experience | flight time last 90 days : 300 flight time total : 3938 flight time type : 1030 |
| ASRS Report | 809027 |
| Events | |
| Anomaly | aircraft equipment problem : critical altitude deviation : excursion from assigned altitude non adherence : clearance |
| Independent Detector | other controllera |
| Resolutory Action | controller : issued new clearance flight crew : exited adverse environment flight crew : overcame equipment problem |
| Consequence | faa : reviewed incident with flight crew other |
| Supplementary | |
| Problem Areas | Flight Crew Human Performance Aircraft |
| Primary Problem | Aircraft |
Narrative:
During climb out of ZZZ at approximately FL387; we noticed the cabin altitude light illuminate. We leveled off and referred to the lear checklist. We requested FL360 from ATC (ZZZ center). During descent there was no change in cabin pressure so I requested FL240. I was using the oxygen mask microphone switch and the reception was poor. I read back the clearance to FL240 and proceeded to descend to FL240. After reaching ATC questioned me why I was at FL240 and not FL340. I replied that was the clearance and in short he said it wasn't but he would 'work on it.' the cabin situation had stabilized and the remainder of the flight continued without incident. Upon reaching ZZZ1 we grounded the aircraft and handed the problem to maintenance.
Original NASA ASRS Text
Title: AN LJ35 FLT CREW EXPERIENCED A PRESSURIZATION PROBLEM CLIMBING OUT OF 38700 FT. THEY MISUNDERSTOOD THEIR CLEARANCE TO A LOWER ALTITUDE AND DESCENDED BELOW CLEARANCE LIMIT.
Narrative: DURING CLBOUT OF ZZZ AT APPROX FL387; WE NOTICED THE CABIN ALT LIGHT ILLUMINATE. WE LEVELED OFF AND REFERRED TO THE LEAR CHKLIST. WE REQUESTED FL360 FROM ATC (ZZZ CTR). DURING DSCNT THERE WAS NO CHANGE IN CABIN PRESSURE SO I REQUESTED FL240. I WAS USING THE OXYGEN MASK MIKE SWITCH AND THE RECEPTION WAS POOR. I READ BACK THE CLRNC TO FL240 AND PROCEEDED TO DSND TO FL240. AFTER REACHING ATC QUESTIONED ME WHY I WAS AT FL240 AND NOT FL340. I REPLIED THAT WAS THE CLRNC AND IN SHORT HE SAID IT WASN'T BUT HE WOULD 'WORK ON IT.' THE CABIN SITUATION HAD STABILIZED AND THE REMAINDER OF THE FLT CONTINUED WITHOUT INCIDENT. UPON REACHING ZZZ1 WE GNDED THE ACFT AND HANDED THE PROB TO MAINT.
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.