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Two line mechanics report deferring the manual pressurization on an emb-145 by deactivating the pneumatic outflow valve in the closed position per MEL 21-17. A rapid loss of cabin pressure occurred a day later; while climbing through FL320; with vibration felt in the yoke. The closed outflow valve had broken two of the three safety wires and opened. An air turnback was performed.
| Attributes | |
| ACN | 851091 |
| Time | |
| Date | 200908 |
| Local Time Of Day | 1201-1800 |
| Place | |
| Locale Reference | ZZZ.Airport |
| State Reference | US |
| Environment | |
| Light | Daylight |
| Aircraft 1 | |
| Make Model Name | EMB ERJ 145 ER&LR |
| Operating Under FAR Part | Part 121 |
| Flight Phase | Parked |
| Flight Plan | IFR |
| Component | |
| Aircraft Component | Pressurization Control System |
| Person 1 | |
| Function | Technician |
| Qualification | Maintenance Powerplant Maintenance Airframe |
| Person 2 | |
| Function | Technician |
| Qualification | Maintenance Powerplant Maintenance Airframe |
| Events | |
| Anomaly | Aircraft Equipment Problem Critical Deviation - Procedural MEL |
Narrative:
August 2009; deferred manual pressurization on an emb-145 by deactivating pneumatic outflow valve per MEL 21-17. The next day; a flight experienced rapid loss of cabin pressure while climbing through FL320 with vibration felt in yoke. Aircraft returned to field (rtf). Found deactivated pneumatic outflow valve had broken 2 of 3 safeties and opened. Exhaust air blowing on primary flight control cables; causing vibration in yoke.the cause of event is not known at this time. Recommend investigation into what force overcame pressurization loads and broke safeties. Discussed procedure with supervisor.MEL 21-17 and emb amm 21-31-04 are extremely vague with poor illustrations. The term 'lockwire' does not specify material or gauge. Actual geometry of safety is not clear. Do not believe MEL 21-17 leaves sufficient fail-safe margin for additional failures.
Original NASA ASRS Text
Title: Two Line Mechanics report deferring the manual pressurization on an EMB-145 by deactivating the pneumatic outflow valve in the closed position per MEL 21-17. A rapid loss of cabin pressure occurred a day later; while climbing through FL320; with vibration felt in the yoke. The closed outflow valve had broken two of the three safety wires and opened. An air turnback was performed.
Narrative: August 2009; deferred manual pressurization on an EMB-145 by deactivating pneumatic outflow valve per MEL 21-17. The next day; a flight experienced rapid loss of cabin pressure while climbing through FL320 with vibration felt in yoke. Aircraft returned to field (RTF). Found deactivated pneumatic outflow valve had broken 2 of 3 safeties and opened. Exhaust air blowing on primary flight control cables; causing vibration in Yoke.The cause of event is not known at this time. Recommend investigation into what force overcame pressurization loads and broke safeties. Discussed procedure with Supervisor.MEL 21-17 and EMB AMM 21-31-04 are extremely vague with poor illustrations. The term 'lockwire' does not specify material or gauge. Actual geometry of safety is not clear. Do not believe MEL 21-17 leaves sufficient fail-safe margin for additional failures.
Data retrieved from NASA's ASRS site as of April 2012 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.