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Reporter stated that the precooler control valve on the B737 is poorly designed and subject to failures.
| Attributes | |
| ACN | 1708549 |
| Time | |
| Date | 201912 |
| Local Time Of Day | 1201-1800 |
| Place | |
| Locale Reference | ZZZ.Airport |
| State Reference | US |
| Aircraft 1 | |
| Make Model Name | B737 Undifferentiated or Other Model |
| Flight Phase | Parked |
| Component | |
| Aircraft Component | Pneumatic Valve/Bleed Valve |
| Person 1 | |
| Function | Technician |
| Qualification | Maintenance Repairman |
| Experience | Maintenance Technician 22 |
| Events | |
| Anomaly | Aircraft Equipment Problem Critical Deviation - Procedural Published Material / Policy |
Narrative:
I would like to inform you that there is a system error in the precooler control system in the engine bleed system on boeing 737 aircraft.the precooler control valve used in this system; when 390 F sensor remains open or if there is air leakage from the 390 F sensor control pressure sense line or wing thermal anti ice solenoid remains open; precooler control valve goes fully open with spring loaded. If precooler control valve full open or hold any position; there is MEL restriction for icing condition as far as I know icing condition is a restriction required for wing anti ice.in the above mentioned cases (precooler control valve goes to full open position) engine bleed system does not give any malfunction or warning. This is a situation that conflicts with MEL item.an important restriction; such as icing condition; is that the system does not give a fault or warning under the conditions I have described above.however; many boeing 737 aircraft may be flying in this condition. Any operator cannot be aware of this situation because no malfunction is seen. This situation create a dangerous situation; especially in winter.
Original NASA ASRS Text
Title: Reporter stated that the precooler control valve on the B737 is poorly designed and subject to failures.
Narrative: I would like to inform you that there is a system error in the precooler control system in the engine bleed system on Boeing 737 aircraft.The precooler control valve used in this system; when 390 F sensor remains open or if there is air leakage from the 390 F sensor control pressure sense line or wing thermal anti ice solenoid remains open; precooler control valve goes fully open with spring loaded. If Precooler control valve full open or hold any position; there is MEL restriction for icing condition As far as I know icing condition is a restriction required for wing anti ice.In the above mentioned cases (precooler control valve goes to full open position) engine bleed system does not give any malfunction or warning. This is a situation that conflicts with MEL item.An important restriction; such as icing condition; is that the system does not give a fault or warning under the conditions I have described above.However; many Boeing 737 aircraft may be flying in this condition. Any operator cannot be aware of this situation because no malfunction is seen. This situation create a dangerous situation; especially in winter.
Data retrieved from NASA's ASRS site 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.