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An aircraft maintenance technician (amt) describes the potentially unsafe condition that would exists if a fire/smoke warning occurred in the main cargo deck areas of factory built all cargo B757-200 aircraft and MEL 21-40-2 had been applied. The fan cont aft cargo circuit breaker (circuit breaker) would be opened and collared at the cockpit overhead panel and the aft air distribution shut-off valve would not close. No fire suppressant system exists in class 'east' cargo compartments on B757s.
| Attributes | |
| ACN | 1226170 |
| Time | |
| Date | 201412 |
| Local Time Of Day | 1801-2400 |
| Place | |
| Locale Reference | ZZZ.Airport |
| State Reference | US |
| Environment | |
| Light | Night |
| Aircraft 1 | |
| Make Model Name | B757-200 |
| Operating Under FAR Part | Part 121 |
| Flight Phase | Parked |
| Component | |
| Aircraft Component | Air Conditioning Distribution System |
| Person 1 | |
| Function | Technician |
| Qualification | Maintenance Airframe Maintenance Powerplant Maintenance Avionics |
| Experience | Maintenance Technician 20 |
| Events | |
| Anomaly | Aircraft Equipment Problem Critical |
Narrative:
B757-200 aircraft displayed an EICAS status message aft cargo fan. The item was placed on MEL 21-40-2. The maintenance dispatch procedures to comply with the MEL; requires maintenance personnel to open and collar circuit breaker (circuit breaker) aft cargo heat fan located on the P11 panel in position N22. This circuit breaker is actually labeled fan cont aft cargo. Although this [circuit breaker] effectively removes control to the aft cargo fan relay K10084; it also removes 28 volt power from relay K10586 [for the] cargo smoke control relay. If this maintenance dispatch procedure is in effect and the flight crew is required to press the cargo depr switch YQPS1; the V10132 aft air distribution shutoff valve is deprived of voltage from the C4186 zone temperature cont vlv close aft circuit breaker. This will result in not adequately closing off the main deck aft distribution manifold. Since package freighters have class east cargo compartments; they rely solely on oxygen starvation in the event of a fire. Rb-211 engines. Heating system.
Original NASA ASRS Text
Title: An Aircraft Maintenance Technician (AMT) describes the potentially unsafe condition that would exists if a Fire/Smoke Warning occurred in the Main Cargo Deck areas of factory built all cargo B757-200 aircraft and MEL 21-40-2 had been applied. The FAN CONT AFT CARGO Circuit Breaker (CB) would be opened and collared at the cockpit overhead panel and the aft air distribution shut-off valve would not close. No Fire Suppressant System exists in Class 'E' Cargo compartments on B757s.
Narrative: B757-200 aircraft displayed an EICAS status message AFT CARGO FAN. The item was placed on MEL 21-40-2. The Maintenance Dispatch Procedures to comply with the MEL; requires maintenance personnel to open and collar Circuit Breaker (CB) AFT CARGO HEAT FAN located on the P11 panel in position N22. This circuit breaker is actually labeled FAN CONT AFT CARGO. Although this [CB] effectively removes control to the Aft Cargo Fan relay K10084; it also removes 28 volt power from relay K10586 [for the] CARGO SMOKE CONTROL RELAY. If this Maintenance Dispatch Procedure is in effect and the flight crew is required to press the CARGO DEPR switch YQPS1; the V10132 Aft Air Distribution Shutoff valve is deprived of voltage from the C4186 ZONE TEMP CONT VLV CLOSE AFT circuit breaker. This will result in not adequately closing off the main deck Aft Distribution Manifold. Since package freighters have Class E cargo compartments; they rely solely on oxygen starvation in the event of a fire. RB-211 Engines. Heating System.
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.