Narrative:

The crew discovered the oxygen system completely empty upon morning preflight at apf. I referenced the MEL and verified that the oxygen system, on our latest version, was deferral as long as we operated below 10000 ft. However, on this particular aircraft (sa-227) an emergency checklist for smoke in the airplane requires the crew to don the crew emergency oxygen masks and turn on the passenger oxygen supply and deploy the passenger oxygen masks. I felt that it was unsafe to depart apf with passenger if we were unable to comply with an emergency checklist. After servicing of the oxygen system we discovered that copilot oxygen mask hose had a rupture and was most probably the culprit for the empty oxygen system. The crew oxygen mask is not deferable so we ferried the flight to mco and used a spare passenger mask for the copilot. The safety conflict arises here when you consider the fact that the oxygen system is deferrable but the crew passenger oxygen masks are not. Also the fact that by deferring the oxygen system you cannot comply with an emergency checklist. My understanding of why this is an approved MEL is because of the extremely low probability of having smoke in the airplane with a deferred oxygen system. I strongly disagree, with any aircraft, especially the SA227. I am aware of an incident of my airline where the liquid tilled lighting system of the circuit breaker panels, which rest on top of the electrical buses and relays, began to leak and created a very acrid, and most likely toxic, smoke. Fortunately the airplane was on the ground when this occurred. This proves to me that this is a very likely event and could happen any time! I believe the MEL is inexcusable and should be changed immediately. Callback conversation with reporter revealed the following: metropolitan sa-227's new MEL revision allows deferral, old one did not. Reporter's decision supported by chief pilot, but reporter informed that FAA approval was based upon probability scenario justification, so, MEL was legal. Reporter reported events to union. MEL doesn't fit with emergency checklist for smoke, and reporter wonders why the masks are required (no MEL) when there is no oxygen. Also, smoke removal system marginal in sa-227, dump valve exhaust located in same place as fresh air fan source -- forward cargo compartment.

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Original NASA ASRS Text

Title: CAPT WOULD NOT COMPLY WITH MEL DUE TO ITS CONFLICTION WITH EMER CHKLIST PROCS. ACFT FERRIED TO MAINT BASE FOR REPAIRS.

Narrative: THE CREW DISCOVERED THE OXYGEN SYS COMPLETELY EMPTY UPON MORNING PREFLT AT APF. I REFED THE MEL AND VERIFIED THAT THE OXYGEN SYS, ON OUR LATEST VERSION, WAS DEFERRAL AS LONG AS WE OPERATED BELOW 10000 FT. HOWEVER, ON THIS PARTICULAR ACFT (SA-227) AN EMER CHKLIST FOR SMOKE IN THE AIRPLANE REQUIRES THE CREW TO DON THE CREW EMER OXYGEN MASKS AND TURN ON THE PAX OXYGEN SUPPLY AND DEPLOY THE PAX OXYGEN MASKS. I FELT THAT IT WAS UNSAFE TO DEPART APF WITH PAX IF WE WERE UNABLE TO COMPLY WITH AN EMER CHKLIST. AFTER SERVICING OF THE OXYGEN SYS WE DISCOVERED THAT COPLT OXYGEN MASK HOSE HAD A RUPTURE AND WAS MOST PROBABLY THE CULPRIT FOR THE EMPTY OXYGEN SYS. THE CREW OXYGEN MASK IS NOT DEFERABLE SO WE FERRIED THE FLT TO MCO AND USED A SPARE PAX MASK FOR THE COPLT. THE SAFETY CONFLICT ARISES HERE WHEN YOU CONSIDER THE FACT THAT THE OXYGEN SYS IS DEFERRABLE BUT THE CREW PAX OXYGEN MASKS ARE NOT. ALSO THE FACT THAT BY DEFERRING THE OXYGEN SYS YOU CANNOT COMPLY WITH AN EMER CHKLIST. MY UNDERSTANDING OF WHY THIS IS AN APPROVED MEL IS BECAUSE OF THE EXTREMELY LOW PROBABILITY OF HAVING SMOKE IN THE AIRPLANE WITH A DEFERRED OXYGEN SYS. I STRONGLY DISAGREE, WITH ANY ACFT, ESPECIALLY THE SA227. I AM AWARE OF AN INCIDENT OF MY AIRLINE WHERE THE LIQUID TILLED LIGHTING SYS OF THE CIRCUIT BREAKER PANELS, WHICH REST ON TOP OF THE ELECTRICAL BUSES AND RELAYS, BEGAN TO LEAK AND CREATED A VERY ACRID, AND MOST LIKELY TOXIC, SMOKE. FORTUNATELY THE AIRPLANE WAS ON THE GND WHEN THIS OCCURRED. THIS PROVES TO ME THAT THIS IS A VERY LIKELY EVENT AND COULD HAPPEN ANY TIME! I BELIEVE THE MEL IS INEXCUSABLE AND SHOULD BE CHANGED IMMEDIATELY. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING: METRO SA-227'S NEW MEL REVISION ALLOWS DEFERRAL, OLD ONE DID NOT. RPTR'S DECISION SUPPORTED BY CHIEF PLT, BUT RPTR INFORMED THAT FAA APPROVAL WAS BASED UPON PROBABILITY SCENARIO JUSTIFICATION, SO, MEL WAS LEGAL. RPTR RPTED EVENTS TO UNION. MEL DOESN'T FIT WITH EMER CHKLIST FOR SMOKE, AND RPTR WONDERS WHY THE MASKS ARE REQUIRED (NO MEL) WHEN THERE IS NO OXYGEN. ALSO, SMOKE REMOVAL SYS MARGINAL IN SA-227, DUMP VALVE EXHAUST LOCATED IN SAME PLACE AS FRESH AIR FAN SOURCE -- FORWARD CARGO COMPARTMENT.

Data retrieved from NASA's ASRS site as of July 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.