Narrative:

Bleed valves and inadequate MEL guidance. Flight manual describes the as soon as possible program as a voluntary, pilot self-reporting program designed to identify and reduce possible flight safety concerns. As soon as possible uses line pilot input to analyze potential incidents and accidents by taking a non-disciplinary, corrective action approach to flight safety. I always took this as a 2-WAY street. We learned from each other in a non-threat environment. Pilots could confess their errors so that others might be told and avoid a repeat. I also, apparently naively, thought that it was an opportunity for line pilots to pass along to management perceived weaknesses in policies and procedures. This second aspect seems completely missing in this particular incident. It appears that you are only concerned with identing how we were wrong. We should have looked at, we might have been confused, we read the MEL too literally (you would prefer figurative or allegorical readings). Details: as we reported, the left isolation valve light was noticed just prior to pushback. We did not consult the MEL because we did not consider the item broken, not yet. I was exercising judgement and working the problem. I did not and do not consider that we were cutting a corner or anything like that. If it makes fleet feel better to have caught us in this error, more power to them but checking the MEL or not, prior to pushback, would not have changed the outcome. After engine start and our determination that the valve was not going to cooperate we consulted the MEL and saw that a return to the gate was required. The weight penalty, the crux of the issue and my own worst failure, plus also where the MEL was the least help. This is where you can improve our airline operations. A crossroad, take the penalty or not. If you take the penalty, the MEL guidance is fine. If you do not take the penalty, the MEL ought to have a procedure to verify that the adp (bleed air driven pump) is operating on APU air, you are counting on it because you did not take the penalty. We were not confused regarding the cycle time. We were shocked. Your reply confidently assures us that the adp was operating. Are you sure about that? Your reply states that fleet could find no guidance that differentiates between the adp operating off of bleed air or APU air. Do you mean there should be no difference? There was, we had pressure lights and an extremely long retraction. Your reply also had fleet stating that APU bleed logic was based on pressure regulation and if the APU air output is greater than the engine bleed air output then the APU bleed should predominate. This is also shocking. APU bleed valve logic has never been taught this way in ground schools I have attended. The B757/767 operating manual states, 'after the engines start the APU bleed air valve does not open unless the center isolation valve is closed or both engine bleed air valves are closed.' nothing is mentioned about who can blow the hardest. Which is it? After takeoff we contacted maintenance center to find out what could have happened. The center isolation valve had been manually closed. We wondered if APU bleed valve logic had been fooled because the valve had not been electrically signaled to close. A mechanic looking at his schematics could not tell us, what is the crew to do. The lesson to be learned, since we did not take the penalty, taking off without the adp operating would be taking off overweight. We need a procedure to ensure the adp is operating after engine start. Maybe it could be as easy as turning off the center electrical pumps and trying to lower the flaps. The answer would be obvious. The MEL has no such procedure or even a warning to check for adp operation. I think this is a weakness. This incident will occur again unless corrective action is taken. You need to tweak the MEL, add the test and add a note about restarting the APU for landing so that the adp has air to operate.

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Original NASA ASRS Text

Title: CONCERN IS EXPRESSED OVER ADEQUACY OF MEL GUIDANCE WHEN A B767 IS TO DEPART WITH ENG BLEED PROBS REQUIRING THE OP OF THE AIR DRIVEN HYD PUMP. TKOF WT PENALTIES AND GEAR RETRACTION TIME ARE ISSUES INVOLVED.

Narrative: BLEED VALVES AND INADEQUATE MEL GUIDANCE. FLT MANUAL DESCRIBES THE ASAP PROGRAM AS A VOLUNTARY, PLT SELF-RPTING PROGRAM DESIGNED TO IDENT AND REDUCE POSSIBLE FLT SAFETY CONCERNS. ASAP USES LINE PLT INPUT TO ANALYZE POTENTIAL INCIDENTS AND ACCIDENTS BY TAKING A NON-DISCIPLINARY, CORRECTIVE ACTION APCH TO FLT SAFETY. I ALWAYS TOOK THIS AS A 2-WAY STREET. WE LEARNED FROM EACH OTHER IN A NON-THREAT ENVIRONMENT. PLTS COULD CONFESS THEIR ERRORS SO THAT OTHERS MIGHT BE TOLD AND AVOID A REPEAT. I ALSO, APPARENTLY NAIVELY, THOUGHT THAT IT WAS AN OPPORTUNITY FOR LINE PLTS TO PASS ALONG TO MGMNT PERCEIVED WEAKNESSES IN POLICIES AND PROCS. THIS SECOND ASPECT SEEMS COMPLETELY MISSING IN THIS PARTICULAR INCIDENT. IT APPEARS THAT YOU ARE ONLY CONCERNED WITH IDENTING HOW WE WERE WRONG. WE SHOULD HAVE LOOKED AT, WE MIGHT HAVE BEEN CONFUSED, WE READ THE MEL TOO LITERALLY (YOU WOULD PREFER FIGURATIVE OR ALLEGORICAL READINGS). DETAILS: AS WE RPTED, THE L ISOLATION VALVE LIGHT WAS NOTICED JUST PRIOR TO PUSHBACK. WE DID NOT CONSULT THE MEL BECAUSE WE DID NOT CONSIDER THE ITEM BROKEN, NOT YET. I WAS EXERCISING JUDGEMENT AND WORKING THE PROB. I DID NOT AND DO NOT CONSIDER THAT WE WERE CUTTING A CORNER OR ANYTHING LIKE THAT. IF IT MAKES FLEET FEEL BETTER TO HAVE CAUGHT US IN THIS ERROR, MORE PWR TO THEM BUT CHKING THE MEL OR NOT, PRIOR TO PUSHBACK, WOULD NOT HAVE CHANGED THE OUTCOME. AFTER ENG START AND OUR DETERMINATION THAT THE VALVE WAS NOT GOING TO COOPERATE WE CONSULTED THE MEL AND SAW THAT A RETURN TO THE GATE WAS REQUIRED. THE WT PENALTY, THE CRUX OF THE ISSUE AND MY OWN WORST FAILURE, PLUS ALSO WHERE THE MEL WAS THE LEAST HELP. THIS IS WHERE YOU CAN IMPROVE OUR AIRLINE OPS. A CROSSROAD, TAKE THE PENALTY OR NOT. IF YOU TAKE THE PENALTY, THE MEL GUIDANCE IS FINE. IF YOU DO NOT TAKE THE PENALTY, THE MEL OUGHT TO HAVE A PROC TO VERIFY THAT THE ADP (BLEED AIR DRIVEN PUMP) IS OPERATING ON APU AIR, YOU ARE COUNTING ON IT BECAUSE YOU DID NOT TAKE THE PENALTY. WE WERE NOT CONFUSED REGARDING THE CYCLE TIME. WE WERE SHOCKED. YOUR REPLY CONFIDENTLY ASSURES US THAT THE ADP WAS OPERATING. ARE YOU SURE ABOUT THAT? YOUR REPLY STATES THAT FLEET COULD FIND NO GUIDANCE THAT DIFFERENTIATES BTWN THE ADP OPERATING OFF OF BLEED AIR OR APU AIR. DO YOU MEAN THERE SHOULD BE NO DIFFERENCE? THERE WAS, WE HAD PRESSURE LIGHTS AND AN EXTREMELY LONG RETRACTION. YOUR REPLY ALSO HAD FLEET STATING THAT APU BLEED LOGIC WAS BASED ON PRESSURE REG AND IF THE APU AIR OUTPUT IS GREATER THAN THE ENG BLEED AIR OUTPUT THEN THE APU BLEED SHOULD PREDOMINATE. THIS IS ALSO SHOCKING. APU BLEED VALVE LOGIC HAS NEVER BEEN TAUGHT THIS WAY IN GND SCHOOLS I HAVE ATTENDED. THE B757/767 OPERATING MANUAL STATES, 'AFTER THE ENGS START THE APU BLEED AIR VALVE DOES NOT OPEN UNLESS THE CTR ISOLATION VALVE IS CLOSED OR BOTH ENG BLEED AIR VALVES ARE CLOSED.' NOTHING IS MENTIONED ABOUT WHO CAN BLOW THE HARDEST. WHICH IS IT? AFTER TKOF WE CONTACTED MAINT CTR TO FIND OUT WHAT COULD HAVE HAPPENED. THE CTR ISOLATION VALVE HAD BEEN MANUALLY CLOSED. WE WONDERED IF APU BLEED VALVE LOGIC HAD BEEN FOOLED BECAUSE THE VALVE HAD NOT BEEN ELECTRICALLY SIGNALED TO CLOSE. A MECH LOOKING AT HIS SCHEMATICS COULD NOT TELL US, WHAT IS THE CREW TO DO. THE LESSON TO BE LEARNED, SINCE WE DID NOT TAKE THE PENALTY, TAKING OFF WITHOUT THE ADP OPERATING WOULD BE TAKING OFF OVERWT. WE NEED A PROC TO ENSURE THE ADP IS OPERATING AFTER ENG START. MAYBE IT COULD BE AS EASY AS TURNING OFF THE CTR ELECTRICAL PUMPS AND TRYING TO LOWER THE FLAPS. THE ANSWER WOULD BE OBVIOUS. THE MEL HAS NO SUCH PROC OR EVEN A WARNING TO CHK FOR ADP OP. I THINK THIS IS A WEAKNESS. THIS INCIDENT WILL OCCUR AGAIN UNLESS CORRECTIVE ACTION IS TAKEN. YOU NEED TO TWEAK THE MEL, ADD THE TEST AND ADD A NOTE ABOUT RESTARTING THE APU FOR LNDG SO THAT THE ADP HAS AIR TO OPERATE.

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.