Narrative:

I am worried about our legal standing with respect to the airworthiness directive about our fuel pumps, as reflected in special message number XXXX. As matters stood last night, when I took this flight, we had discovered that the fuel scavenge system on the B757 does not work in the manner described in the special message. We had brought this airplane from ZZZ in the morning and noted that none of the 1000 pounds was scavenged from the center tank in 2 hours running time. We believed based on the information in the message that we should have seen approximately 800 pounds disappear out of that tank in those two hours. It is based on that assumption that the 1000 pounds had been considered usable. In discussions with dispatch, tech, and fot, I learned boeing has given us incorrect and conflicting information as to the left main tank fuel level at which scavenging begins. The information on which our compliance procedure is based is 9000 pounds. If that were correct, there would indeed be sufficient time remaining in reasonable fuel use scenario for that fuel to be completely scavenged, thus enabling us to consider it usable. Since our system did not scavenge at all down to a tank level of 6100 pounds, either our system was inoperative or that information is incorrect. Research in the maintenance manual, facilitated by tech, revealed a statement to the effect that it begins at approximately the half-full level. That would be about 7150 pounds, with the light, density fuel we had... The tank is full at 14-300 pounds. Clearly, that is incorrect as well, because there should have been at least a couple hundred pounds worth of scavenging on our flight. As of yesterday afternoon, we cannot consider that 1000 pounds of fuel in the center tank usable, as there is not sufficient time remaining even to exhaustion to scavenge all of that fuel. When I shared with the fot captain my concern about having a legal way to comply with the ad on this flight, regarding my particular airplane, the scavenge system test was accomplished by the maintenance manual procedure and it worked exactly as specified. The left main tank fuel level specified for the test was 5300 pounds or less in order to ensure that the check valve would allow scavenging to take place. Since the system worked perfectly in the test, we now know that the actual beginning of the scavenging process is somewhere between 6100 pounds (the fuel load with which I parked) and 5300 pounds with which scavenging actually happened. I am writing this report for two reasons, 1) in case the fot captain was incorrect and I was not legal to take the airplane based on a verbally-coordinated compliance procedure, and 2) my concern that we had to do this at all--that we have a compliance procedure in use in our operation that is based on bogus information. The special message and its associated compliance procedure must be re-written immediately to account for the manner in which the system actually operates, now that we have made this discovery. I am disappointed that it could get as far as having to be taken care of out in the live line operation, by line crews, after its official implementation, on a figure-it-out as-we-go-along basis. Callback conversation with reporter revealed the following information: the reporter stated the company is changing the procedures to carry the 1000 pounds in the center tank and listing it as unusable fuel. The reporter said it is hard to believe a required procedure is issued that is not tested first to determine if the aircraft is configured to conform to the procedures. The reporter stated to carry usable fuel in the center tank that must be scavenged out when the start of scavenge is anywhere between 6100 pounds and 5300 pounds is way to low to empty the center tank before reaching flight termination.

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Original NASA ASRS Text

Title: A B757-200 CAPT RPTS SERIOUS ERRORS IN AIRWORTHINESS DIRECTIVE AD 2002-19-52. ACFT CANNOT SCAVENGE CENTER TANK AS RPTED IN FLT MANUAL.

Narrative: I AM WORRIED ABOUT OUR LEGAL STANDING WITH RESPECT TO THE AIRWORTHINESS DIRECTIVE ABOUT OUR FUEL PUMPS, AS REFLECTED IN SPECIAL MSG NUMBER XXXX. AS MATTERS STOOD LAST NIGHT, WHEN I TOOK THIS FLT, WE HAD DISCOVERED THAT THE FUEL SCAVENGE SYSTEM ON THE B757 DOES NOT WORK IN THE MANNER DESCRIBED IN THE SPECIAL MSG. WE HAD BROUGHT THIS AIRPLANE FROM ZZZ IN THE MORNING AND NOTED THAT NONE OF THE 1000 LBS WAS SCAVENGED FROM THE CENTER TANK IN 2 HRS RUNNING TIME. WE BELIEVED BASED ON THE INFO IN THE MSG THAT WE SHOULD HAVE SEEN APPROX 800 LBS DISAPPEAR OUT OF THAT TANK IN THOSE TWO HRS. IT IS BASED ON THAT ASSUMPTION THAT THE 1000 LBS HAD BEEN CONSIDERED USABLE. IN DISCUSSIONS WITH DISPATCH, TECH, AND FOT, I LEARNED BOEING HAS GIVEN US INCORRECT AND CONFLICTING INFO AS TO THE L MAIN TANK FUEL LEVEL AT WHICH SCAVENGING BEGINS. THE INFO ON WHICH OUR COMPLIANCE PROC IS BASED IS 9000 LBS. IF THAT WERE CORRECT, THERE WOULD INDEED BE SUFFICIENT TIME REMAINING IN REASONABLE FUEL USE SCENARIO FOR THAT FUEL TO BE COMPLETELY SCAVENGED, THUS ENABLING US TO CONSIDER IT USABLE. SINCE OUR SYSTEM DID NOT SCAVENGE AT ALL DOWN TO A TANK LEVEL OF 6100 LBS, EITHER OUR SYS WAS INOP OR THAT INFO IS INCORRECT. RESEARCH IN THE MAINT MANUAL, FACILITATED BY TECH, REVEALED A STATEMENT TO THE EFFECT THAT IT BEGINS AT APPROX THE HALF-FULL LEVEL. THAT WOULD BE ABOUT 7150 LBS, WITH THE LIGHT, DENSITY FUEL WE HAD... THE TANK IS FULL AT 14-300 LBS. CLRLY, THAT IS INCORRECT AS WELL, BECAUSE THERE SHOULD HAVE BEEN AT LEAST A COUPLE HUNDRED LBS WORTH OF SCAVENGING ON OUR FLT. AS OF YESTERDAY AFTERNOON, WE CANNOT CONSIDER THAT 1000 LBS OF FUEL IN THE CENTER TANK USABLE, AS THERE IS NOT SUFFICIENT TIME REMAINING EVEN TO EXHAUSTION TO SCAVENGE ALL OF THAT FUEL. WHEN I SHARED WITH THE FOT CAPT MY CONCERN ABOUT HAVING A LEGAL WAY TO COMPLY WITH THE AD ON THIS FLT, REGARDING MY PARTICULAR AIRPLANE, THE SCAVENGE SYS TEST WAS ACCOMPLISHED BY THE MAINT MANUAL PROC AND IT WORKED EXACTLY AS SPECIFIED. THE L MAIN TANK FUEL LEVEL SPECIFIED FOR THE TEST WAS 5300 LBS OR LESS IN ORDER TO ENSURE THAT THE CHK VALVE WOULD ALLOW SCAVENGING TO TAKE PLACE. SINCE THE SYS WORKED PERFECTLY IN THE TEST, WE NOW KNOW THAT THE ACTUAL BEGINNING OF THE SCAVENGING PROCESS IS SOMEWHERE BTWN 6100 LBS (THE FUEL LOAD WITH WHICH I PARKED) AND 5300 LBS WITH WHICH SCAVENGING ACTUALLY HAPPENED. I AM WRITING THIS RPT FOR TWO REASONS, 1) IN CASE THE FOT CAPT WAS INCORRECT AND I WAS NOT LEGAL TO TAKE THE AIRPLANE BASED ON A VERBALLY-COORDINATED COMPLIANCE PROC, AND 2) MY CONCERN THAT WE HAD TO DO THIS AT ALL--THAT WE HAVE A COMPLIANCE PROC IN USE IN OUR OP THAT IS BASED ON BOGUS INFO. THE SPECIAL MSG AND ITS ASSOCIATED COMPLIANCE PROC MUST BE RE-WRITTEN IMMEDIATELY TO ACCOUNT FOR THE MANNER IN WHICH THE SYS ACTUALLY OPERATES, NOW THAT WE HAVE MADE THIS DISCOVERY. I AM DISAPPOINTED THAT IT COULD GET AS FAR AS HAVING TO BE TAKEN CARE OF OUT IN THE LIVE LINE OP, BY LINE CREWS, AFTER ITS OFFICIAL IMPLEMENTATION, ON A FIGURE-IT-OUT AS-WE-GO-ALONG BASIS. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THE COMPANY IS CHANGING THE PROCS TO CARRY THE 1000 LBS IN THE CENTER TANK AND LISTING IT AS UNUSABLE FUEL. THE RPTR SAID IT IS HARD TO BELIEVE A REQUIRED PROC IS ISSUED THAT IS NOT TESTED FIRST TO DETERMINE IF THE ACFT IS CONFIGURED TO CONFORM TO THE PROCS. THE RPTR STATED TO CARRY USABLE FUEL IN THE CENTER TANK THAT MUST BE SCAVENGED OUT WHEN THE START OF SCAVENGE IS ANYWHERE BTWN 6100 LBS AND 5300 LBS IS WAY TO LOW TO EMPTY THE CENTER TANK BEFORE REACHING FLT TERMINATION.

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.