Two mechanics and a Line Inspector report there is a need to clarify MEL 28-13-01-C Maintenance Procedure to have Maintenance verify the tip tank transfer valve is 'INOP OPEN' or 'INOP CLOSED' when deferring the valve on a DC-10-30. MEL required 11;600 LBS of additional fuel that had not been loaded; forcing pilot to severely restrict number 2 engine performance.
Synopsis
Two mechanics and a Line Inspector report there is a need to clarify MEL 28-13-01-C Maintenance Procedure to have Maintenance verify the tip tank transfer valve is 'INOP OPEN' or 'INOP CLOSED' when deferring the valve on a DC-10-30. MEL required 11;600 LBS of additional fuel that had not been loaded; forcing pilot to severely restrict number 2 engine performance.
Narrative
My partner and I were assigned to a DC-10-30 aircraft [in ZZZ]. On the post flight inspection we found 'tip tank 1 lo' alert displayed and created a write-up under Chapter 28-40-00. We trouble shot and found the gravity fill valve to be inoperative (inop) 'Open'. We then released the aircraft under MEL 28-13-01-C and followed the maintenance procedures per the MEL. Four days later; our Manager informed us that we accomplished the MEL procedures incorrectly because the gravity fill valve was inop 'Closed' via Centralized Fault Display System (CFDS) Fuel System Control (FSC); although we used the MEL [to defer] for valve inop 'Opened'. We followed the steps under Maintenance in the MEL to declare the gravity transfer system 'inop' via the CFDS FSC (Line Replaceable Unit) LRU/RESET; but were misled by Step '1.C' in the MEL that states; verify the word 'inop' is displayed. The MEL does not continue on to say 'inop closed' or 'inop open'. We feel that the MEL should be more clear and state under [MEL] Maintenance Procedure Step 1-C: 'Verify the word 'inop open' or 'inop closed'. Our company is putting in an MEL change request to make the steps under the maintenance procedure clearer and to assure this does not happen in the future.
Second reporter narrative
Upon arrival of DC-10-30 aircraft [in ZZZ1]; found fuel in number 2 tank at 3;400 LBS (pounds) with number 1 at 9;000 LBS and number 3 at 6;900 LBS. When checking the deferral; found the Tip Transfer Valve was (inoperative) inop'ed Closed'. When the aircraft has the valve inop'ed 'Closed'; the Fuel System Controller (FSC) automatically transfers the fuel from number 2 tank to compensate for this problem. The 'A' and 'B' MEL's require an additional 11;600 LBS of fuel to compensate for the deferrals. The MEL 28-13-01-C does not give clear instructions to look for the words (in plural) 'INOP OPEN'; it just states look for the word (in singular) 'INOP'. The first words that appear when deferring the Tip Transfer System are the words; 'INOP CLSD'. Looking at the three MEL possibilities for deferring the Tip Transfer System; I submitted a change request for the MEL's affected as follows:For each MEL 28-13-01-A; 28-13-01-B; and 28-13-01-C; the Maintenance Procedure tells the Mechanic to 'verify the word 'INOP' displays.' The Fuel System Controller (FSC) does not have option to choose the single word 'INOP'. It only has the choices 'INOP CLSD' and 'INOP OPEN'. The MEL 28-13-01-A and 'B' deferral needs a Step 1-C; listed under the heading 'Maintenance' to read: 'Verify the words 'INOP CLSD' appear.' The deferral 28-13-01-C needs to read: 'Verify the words 'INOP OPEN' appear.'I correctly inop'ed the valve to the 'INOP OPEN' position [here at ZZZ1] per the MEL and dispatched the aircraft.I COULD HAVE EASILY MADE THE SAME MISTAKE and saw the 'INOP' word displayed; not paying attention to the OPEN or CLSD part; simply by following the MEL's instructions as written. Also; not realizing the Tip Tank fuel bleed down occurred because of a breech internally between the Tip Tank and the lower tank which is not an uncommon occurrence after [aircraft] overhauls.
NASA callback
Reporter stated he has not heard from his company yet about his request to clarify MEL 28-13-01-C to include the words: verify valve 'INOP OPEN' or 'INOP CLOSED'.
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.