Narrative:

Aircraft was carrying an MEL 29-4 (inoperative #1 system a low pressure indicator light). After 2 legs, I noticed that the system a pressure increased upon starting engine #1. Consequently, MEL 29-10 was added. The text in MEL 29-10 only states not to start the engine with the towbar connected. I did not go back and review MEL 29-4, which requires the a-pump be able to be depressurized with the switch. In other words, you are not allowed to have both MEL's at the same time. The MEL paperwork was done by our maintenance and all I asked was if they were adding the 29-10 or if it replaced the 29-4. I was told that they were adding the 29-10 and also carrying the 29-4. I thought by reviewing the restrs of the 29-4, but just didn't do it since our maintenance was handling the paperwork. If the text in MEL 29-10 referred to 29-4 in some way, the mechanic or I would have caught it. I flew the airplane 1 leg where it over-nighted. The pilot flying the airplane the next day flew to YYY. Apparently maintenance control caught the error and grounded the aircraft there. Lesson learned: always go back and read the limitations on each MEL if you add another to make sure they all work together. I found out that I had flown the airplane with this illegal MEL because I took an aircraft today, jun/sat/03, from the captain that got the airplane from me in on jun/fri/03. Supplemental information from acn 586142: I released flight with 2 MEL's and one of them could not be deferred with the other. I do wonder why we don't have something in our system that would flag conflicting MEL's or at least give you a pop-up type warning.

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Original NASA ASRS Text

Title: A B737-200 WAS DISPATCHED IN NON COMPLIANCE WITH A HYD LOW PRESSURE WARNING LIGHT AND AN ENG DRIVEN HYD PUMP DEPRESSURIZATION VALVE DEFERRED AS INOP IN CONFLICT WITH THE MEL.

Narrative: ACFT WAS CARRYING AN MEL 29-4 (INOP #1 SYS A LOW PRESSURE INDICATOR LIGHT). AFTER 2 LEGS, I NOTICED THAT THE SYS A PRESSURE INCREASED UPON STARTING ENG #1. CONSEQUENTLY, MEL 29-10 WAS ADDED. THE TEXT IN MEL 29-10 ONLY STATES NOT TO START THE ENG WITH THE TOWBAR CONNECTED. I DID NOT GO BACK AND REVIEW MEL 29-4, WHICH REQUIRES THE A-PUMP BE ABLE TO BE DEPRESSURIZED WITH THE SWITCH. IN OTHER WORDS, YOU ARE NOT ALLOWED TO HAVE BOTH MEL'S AT THE SAME TIME. THE MEL PAPERWORK WAS DONE BY OUR MAINT AND ALL I ASKED WAS IF THEY WERE ADDING THE 29-10 OR IF IT REPLACED THE 29-4. I WAS TOLD THAT THEY WERE ADDING THE 29-10 AND ALSO CARRYING THE 29-4. I THOUGHT BY REVIEWING THE RESTRS OF THE 29-4, BUT JUST DIDN'T DO IT SINCE OUR MAINT WAS HANDLING THE PAPERWORK. IF THE TEXT IN MEL 29-10 REFERRED TO 29-4 IN SOME WAY, THE MECH OR I WOULD HAVE CAUGHT IT. I FLEW THE AIRPLANE 1 LEG WHERE IT OVER-NIGHTED. THE PLT FLYING THE AIRPLANE THE NEXT DAY FLEW TO YYY. APPARENTLY MAINT CTL CAUGHT THE ERROR AND GNDED THE ACFT THERE. LESSON LEARNED: ALWAYS GO BACK AND READ THE LIMITATIONS ON EACH MEL IF YOU ADD ANOTHER TO MAKE SURE THEY ALL WORK TOGETHER. I FOUND OUT THAT I HAD FLOWN THE AIRPLANE WITH THIS ILLEGAL MEL BECAUSE I TOOK AN ACFT TODAY, JUN/SAT/03, FROM THE CAPT THAT GOT THE AIRPLANE FROM ME IN ON JUN/FRI/03. SUPPLEMENTAL INFO FROM ACN 586142: I RELEASED FLT WITH 2 MEL'S AND ONE OF THEM COULD NOT BE DEFERRED WITH THE OTHER. I DO WONDER WHY WE DON'T HAVE SOMETHING IN OUR SYS THAT WOULD FLAG CONFLICTING MEL'S OR AT LEAST GIVE YOU A POP-UP TYPE WARNING.

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.