A B737 Captain expressed his concerns about his airline's failure to comply with MEL admonitions that repairs are to be accomplished at the earliest opportunity. He illustrated the negative possibilities of that policy with an emergency diversion when the second and last fuel quantity indicator became inoperative enroute after being dispatched repeatedly with the first on MEL.

Narrative

Our company is continuing to violate the MEL Preamble which states: 'It is important that repairs be accomplished at the earliest opportunity'. They were operating Aircraft X repeatedly through maintenance bases with part availability and maintenance capability without an attempt to fix. In this case; Aircraft X was operating with the #2 fuel quantity indicator inoperative. The procedures for applying that MEL require the deactivation of the fuel summation unit which results in no VNAV and no ability to monitor and calculate fuel using the FMC. It also requires the tank to be drip sticked to verify fuel on board. This requires fueling personnel who are proficient in this procedure--a skill for which the company doesn't pay. While enroute the #1 fuel quantity indicator; the only remaining 'good' indicator; displayed a quantity of 12;000 LBS. The tank only holds 10;000 LBS when full. The indicator then went to a zero reading with error code 9 displayed. This inaccuracy continued until after landing; so there was no way to determine how much fuel was aboard. We carefully reviewed the fuel slips to assure ourselves we indeed had the required fuel onboard. Remembering the difficulty the fueling personnel were experiencing dripping the tank was not very comforting. Additionally; ATC had issued us an extensive reroute so I had no flight plan fuel figures to verify fuel periodically in-flight; and the new route was 130 miles longer than the original. After discussions with Dispatch we obtained routing direct to an airport which required declaring an emergency with ATC. We landed without incident and terminated the emergency with Tower upon landing. On one of my ACARS messages sent to Maintenance and Dispatch; I told them that 'this is precisely why our company should not be operating an aircraft with known inoperative equipment repeatedly through maintenance bases with no attempt to fix.' So there is documentation of that. Additionally; in an ACARS message sent to the aircraft; maintenance said we could pull and reset the fuel [quantity] circuit breakers. I replied that I would rather risk dead sticking than blow up in midair....thanks anyway.