A Mechanic expressed concern about the lack of sealant and a vapor barrier applied to the Center Fuel tank Access door 131AB for Boeing's B737-700 and -800 series aircraft. The access door is directly above the left Air Conditioning Pack and if the door develops a fuel leak over the extremely hot pneumatic ducts; a fire or explosion could occur.
Synopsis
A Mechanic expressed concern about the lack of sealant and a vapor barrier applied to the Center Fuel tank Access door 131AB for Boeing's B737-700 and -800 series aircraft. The access door is directly above the left Air Conditioning Pack and if the door develops a fuel leak over the extremely hot pneumatic ducts; a fire or explosion could occur.
Narrative
Subject: Center Fuel Tank Access Door (131AB) 1. I have a concern about the Center Fuel tank Access door on the Boeing 737-700 and 800 series aircraft. This particular Access Door is located above the Air Conditioning pack like all generation B737's. The older 737's require the Center Tank Access door to be sealed with a fuel tank sealant in order to act as a secondary seal; however the newer -700 and -800 series do not require a secondary seal. 2. Although the access door on the -700 and -800 series has a different Part Number than the older B737's; the fact remains that if the door develops a leak with an extremely hot Air Conditioning pack located just below; there is a high probability that a fire or explosion could occur. 3. In the wake of all the new measures currently in force to make Fuel Tank Safety a priority; the omission of a secondary seal; or Mylar seal at this critical non-vented area; is in my opinion an accident waiting to happen. 4. I would appreciate your assistance in this matter in providing some form of background if this is in fact; a correct procedure; or if it has just been overlooked and the concern I have is justifiable. Thank you for your assistance in this matter.
NASA callback
Reporter stated his company has performed fuel tank modifications for years on numerous types of aircraft for commercial and private operators. He has personally worked fuel tanks for over twenty-four years and is very familiar with the B737 Classics and the NexGen B737's Wing and Center tanks. The B737 Center tank sections he has worked in over the years are 'Wet' tanks; all fuel; no rubber bladders or cells. Reporter stated the older 'Classic' B737 Center tank access door; or plate; is secured by protruding hex-head bolts with a fuel tank sealant applied over each of the bolt heads. A Mylar material would also be applied covering the bolts and the seam gap where the access door and tank lower wing skin meet. The Mylar material acts as a vapor barrier between the fuel tank access door and the Air Conditioning compartment with the extremely 'hot' pneumatic ducts below. Sometimes the Mylar was not applied; but in those cases; the bolt heads and seam gaps would always have sealant applied. The newer B737's; or NextGen aircraft; now use counter-sunk screws to attach the same access door to the lower skin; just like the wing tank access plates outboard of the fuselage. Reporter stated he read the Maintenance Manual and it does not have any steps to apply any sealant or install a Mylar seal to the access door. There are hundreds of B737's flying today without this seal on fuel door 131AB. A leaking fuel tank access door is not an unusual occurrence; it's just a matter of time before this door leaks. Reporter stated that since this door is not visible during the normal walk around; it is imperative that this problem gets solved.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.