Extracted From:    AC No. 43-16A
    ALERT NO. 306
    January 2004

The Airframe Propulsion and Services Branch (ACE-118W) of the Aircraft Certification Office (ACO), located in Wichita, Kansas, submitted the following article. (This article is published as it was received.)

Recently the FAA received a Safety Recommendation on Cessna 120, 140, and 140A model
airplanes that had been equipped with replacement fuel caps provided by Monarch Air. Subsequently, Monarch issued a Service Bulletin 120/140-875-2453-001 Rev. A, dated November 2003, that describes a test procedure for their fuel caps to ensure adequate venting of fuel caps. The description below is an excerpt from their Service Bulletin and is recommended being accomplished on an  annual basis for all vented fuel caps. However, the venting pressure requirements may be different for other vented fuel cap installations. Recently Monarch Air was reported to have ceased operations and we are providing this to operators who may not have access to their Service Bulletins.

Fluid         Minimum Acceptable Height – in.         Maximum Acceptable Height – in.
water             0.56 (9/16)                     1.93 (1 15/16)
gasoline         0.77 (13/16)                     2.69 (2 11/16)

The pass/fail criterion is defined as follows: The cap passes if it allows air into the bulb after applying a small vacuum (0.02 – 0.07 psi) and it fails if it opens immediately or is sealed and does not allow air to pass thru and thus vent the tank. These vacuum pressures correspond to the range of height values, h, shown in Table 1. Caps that open before the minimum pressure is reached or fail to open before the maximum pressure is reached fail this test. Caps that fail this test are to be replaced before the aircraft is returned to service. This inspection should be performed every 100-hours of flight operation or every twelve months, whichever occurs first, and entered in the aircraft log book.

Recommendation
Pilots operating aircraft with a fuel selector that enables them to select both fuel tanks are strongly encouraged to select this setting for take-off and landing provided one tank is not completely exhausted. Flight operations with the fuel selector set to “Both” may cause engine failure when one tank is empty.