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James Peterson at ACE115W


5/25/2000 11:58 AM




Dudley McHone


Doyle King, Everett Pittman, Jeff Janusz


Cessna high-wing airplanes with integral fuel tanks


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Mac -- Per your request, this is a brief description of the unsafe condition we have determined exists in the Cessna 172P airplanes.


The internal structure of the integral fuel tanks on the Cessna 172P airplanes does not provide adequate passages for contamination (such as water) to migrate to the fuel sump where it could be removed through the single sump drain in each tank. (There is a Service Bulletin that adds other sump drains, but it is not mandated by AD to be installed, and the additional sump drains are also ineffective in removing water.) The inability to remove the water from the tanks via the fuel sump drains allows the water to continue to accumulate. Over time, a significant amount of water can accumulate. In the event that the water becomes large enough, flight maneuvers can cause the water to move over the fuel outlet, where it will be induced into the fuel supply line leading to the engine. If the quantity of water induced is of sufficient quantity to effect engine performance, either through a reduction in power or total loss of engine power, then, by definition, a hazardous amount of water has been allowed to accumulate without being able to remove from the fuel sumps via the sump drains. This is the situation which our engineers have determined to exist on the Cessna 172P airplanes, and which we have identified as an unsafe condition, and will propose an Airworthiness Directive to the Small Airplane Directorate.


In our letter to Cessna, advising them of our determination of unsafe condition on the 172P, we asked Cessna DOA to review the type design of the other high-wing airplane models that utilize an integral fuel tank. We asked that they perform their review and report to us if the same or similar type design concepts are used on those airplane models as is to be found in the 172P. At this time, Cessna has not responded to our direction/request under 21.277 for these additional airplanes. However, in our telecon this morning with Stan O'Brien of Cessna, he stated that they had a plan to test a 172R fuel tank to rebutt our determination of unsafe condition on the 172P fuel tank, since they were of similar design. This increases our concern for the safety of additional Cessna models of airplanes both in service and in current production. With O'Brien's statement of similarity, I believe we must consider the unsafe condition may exist on the current Independence production airplanes, unless Cessna can provide us with evidence to the contrary.

Jim Peterson


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