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May 30, 2000



Federal Aviation Administration
Aircraft Certification Office
1801 Airport Road
Wichita, Kansas 67209


Mr. Carlos Blacklock


Model 172 Aircraft Equipped with Integral Wing Fuel Tanks


1) FAA Letter dated 13 March 2000
2) Cessna Letter dated 10 April 2000


Dear Mr. Blacklock;

The FAA provided the letter of Reference Item 1, stating that an unsafe condition had been identified on the Model 172P, in accordance with FAA Safety Recommendations 99.283 and 99.284. These Safety Recommendations surrounded tests performed by a 172P operator, in which he demonstrated to the FAA that all of the water poured into his aircraft's fuel tank was not recoverable. The operator, one Mr. Robert Scovill, had recently experienced engine problems with his aircraft for the first time since the aircraft was new in 1982, and felt that the integral tank design of the aircraft was to blame, due to what he felt to be an excessive amount of undrainable fluid. Cessna responded to the referenced FAA letter with the letter of Reference Item 2, dated 10 April 2000. No written response was provided to that letter; however, via teleconference on 25 May 2000, Mr. Peterson of the FAA notified Cessna that the response letter was considered unsatisfactory, and that action is immediately required. He further stated that the FAA's position is that the amount of undrainable water in the fuel system is hazardous if it exceeds the fuel strainer capacity. This response will apply to issues related to the Model 172 aircraft equipped with integral tanks. Cessna intends to work with the FAA to resolve representative issues on the 172, then address separately the other models equipped with integral tanks, as requested on page two of the referenced FAA letter. The current 182T and T182T project issues will also be addressed separately.

In 1980, Cessna began production of the Model 172P with integral fuel tanks. With Service Bulletin SEB92-25, Cessna required installation of four additional drains per tank, each placed in a corner to facilitate more complete removal of contaminants from the fuel tank, regardless of the ground attitude of the aircraft. This integral tank design was largely incorporated into the 172R and 172S at restart of production operations in 1996, based primarily upon its excellent field service record. During the process of certification basis negotiations between the FAA and Cessna in 1995, FAA Service Difficulty Reports were reviewed, as were Cessna's records. At that time, the integral tanks were regarded by all parties as having substantially reduced the number of suspected fuel contamination cases reported for those aircraft so equipped since their inclusion into the design, and the added drains were only considered to improve on a successful design. A further review of the tanks in the fall of 1997 confirmed again that the FAA considered the tank design to meet regulatory requirements.

Page 2 not provided by FOIA.

Page 3 not provided by FOIA.

cause retained water to interfere with the ability of the engine to continuously produce power. Cessna will provide a copy of the proposed flight test plan to the Wichita ACO for review, and the FAA is invited to participate.

This activity will be Cessna's highest priority and will be completed as expeditiously as possible.

Cessna flight test activity will determine whether or not design changes are needed.

Included with this letter are the following Attachments in support of the stated position:
Attachment 1-"Induced Water Tests of 172R"
Attachment 2-
172R POH/AFM Preflight Procedures
Attachment 3-
"Pilot Safety & Warning Supplement" Section 10
Attachment 4-Cessna Fuel Contamination Service Documentation Listing [
4a, 4b, 4c]
Attachment 5-
FAA Advisory Circular AC20-125, "Water in Aviation Fuels"

Yours very truly,


Stan O'Brien
Cessna Aircraft Company
Director, Product Engineering
Single Engine Division




Doyle King, FAA Wichita MDO



"Mac" McHome, FAA Wichita MDO




The Cessna Aircraft Company 5800 E. Pawnee Wichita, Kansas 67218 316/831-4005, FAX 316/831-4188


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