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Robert E. Scovill, Jr.
June 5, 2000

Mr. Jim Hall, Chairman
National Transportation Safety Board
490 L'Enfant Plaza East SW
Washington, DC 20594-0003


 Subject: Safety Recommendation


Dear Mr. Hall:

This letter and its attachments contain important information that indicates a design flaw in the integral wing tank (also called a wet wing) manufactured by Cessna Aircraft Company; Wichita, Kansas. The Federal Aviation Administration (FAA) is reviewing the same information that I have provided to you as attachments. You may contact Craig Roberts, Airworthiness Inspector, FAA Flight Standards Office (FSDO); Nashville, Tennessee [(615) 781-5430] as needed. He is familiar with the problem, and he can provide you with other FAA contacts.

Within the NTSB, you are not the first person with whom I have communicated. I first contacted the NTSB on October 26,1999 by phone, which lead to e-mail communications. Back then I provided the same information to the NTSB that you have received with this letter. Recently, Gene Doub, a staff member at the U.S. Department of Transportation's Transportation Safety Institute in Oklahoma City, recommended that I submit my safety recommendations directly to you by certified mail.

The Problem

The Cessna wet wing design has been in production since 1979. It is installed on several Cessna aircraft models. My estimate is that the indicated flaw affects thousands of general aviation aircraft. The flaw may cause fuel contaminated with water to not be detected in a proper preflight check. Consequently, engine failure due to water may occur, which can lead to life threatening situations for souls on board and people over whom these aircraft fly. The problem affects immediate flight safety.

I have reviewed National Transportation Safety Board (NTSB) aircraft accident reports over the years 1983 to present. There is a clear indication that NTSB reports on accidents involving Cessna wet wing equipped aircraft that experienced in-flight engine failure are not being investigated in a way that will discover the indicated flaw. Clearly, accident investigators are assuming that Cessna's FAA certified wet wing's fuel-drainage system works properly. This assumption leads investigators to report probable causes such as the following.

Conditions conducive to carburetor ice.

Carburetor ice.

Pilot Performed insufficient preflight check.


I have not found a NTSB accident report that challenges the proper functioning of Cessna's wet wing fuel drainage system, which if done, will reveal the indicated flaw that has gone undetected for over twenty years. (A clear indication that too much confidence is placed in the FAA's certification process for general aviation aircraft.)


Recommended Solution

Both FAA and NTSB investigators should be informed of the information contained in the attachments. Given this knowledge, they should then be instructed to approach future investigations of aircraft accidents involving an engine failure or a rough running engine of aircraft equipped with Cessna's wet wing with the assumption that the fuel drainage system does not drain properly. This assumption should lead investigators to test the fuel drainage system.

In the mean time, the NTSB should work jointly with the FAA to investigate the results of the tests that are already available, which are attached to this letter. NTSB should give this matter high priority and submit a safety recommendation to the FAA as soon as possible.

The above actions taken by the FAA and the NTSB should lead to an Airworthiness Directive (AD) that reveals the design flaw and requires an engineering solution.

When an AD is issued both the FAA and the NTSB should be tasked with reviewing existing NTSB reports for the purpose of identifying accidents that have been reported with probable causes as stated further above in the description of the problem. As these reports are identified, they should be reviewed in-light of the new evidence, and where appropriate, change the probable cause to the following or something similar:

Probable Cause: Manufacture's design flaw in fuel drainage system, which prevented the pilot from detecting fuel contamination during his or her properly, performed preflight check.

Additionally, the FAA and the NTSB should use their database of pilot and aircraft owner contact information to inform these people of the indicated design flaw. Likewise, among these people who have NTSB accidents reports with probable causes that are subject to change as indicated above, these people should be informed when their accident's probable cause is changed.


Explanation of Attachments


Attached letter to FAA, FSDO; Nashville, Tennessee dated April 19, 1999

The attached letter from Robert E. Scovill, Jr. addressed to FSDO; Nashville, Tennessee dated April 19, 1999 is my notification to the FAA alerting them of a problem that affects immediate flight safety and may lead to life threatening situations. This attachment contains a chronological history of how I came to conjecture the problem. This history also includes facts from events that demonstrate weaknesses in how general aviation accidents and incidents are reported. In this attachment, I do not comment on these weaknesses, but the history does provide factual evidence for future comments.


Attached Report by Bill Allen, Facilities Manager for MTSU dated June 2, 1999

After submitting the above letter in April, the FAA performed inspections on May 19, 1999 and May 21, 1999. The June 2, 1999 report, written by Bill Allen, Facilities Manager for Middle Tennessee State University (MTSU) Aerospace, explains how the inspections were performed, list data that were recorded, and comments on observations that were made.


Attached Report by Matt Taylor, Director of Maintenance for MTSU dated October 10, 1999

Matt Taylor, Director of Maintenance, Middle Tennessee State University (MTSU), Flight Operations Maintenance, uses the FAA's test methods discussed in the above June 2, 1999 report to inspect MTSU's Cessna 172RG that is equipped with integral wing tanks. His report reveals similar results as those stated in Bill Allen's report


Attached Report by Robert E. Scovill, Jr. dated February 1, 2000.

Robert E. Scovill, Jr. reports the results of a drainage system test with the aircraft leveled relative to the ground.

Attached three 5 x 7 and three 8 x 10 color photos

These photos show an interior view of Cessna's integral wing tank taken during tests mentioned in the above-attached reports.

The above attachments (including more images), this letter, and more information are available on the Sump This web site. Its URL is http://www.sumpthis.com/. You may refer people to this site as needed.

Please contact me if you have questions or comments regarding my recommendations.

Thank you for your considerations. I look forward to your actions that will address this matter with the urgency that is needed. I have studied the RAND report that was generated at your request. Statements in that report indicate that my recommendations offer you an opportunity to act upon RAND's suggestions. In the future, you may expect more people from the public to seek a future opportunity to communicate with you and Congress on general aviation investigation laws and procedures. I look forward to working with NTSB on this topic.




 Robert E. Scovill, Jr.


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