April 10, 2000

Wichita, Kansas 67209

ATTENTION:

Mr. Carlos Blacklock

Subject: Identification of an Unsafe Condition on Cessna Model 172P Equipped With Integral Wing Fuel Tanks.

The following outlines Cessna's response to the FAA March 13, 2000 letter relative to the Cessna Model 172P with integral fuel tanks. In reviewing this letter, it is apparent that there are at least two separate issues to address.

These are:

As a means of initially placing this issue in the context of the regulation, the certification basis for the Cessna 172P is CAR 3 dated November 1, 1949 with amendments 3-1 through 3-12. In addition, there are a variety of FAR 36 noise requirements and a part 23 airspeed marking requirement which is not germane to the primary issue of 3.444 compliance. In reviewing paragraph CAR 3.444 it would appear that the paragraph has existed in the regulations for a significant period of time (even prior to November, 1949) and was carried over with a similar regulation when this rule was recodified in the form of FAR 23.971. In addition, a similar rule exists in FAR 25.971 and apparently has existed in part 25 from its published beginning.

CAR 3.444 has three segments, paragraph (a), (b), (c). Without repeating the entire rule, basically paragraph (a) permits each tank to have either a drainable sump with a specified capacity or the use of a sediment bowl of a specified capacity. CAR 3.444 (a) was also carried over in the May 15, 1956 amended version of CAR 3 and additionally shows up in FAR 23.971 with minor variations in language. CAR 3.444 (b), however, is a slightly different matter. The 1949 version of CAR3.444 (b) reads as follows: "(b) if a fuel tank sump is provided, the capacity specified in paragraph (a) of this section shall be effective with the airplane in the normal ground attitude and in all normal flight attitudes. In part 23 paragraph FAR 23.971, as amended by amendment 23-43 effective May 10, 1993, paragraph FAR 23.971 (b) states that "(b) each fuel tank must allow drainage of hazardous quantity of water from any part of the tank to its sump with the airplane in the normal ground attitude. In addition, Amendment 23-43 developed a requirement for both a fuel tank sump and a sediment bowl for reciprocating engine fuel systems as well as the notation that "and each fuel tank outlet is located so that in the normal flight attitude water will drain from all parts of the tank except the sump to the sediment bowl or chamber." In the preamble to amendment 23-43, proposal 26 proposes "that hazardous quantities be allowed to drain to a sump in the normal ground attitude." Further to this subject, in a letter dated July 25, 1983, signed by Barry Clements, Manager Aircraft Certification Division, ACE 100, Mr. Clements states: "most airplanes utilize this type design since it is very difficult to insure that the fuel tank is drainable to the sediment bowl in all normal ground and flight attitudes." Mr. Clements reference to most airplanes using this type design refers to both a sump and sediment bowl, however, he recognizes the difficulty in draining all fluids to the sediment bowl. This is consistent with the amendment 23-43 incorporating the quantity "hazardous."

To further review the history of fuel tank sump requirements CAR 3.444 (c) was amended by amendment 3-8 effective June 23, 1952. This amendment was an effort to clarify the term "outlet" and is amended to read as follows: (c) if a separate sediment bowl is provided in lieu of a tank sump, the fuel tank outlet shall be so located that, when the airplane is in the normal ground attitude, water will drain from all portions of the tank to the sediment bowl. This version of 3.444 (c) was carried over in the CAR 3 issue dated May 15, 1956. In addition, the recodification of part 3 to part 23 has a similar paragraph numbered FAR 23.971 (c) however, the FAR paragraph was expanded somewhat. The portion of this for our consideration, however, reads as follows: "and each fuel tank outlet is located so that, in the normal flight attitude, water will drain from all parts of the tank except the sump to the sediment bowl or chamber."

As well as the regulatory changes above, the FAA has on several occasions recognized the need for careful fuel handling and aircraft preflighting to assure that uncontaminated fuel is available to the engine at all times. This recognition is expressed and advisory circular AC 20-43 (c) dating back to October of 1976 and advisory AC-125 dated December, 1985.

As well as the regulatory changes above, the FAA has on several occasions recognized the need for careful fuel handling and aircraft preflighting to assure that uncontaminated fuel is available to the engine at all times. This recognition is expressed and advisory circular AC 20-43 (c) dating back to October of 1976 and advisory AC-135 dated December, 1985.

In addition to the regulations, revisions to regulations, and advisory circulars noted above, an FAA audit in the fall of 1997 on the 172R integral fuel tank system was reviewed and found to the FAA's satisfaction that the fuel tanks met regulatory requirements and performed as intended.

In Summary, on the subject of regulatory requirements the following appears to be consistent with the facts:

1.

The FAA has recognized that certain quantities of fluid may not find it's way to the sediment bowl

2.

That these quantities may not be hazardous in nature.

3.

The FAA has not traditionally administered CAR 3.444 as stringently as the March 13, 2000 letter implies.

4.

The regulations permit the incorporation of either a fuel tank sump or sediment bowl or both depending on the certification basis.

5.

The 172P incorporates a sediment bowl consistent with regulatory requirements.

6.

The 172P fuel tank incorporates drains for various areas of the tank especially in the area of the tank outlets. These are incorporated in the original design and SEB 92-95.

7.

Consistent with the requirements for a manufacturer functioning under DOA authorization as set out by FAR part 21, Cessna has kept the FAA apprised on various design changes for the 172 and other models which includes the aircraft with integral wing tank fuel systems.

In consideration of the foregoing, it is Cessna's belief and opinion that the 172P meets the requirements of the regulations and is in regulatory compliance.

In reviewing the FAA letter dated March 13, 2000 the FAA states that an unsafe condition has been identified as well as a condition of non compliance. As noted above, Cessna believes that the fuel system on the 172P is in compliance with applicable regulations and as a result the identification of an unsafe condition must be based on field service experience as well as field service reports. It would be beneficial to a mutually satisfactory resolution to this issue if the FAA could provide us with details of the field reports that they have received. Based on these field reports, it is Cessna's belief that a rational decision relative to an unsafe condition can be made. One of the considerations in a review of the field service history clearly is the number of aircraft incorporating a design of this nature. It appears that there are in excess of 20,000 aircraft incorporating a similar fuel system.

In the meantime, however, it is Cessna's plan to initiate a significant investigative program to identify and isolate any condition in the integral tank fuel system that may be unsafe. A schedule, as well as, a program plan will be provided to the FAA in the near future.

It is our belief that a mutually satisfactory resolution to this issue can be accomplished with cooperation between Cessna and the FAA and we look forward to working with you as this project progresses.

Stan O'Brien