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April 19, 1999
Greg Roberts
Nashville Flight Standards District Office
#2 International Plaza Drive, Suite 700
Nashville, TN 37217

Dear Greg Roberts,

My name is Robert E. Scovill Jr. a pilot and aircraft owner. My pilot certificate # is 2146452.

This letter reports the potential for improper drainage of a hazardous quantity of water from some part or parts of the fuel tanks of a certain Cessna 172P integral fuel bay (wet wing) equipped aircraft (aircraft number 17274599, year 1981). Federal Aviation Regulation, FARS Section 23.971 Fuel tank sump, part b states, "(b) Each fuel tank must allow drainage of any hazardous quantity of water from any part of the tank to its sump with the airplane in the normal ground attitude." This letter will demonstrate that there is potential--due to improper drainage--for water in the above aircraft's fuel tanks not to drain to the sumps. This condition, if not corrected, can lead to a rough running engine or engine failure with consequent danger of crashing, depending on the pilot's ability to control the stalled aircraft to an area for safe landing. The condition affects immediate flight safety, and it is life threatening. Consequently, I recommend that the conditions stated in this letter be given a high priority evaluation for immediate action.

NOTE 1: This letter's report applies to my airplane identified in the preceding paragraph. I have not physically checked the improper drainage-through several months of troubleshooting rough running engine and engine failure problems with my airplane, I have concluded that an improper drainage problem exists. If my troubleshooting conclusions are correct, then the potential for improper drainage conditions exist for any Cessna airplane that has a fuel tank with the same or similar design as the fuel tanks in my airplane. Consequently, I have not physically checked the improper drainage condition to avoid disturbing or losing information that may be valuable to experts who can perform their own assessments to determine fuel tank modification, alteration, or maintenance that addresses the unsafe condition. In order to bring this unsafe condition to the attention of experts, I am referring my experiences with what I suspect is improper drainage to the responsible offices within the FAA. I am requesting that the FAA in joint effort with Cessna, the manufacture of my airplane, evaluate the conditions stated herein to determine whether or not an investigation that leads to specific actions that eliminate the unsafe conditions should be conducted. I am submitting this letter for your evaluation of my findings, and I am preserving my airplane's condition pending your decision to perform an investigative inspection.

Page A1 in Appendix A of this letter is a copy of page 12-19 of the Cessna Model 172 Series Service Manual. This service manual page contains Figure 12-8A-a figure of the left-hand, wet-wing fuel bay area. In the figure, item 22 describes the part of the fuel tank to which your attention should be focused, but first consider the design of the ribs (item 22). Notice that the ribs are shown in the figure with two holes located on their edges that touch the bottom of the tank. Based on comments from my mechanic, I believe the diameter of these holes is about the size of a number two pencil's diameter. I do not know if there are more than two holes along the bottom edge of each rib. I am relying on the diagram to accurately depict the fuel bay area. If the diagram is correct, then it is important to notice the position of the holes--they are located about one-third the length of a rib from each end. The ribs, item 22, partition the tank into three parts and the holes are intended to permit fluid flow from one part to another. The tank's original design (year 1981) included a single sump located in the aft corner near where the screen is located-item 25 in the figure.

 Sumps

In 1992, Cessna released a service bulletin, SEB92-25. This service bulletin provides "A modification for installing additional fuel quick drains [sumps] in the wing integral fuel tanks" for Cessna model series 172 and other models (see the service bulletin SEB92-25 which accompanies this letter for a complete list of models). Service Kit SK182-100 contains the procedures for installing the additional sumps. Page A2 in Appendix A of this letter is a copy of Page 4 of the Service Kit SK182-100. This page contains a figure of the "Fuel Drain Valve Installation." Please refer to page A2 in Appendix A of this letter and notice in the figure where the additional sumps are located. From the figure, it can be seen that four sumps have been added. Each sump is labeled with a bold uppercase letter A (each tank now has five sumps). Additionally, notice the vertical lines labeled W.S. 51.50 and W.S.40.08. These lines represent the ribs (item 22, in the figure on page A1). It is important to notice in the figure on page A2 that the middle part of the tank partitioned by the ribs can not be drained directly because there is no sump installed in that part of the fuel tank. Fluid in the middle part of the tank can only be drained if it flows to one of the other parts of the tank where a sump is installed. Compare the figures on pages A1 and A2.

In the paragraphs that immediately follow, I use the above information contained in the figures on pages A1 and A2 to conjecture the behavior of fluid flow in my airplane's fuel tanks. Further below, under the topic of history, I give factual information that supports my conjectures.

My intuition of fluid flow for fuel and water contained in the tanks as shown in the figures of pages A1 and A2 is such that:

When my airplane is in the normal ground attitude:

Conjectures

1. There will normally be a much larger portion of fuel than water.
2. Water is heavier than fuel, so water will rest on the bottom of the tanks.
3. The heavier fluid (water) will rest at the aft part of the tank.
4. There is some quantity of water that can occupy a fuel tank's middle part partitioned by the ribs (item 22 in the figure on page A1). This quantity of water occupies an area located in the bottom aft section of the middle part of the fuel tank. Furthermore, this quantity of water can not flow to other parts of the fuel tank because either:

1. The water does not reach a hole at the base of the ribs.
2. A hole is blocked with debris.

The following history of events given in chronological order details factual information that supports my conjecture that an improper drainage problem exists.

Important Note: Prior to every flight for the duration of ownership of this aircraft, fuel samples have always been taken from the sumps without fail. At no time has there ever been even one drop of visible water drained from a sump during a preflight check except one time as noted further below in the event dated August 28, 1998.

(My airplane's fuel tanks were not retrofitted with the SK182-100 sump drain kit until October 20, 1998, so each fuel tank has its original single sump during the events occurring before October 20, 1998.)

June 6, 1997: My aircraft was flown from Murfreesboro, TN to Fayetteville, TN, for its annual inspection. As part of that inspection, both the fuel strainer and lower belly T-fitting were drained. There was no evidence of water noted.

June 10, 1997: My aircraft was flown back after its annual inspection from Fayetteville, TN to Murfreesboro, TN.

August 24, 1997: My aircraft was flown with one passenger non-stop over the Centerville, TN area where I made many steep turns around a number of farms. Upon completion of the steep turns, I leveled off at three thousand feet for the return flight to my home base, Murfreesboro, TN. I established contact with Nashville Approach Control. At approximately 28 miles from Murfreesboro, while receiving radar flight following, the engine began to run extremely rough. Application of carburetor heat was ineffective. Outside conditions were not conducive to the formation of carburetor icing. I was able to fly the plane and land at the Murfreesboro airport albeit the engine continued to run very rough.

After landing, I called my mechanic, Mark Cobb with Fayetteville Aviation, and informed him of the rough running engine. He suggested that it was probably carburetor ice. I suggested that the onset of the rough running engine came on too abruptly and that it was unlike carburetor ice, which comes on slow with a smooth decrease in rpm. Relying on Mark Cobb's expertise as a mechanic, I accepted his opinion that the rough running engine was caused by carburetor ice, however, I still wanted Mark Cobb to check the engine. The aircraft's annual inspection had been performed a little over two months before this rough running engine occurred, so I scheduled maintenance with Mark Cobb to re-shim the wheel pant cover on the right main and to check for causes of the rough running engine.

August 28, 1997: My aircraft was flown from Murfreesboro, TN to Fayetteville, TN for the above mentioned maintenance. Mark Cobb made the adjustment to the wheel pant cover and remarked there was nothing he could do for the rough running engine as it was probably just carburetor ice.

On the return flight home from Fayetteville, TN during a descent out of five thousand feet, the engine began to run extremely rough. I applied carburetor heat, but it was ineffective. Eventually, the engine quit-a total engine failure. Fortunately, I was able to make the Murfreesboro airport. After landing, I coasted off the end of the runway and immediately called Mark Cobb at Fayetteville Aviation and informed him that the engine had just shut down in flight. I informed Mark Cobb that I had barely made the runway and that a definite problem exists with this aircraft, and if not corrected, might very well lead to my being killed.

While still parked off the runway, I held my cell phone in a manner that let Mark Cobb hear the engine as I attempted to start the aircraft. For a period of time, it would not start. After a time lapse of several minutes, the engine did start, and I taxied it to my hangar.

September 5, 1997: Mark Cobb flew to Murfreesboro to troubleshoot my aircraft. Mark Cobb checked the engine, the carburetor, the magnetos and the timing. Nothing seemed out of the ordinary. We took fuel samples from the fuel tank sumps, but we did not find any water in the samples.

We did an aircraft run-up for over thirty minutes and only when switching from one magneto to the other did we notice a slight vibration. Mark Cobb suggested that we change all of the spark plugs. After installing the new plugs, we ran the engine for another thirty minutes. Again, we noticed a slight vibration and missing of the engine when switching magnetos.

Mark Cobb loosened the belly plug on the fuel T-fitting. When I turned on the fuel selector, a large quantity of water drained from the belly plug. At no time did we find any water in our samples from either wing sump. We both felt relieved that we finally had our answer to the rough running engine and the engine failure in flight.

After draining large quantities of fuel from the bottom of the fuselage, we added alcohol to both wing tanks and felt comfortable that our problem was solved. I let the plane sit for a few days, and on a number of occasions, I sampled each wing tank from the sumps. I did not find water in any of the samples. Important Note: As of the date of this event, after some seventeen years of sumping this aircraft's fuel tanks, I have never found one drop of water in the fuel sample cup.

September 26, 1997: I flew the aircraft to Hohenwald, TN where I landed, and after a few hours there, I flew the aircraft back to Murfreesboro, TN.

January 26, 1998: I flew the aircraft for my BFR with no problem.

August 21, 1998: I flew the aircraft from Murfreesboro, TN to Fayetteville, TN for its annual inspection. During this flight, I lost my vacuum pump in flight and used the back-up electric horizon on the co-pilots side.

August 28, 1998: I arrived at Fayetteville, TN to pickup my aircraft from its fresh annual. I sumped my wing tanks in front of Mark Cobb. Both of us noticed that there was no water in the sample cups. Mark Cobb said that as part of the annual inspection he drained fuel from the T-fitting under the belly and also disassembled the fuel strainer with no evidence of water.

I departed Fayetteville climbing to five thousand feet IFR to cruise to Murfreesboro, TN. During the flight, Nashville Approach Control instructed me to descend to three thousand feet. Immediately after the descent, upon reaching three thousand feet, the engine lurched, vibrated and stopped-a total engine failure. I made an emergency landing in a farmer's field.

A passerby took me to the Shelbyville airport. Once there, I contacted Mark Cobb, who later met me at the airport. I notified the FAA, and they said an inspector was in route also. When George Erdel (a FAA Inspector), and Mark Cobb arrived on site, they entered the aircraft and started it right up with no apparent problems.

Fuel samples were taken from the wing and also from the belly of the aircraft with no evidence of water. Mark Cobb, George Erdel (a FAA Inspector), and the property owner, who is also a pilot, suggested that it must have been carburetor ice, to which I responded with an expletive.

A farmhand mowed a makeshift runway for me. The terrain of the field was very rough, and during my taxi attempt to the runway, the airplane was abruptly bounced around. Suddenly, the engine began to run rough. It backfired, and I could not get a good magneto check, so I shut the engine down.

Immediately, Mark Cobb and George Erdel (a FAA Inspector) took fuel samples from the wing sumps, using a 32-ounce Gatorade bottle for a sampling cup. The bottle was filled with a sample drained from one of the fuel tank sumps. The contents of the sample contained about two-thirds fuel and one-third water--approximately 10 to 12-ounces of water. This sample is the first time in the life history of the airplane that I have observed water draining from one of its fuel tank sumps. Furthermore, my observation of water draining from the sump is coincidental to my having just taxied the airplane on a rough terrain surface, another first. The evidence of this water finally put to rest the theory of carburetor ice.

(Read George Erdel's written statement of the events mentioned for the August 28, 1998 history.)

(Read Mark Cobb's account of the events mentioned for the August 28, 1998 history.)

Due to the large quantity of water that was obtained from the sample, the spark plugs were cleaned and the wing tanks were drained until there was no more evidence of water. Alcohol was added to both tanks. I took off from the field using the makeshift runway and returned to my home field hangar in Murfreesboro, TN.

After the events of landing in the farmer's field due to engine failure caused by water, I met with Larry Skelley (a FAA Representative) and the Murfreesboro Airport Manager. Our goal was to determine if the source of the water found in my tanks was coming from fuel services at Murfreesboro Airport. A sample was taken from the 35 year-old underground tank that services the airport as well as MTSU flying school. The sampling procedure consisted of putting a water sensitive paste on the end of a wooden fuel measuring stick. The end of the stick, about the size of a postage stamp, was then lowered into a ten thousand, gallon tank and permitted to touch the bottom of the tank. Our sample did not reveal any evidence of water. We took one sample that tested only one particular area of the tank. I felt the manner in which the tank was sampled left much to be desired, but Murfreesboro Airport did replace their underground tank with an above ground fuel tank a few days after we took the above sample. I do not know if the replacement of the underground tank was due to our sampling. The replacement may have been planned prior to our sampling.

After sampling the fuel tank at Murfreesboro Airport, the FAA Inspector and I went to the MTSU Aerospace building. There, we spoke to Erick Holmbjork, who stated that they had water in their fuel all the time when IFC was running the Murfreesboro Airport.

In the following days, plans were made to drain the aircraft of all its fuel. This was accomplished in the presence of a FAA representative, the Murfreesboro Fire Department and the Murfreesboro Airport Manger. We drained all of the fuel that we could get from the aircraft into a clear plastic jug. We dipped the nose of the aircraft into a low spot, we rocked the wings, and we dipped the tail in an effort to extract more fuel and water. With all of these efforts, we did finally get a very small quantity of water out of the airplane.

 While seeking solutions to the above engine failures due to water, I learned of a Cessna Service Bulletin that is applicable to my airplane's model. The service bulletin dated September 1992 installs additional fuel sump drains. Because this service bulletin was not delivered to me as a registered owner of one of the aircraft models to which the service bulletin applies, I was not aware of its existence until September 1998.

October 20, 1998: I flew my aircraft from Murfreesboro, TN to Fayetteville Aviation for the retrofit of the SK182-100 sump drain kit. During the course of this installation, the aircraft was again completely de-fueled to facilitate the kit installation.

October 30, 1998: I flew the plane home to Murfreesboro, TN.

March 27, 1999: I flew the aircraft from Murfreesboro, TN to Columbia, TN where I landed. After less than one hour on the ground, I departed Columbia destined for Centerville, TN. Along the way, I made a number of steep turns around some farms and later landed at Centerville, TN. After a few hours, I flew the plane home to Murfreesboro, TN.

April 5, 1999: I departed Murfreesboro, TN with a friend for a tour of Nashville, TN. I climbed to five thousand five hundred feet in radar contact with Nashville Approach Control and made a wide loop of the city. While in a descent to around three thousand feet in preparation for a landing at Murfreesboro, TN, the engine ran very rough, shuddered and quit-another total engine failure. I made a dead stick landing at Smyrna Airport. After landing, the plane would not move from the runway, so I requested a tow. While waiting for the tow, the engine's rpm increased and began to run normally. I taxied to the ramp where I tied the airplane down.

Later that evening, I called Mark Cobb and requested his assistance because I was leaving for an out-of-town trip the next morning. I understand that Mark Cobb arrived at the plane on Wednesday, April 7^th. He could not find water or any other malfunction, so he introduced alcohol into both tanks and flew the plane home to my hangar in Murfreesboro, TN.

In closing, it is my hope that you will evaluate the above history and compare it to my conjectures mentioned earlier in this letter's report. The goal of my effort is to determine if my aircraft meets the requirements of FARS Section 23.971. Furthermore, while I feel secure in the knowledge that I have garnered from my personal experience, it is my sincere hope that this matter will be available to other pilots who are flying similar aircraft to prevent any further mishap. As for me, my aircraft is in the hangar and shall stay there pending a response from you.

Sincerely,

Robert E. Scovill, Jr.
P.O. Box 347
Smyrna, TN 37167

Attachments:
Appendix, pages A1 and A2
Service Bulletins SEB92-24 and SEB92-25
Cessna Service Information Letter, October 27, 1980; SE80-87, CPC80-5, AG80-4

/res

Page A1

Page A2

End of Appendix A

This inspection was performed by the FAA in response to the letter dated April 19, 1999 addressed to Greg Roberts at the Nashville Flight Standards District Office to which this summary is attached.

Date of inspection: May 19, 1999

Place of inspection: Murfreesboro Airport within a MTSU Aerospace hanger.

FAA Aviation Safety Inspectors present: Greg Roberts and Paul Jones

MTSU Inspector under supervision of FAA:

Bill Allen, M.Ed.
Facilities Manager/Instructor
Aerospace Department
Middle Tennessee State University
Murfreesboro, TN 37132
A&P, IA, Private Pilot ASEL

Others attending:

Robert E. Scovill Jr., Owner of Aircraft 1724599 (Model 172P, Year 1981)
Commercial Pilot
Cert. No: 2146452
Airplane Single & Multiengine Land
Instrument Airplane

Glenn Tarpley, Observer.
ATC experience from US Navy enlistment (1974-1985).
Qualifications during enlistment:
Control Tower Operator, NAS Whiting Field
GCA Controller, NAS Whiting Field
Carrier Control Approach Supervisor, USS Dwight D. Eisenhower

Purpose of inspection: To test the conjecture made in paragraph 5 of the conjectures stated in the May 21, 1999 amendments to the letter as given in Appendix C, which is repeated here for convenience.

1. I submit that the design of each fuel tank in my 1981 Cessna 172P does not allow drainage of the entire fuel system as required by CAR 3.553. Specifically, all fluid from all parts of a tank with the airplane in the normal ground attitude can not be drained. Furthermore, I submit that this condition has potential to exist in other Cessna Models using the same or similarly designed fuel tanks.

Important Note: Paul Jones, one of the FAA inspectors, explained that the FARS Section 23.971; part B regulation used as the basis for the conjectures in the original letter do not apply to the aircraft. Instead, he explained that Part 3 of Civil Air Regulations effective November 1, 1949 applies. Therefore, an amendment to the letter has been added to appendix C. This amendment replaces references to FARS 23 with references to Part 3 CAR. See appendix C for the May 21, 1999 Amendment to Letter.

CAR PART 3-1949-SUBPART E, 3.553 Fuel system drains: Draining shall be provided to permit safe drainage of the entire fuel system and shall incorporate means for locking in the closed position. The provisions for drainage shall be effective in the normal ground attitude.

Thus, the inspection was performed in a hanger with the aircraft in a normal ground attitude. The left wing's fuel tank was inspected. The right wing fuel tank was not inspected (Its condition was preserved for future inspections).

During the inspection, the sumps on the left wing were drained several times. Page A2 in Appendix A of the letter is a copy of Page 4 of the Service Kit SK182-100 that shows the five sumps that were drained. The term five-sump sample as used in this summary refers to the sampling of each of the five sumps whereby a one-sump sample is a 1.75-ounce volume of fuel drained from one sump and visually inspected to determine if the sample contained water. Thus, the term five-sump sample means that each of the five sumps was sampled.

At the start of the inspection, it was not known if the left wing contained water. A left wing five-sump sample was taken, and no water was detected. After this sample was taken, the inspection team removed the three fuel tank access plates from the left wing and performed a visual inspection of the interior of the tank. The tank contained approximately 30-gallons of fuel. No water was visible from the access holes in this visual inspection.

Next, the inspection team prepared known quantities of water using 1.75-ounce volumes as the unit-measure to be introduced into the left wing fuel tank. A red food color was added to the water to make it more visible. The food colored water was tested in a fuel sample, and the test demonstrated that the food color ingredient did not change the water behavior (fluid motion) visible in the fuel.

Additionally, the inspection team planned to introduce the colored water into areas of the left wing tank described by ribs and stiffeners that partition the tank into compartments. Bill Allen managed the data collection of the inspection, and he recorded the results of each test. When the inspection is complete, he will prepare a report that will include the data and the test results. This summary does not include the data.

In the first colored water test, two 1.75-ounce volumes of colored water were poured into the tank through the access holes directing the colored water to specific regions of the tank partitioned by its ribs and stiffeners. The inspection team agreed that the total 3.5-ounces of water that was added constituted a hazardous quantity of water.

After introducing the colored water into the tank, a time interval of a few minutes was permitted to pass. Then a five-sump sample was taken. There was no water detected in this first five-sump sample that was taken when a known quantity of 3.5-ounces of colored water was in the left wing tank. The inspection team also visually checked the location of the colored water by looking in the fuel tank's access holes. From these holes, they were able to see that the colored water could not be drained from a sump. Thus, the first test substantiated the first part of the conjecture in paragraph 5 for the left wing.

5. I submit that the design of each fuel tank [left wing and right wing] in my 1981 Cessna 172P does not allow drainage of the entire fuel system as required by CAR 3.553.

After this first test, the inspection team performed several others using the same methods as described above for the first test. The results of several tests indicate that a five-sump sample may or may not enable a pilot to detect water in the left wing tank, dependent upon where the water is located in the tank, where located refers to the different partitions as described by the tank's ribs and stiffeners. Bill Allen's report will provide the details of these several tests.

In addition to the above tests, the inspection team performed a wing displacement test by shaking the left wing, displacing it vertically in approximately 4-inch displacements above and below the wing's normal plane of rest. There was approximately a twelve-ounce volume of colored water in the left wing when this test was performed. Prior to shaking the wing, the last five-sump sample did not indicate that water was present. After shaking the wing, approximately four-ounces of water was detected in the next five-sump sample. The remaining eight-ounces of colored water known to be in the left wing tank were not detected. That is, after draining four-ounces of colored water, the remaining eight ounces of water could not drain from the sumps due to the location of the water in the tank. Shaking the wing caused four-ounces of the known twelve-ounces to flow to a part of the tank from which the four-ounces of water could be drained from a sump.

After completing the above-mentioned tests, approximately 30-gallons of fuel were drained from the left wing. Fluid was removed using a hand pump with an attached hose that was inserted into the left wing's fuel tank access holes. Fluid was removed until no fluid drained from the left wing sumps. Residual fuel and/or residual colored water that could not be removed by draining were permitted to remain in the tank. A probe equipped with a camera lens attached to a video display with a videocassette recorder (VCR) was used to inspect and record the left wing's tank interior. This probing revealed that holes in structural ribs intended to permit fluid flow between partitions were not clogged with debris. Furthermore, this probing revealed that the rib holes were located a distance above the base floor of the tank that prevented volumes of residual fluid from flowing between partitions. Additionally, it could be seen with the probe that the design and location of a sump in at least one of the partitioned compartments containing a considerable amount of residual fluid could not drain the fluid. To verify this visual observation, an attempt to drain residual fluid from the sump being observed resulted in no fluid drained from the sump, yet a considerable amount of residual fluid could be seen with the probe in the compartment for which the sump is suppose to service.

The inspection was concluded on this date with the above probing of the interior of the left wing's tank. Further inspection was scheduled to resume Friday morning at 8am, May 21, 1999.

End of Appendix B

Appendix C corrects the reference to FARS Section 23.971 Fuel tank sump, part b originally stated in the letter to reference appropriate parts of Civil Air Regulations (CAR) Part 3, subpart E. FARS Section 23 does not apply to aircraft model 172P, number 17274599 (year 1981) type certificate. Instead, Part 3 of CAR effective November 1, 1949 applies to this aircraft's type certificate as given in the following references (Note: The Type Certificate Data Sheet referred to below has been delivered with Appendix C as an attachment. Please refer to this attachment as the following quotes were taken from it):

Department of Transportation Federal Aviation Administration, Type Certificate Data Sheet No. 3A12 with header title, 3A12-Revision 63-CESSNA AIRCRAFT COMPANY, page 1 states that:

At the bottom of page 10 of this Type Certificate Data Sheet is the following heading:

The contents under the above heading are printed on page 11 (see page 11 of the attachment).

Important note: The Fuel capacity item on page 11 does not include integral tank capacity. If omission of this capacity excludes the integral tanks in question for aircraft number 17274599 (Model 172P), then the appropriate type certificate data sheet must be obtained. Otherwise, it is assumed that this type certificate data sheet includes aircraft 17274599, a serial number that is among the Serial numbers eligible item on page 11 (see the first line of serial numbers on page 11).

Now, turn to the DATA PERTINENT TO ALL MODELS 172 THROUGH 172Q topic on page 12. Under this topic, the item Certification basis states that for Models 172 through 172P, Part 3 of the Civil Air Regulations effective November 1, 1949, as amended by 3-1 through 3-12 apply. Thus, this type certificate data sheet tells us to use Part 3 of CAR.

CAR PART 3-1949-SUBPART E has been delivered with Appendix C as an attachment. The following quotes have been taken from this attachment.

The General section of CAR PART 3-1949-SUBPART E, page 1 states:

3.442 Fuel tank installation

Using the above references, the following amendment is submitted to correct the use of FARS 23 in the original letter. The amendment restates references to FAR 23 in terms of Part 3, Civil Air Regulations.

The following sentences at the beginning of the letter:

This letter reports the potential for improper drainage of a hazardous quantity of water from some part or parts of the fuel tanks of a certain Cessna 172P integral fuel bay (wet wing) equipped aircraft (aircraft number 17274599, year 1981). Federal Aviation Regulation, FARS Section 23.971 Fuel tank sump, part b states, "(b) Each fuel tank must allow drainage of any hazardous quantity of water from any part of the tank to its sump with the airplane in the normal ground attitude."

This amendment reports the potential for nonflammable fluids not to drain from some part or parts of the fuel tanks of a certain Cessna 172P integral fuel bay (wet wing) equipped aircraft (aircraft number 17274599, year 1981). That is, CAR 3.553, Draining shall be provided to permit safe drainage of the entire fuel system . . . is not satisfied.

The following amendment replaces the original sentences beginning with the sentence:

When my airplane is in the normal ground attitude:

Conjectures

1. There will normally be a much larger portion of fuel than water.
2. Water is heavier than fuel, so water will rest on the bottom of the tanks.
3. The heavier fluid (water) will rest at the aft part of the tank.
4. There is some quantity of water that can occupy a fuel tank's middle part partitioned by the ribs (item 22 in the figure on page A1). This quantity of water occupies an area located in the bottom aft section of the middle part of the fuel tank. Furthermore, this quantity of water can not flow to other parts of the fuel tank because either:

1. The water does not reach a hole at the base of the ribs.
2. A hole is blocked with debris.
3. The water is blocked or damned by various structural members

1. I submit that the design of each fuel tank in my 1981 Cessna 172P does not allow drainage of the entire fuel system as required by CAR 3.553. Specifically, all fluid from all parts of a tank with the airplane in the normal ground attitude can not be drained. Furthermore, I submit that this condition has potential to exist in other Cessna Models using the same or similarly designed fuel tanks.

Finally, amend the sentence in the concluding paragraph of the letter, "The goal of my effort is to determine if my aircraft meets the requirements of FARS Section 23.971," to read:

The goal of my effort is to determine if my aircraft meets the requirements of Part 3 of Civil Air Regulations effective November 1, 1949, as amended by 3-1 through 3-12.

Name Correction:

Amend all references in the letter to Greg Roberts to Craig Roberts (a FAA Airworthiness Inspector). Additionally, amend all references to Greg Roberts to read Craig Roberts in Appendix B of the letter.

Most notably, the letter's addressee and salutation are amended.

From:

Craig Roberts
Nashville Flight Standards District Office
#2 International Plaza Drive, Suite 700
Nashville, TN 37217

Dear Craig Roberts,

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