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Data Source: NTSB Recommendations to FAA and FAA Responses
Report No: A-83-6
Subject:
Letter Date:01/13/1986
Status: CLOSED UNACCEPTABLE ACTION
<Recommendation>
[O] During the period 1975 to 1981, there were 396 engine failure or malfunction
accidents in United States general aviation aircraft involving water in the fuel as
a cause/factor. These accidents involved, primarily, small, single-engine airplanes
and resulted in 72 fatalities, serious injuries to 93 persons, and minor injuries to
127 persons. Engine stoppage because of water in the fuel occurred most often
during the takeoff and initial climb phase of flight, and frequently involved older,
high-wing Piper airplanes with metal fuel tanks such as the Piper Models J-3, PA-12,
PA-18, and PA-22; low-wing agricultural airplanes such as the Piper Pawnee (Model
PA-25) and the Cessna Agwagon (Model C-188); and high-wing Cessna airplanes, both
old and new, with rubberized bladder-type fuel cells such as Cessna Models C-180, C-
182, C-185, C-206, and C-207. The Safety Board believes that many accidents
involving water in the fuel can be prevented and that the FAA should act immediately
to address this fuel problem involving general aviation airplanes.
[Recommendations]
A-83-6. Require a fuel system modification to Cessna single-engine airplanes with
rubberized bladder-type fuel cells which will provide a means for positive detection
and/or elimination of water from the fuel, such as an increased capacity fuel
strainer or a separate water collector system and quick drains at the low point of
the fuel system.
[Responses]
FAA LTR DTD: 5/24/83
The FAA Small Airplane Certification Directorate in the Central Region advises that
their engineering evaluation of these recommendations is taking longer than
anticipated. They expect to have their evaluation completed during the month of
August 1983, at which time we will further advise the Board of our actions.
NTSB LTR DTD: 7/29/83
Pending completion of the FAA engineering evaluation, the above recommendations will
be held in an "Open--Acceptable Action" status.
FAA LTR DTD: 9/19/83
The FAA's Small Airplane Certification Directorate in the Central Region advises
that their engineering evaluation of these recommendations is taking longer than
anticipated. They expect to have their evaluation completed during the month of
November 1983, at which time we will further advise the Board of our actions.
NTSB LTR DTD: 6/1/84
Because of the number of delays in producing the several engineering evaluations,
the Safety Board has reclassified these 7 safety recommendations as "Open--
Unacceptable Action." The Safety Board urges the FAA to act expeditiously in
completing the studies that will lead to action on these recommendations.
FAA LTR DTD: 7/9/84
The manufacturer and the FAA have completed their investigations and tests to
determine the behavior of water in the bladder cells and fuel system. Accordingly,
on May 4, 1984, the FAA issued Airworthiness Directive (AD) 84-10-01 (copy
enclosed), a final rule, which was effective May 22, 1984. This AD is applicable to
certain models and series of Cessna airplanes which requires inspection and
Data Source: NTSB Recommendations to FAA and FAA Responses
modification of the fuel system. The prescribed action will identify airplanes
having bladder fuel cells which tend to retain water contamination, provide fuel
tank drainage provisions, and reduce the possibility that water may enter and be
retained in the fuel tanks. The provisions of the AD must be accomplished within
the next 50 hours time-in-service after the effective date.
We consider action completed on these recommendations and trust our actions meet
with the Board's approval.
NTSB LTR DTD: 1/10/85
Although the Airworthiness Directive issued by the FAA requires the installation of additional quick drains, we are uncertain as to the effectiveness of this requirement as the sole "fix." If wrinkles are present after the completion of the Airworthiness Directive or redevelop during service usage, water again will be entrapped. The Safety Board believes that few pilots will go through the procedure of bringing the tail of the aircraft within 5 inches of the ground and then rocking the wings 10 inches up and down. If the pilot does not rock the wings high enough and for a sufficient period, water will remain in the system or accumulate beyond the capacity of the fuel strainer. The Safety Board reiterates that a means for positive detection and/or elimination of water should be a required modification for the affected airplanes. Compliance with this Safety Recommendation through distinct design modifications would provide a definitive long-term solution to the problem of Cessna fuel-bladder water entrapment. Safety Recommendation A-83-6 has been classified as "Open--Unacceptable Action" pending further response.
FAA LTR DTD: 5/30/85
The FAA's investigation of Cessna and Beech bladder-type fuel systems to determine
the best means for improving the detection and elimination of water from these
systems revealed the following:
1. Wing dihedral influences trappable fluid retention in fuel tanks, and
wrinkles exist to some extent in all fuel bladder tanks.
2. Fuel bladders need careful handling and thorough inspection during initial
and field installation. Bladders should be warmed to eliminate shipping wrinkles
which may be formed by tightly compressing the bladders for insertion through the
tank cavity access door during installation. If these wrinkles are not removed,
they may trap fluid and prevent complete drainage of the tank. Bladders need to be
thoroughly inspected after installation to assure that the bladder fit or
installation discrepancies have not resulted in wrinkle formation.
3. The primary source of water in fuel bladders is entrance of precipitation
due to poor maintenance of the filler cap installation.
4. Quick drains should be utilized at drain locations rather than drain plugs,
caps, etc., to encourage use of drains.
5. All airplane models have some problems with water contamination. However,
Cessna single-engine fuel bladder equipped airplanes have had more unsatisfactory
service experience with fuel system water contamination than similar airplanes. It
was determined that an acceptable fuel system configuration could be obtained on
Cessna single-engine airplanes by elimination of critical fluid trapping diagonal
corner wrinkles.
When the diagonal corner wrinkle was identified as the major cause for undrainable
trapped fluid in Cessna bladder tanks, action was taken to eliminate that condition.
Data Source: NTSB Recommendations to FAA and FAA Responses
Airworthiness Directive (AD) 84-10-01 requires that the diagonal corner wrinkle be
eliminated by installation of the Cessna drain kit, or the fuel bladder replaced on
airplanes which are found to have diagonal corner wrinkles that trap fluid. Once
eliminated, the diagonal corner wrinkle will not redevelop. The permanent removal
of the diagonal corner wrinkle is possible because this wrinkle was caused by
improper drain nipple location or excessive drain nipple length during manufacture
of the fuel bladder. Cessna Service Information Letter SE-84-9, Revision 1, covers
both these discrepancies, as well as the procedure to follow during future fuel
bladder replacement. While an increased capacity fuel strainer or water collector
system has some merit, the quantity of water which may be trapped by a diagonal
corner wrinkle could easily exceed the capacity of any envisioned water collector
system.
For this reason, efforts were taken to eliminate the cause (diagonal corner wrinkle)
rather than deal with the symptom (trapped water) by requiring a larger water
collector system.
The FAA found no service data which indicated that the absence of a quick drain at
the low point of the fuel system in itself caused an unsafe condition; therefore, we
did not include a requirement for quick drains at these points on the fuel system on
airplanes affected by AD 84-10-01. Further, other Cessna aircraft with similar fuel
systems which do not have bladder tanks have sufficiently satisfactory service
experience to support this action.
NTSB LTR DTD: 9/6/85
As indicated in our letter of January 10, 1985, we believe that AD 84-10-01 does not
provide an adequate and reliable means for the positive detection and elimination of
water in the fuel. Some maintenance personnel who have carried out the provisions
of the AD have expressed grave doubt as to its effectiveness. More importantly,
these doubts appear to have been substantiated by the continued occurrence of water
in fuel accidents such as those at Basille, Louisiana, on November 22, 1984,
involving a Cessna 182 (Nl857X); at Elmonte, California, on January 5, 1985,
involving a Cessna 182 (N58816); and at Cold Foot, Alaska, on July 19, 1984,
involving a Cessna U-206 (N39486).
While AD 84-10-01 may provide partial alleviation of the water-in-fuel problem,
installation of a water separator and a quick drain at the low points of the fuel
system also should be required in airplanes affected by this AD. Such a water
separator, available for installation on Cessna Model 180 and 182 airplanes, already
has been certified by the FAA through issuance of Supplemental Type Certificate
(STC) SA-2628NM.
We believe that a requirement for the installation of a water separator in the many
thousands of Cessna airplanes covered by AD 84-10-01 to be logical, feasible and
acceptable, and we urge the FAA to reconsider the full implementation of this
recommendation. Pending the FAA's further response, Safety Recommendation A-83-6
remains classified in an "Open--Unacceptable Action" status.
FAA LTR DTD: 1/13/86
In response to your letter dated September 6, 1985, I believe that Airworthiness
Directive (AD) 84-10-01 does provide an adequate and reliable means of positive
detection and elimination of water in fuel systems of Cessna single-engine airplanes
equipped with bladder fuel tanks.
The FAA initiated an investigation of all water-in-fuel-related accidents which have
Data Source: NTSB Recommendations to FAA and FAA Responses
occurred since 1980, involving airplanes affected by AD 84-10-01, to determine the
effectiveness of the AD. The FAA's investigation disclosed that there were 88
accidents of this type reported from 1980 through October 10, 1985. Seven of these
accidents occurred after May 22, 1984, the effective date of AD 84-10-01. Three of
the accidents involved Cessna Model 182 airplanes, there was also one each involving
Models 180, 206, 207, and 210 airplanes. A survey was conducted of the FAA
inspectors and NTSB investigators involved in these investigations to determine
whether AD 84-10-01 had been accomplished on the airplanes involved in the accidents
and the finding of probable cause for the accidents. The survey disclosed that the
AD had not been accomplished on three of the seven airplanes as follows:
Model 182 (Nl857X) Basille, LA, November 22, 1984 Model 182P (N58816) Elmonte, CA,
January 5, 1985 Model 210 (N101PQ) Lordsborg, NM, January 2, 1985
The two Model 182 accidents were cited in your September 6, 1985, letter to
substantiate the Board's position on the effectiveness of AD 84-10-01.
The AD had been accomplished on the remaining four airplanes as listed below.
Noteworthy comments concerning factors pertinent to the accidents are included.
Model 182 (N2910F) Champaign, IL, December 4, 1984. The airplane sat outside with
almost empty fuel tanks for several months. Two to three gallons of water were
drained from the tanks before being serviced with fuel. A 2-inch icicle was found
in the right-hand tank at the fuel pickup location after the accident.
Model 180 (N91224) Kanai, AK, March 23, 1985. Fuel mismanagement, right-hand tank
service with small amount of fuel for a short flight. The right-hand tank fuel was
consumed, pilot switched to left-hand tank. Left-hand tank was not sumped prior to
flight.
Model U-206 (N3948G) Cold Foot, AK, July 19, 1984. Service with unfiltered
contaminated fuel (water and other contaminants). Airplane was not sumped prior to
flight after refueling.
Model 207 (N3036) Togiak, AK June 8, 1985. Serviced with suspected contaminated
fuel through questionable filters. Airplane was not sumped prior to flight after
fueling.
Of the 88 water-in-fuel accidents reported since 1980, 46 have occurred on Cessna
Model 182 series airplanes, with 13 of these accidents in 1980, 5 in 1981, 11 in
1982, 14 in 1983, 2 in 1984, and 1 through October 10, 1985. Since the issuance of
AD 84-10-01, there has been a notable decrease in these kinds of accidents, i.e., 3
during the years 1984 and 1985, as compared to 14 during 1983. Of the three
accidents in 1984 and 1985, only one occurred on an airplane on which compliance
with AD 84-10-01 had been accomplished. Prior to the accident, as noted above, this
airplane sat outside for several months with almost empty fuel tanks. Several days
prior to the day of the accident, approximately 2 to 3 gallons of water were drained
from the tanks before servicing the tanks with 54 gallons of fuel. Due to freezing
temperatures, difficulty was experienced during preflight on the day of the
accident. Nothing could be drained initially through the wing tanks quick drains.
After about an hour, some fuel was able to be drained. However, the FAA believes
that any water that may have been in the fuel system was probably frozen. After the
accident some ice was found in the right-hand fuel tank outlet, and about a half a
cup of water was found in the fuel drained from the airplane. Considering the
circumstances described, I do not believe that this accident should be attributed to
the fuel tank drains.
Data Source: NTSB Recommendations to FAA and FAA Responses
I believe that AD 84-10-01 is providing a demonstrated effective alternate means for
elimination of water from the fuel systems of Cessna airplanes equipped with
bladder-type tanks. In fact, I believe that the overall data indicates that the AD
is extremely effective.
Based on the above, I consider the FAA's action completed on this recommendation.
NTSB LTR DTD: 3/25/86
The Safety Board remains concerned that Airworthiness Directive (AD) 84-10-01 may
not be completely effective in preventing water from entering the fuel system. In
fact, one member of the Safety Board staff found a significant amount of water in
the fuel tanks of his Cessna airplane shortly after complying with the AD. While AD
84-10-01 may help to reduce the entrapment of water within the fuel tanks, it does
not provide for the positive detection and/or elimination of water from the fuel.
Additionally, as the aircraft that have complied with the AD have recently had their
fuel tanks completely "purged" and fuel caps resealed, it is expected that it may be
some time before the problem redevelops.
The Safety Board concludes that an impasse has been reached in our efforts to
convince the FAA that further attention is needed to assure the elimination of water
form the fuel tanks of the affected airplanes. As we have no further information to
offer in defense of this recommendation, Safety Recommendation A-83-6 has been
classified as "Closed--Unacceptable Action." Although we have closed this
recommendation our concern for this safety issue has not diminished and we will
continue to voice our concerns in future pertinent accident investigations.
</Recommendation>
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