Dr. Leaky Lines

Lines to oil and fuel gauges can spell trouble if not maintained


The following information is derived from the FAAs Service Difficulty Reports and Aviation Maintenance Alerts.

The FAA is looking into a number of reports and safety recommendations that have arisen as a result of lines behind the instrument panel leaking flammable fluid. The problems are encountered in a variety of models, from old models of aircraft currently in production to out-of-production vintage models to current production models.

Part 23 certification rules require a means to minimize the ignition and resultant hazard of ignition associated with the installation of flammable fluid systems. However, many older models do not have to comply with current Part 23 rules.

The FAA has recommended that the manufacturers issue service information that provides detailed inspection information applicable to flammable fluid systems as well as flammable fluid lines behind the instrument panels of their aircraft. Cessna is currently preparing manual revisions covering this subject, however the problem also extends to aircraft whose manufacturers are no longer in business.

The FAA also notes that corrosion and chafing of these lines may be prevalent under the floor panels of older airplanes. The FAA considers this an aging aircraft issue and urges maintenance technicians to closely inspect these fluid lines, both oil and fuel, for condition and security.


Beech F-33A Bonanza
Defective Wing Flap Drive Cable

While complying with Safety Communique 182, a technician found the left wing flap drive cable had a suspect date of manufacturer.The technician installed a new left wing flap drive cable that bore a date of manufacture of 03-2001. The new cable failed on the first activation during an operational test.Part total time – 0 hours.


Beech C90 King Air
Fuel Gauge Defect

The pilot reported that the left fuel quantity indicator was unreliable and appeared to read low.A technician replaced the gauge with an overhauled unit and calibrated it. The problem recurred on the next flight. The technician swapped the left and right indicators and discovered the problem was in the indicator. The technician installed another overhauled unit, but the problem again recurred.During a scheduled inspection, the technician discovered several corroded electrical grounding points, so he cleaned and recalibrated the system. The problem again recurred and was again traced to the indicator. The technician then discovered all of the failed fuel quantity indicators were overhauled by the same repair station at approximately the same time. An indicator from a different supplier solved the problem.


Beech 95-B55 Baron
Defective Wing Attachment Hardware

While complying with a required inspection of the wing attachment hardware, the owner decided to replace it with new bolts and nuts received from Beech. The new hardware was sent to a nondestructive inspection repair station, which found that two of the nuts had a rough inside surface, and there were linear crack indications in the threaded area. The nuts were returned to Beech for further inspection and evaluation.Part total time – 0 hours.


Beech 95-B55 Baron
Induction Airbox Damage

During an annual inspection, the technician discovered the right engine induction airbox displayed severe wear and numerous cracks. Approximately 69 hours prior to this finding, the airbox assembly was repaired due to the same type of damage.Part total time – 2,357 hours.


Cessna 152
Loss of Engine Power

While doing touch-and-go landings, the pilot applied carburetor heat and lost engine power. The engine performance did not change when the carburetor heat control was reversed.A technician found the starter lubrication decal lodged in the carburetor venturi, which restricted airflow to the engine and produced an extremely rich mixture. Part total time – 43 hours.


Cessna 172N Skyhawk
Serious Wing Structural Damage

During a scheduled inspection, the inspector noticed that a large number of rivet heads were broken and missing under the right wing leading edge skin at the forward spar.The wing was disassembled and the technicians found severe corrosion over much of the wing structure, including skins, spars, ribs and stringers.Part total time – 7,178 hours.


Cessna 172R Skyhawk
Defective Electrical Wiring

The pilot reported losing electrical power to approximately one-half of the avionics buss in flight.A technician found a 22-gauge wire burned from the navigation light circuit breaker switch to a connector. Most of the wire to the tail navigation light was damaged and the forward portion of the wire was burned down to the bare conductor. Part of the wire melted into adjacent wires in the bundle, causing an electrical overload.


Cessna 172S Skyhawk
Defective Landing Gear

The pilot reported a popping noise coming from the left brake when the brakes were applied. A technician found the left inboard main gear attachment fitting hardware was loose and the bolts and the holes in the gear were severely worn.Part total time – 1,345 hours.


Cessna U-206G Skywagon
Communication Interference

The pilot reported electrical noise in the headset.A technician determined the noise occurred when the alternator was on line, but there was no noise when the alternator was off line. In addition, the wet compass deviated by about 20 degrees when the alternator was on line. The technician could not find the cause of the defect.The technician installed three alternators, attempting without success to solve the problem. Finally he installed an alternate alternator and the problem was resolved.Part total time – 187 hours.


Cessna 414A Chancellor
Wheel Brake Defect

The pilot discovered while taxiing the right wheel brake was not effective. A technician found the line running to the right brake was leaking. The brake line is routed under the heater duct and had chafed against the heater duct until it was penetrated.Part total time – 4,094 hours.


Cirrus SR-22
Fuel System Defect

During a flight, the right fuel quantity indicator went to zero when the pilot selected the right fuel tank.A technician found the fuel sender was operating correctly. The right collector tank fuel inlet line was clogged by a foreign material that may have been deposited on the check valve when the airplane was manufactured.The investigation of the check valve problem led the technician to conclude that even with a fully functioning check valve, the main fuel tanks will not supply adequate fuel to keep the collector tanks full if the selected main fuel tank quantity is less than half a tank.Part total time – 31 hours.


Piper PA-28-161 Warrior
Engine Starting System Defect

The pilot said the starter continued to turn the engine with the key off and removed.A technician determined the wrong starter solenoid was installed. The aircrafts maintenance records did not show a replacement of the starter solenoid since the aircraft was new. The electrical contacts in the solenoid were welded together.Part total time – 2,109 hours.


Piper PA-28-161 Cadet
Flight Control Defects

During a scheduled inspection, the inspector discovered a stabilator control cable was defective.The damage was located at the bank of pulleys adjacent to the rear spar. Many of the pulleys at this location do not have bearings, and there is not much cable deflection to apply pressure on the pulleys to turn them.Part total time – 7,000 hours.


Piper PA-28-180 Cherokee
Engine Oil Leakage

A technician discovered an oil film on the engine firewall disk/retainer adjacent to a grommet used to accommodate the oil pressure indicator line. Oil was also found in the firewall blanket in the cockpit. The technician applied approximately 15 psi of pressure to the aluminum oil line and the line separated due to severe corrosion in the area where it passed through the firewall disk/retainer assembly.Aircraft total time – 1,931 hours.


Piper PA-28R-201 Arrow
Landing Gear Position Indicator

When the pilot extended the landing gear for landing, the right main gear did not indicate down and locked. A technician found the right main gear down limit switch was not properly rigged. He adjusted and rigged the switch and performed a retraction test. When he checked the emergency extension system, the switch arm hinge pin became dislodged and allowed the switch to de-activate. He replaced the switch and the landing gear functioned properly.Part total time – 471 hours.


Piper PA-32RT-300 Turbo Lance
Exhaust System Muffler Failure

An inspector discovered that the center muffler housing was split open at the upper weld seam.The defect allowed hot exhaust gases to damage the upper aluminum muffler shroud and the engine induction air cover.Part total time – 2,049 hours.


Piper PA-32-301T Turbo Saratoga
Flight Control Defect

While conducting an annual inspection, the inspector discovered that a rudder control cable turnbuckle was broken at the threaded portion. The safety wire was the only thing keeping the cable from separating and causing complete loss of rudder control. Part total time – 2,720 hours.


Piper PA-46-500 Meridian
Smoke in the Cockpit

The pilot reported smoke in the cockpit. The cabin fan circuit breaker opened, and the smoke dissipated.A technician discovered the electrical load buss relay was severely burned and heat-damaged. The relay is located below the right circuit breaker panel. Since this was a new aircraft, it was returned to the manufacturer for repair.Part total time – 17 hours.


Disintegrating ELT
While conducting an annual inspection on an Aeronca 7EC, a technician discovered the negative electrical lead running from the ACK Technologies E-01 ELTs battery compartment to the transmitter was broken.

Evidence indicated that the electrical lead was consumed by severe corrosion, which caused the wire to separate. Both the lower and upper ELT battery contacts were severely corroded and the plating had fallen off of the contacts. One of the eight batteries was completely dead, but it was not corroded and had not leaked.

Despite the fact that the manufacturer stipulates the cover screws are not to be removed, the technician in this case did open the transmitter for further inspection.


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