Crumbling Wire

Aging wire insulation may be tough to inspect, but neglect may cause shorts


The following information is derived from the FAAs Service Difficulty Reports and Aviation Maintenance Alerts. Click here to view “Flight Control Hardware.”


During an aircraft accident investigation, an investigator discovered that the starter and the generator 6-gauge wires had numerous lateral splits in the wire insulation. The accident was not related to the defective wire insulation.

Splitting of the wire insulation appears as small, fine dark scratches on the outer covering of the wires and runs lengthwise along the wire. In some cases, the wire insulation splitting has penetrated the covering and exposed the center electrical conductor. This defect presents the possibility of electrical arcing of the high amperage direct current carried by these wires. The wires may be subjected to carrying high amperage electrical power for short periods of time during operation.

The manufacturers maintenance manual contains general wiring inspection criteria, but does not specify inspection criteria that specifically addresses splitting of the wire insulation. These types of large gauge electrical wire may be used on several other models of aircraft.

The FAA has issued Safety Recommendation number 01.172 and an Airworthiness Concern Sheet, dated October 2, 2001, both of which deal with this subject.

It was recommended that the starter and generator wires be inspected for the defects mentioned here at least once a year. If wire insulation splitting is discovered the wire should be replaced.

Aviat A-1 Husky
Wing Flap Control Structural Defect

While replacing the wing flap control handle, the technician discovered a crack in the full flap notch of the flap setting stop assembly. The flap-stop assembly had been inspected 129 operating hours earlier but no defects were present at that time. Part total time – 4,048 hours.

Beech A-36 Bonanza
Nose Landing Gear Wheel Defect

While changing the nosewheel tire, the technician discovered that the wheel bearings were damaged.The right side bearing seal was not securely installed, which allowed water and other contaminants to enter the bearings. The right side bearing was severely corroded, and the evidence indicated the inner bearing race was turning on the axle, damaging the axle beyond limits. Part total time – 1,049 hours.

Beech 58 Baron
Starter Failure

The left engine would not rotate when the starter was engaged, even though the battery and electrical system were in good condition. The technician discovered the starter adapter clutch assembly spring was broken.The unit had recently been installed after being overhauled.Part time since OH – 59 hours.

Beech 58 Baron
Fuselage Structural Defects

During an annual inspection, a technician discovered cracks in a fuselage bulkhead.These defects are described in Beech Class I Service Instruction 0990, Revision II, however SI 0990 is not applicable to this particular aircraft serial number.Part total time – 6,163 hours.

Beech 58 Baron
Air-Conditioning System Defect

During a scheduled inspection, a technician discovered an air-conditioning compressor bracket was cracked on the left engine.The technician said it appeared the bracket was not shimmed correctly during the previous installation. The crack had progressed to the point of making complete failure of the bracket imminent.Part total time – 94 hours.

Beech 200 King Air
Defective Propeller Deice System

After returning from a flight, the pilot reported that the right propeller deice system circuit breaker tripped open.The right engine propeller was recently overhauled, and the deice brush block assembly had been replaced.A technician inspected the right engine propeller; and when he applied side pressure to the right side of the brush block stack, the washers on the wiring attachment screws contacted each other. Due to the contact, an electrical short circuit occurred, which tripped the circuit breaker.Part total time – 6 hours.

Cessna 152
Rudder Control System Defect

After returning from a training flight, the instructor reported that the copilots left rudder pedal seemed loose.A technician discovered the right rudder cable was damaged where it passed through the aft fuselage bulkhead. The cable had worn through the phenolic rub block on the aft bulkhead and was damaged when it contacted the metal bulkhead, probably due to the cable being mis-routed during installation.Part total time – 518 hours.

Cessna 172R Skyhawk
Erroneous Fuel System Indication

The maintenance department of a large flight school received numerous reports of the Low Fuel warning light flickering during flight. The operator experienced this problem on 9 out of the 10 like aircraft they operate. The problem is almost always intermittent, which makes ground duplication very difficult. After a recent report, the technician removed the left fuel quantity sending unit and observed the low fuel light illuminate when he moved the sending unit float arm to approximate the 24-gallon level. In this case, the left tank fuel quantity sending unit was defective.Part total time – 1,742 hours.

Cessna T182T Turbo Skylane
Electrical System Design Difficulty

While changing the alternator control unit and relay, the technician experienced difficulty in removing the plastic electrical system junction-box cover because of interference with the engine-mount assembly and the aluminum cooling cover. The interference would not allow the plastic junction-box cover to flex enough for removal. He stated, The only way to remove the junction-box cover is to remove the junction box from the firewall, remove the engine mount from the firewall, or break the cover. Also, the screws used to mount the cooling cover are installed from inside the junction box, and the nut plates are on the outside of the cooling cover.Part total time – 117 hours.

Piper PA-24 Comanche and PA-30 Twin Comanche
Defective Elevator Security

While flying a PA-30 aircraft prior to an annual inspection, a technician/pilot noticed the elevator trim changed several times without input.A technician discovered the two bolts used to attach the elevator torque tube to the control horn were severely corroded and worn in the contact area, allowing the elevator torque tube to rotate in the control horn.The technician then inspected seven other PA-24 and PA-30 aircraft. All displayed evidence of severe corrosion on the bolts. All the aircraft inspected had accumulated more than 5,000 operating hours.

Piper PA 32-260 Cherokee Six
Smoke in the Cockpit

The pilot delivered the aircraft to a maintenance shop and reported there was smoke in the cockpit.A technician discovered hydraulic fluid leaking from the wheel brake reservoir, which saturated the defrost scat hose and was atomized and distributed into the cockpit by the defrost system. The leak was coming from a cracked attachment fitting on the brake reservoir.Part total time – 14,778 hours.

Piper PA 32RT-300 Lance
Cockpit Fuel Odor

The pilot detected a strong fuel odor in the cockpit.A technician discovered a leak in the fuel line that runs from the fuel pressure indicator to the forward bulkhead due to severe corrosion. Water and other contaminants may have leaked from the defrost ducts or windshield and dripped onto the fuel line.

Piper PA 32RT-300T Turbo Lance
Failed Magento Housing

During initial climb, the engine lost power resulting in an off-airport accident.An FAA inspector concluded magneto failure caused the accident. The magneto had been expelled from the engine case and was found inside the cowling. While examining the magneto, the inspector discovered the case was cracked. It appeared the magneto housing failed due to metal fatigue, which developed over a short period of time.Part total time – 18 hours.

Piper PA 34-200 Seneca
Nose Landing Gear Failure

During a landing approach, the nose landing gear failed to extend when the pilot selected the down position. While moving the aircraft off of the runway, a technician found that the nose gear was not held by the uplock but by hydraulic pressure. When he relieved the hydraulic pressure, the nose gear extended and locked in the down position.The hose from the actuator down port was completely plugged with rubber particles and other debris. The hose inner lining was deteriorated and had collapsed. The markings on the hose indicated the cure date was 2nd quarter 1972. Part total time – 7,209 hours.

Piper PA 34-220T Seneca
Defective Engine Throttle Cable

After returning from a flight, the pilot reported the left engine throttle control was very stiff. The technician discovered that the throttle push-pull cable was damaged in the engine nacelle near where the cable is routed past the turbocharger. Part total time – 303 hours.

Piper PA 38-112 Tomahawk
Defective Landing Gear Attachment

Because of a finding on a like aircraft, the technician removed the main landing gear attachment bolts for inspection and discovered both main gear inboard attachment bolts were bent in the shank area. Excessive side loads during landing may have caused the defect.Airworthiness Directive 90-19-03 and Piper Service Bulletin 673B deal with landing gear defects but do not address these bolts. Part total time – 6,584 hours.

Piper PA 46-350P Malibu Mirage
Defective Nose Landing Gear

During an annual inspection, a technician discovered the nose landing gear trunnion was cracked where the actuator attaches. One of the trunnion attachment lugs was severely cracked and in danger of failure. The problem may have extended from exceeding the turn limits while towing the aircraft.Part total time – 1,914 hours.


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