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for a discussion of wiring associated with the FQIS.
One auxiliary fuel boost pump is located within the collector bay of each standard fuel tank. The
pumps are powered from the 115-V AC bus. The pump wires routed within the fuel tank are
located within aluminum conduit. The conduit is connected to the wing structure where the pump
wiring enters the tank, and to the pump housing where the wire interfaces with the pump motor.
The low-level warning system comprises a float switch located in the collector bay of each
standard fuel tank. The float switch is powered from the 28-V DC bus. The pressure relief valve
indication system comprises a switch integral with the pressure relief valve located at the outboard
extremity of each standard tank. The pressure relief valve indication switch is powered from the
28-V DC bus. The float and relief valve switch wiring routed within the tank is also in aluminum
conduit. This conduit fully encloses the wiring, as in the case of the fuel pump.
The wiring and conduit design for the three systems described above are similar. The wiring and
conduit for the fuel pump and pressure relief valve were removed during the inspection program.
No evidence of chafing or degradation of the wiring was observed.
The DHC-8 aircraft uses numerous bonding jumpers for electrostatic bonding of fuel tubing. The
bonding jumpers are fabricated from stranded aluminum wire with an aluminum mating terminal
at each end. The inspection program carried out resistance measurements of the bonding jumper
installation as well as a visual inspection for evidence of deterioration and wear, breakage,
corrosion, deposits, security of attachment, and missing jumpers.
The inspection program showed the vast majority of bonding jumpers complied with the aircraft
build standard. A small percentage of discrepancies was observed including missing jumpers,
loose jumpers, jumpers with broken strands, and jumpers exceeding the build-standard resistance.
There were no visible signs of corrosion or deposits. The bonding jumper discrepancies were
rectified during the inspection program. These discrepancies are summarized in the table below.
Issue Findings (% of inspected jumpers)
Damaged bonding jumpers (broken strands) and
jumpers exceeding build-standard resistance 1.3
Missing bonding jumpers 0.4
Loose bonding jumpers 1.1
Figure 6–4: de Havilland Bonding Jumper Discrepancies
6.0 Bombardier Working Group Report (continued)
August 4, 2000 Industry AFFSP Report Page 61
Because of the presence of redundant electrostatic bonding paths, the discrepancies associated
with the missing and loose bonding jumpers did not impact the continued airworthiness of the
aircraft inspected. The bonding jumper resistance levels that exceeded the build-standard
resistance are well within the safety margin for electrostatic bonds.
Bombardier will issue a service bulletin recommending a one-time visual inspection of DHC-8
fuel tanks for missing, damaged, or loose bonding jumpers. Bombardier proposes that this
inspection be accomplished during regularly scheduled maintenance activity. Also proposed is a
periodic visual inspection of bonding jumper integrity as part of the aircraft maintenance program.
This periodic inspection is also to be carried out during scheduled fuel tank maintenance activity.
Bombardier will also undertake a review of possible improvements to the bonding jumper
specifications used on DHC-8 products.
6.6.2 FQIS
The primary FQIS for the DHC-8 uses a capacitance measurement system that includes six
capacitance probes located throughout each standard fuel tank. The wiring that interconnects the
probes inside the fuel tank is routed for support within segments of aluminum conduit.
Two magnetic dipsticks located within each standard tank provide an alternate means of
measuring fuel quantity on the ground. The dipsticks use a mechanical design consisting of a
calibrated rod sliding within a tube that extends vertically from the lower wing skin. The magnetic
dipsticks are electrically bonded to the external surface of the lower wing skin for lightning
protection. The magnetic dipsticks were visually examined for damage. In addition, the electrical
resistance was measured between the dipstick and aircraft structure. The inspection program found
no visible damage to the dipstick. The electrical bonding measurements indicated resistance levels
that exceeded the build standard. The resistance levels are attributed to oxidation between the
magnetic dipstick and the lower wing skin external to the fuel tank. The magnetic dipstick
installation is designed to prevent lightning ignition sources within the fuel tank because of the use
of a nonmetallic nut and internal sealing process. The increased resistance levels associated with
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