Circuit Breaker Problem:
During the last aircraft inspection, DC electrical system circuit breaker CB2-4 was replaced due to high resistance across the contacts. This condition was detected during the routine inspection/test. The circuit breaker was replaced with a new unit. However, after the CB was replaced, the right STARTER & GEN ½ amp circuit breaker on the cockpit overhead panel opens immediately whenever DC power is applied to the bus system. Attempts to reset the CB are unsuccessful.
You suspect that the problem may be related to replacement of circuit breaker CB2-4 in the right DC contactor box. A visual inspection shows the CB is closed, and everything appears normal inside and outside of the DC contactor box.
Answer:
Circuit breaker CB2-4 located on the right DC contactor box was replaced due to high resistance. The circuit breaker contains auxiliary contacts that, when closed, provide a ground to the generator trip relay (GTR). This condition would exist if the circuit breaker opened for any reason, such as a short on the generator field wiring. When the circuit breaker was replaced, a small bit of solder flowed across this grounding circuit connection on the rear of the circuit breaker, shorting the GTR monitor circuit to ground. Whenever the distribution bus is powered, the GTR coil has bus power. This short is providing a ground on the fault monitor circuit to the GTR. The GTR senses the “fault” and does its job of opening the generator control circuit breaker on the overhead panel, protecting the field wiring from further damage. The lesson here is to pay particular attention to your soldering techniques when replacing either CB1-4 or CB2-4.
Friday, September 30, 2005
ATA 30
Surface De-ice Boot Care and Maintenance
Things that could help Westwind operators identify problem areas with the de-ice boots.
Electrical Bonding:
The number one problem I have attributed to premature de-ice boot removal and installation is not neglect – that would be number two on the list – but the lack of electrical bonding. As the Westwind flies very fast through the atmosphere, the de-ice boots will generate static electricity. If the de-ice boot cannot dissipate this static electricity to the airframe, the charge will build up and finally blow out of the de-ice boot leading edge, leaving small cuts in the shape of half circles. Sometimes the damage will be a whole circle if the static electricity is heavy enough. How can this be prevented? First of all, make sure the static dischargers are within limits per the Aircraft Maintenance Manual (AMM) Chapter 23-60-00. The next thing to inspect would be the “DEICER CONDUCTIVE CEMENT” at the trailing edge of the de-ice boots. Without conductive cement, the de-ice boot has no way of discharging static electricity to the airframe. The conductive cement should overlap the de-ice boot and the painted surface. On many occasions I have seen black paint used instead of conductive cement and, of course, the de-ice boots showed severe wear from static discharge.
• Neglect:
“Application of AGEMASTER No. 1 should be made every 150 flight hours” according to AMM Chapter 30-10-00. I prefer Jet Stream PBS Boot Sealant, as it protects against ultraviolet (UV) damage, and it is much easier to remove the old sealant with PBS Prep in order to recondition the de-ice boots. Failure to condition the de-ice boots will cause UV damage and impact erosion, which leaves small pits and holes of irregular shapes along the leading edge. Plus it doesn’t look very pretty. In either case, the de-ice boots will get holes in them and if bad enough, they will not inflate properly, causing a safety-of-flight problem.
Things that could help Westwind operators identify problem areas with the de-ice boots.
Electrical Bonding:
The number one problem I have attributed to premature de-ice boot removal and installation is not neglect – that would be number two on the list – but the lack of electrical bonding. As the Westwind flies very fast through the atmosphere, the de-ice boots will generate static electricity. If the de-ice boot cannot dissipate this static electricity to the airframe, the charge will build up and finally blow out of the de-ice boot leading edge, leaving small cuts in the shape of half circles. Sometimes the damage will be a whole circle if the static electricity is heavy enough. How can this be prevented? First of all, make sure the static dischargers are within limits per the Aircraft Maintenance Manual (AMM) Chapter 23-60-00. The next thing to inspect would be the “DEICER CONDUCTIVE CEMENT” at the trailing edge of the de-ice boots. Without conductive cement, the de-ice boot has no way of discharging static electricity to the airframe. The conductive cement should overlap the de-ice boot and the painted surface. On many occasions I have seen black paint used instead of conductive cement and, of course, the de-ice boots showed severe wear from static discharge.
• Neglect:
“Application of AGEMASTER No. 1 should be made every 150 flight hours” according to AMM Chapter 30-10-00. I prefer Jet Stream PBS Boot Sealant, as it protects against ultraviolet (UV) damage, and it is much easier to remove the old sealant with PBS Prep in order to recondition the de-ice boots. Failure to condition the de-ice boots will cause UV damage and impact erosion, which leaves small pits and holes of irregular shapes along the leading edge. Plus it doesn’t look very pretty. In either case, the de-ice boots will get holes in them and if bad enough, they will not inflate properly, causing a safety-of-flight problem.
ATA 32
Brakes
When changing the main tires, take the time to closely inspect the brake keyways riveted to the wheel half. We are finding them completely worn through at the most inboard brake tangs and destroying the main wheel half. One trick you can use to maximize the life of these parts is to swap the wheels side-to-side to even out the wear on the keyways.
When changing the main tires, take the time to closely inspect the brake keyways riveted to the wheel half. We are finding them completely worn through at the most inboard brake tangs and destroying the main wheel half. One trick you can use to maximize the life of these parts is to swap the wheels side-to-side to even out the wear on the keyways.
ATA 5/55
Horizontal Stabilizer
Airworthiness Directive (AD) 89-12-08 has a 300-hr. horizontal stabilizer inspection requirement, and AD 96-24-11 has a 600-hr. aileron push-pull tube/guider roller inspection requirement. However, operators need to be aware that Chapter 5 of the Maintenance Manual requires them to be accomplished at 200-hr. and 400-hr. intervals, respectively. Please make sure that your maintenance facility is aware of this and makes the proper logbook entries.
Airworthiness Directive (AD) 89-12-08 has a 300-hr. horizontal stabilizer inspection requirement, and AD 96-24-11 has a 600-hr. aileron push-pull tube/guider roller inspection requirement. However, operators need to be aware that Chapter 5 of the Maintenance Manual requires them to be accomplished at 200-hr. and 400-hr. intervals, respectively. Please make sure that your maintenance facility is aware of this and makes the proper logbook entries.
ATA 21
Bleed Switching Valve
When your aircraft is in for maintenance, pull both bleed source and engine anti-ice circuit breakers (C/Bs). The bleed switching valves (BSVs), dump solenoids, and engine solenoids are energized when the aircraft power is turned on, and they get very hot!
When your aircraft is in for maintenance, pull both bleed source and engine anti-ice circuit breakers (C/Bs). The bleed switching valves (BSVs), dump solenoids, and engine solenoids are energized when the aircraft power is turned on, and they get very hot!
ATA 25
Equipment and Furnishings/Interior Refurbishment
While your Westwind is in for a C Check, structural inspection, or other heavy maintenance, it is generally required that the interior be removed to facilitate access. This would be a good time to tell your maintenance facility about any interior gripes. Most items can be fixed easily when components are already removed. Proper operation of the crew and passenger seats, lighting, and entertainment systems are essential for safety and customer comfort.
While your Westwind is in for a C Check, structural inspection, or other heavy maintenance, it is generally required that the interior be removed to facilitate access. This would be a good time to tell your maintenance facility about any interior gripes. Most items can be fixed easily when components are already removed. Proper operation of the crew and passenger seats, lighting, and entertainment systems are essential for safety and customer comfort.
ATA 80
Engine Start/Fail
During the first engine start, the pilot squawks that the engine will rotate when the START button is depressed, but spools down as soon as they releases the switch.
Questions:
Answer:
Please refer to the schematic on page 24-33 of the FlightSafety Westwind Maintenance Training Manual. The start relay (SR) is a two-pole switch with two functions. One pole function routes start control power coming from the GCU through auxiliary start relay (ASR) contacts to the generator start contactor (GSC) coil. This power energizes the GSC, and the starter will then rotate. The other pole function provides a start control holding circuit that closes when the SR is energized, allowing the operator to release the START switch. The start circuit will remain latched until terminated by the EEC/DEEC or manually by pressing STOP. In this scenario, the starter rotates as long as the START switch is held in the start position, but stops as soon as the switch is released. The most likely defective component is the holding circuit electrical contacts in the start relay. Because the starter will operate when START is pressed, we have proven the circuit to and through the GCU is functioning. Also, the ASR is functioning normally and energizing the SR. The SR coil is functioning along with the contacts that energize the GSC because the starter is rotating. Replacing the SR should resolve the fault.
During the first engine start, the pilot squawks that the engine will rotate when the START button is depressed, but spools down as soon as they releases the switch.
Questions:
- What is the most likely defective electrical component?
- Can you start the engine by holding the START button?
Answer:
Please refer to the schematic on page 24-33 of the FlightSafety Westwind Maintenance Training Manual. The start relay (SR) is a two-pole switch with two functions. One pole function routes start control power coming from the GCU through auxiliary start relay (ASR) contacts to the generator start contactor (GSC) coil. This power energizes the GSC, and the starter will then rotate. The other pole function provides a start control holding circuit that closes when the SR is energized, allowing the operator to release the START switch. The start circuit will remain latched until terminated by the EEC/DEEC or manually by pressing STOP. In this scenario, the starter rotates as long as the START switch is held in the start position, but stops as soon as the switch is released. The most likely defective component is the holding circuit electrical contacts in the start relay. Because the starter will operate when START is pressed, we have proven the circuit to and through the GCU is functioning. Also, the ASR is functioning normally and energizing the SR. The SR coil is functioning along with the contacts that energize the GSC because the starter is rotating. Replacing the SR should resolve the fault.
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