Generator Control Unit (GCU)Troubleshooting
When you have a suspected bad GCU, try that unit in the known good side first and see if it works. Do not install the good one in the inop side. Remember, IT IS NOT A FUSE !! A faulty GCU can't hurt anything, but a faulty system can damage a good GCU. Before you even remove the units, look closely at the generator A&D leads for damage and chafed areas. If you use a GCU as a fuse, your vendor will charge you for an overhaul…again.
Friday, December 29, 2006
ATA 27
Flap Limit Switches
With the issuance of Service Bulletin 1124-27-153, Mandatory Replacement of the Inboard Flap Actuators, it is an excellent time to inspect the position switches on the actuators. The left actuator has six and the right has two. Pay particular attention to the rollers; check them for flat spots and ease of turning. A drop of LPS 1 on each one will help prevent further problems. Make sure the arms are true and not bent; if they are bent, now is a great time to replace them. Wringing out the switches can also be done at this time. Make sure the 0°, 40°, and 42° switches are good; if high resistance is noted, replace the switch. If you find multiple problems, you would be money and time ahead to replace the entire switch rack.
With the issuance of Service Bulletin 1124-27-153, Mandatory Replacement of the Inboard Flap Actuators, it is an excellent time to inspect the position switches on the actuators. The left actuator has six and the right has two. Pay particular attention to the rollers; check them for flat spots and ease of turning. A drop of LPS 1 on each one will help prevent further problems. Make sure the arms are true and not bent; if they are bent, now is a great time to replace them. Wringing out the switches can also be done at this time. Make sure the 0°, 40°, and 42° switches are good; if high resistance is noted, replace the switch. If you find multiple problems, you would be money and time ahead to replace the entire switch rack.
ATA 73
Engine DEEC
If your Westwind was recently retrofitted with digital electronic engine controllers (DEECs). And your flight crew has contacted you to advise that the left fuel computer annunciator light illuminated steady in flight and is now flashing once every half-second after engine shutdown.
A slow-flashing annunciator light is your cue to download the DEEC memory, a fast-flashing annunciator indicates the real-time existence of a non-dispatchable fault. If the aircraft is located near a service facility that is equipped to interrogate the DEEC, this will reveal the fault in most cases. The crew can also help using the following technique. With the DEEC powered, press and hold the ENRICH position of the DEEC control switch for five seconds. When the switch is released, count the number of flashes on the annunciator light. This number will translate to a fault code listed in the Honeywell Service Information Letter (SIL) that details DEEC operation and fault isolation.
Second Note:
We recently discovered a problem with the manual mode light flashing within 1-3 minutes after downloading the Digital Engine Electronic Control (DEEC). After a lot of troubleshooting, we determined that the wires from the computer connector (pins 28 and 29) to the ENRICH/EVENT/OVERSPEED switch were shorted to ground. This loaded up the computer buffer quickly. We discovered that there are filters in those wires, and they had shorted to ground. These wires are not powered and are providing only a ground loop for the computer that the cockpit switch completes when pushed. On some aircraft, these filters are above the computers; on others, one is above the BSVs.
It would be a good idea to check your aircraft the next time you are in that area. Put a multimeter between the pins and have someone push the switch to EVENT. See if you get continuity. If so, you are ok. If you don’t get continuity, you can’t get an EVENT recording or an ENRICH if needed. This same procedure applies to aircraft still using the electronic engine controls (EECs). If the wiring is grounded on those aircraft, hot starts might be the result, as the switch is the ENRICH control.
It takes just a few minutes to check these, and it might save you some downtime later.
If your Westwind was recently retrofitted with digital electronic engine controllers (DEECs). And your flight crew has contacted you to advise that the left fuel computer annunciator light illuminated steady in flight and is now flashing once every half-second after engine shutdown.
A slow-flashing annunciator light is your cue to download the DEEC memory, a fast-flashing annunciator indicates the real-time existence of a non-dispatchable fault. If the aircraft is located near a service facility that is equipped to interrogate the DEEC, this will reveal the fault in most cases. The crew can also help using the following technique. With the DEEC powered, press and hold the ENRICH position of the DEEC control switch for five seconds. When the switch is released, count the number of flashes on the annunciator light. This number will translate to a fault code listed in the Honeywell Service Information Letter (SIL) that details DEEC operation and fault isolation.
Second Note:
We recently discovered a problem with the manual mode light flashing within 1-3 minutes after downloading the Digital Engine Electronic Control (DEEC). After a lot of troubleshooting, we determined that the wires from the computer connector (pins 28 and 29) to the ENRICH/EVENT/OVERSPEED switch were shorted to ground. This loaded up the computer buffer quickly. We discovered that there are filters in those wires, and they had shorted to ground. These wires are not powered and are providing only a ground loop for the computer that the cockpit switch completes when pushed. On some aircraft, these filters are above the computers; on others, one is above the BSVs.
It would be a good idea to check your aircraft the next time you are in that area. Put a multimeter between the pins and have someone push the switch to EVENT. See if you get continuity. If so, you are ok. If you don’t get continuity, you can’t get an EVENT recording or an ENRICH if needed. This same procedure applies to aircraft still using the electronic engine controls (EECs). If the wiring is grounded on those aircraft, hot starts might be the result, as the switch is the ENRICH control.
It takes just a few minutes to check these, and it might save you some downtime later.
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