ATA 24

Aircraft Grounding Points
Several instances have been reported of failing electrical grounding points. These connections have developed significant arcing, enough so that the cables have eroded a hole completely through the bulkhead frames. Compliance with the Service Bulletins 1124-24-120 will help minimize this. The areas to pay special attention to are the grounding cable GND 87, 88, 89 and 90, these are the attached at frame station 383 on the ceiling. Also the external power connection to the airframe, this is located at frame station 402.810. Holes in the frame may not be visible until the cables are removed.

ATA 24

Several instances have been reported of electrical grounding points failing. These connections have developed significant arcing, enough so that the cables have eroded a hole completely through the bulkhead frames. Compliance with the Service Bulletins 1124-24-120 will help minimize this. Pay special attention to the grounding cable GND 87, 88, 89 and 90. These are the attached at frame station 383 on the ceiling. Also, pay attention to the external power connection to the airframe. This is located at frame station 402.810. Holes in the frame may not be visible until the cables are removed.

ATA 24

Reverse Current Relay (RCR)

Have you experienced trouble getting the left or right generator to come on line after an engine start? Mechanics have experienced this many times and have fixed this problem by simply swapping the two generator Reverse Current Relays (RCRs). The RCRs have an internal case ground, and once the RCR is installed in the DC Contactor Box, it is then grounded to the airframe. The wiring prints do not show this case ground anywhere except in 24-30-00 (the large generic schematic). When I talked to the repair shop that overhauls the RCRs, I was told that the internal case ground is a common problem with those particular units due to corrosion and fatigue issues. So, it's not by magic that the RCRs tend to fix themselves by swapping them. In actuality, removing and installing the RCR from the DC Contactor Box more than likely cleans the corrosion from the grounding points at the mounting bolts. The first step in troubleshooting the RCR is to find out if it has power going to it. I use a simple test light made for a 28 VDC circuit with two insulated alligator clips. Clip one end of the test light to the SW terminal of the RCR and the other end of the test light to a known good airframe ground. After engine start, see if the test light is illuminated; if so, power is good, so you then have a "ground" issue with the RCR. After engine shutdown, you can check the case ground using an ohmmeter. Disconnect the SW lead from the RCR and check for continuity between the SW terminal on the RCR and a known good airframe ground. Remember that you will get resistance having to go through the coil inside the RCR, but you should have some continuity and not an open line. An open line more than likely means that the internal case ground is no longer good and the unit will need to be replaced or sent out for repairs. Compare this reading with the opposite "good side." If your resistance reading is higher on the "bad side" than the "good side," then you probably just need to clean the mounting bolts and pads by removing the RCR and cleaning all points of contact between the DC Contactor Box and the RCR, and then re-installing and re-checking. This should fix your problem, but if not, you will need to replace or repair the RCR.

ATA 24

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.

ATA 24

Electrical Performance Deterioration
Electrical gremlins have been teasing us since Benjamin Franklin hung that key on his kite string so long ago. With that in mind, I thought a quick refresher on the importance of proper grounding was in order. How many times has troubleshooting led us down the wrong path because of either a poor or non-existent grounding point? It is easy to forget the simple things when we are looking for power supply or component integrity, a blown fuse, or a popped circuit breaker. A simple ground connection overlooked can be a missed opportunity to look like a troubleshooting genius. Our venerable fleet of Westwind Aircraft has been in service now for quite sometime with the newest aircraft having more than 20 years of duty. With time, corrosion, dirt, vibration, and/or combinations thereof can play havoc on the overall performance of an electrical system. Anything that will increase the ground path resistance is a gremlin’s paint brush slowly eliminating the required bonding. It is important that electrical bonds are properly maintained in order to minimize radio interference due to precipitation of static electricity and to provide effective electrical grounding of the aircraft. Static discharge build-up, St. Elmo’s fire, and lightning strike damage potential are all affected by poor electrical bonding. Good electrical continuity is required between all wing panels, fuselage panels, doors, stabilizers, and flight controls. When inspecting the aircraft for continuity, the use of stainless steel test probes is recommended to ensure penetration of protective metal coatings and accurate resistance readings. It is also important to use calibrated testing equipment that is in good repair. Resistance of test leads and jumper cables must be subtracted from readings obtained to get the actual bonding resistances. For surfaces fitted with bonding straps, measure resistance across structures adjacent to the bond strap attachment points. Do not measure at either end of the strap at fasteners or terminal lugs. Visually check bonding jumpers to assure that they are not broken, frayed, or missing. If you’re new to the aircraft, you may not catch a missing jumper, but if the area looks to you like it should probably have one, check the manuals. The Aircraft Maintenance Manual (AMM) has the specific details for the correct resistance between each measurement point and the zero reference point; it will vary between bonded and un-bonded components and surfaces. Never leave it to memory. Always use the latest revision of the appropriate manual when working on an aircraft, as we continue to update and improve the manuals on a regular basis.

ATA 05/24

Emergency Battery Maintenance
The Emergency Gyro and Emergency Lighting Batteries are an important part of your Westwind’s operating systems. Chapter 5-25-00 of the 1124/1124A Westwind Maintenance Manual requires the batteries to be checked every 200 hours or 3 months. Many people consider this requirement to be a nuisance. Quite often we find the batteries have been run down or their inspection interval was ignored. Do not let this happen to you. Take the time to check your batteries. Try putting them in sync with your “A” Inspection, if possible. If you are tracking them by calendar time, be sure to give yourself enough turn time, as they require 16 hours to charge. Considering their importance in the event you should need them, you will be glad you took the time to ensure their airworthiness.

ATA 24

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.

ATA 24

Lead Acid Batteries
Supplemental Type Certificate (STC) SA1214SO installs Gill batteries into the 1124 aircraft. Please be aware that this STC DOES NOT include the 1124A models. We have found that most Flight Standards District Offices (FSDOs) will not field approve the installations, because there is no flight manual supplement approved for that installation. When you install the batteries into an 1124 model, Gill will provide a letter stating the sealed series batteries are a replacement for the vented type, and that the sump jar is no longer needed when the sealed series are installed. We can provide you a copy of the letter if you need it. As for Concorde batteries, no STC exists for them, but they do have Parts Manufacturer Approval (PMA). This is not an approval for installation, however, so ask your local FSDO if they will approve the installation. Most of the installations we have seen were done with Gill’s paperwork, which DOES NOT include the A models.