Date: 201405
Local time of day: 1801-2400
Location: ZZZ.Airport, US
Light: Night
Aircraft: Citation V/Ultra/Encore (C560)
Operator: Fractional
Operating under: Part 91
Flight phase: Parked
Aircraft component: Air Conditioning and Pressurization Pack
Reporter organization: Fractional
Reporter function: Technician
Reporter qualification: Maintenance Powerplant; Maintenance Airframe
Human factors: Distraction; Time Pressure
Anomaly: Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Maintenance
When detected: Other During Maintenance
Result: Aircraft Aircraft Damaged; General Maintenance Action
Contributing factors: Aircraft; Equipment / Tooling; Human Factors; Procedure
Primary problem: Human Factors

Narrative: I was beginning to remove the R-134A Air Conditioning Unit from the aft equipment area of [aircraft] to prepare for a flight control cable inspection. We had several jobs at the time by other technicians. I was following the procedure from CE560 MM 21-52-00 says to disconnect battery and external power. I knew other techs were using power so I decided to prepare the air conditioner pallet for removal and leave the power disconnection for last. As I was loosing the mount bolts of the pallet (the forward left mount bolt is closest to the power relay) my socket had slipped off the bolt and made contact with the power relay positive terminal. This caused some arcing between the positive terminal and the pallet frame. Once power was secured and I was able to fully remove the air conditioning pallet I did find that both the ground and power terminal boots were torn. Also the power terminal boot was not installed correctly. The boot was rolled back from the terminal end exposing the connection.Most obvious suggestion is to follow MM procedures. The air conditioning pallet should be planned to be removed during a scheduled power off situation during the inspection. Once I had the pallet removed from the aircraft I could fully see where the arcing occurred. As I mentioned above the power terminal boot was not installed correctly. This however would not make a difference in my situation. The design of the power relay is such that both the power and ground terminals are exposed even with the boot properly installed. The concern that I have is that if a technician would be in the aft equipment area working on another system with power on they could easily drop a tool and make contact with the power relay of the air conditioning pallet.

Callback: Reporter stated the R-134A Air Conditioning (A/C) Unit is very similar to an automotive A/C unit with a condenser and evaporator. The R-134A is the type of refrigerant used in the Unit. The A/C is mounted to a metal pallet frame. The A/C is used for ground operations only and mounted in a very tight compartment; accessed through the forward bulkhead of a small aft baggage compartment in the lower fuselage; between both tail engines. The Power Relay; also known as the J-Box; is just forward of the Air Conditioning Unit. An electrical 'Power' cable connects from the Relay terminal to the A/C Unit. The rubber type boots that are installed over the terminals appear to be Original Equipment Manufacture (OEM); but the same boots do not adequately cover the ends of the terminal 'stud' through bolts and the ends remain exposed. His wrench socket had contacted one of the terminal studs and caused an arc. Reporter stated he realizes that had he followed the Job Card and removed electrical power from the aircraft prior to even working around the A/C Unit; instead of leaving power-on to allow other technicians to do their job; the arcing would not have occurred. But the concern he has; besides the inadequate design of the protective boots on the terminal studs; is the current exposure other technicians could be faced with when working in the same compartment when power-off is not called for on their work documents. He has not heard of any changes to the boot design from the Aircraft Manufacturer or from the Engineering Department.



Synopsis: An Aircraft Maintenance Technician (AMT) reports that protective boots currently installed over the R-134A Air Conditioning Unit Relay 'Positive' and 'Ground' terminal end studs are not adequate to protect technicians and tools from exposure to electrical power. The Air Conditioning Unit is mounted on the forward side of the aft equipment area of Cessna-560 aircraft.