Troubleshooting the Right Way

By Lt. Courtney Mason, VQ-1

As the EP-3E Aries approaches its sundown date, we have seen a rise in uncommon electrical malfunctions that require extensive systematic troubleshooting. More often than not, we replace multiple parts and never pinpoint the actual failure, attributing it to gremlins. During detachment to Kadena Air Base, Japan, our crew’s electrical gremlin was a mysterious FLAP ASYM light that illuminated when the aircraft boarding ladder was retracted on the deck.

The first time our crew faced the FLAP ASYM light, it illuminated as the flight station called for the ladder up to begin the Before Start Checklist. Maintenance was called and discovered the flap brake in the port wheel well had popped. They reset the flap asymmetry valve in the hydraulic service center and the port flap brake, and we tried again.

Again, during the Before Start Checklist, as the ladder was raised, the FLAP ASYM light illuminated. Maintenance conducted troubleshooting, noting only the starboard flap brake popped this time. The initial determination was to replace the flap brakes. As this was the second time, we began to develop another theory that somehow power for the ladder (Main DC/ BUS A) was tripping the flap asymmetry system (Main DC). After the flap brakes were replaced, the aircraft successfully taxied for a plane wash with the ladder raised – and without the FLAP ASYM light illuminating during the Before Start Checklist.

Believing the issue was fixed, we decided to take the aircraft for a mission flight the next day. When we began the Before Start Checklist, the FLAP ASYM light illuminated again, with the ladder down. Our flight engineers and maintenance department were determined to find the gremlin to avoid canceling additional missions.

The flight engineers decided to recreate the scenario to determine the exact point the FLAP ASYM light would illuminate during a normal preflight initially, but it was to no avail. They then used a multi-meter to test the current flowing through each line from the terminal to the asymmetry switches located in our hydraulic service center. Expecting to see 28-volt DC power, the normal rated DC power for the FLAP ASYM system, they were shocked to see 105-volt AC power. They systematically turned each electrical AC bus off to determine which one was supplying the power, and the culprit was Main AC Bus A.

With that knowledge, they worked through the Before Start Checklist to see if a particular step was powering the FLAP ASYM system with Bus A power. When the No. 1 boost pump was turned on, the flap asymmetry system went from 28-volt DC to 105-volt AC. The No. 1 boost pump and the flap asymmetry system circuitry flows through the same cannon plug in the port flap well. The cannon plug was completely corroded, and it was also the cause of the wrong power flow to the flap asymmetry system.

The P-3 community has experienced multiple fires of unknown origin due to this particular cannon plug. Through diligent and tireless systematic troubleshooting, our flight engineers and maintenance team prevented a situation which could have led to another hazard report, or worse.