Man Overboard Indicator (MOBI) Malfunctions & Testing

By LT Steven Scoville

Throughout April 2017, Carrier Air Wing (CVW) 11 was embarked on USS Nimitz (CVN 68) for Composite Training Unit Exercise (COMPTUEX) prior to our 2017 deployment. It was the last night of the exercise, so the air wing was doing a pack-out, which started much later than anticipated; causing everyone to feel rushed. Our team needed to get our entire squadron packed up and ready to debark from the ship in San Diego, California, early the next morning.

As we proceeded with the job at hand, a Sailor had confused a bag full of float coats for a bag of trash. Unfortunately, going against better judgment the Sailor had decided to throw the bag overboard, which meant that five of Strike Fighter Squadron (VFA) 154’s float coats ended up in the water that night. This of course resulted in the activation of Man Overboard Indicators (MOBI), leading to a long search for who had gone overboard that ended in the discovery that all Sailors were accounted for and that the bag of float coats containing the MOBIs had been thrown overboard. Once the float coats had been retrieved, we realized that only two of the five MOBIs inside the float coats had actually transmitted a signal; a situation that could be extremely dangerous in the event of an actual man-overboard.

Once we arrived back to Naval Air Station Lemoore, California, our safety department began an investigation into the malfunctions and inspected all the command’s MOBIs. Our safety petty officer found that we had two separate manuals from BriarTek©, the MOBI manufacturer. Both manuals described the testing process of the battery and transmitter of the TX-104 model MOBI, but they each had conflicting statements on how to properly test the devices. The first manual stated that you place the tip of the antenna on the manual activation/deactivation recess and hold it there for a minimum of three seconds. This would cause the LED on the front of the device to illuminate with a solid light. The second manual stated that after doing the same steps, the LED would flash rapidly. We contacted the manufacturer for clarification on the correct way to test the MOBIs. During discussions with BriarTek©, we discovered that both manuals were actually incorrect, and that neither manual included the correct steps for testing the MOBI transmitters.

According to the manufacturer, the proper test of the battery is to place the tip of antenna on the manual activation/deactivation recess for a minimum of three seconds. To test transmitter activation, you must either connect the two screws on each side of the device with a metal object or submerge the device in salt water. We found a paperclip worked well to connect the two screws. Either method of testing will result in a rapidly flashing light. After testing the three MOBIs that malfunctioned in the Pacific Ocean, we determined that the transmitters were faulty. After a subsequent command wide inspection, we found 25 TX-104s and 15 TX-103s (previous model) that did not properly work. The TX-103 is a completely different model that has a simple on/off switch to test both the battery and transmitter activation. The 15 malfunctioning TX-103s were due to bad batteries, not a faulty transmitter. Of the 25 TX-104 models that did not function, four malfunctioned due to failed batteries and 21 had faulty transmitters. Even though there were several that only failed the battery test, there is still a serious safety concern with these devices. Overall, our command had a 24 percent MOBI failure rate a total of 40 of 160 devices.

During the investigation into our MOBI inventory, we found two additional key discrepancies that could cause the devices to not function properly. The first issue discovered was improper antenna routing. The manuals for both TX-103 and TX-104 MOBI models state that the transmitter must be worn so that when the water sensors are under water and wet, the antenna remains above the water surface. When installed in a float coat, the antenna should be routed up and over the shoulder to ensure that part of the antenna will be above water while the person is floating. The second discrepancy was slightly more difficult to detect. If the battery door is overtightened, the MOBI will not transmit. Our team discovered the battery door should be tightened to 45 inches per ounce of torque; even though the manufacturer’s recommendation is to simply hand tighten the door. To mitigate this potential malfunction after battery replacement, always test the transmitter for proper functionality.

To ensure the safety of personnel and promote an effective safety culture, processes should be established to ensure equipment is always maintained and in good working order. Our team recommends that every command equipped with MOBIs in their inventory test the batteries and functionality of their transmitters, and verify the antennas are properly routed over the shoulder.

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