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AH-64E: Keep Moisture Out of NIU

| July 6, 2020

A Soldier conducts maintenance on parts of an AH-64E Apache helicopter tail.
Photo by Spc. Alexander Holmes
 
The AH-64E Apache’s nitrogen inerting unit (NIU), NSN 1560-01-587-1028, is designed to reduce oxygen in the aircraft’s fuel cells to prevent combustion. That enhances its crashworthiness and ballistic tolerance.

But there’ve been some problems with the NIU. After analyzing some 785 units returned for upgrade, overhaul or repair, 31 percent were returned because of moisture damage. 

The NIU has a small amount of zeolite material to absorb atmospheric moisture from aircraft operation, but it isn’t designed to absorb moisture from direct sources, such as a power washer. If this kind of moisture gets inside the NIU, it can cause the NIU to immediately or prematurely fail for these reasons:
 
  • Moisture causes the motor and fan inside the NIU to corrode or rust, possibly causing the motor and fan to stop completely or produce a rattling noise.
     
  • Moisture deteriorates the zeolite material. It initially clumps, then breaks down into a fine dust that escapes the unit, causing a dusting effect in the aircraft.
     
  • Moisture in the NIU clogs the orifice in the pressure reducer, leading to failure.
To prevent moisture and other damage to the NIU, follow these steps if removing the NIU isn’t possible:

      1.  When cleaning and washing the aircraft ammunition bay, cover the NIU with barrier material to keep water out.

      2.   Cap all NIU openings with protective material when you’re cleaning or performing aircraft maintenance.

      3.  During refueling, make sure fuel doesn’t spray onto the NIU.

      4.  When ready for storage, keep the NIU in its original shipping container, wrapped in plastic, and with all caps in place.

 
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