Check out R/TRU.

Mechanics and pilots, your AH-64D's regulated transformer rectifier unit (R/TRU), NSN 6120-01-440-5711, can lose electrical power and you won't notice it.

You'll get an indication that an R/TRU has failed because of thermal overload, but not when there's a lost ground or other electrical problem.

The two R/TRUs provide primary DC electrical power for your bird. Since the maintenance data recorder (MDR) doesn't alert you to a R/TRU electrical failure, the bird could have a complete failure of primary DC electrical power if one is already out and the other one goes out in flight.

Some aircraft have flown for hours when only one R/TRU was working and that can put you and your bird in harm's way.

AMCOM message AH-64-05-ASAM-05 tells you to inspect both R/TRUs within 30 days and implement a 125-hour inspection to perform an R/TRU voltage check and to check the terminal connections for condition and security.

When you power up your bird, check the back of the R/TRU on both sides of the forward transmission bay area. Make sure the fan is blowing air on each one and there's air flow before you take off.

If an R/TRU is not working, call your AVUM shop and they will test it following the ASAM instructions to make sure your aircraft stays mission ready.