CHIEF WARRANT OFFICER 5 CHRISTOPHER R. TENARO
Army Aviation Support Facility No. 2
Florida Army National Guard
Brooksville, Florida                            

Our unit conducted a field training exercise during a drill weekend, and I was given an assigned aircraft to fly. On the first day, we conducted a health indicator test, or HIT check, which resulted exactly in the middle of the range on the HIT card. Crew chiefs sometimes take care of the logbook, if allowed, and “run the numbers” during the HIT check. This means the helicopter is run up, the HIT procedure accomplished and engine indications are compared with the HIT log to verify the engines are working properly.

For the first flight, everything went as planned and we flew the aircraft without any problems. Later that afternoon, we finished flying and performed preventive maintenance daily. The next morning, we preflighted the aircraft for airworthiness and were ready to go. During the run-up, we conducted the HIT check. The crew chief said, “That was a good HIT check, sir. We’re ready to go.”

I didn’t verify the numbers, having flown the previous day with the same crew chief and same aircraft. I replied, “Roger,” and drove on. We completed our flight home, conducted PMD and readied the aircraft for the next mission.

As fate would have it, I was scheduled for the mission the next day. I asked the folks in operations to give me the same aircraft for that mission and they granted my wish. The next morning, we preflighted and were ready to go. Everything was the same except I got a new pilot and crew chief. We were a flight of two for this mission.

During our preflight mission planning, we noticed some early thunderstorms in the area that were slowly making their way toward the airfield. As we taxied out for the HIT check and departure, the rainstorms were quickly approaching. We deferred the HIT check until we reached our first destination, an airfield about 45 minutes away. What made my decision was the fact I had flown this aircraft for the past two days and the HIT check was fine on both occasions.

We arrived at our first destination and, before shutdown, did the HIT check. I started with the No. 1 engine, got the numbers and, while waiting for the crew chief to run them, went on to the No. 2 engine. Imagine my surprise when the crew chief said, “That was a bad HIT check, sir, on the No. 1 engine.”

“Are you sure?” I asked. He said he was sure, so I asked him to read the numbers back to me. We were over on the HIT check by 3 degrees. I decided we would finish the No. 2 engine and then we’d recheck No. 1. We did the HIT check again and it barely passed by 1 degree. To top it off, the next thing I heard from the crew chief was, “It looks like it failed yesterday too.”

Now I’m truly in disbelief. I shut down the aircraft and grabbed the logbook to look at the HIT check. Sure enough, the numbers the crew chief wrote down the day before showed the HIT check was over by 2 degrees.

I don’t know why he said the numbers were good. What bothered me more was that I deviated from my normal procedure of having the crew chief read back all the numbers to confirm the HIT check. We had a 15-degree difference from the HIT check I did three days ago. Now what? We got the HIT to pass within limits on the second try.

After a brief discussion, we decided to drive on with the mission since it was a short one. The only problem I had was the anxiety of a 15-degree rise in the HIT check. We completed the mission and returned home. Upon arriving home, I asked the crew chief to write up the HIT check as being within 5 degrees of failing. I then went and had a talk with the maintenance officer and relayed my concerns.

The next morning while going about my daily business, one of the mechanics came to me and said, “You have to come check this out.” I followed him to the hangar, where he showed me the answer to the HIT check mystery. The bearing in the inlet particle separator blower had failed, stripping the shaft that goes into the accessory gearbox. This failure manifested itself in the high HIT check.

The moral of the story is to pay attention to the HIT check and verify the numbers. Take a look at the previous checks and look for a trend or a deviation from the trend. One more item of concern: Remember the pilot in command of an aircraft is directly responsible for the operation of the aircraft and the safety of all personnel onboard.