This entry was interesting:

The question was asked if a private could work on a helicopter and completely tear it down to fix it in the field. Seeing as my primary MOS was aircraft engine mechanic I can answer that one.

First of all a private , rank is E-1 , would not be working on anything because a soldier has to go through all of their training and then schools before they got assigned to a unit. By the time they got into the field to work on anything their rank would now normally be at least an E-4 which is normally a specialist rank. Next any aircraft work is done in staged levels.
That means that the crew chief that is responsible for an individual aircraft would check fluid levels and clean filters plus check for any metal shards that get attracted to the magnetic chip detector plugs on the aircraft. These were installed in any area that had oil flowing through it.
The type and amount of metal gave you a heads up as to what was wearing out in your aircraft. If to much metal got into certain fluids it would generate an alarm for the crew to land immediately before the aircraft components failed. If it was the wrong component and it failed in flight the aircraft just might attain the glide ratio of a crowbar which is 10 feet down for every foot forward. It is called Preventive maintenance and has to be done every 25 hours of operational flight time. The crew chief looked at all of the components that make up his entire aircraft and made sure they all worked right.

Every 100 hours of operational flight time the aircraft has to go to a higher level of maintenance for two very important reasons. One is contamination of critical parts in the field and the other is tools. I worked at that level but under an odd set of circumstances. Normaly that level is called Direct support and you could think of it as having to go to the local garage. They were a separate unit and would support all of the helicopter units in a geographic area of Vietnam. That system is the same all over the world. Think of it as leaving your car at the dealership and trusting them to do the work on your vehicle. At this level of support people were very specialized and normally worked only on certain items on an aircraft. An engine man would only work on engines while a power train person did the transmission and any connecting power transfer tubes. Another person worked on the tail rotors and the main blades. Others worked on Avionics and others on Armament. Another group did all the sheet metal work to repair any normal wear or bullet holes.

As I said before I was supposed to only work on engines. In my case the Army ran a special test program that I was transferred to and they took one person from each specific job type and every direct support unit in Vietnam and put them into D troop 3/5 Cav. They then placed civilians to do the same job with A company of the 9th Av. This was to improve the availability of aircraft plus see if the Army people could do a better job than the civilians. Think of it as going out to your garage to work on your car and the local dealership had their mechanic drop in to help you. In this instance I did my job plus helped all of the other guys do their job. With only one guy for each specific job plus 27 aircraft to keep flying it was hard to keep up. If I finished my work then I helped the other guys with their work and we did that for a minimum of 14 hours a day 7 days a week.
Because we were now in an active unit rather than the garage that meant I also flew as a door gunner and had to go with the aircraft if we did any missions that took us away from our main base for 2 or more days. While a specific aircraft was being worked on the crewchief for that aircraft was usually there with us to check , verify and look over everything we did.
They needed to know what changes there were and what needed to be updated for the pilots that flew that aircraft.

Now while I could pull off the "hotend" of the engine to do all the required checks even I was limited as to what I could do because of equipment and some critical calculations. Just to pull the hotend , which was the back third of an engine I had to use a 10 foot long fence post on the end of 3/4 inch ratchet to break the heat sealed torque of the main bolt. It was put on with 100 foot pounds of torque. To break down the rest of the components of an engine a person would need several special benches just to hold the parts so they did not move and use hydraulic wrenches to separate them. At that point the engine was sent to a general support unit that was stationed on a ship in Vung Tau harbor where they did more technical work. Even their people had limitations and at a certain point the engines were sent to the states to be overhauled. The original engine on the aircraft was then replaced with either a new or remanufactured engine. For a long time the engines had to be replaced about every 1200 hours just to be checked out for normal wear. The reality is in a combat situation neither aircraft or engines last that long before being shot up or down. For the rest of the aircraft we also had areas that we could not work on like the main frame of an aircraft. If a bullet or a hard landing bent a floor spar , think of that as a support beam in a house , on an aircraft it had to be sent out to a GS level group because again they had the specialized equipment.