My introduction to the CH-47D Chinook.

From the time I started thinking about becoming an Army pilot, I’d had a goal to fly the CH-47. Partially because I knew what I didn’t want to do and that was fly an Attack Helicopter.  There are four types of Army helicopters:

•          AH – Attack Helicopters (Combat Arms, front line, you shoot and get shot at)
•          OH – Observation Helicopters (Combat Arms, Front Line, you tell AHs where to shoot)
•          UH -  Utility Helicopters (Combat Support, near front line, you haul troops mostly)
•          CH – Cargo Helicopters (Combat Service Support, you haul it toward the front lines)

I preferred the cargo helicopter mission. Generally, you were not in the front of the battle and usually in the safer rear areas. I liked to look after my own hide, you could say without question.

The main thing I liked about the Chinook was it was powerful. I also liked the twin rotor design and I just thought it was a pretty cool aircraft. Some of the drawbacks of the CH-47 are that it is a very complicated aircraft with as many moving parts; 2 Engines, 5 Transmissions, 9 drive shaft sections, 2 rotor systems, 2 flight control systems and 1 utility hydraulic system. There was a lot to know and a lot to learn. The D model Chinook, in almost all cases, were converted A, B or C model Chinooks re-worked in Philadelphia at the Boeing plant.  The airframes for most of these aircraft were originally built between 1967 and 1969. The ones I trained in were converted to D models in 1982.

A little background on the Chinook. The A model began service in 1962 and had a max payload of 4 tons. There were some mid-model upgrades and it ended up with a capacity of 10,000 lbs. after a major engine upgrade. The B model was an interim solution while the C model was developed and included the better engines and many airframe improvements.  The C model was the most built version and it had 3 sub-versions based on engine variants and control improvements. All of these variants had major drawback, a lack of redundancy in the flight control systems.

The D model Chinook took all the best parts of the previous designs and added in a slew of new items. Upgraded engines, transmissions and rotor systems increased the maximum payload to around 25,000 lbs. A redundant flight control system allowed for increased safety in design and the addition of devices called power transfer units (PTUs) allowed for pressurization of the flight controls using the third utility hydraulic system for even further safety. This also gave the ability to test the flight controls without running the engines for the first time. A computerized and redundant Advanced Flight Control System (AFCS) allowed for must easier control of the aircraft and the addition of forward and aft cargo hooks in addition to the original center hook allowed for more complex, larger load configurations that had increased stability in forward flight. For this that are curious, you can check out Wikipedia.

My training started in the Spring of 1989. My class consisted of seven students and four instructor pilots. As usual, students were paired two to an instructor and that left one student for the fourth instructor. I don’t remember how it came about, Another student and I were originally paired with a CW3 instructor pilot, but before training started things changed and I ended up the odd student assigned to the detachment Commander. He was a captain and was straight out of CH-47D Methods of Instruction (MOI) flight instructor training. Another interesting item was that this class contained new aviators like myself and experienced aviators that were qualifying in a new aircraft. This was my first realization that pilots with 20 years’ experience could be changing aircraft qualifications (From UH-1 to CH-47 for example) and it created a different classroom dynamic working with other experienced pilots.

Like all flight training, the day was split into an academic portion and a practical skills (flying) portion. The academics were instructed by civilian instructors who had decades of experience in Army aviation and they were quite well versed in the CH-47D. We spent many days learning about the various systems in the aircraft and the “Utility Hydraulics” class was enjoyable because the instructor for that class would often get super excited and trip over his words. Utility Hydraulics one day became “Futility Hydrastics”. One of our classmates was an amateur cartoonist and he made a caricature with that title and gave it to that instructor who retired soon after our class.

Most of my memories are from the flight line and the ready room. Each day at the flight line started the same way they had in flight school with table talk with your instructor on the topic(s) of his choice. Then you pre-flighted your assigned aircraft and then you and your stick buddy took turns training with the instructor or riding in the jump seat while the other trained.

Since I was one to one with my instructor, this meant that I had the entire first period to sit with my instructor and talk about the topic of the day. This resulted in diagrams of the flight and utility hydraulic systems drawn from memory, discussing the various pumps and pressures associated with them, hours upon hours of discussing emergency procedures and me pretty much being stuffed with information like a Strasbourg goose.

As a result of all of this intense study of the aircraft training manual (TM 1-1520-240-10) I achieved my first nickname from my fellow students. It had become almost instantly obvious to everyone that I was getting pounded severely about the head and shoulders with the manual. I was quickly becoming a CH-47D manual subject matter expert. One day before the instructors came into the briefing room, one of the students behind me asked his stick buddy a question and the buddy replied “Why don’t you ask Don? He is the walking -10!” as re referred to my apparent encyclopedic knowledge of the manual.

I can honestly say that every instructor pilot I flew with in the army was a good instructor and in the same breath I can say that some are exceptional. My CH47D instructor was one of the better ones. This was likely for 3 reasons:

•          He was fresh out of MOI and had just been schooled in the proper manner to teach
•          He was very personable and taught by example, so he was a very technically proficient pilot
•          He actually wanted me to learn about the helicopter and know everything about it.

One of the most important things that my instructor taught me (I wish I could remember names) was the proper way to make a landing approach with a heavy load. Cargo helicopters get that name because you spend a lot of time carrying heavy stuff from one location to another. Most of this is done as an external load suspended from one or more of the three cargo hooks on the D-model Chinook. Since we didn’t have manpower to practice internal loads, during all cargo training was done with external practice loads. These practice loads were blocks of concrete with hook eyes embedded in them and my instructor’s favorite load weighted a tad bit over 18,000 lbs.

Hauling around nine tons of cargo is pretty impressive but you have to respect that weight and be ready to deal with it when bad things happen. My greatest error in training was having too much faith in the aircraft and not thinking about what could go wrong and being prepared to deal with it. I had a series of great CH-47 instructors who got me in the correct mind set about always being prepared for the “What If?” scenario, but one from the transition stands out in my mind.

A quick bit on helicopter aerodynamics again, sorry. A slow or stationary hover requires more power than forward flight because you are flying in turbulent air and it doesn’t produce as much lift as undisturbed (clear) air. Even with the 7500 shaft horsepower available in a D-Model you can run out of power especially with a heavy load. In the configuration we were using for external loads, you could hover with the 18k block hanging below the aircraft 10 feet off the ground at about 86% on the torque meter. I had developed a bad habit of using nearly 100% power to stop an approach and come to a hover with a heavy load and my instructor decided to break me of that habit.

What we did, was at the beginning of the period, we went out to the remote training (RT) field where the big block was located and picked that sucker up. During the before takeoff check I noted we were using 86% torque to hover with the load and my instructor told me that for the rest of the day, I could pull no more than 86% torque during any maneuver. This wasn’t important to any practical extent until something goes wrong while you are flying and carrying a heavy load. You can (and I have) lose an engine, or lose partial power in an engine during flight. Empty, it is not big deal, a Chinook can easily fly on one engine. (Hence the running joke in the dual engine helicopter community that all single engine helicopters are a “Constant State of Emergency” aircraft, since we only fly with one engine during a state of emergency). When you were carrying a load close to the weight of the helicopter itself, things got complicated when you lost power in or lost one engine altogether.

From a hover, you could takeoff with no additional power by simply starting to move forward slowly and then slowly increasing your airspeed. Hovering forward takes no additional power if you were smooth with your control application. There was a small control on the very top of the cyclic that let you adjust the trim pressure in all four directions and was really handy for starting to move forward in your hover. As you reached effective translational lift (about 30 knots in a Chinook) you moved into clear air and lift improved and you started to climb. As you climbed, you adjusted to your best climb airspeed (usually around 70 knots) until you got to your desired altitude, then you accelerated to cruise airspeed (usually 90 knots) then reduced power to maintain the 90 knots and you desired altitude.

Making your approach was just the opposite. You reduced power  and speed to 70 knots, and started a decent between 300 and 500 feet per minute (FPM). There was a vertical speed indicator (VSI) to help you with that. With a heavy load 300 FPM was preferred. As you descended from traffic pattern altitude (600 feet AGL) toward 200 feet AGL you continued to slow your airspeed from 70 to 40 knots and this required you to slowly add power while slowing the aircraft. As you descended through 200 ft. AGL you again decelerated more and added more power. The transition through ELT going from forward flight to a hover was the most critical point and when done with finesse you could do it with the exact hover power you used to take off. This finesse was what I practiced all period that day. I think I made 20 approaches and the last five or so were done to his standards. (Yay for me!)

This entire saga has a point, (fast forward about 5 years into the future). It was about 8AM eastern time and I picked up an 18,000 lb. John Deere light bulldozer for a mission to deliver the load to Fort Stewart GA, from Beaufort Naval Air Station (NAS) in Beaufort SC. We were flying tail number 85-24326 the “Lucky Dog” crewed by SSG Darrell “Smitty” Smith. I was the Pilot-in-Command and my boss on the ground and my platoon leader (1LT) was my co-pilot. This was always an interesting dynamic because with the exception of when we were flying together, he was my boss. But when flight operations were in motion, I was the aircraft commander and made all the decisions on the aircraft.

We’d originally picked up a different load, but Smitty didn’t like the way it was rigged and rejected it. So we put it down and opted for the next load in line, the bulldozer. Smitty was pleased with the rig on this load and we took off for Fort Stewart. The mission was originally planned as a NVG mission the night before but our aircraft had a N2 control box failure on the #2 engine and we were down during the mission. (The N2 control box controls the power turbine section of the engine and allows you to increase and decrease power to the engines.) We completed repairs on the helicopter by 9PM and we were told to wait till morning due to crew rest and fog that was setting in at the Landing Zone (LZ) at the fort. So we took off with our newly repaired engine control and external load, we climbed up to 1500 feet for the 40+ mile flight to the LZ. We’d leveled off and completed our cruise checks and I had just called the Beaufort tower to tell them we were clear of the control zone and were frequency changing to out unit internal frequency when things got exciting. The Master Caution Light illuminated and we had a warning on the #1 engine transmission that a chip had been detected in the oil.

Each engine on a Ch-47 had a 90-degree gearbox (transmission) on the inlet (front) of the engine that transfered the power from the engine shaft running parallel to the airframe to a shaft that went into the aft pylon to the combining transmission. The combining transmission did exactly that, combined the power of both engines and sent power to the front and rear rotors using drive shafts. This warning indicated that there might be a mechanical failure in the gearbox. If severe enough, the failure could cause the casing to crack open and dump about 15 quarts of oil into the inlet of the engine. This event would just be plain bad news. You see the gearbox (nosebox) was surrounded by the air inlet for the engine and incredible amounts of air were being continuously drawn into the compressor section of the turbine (call the N1 section), where it is compressed through seven stages of compressor blades until it got to the combustion chamber. Oil flowing into this part of the engine would most likely have resulted in a large explosion that would have destroyed the aircraft. The emergency procedure for this warning light is:

“If the engine is required for flight, land as soon as possible.”

No doubt, no decision to make except where could I land RIGHT NOW!

I was flying the aircraft when the Master Caution illuminated and I did three things:

•          I called Smitty on the intercom and said “Chief Check #1 for Fire!”
•          I made a MayDay Call to Beaufort NAS control tower: “MAYDAY MAYDAY MAYDAY. Army Copter 24326 making an emergency landing 15 miles west of Beaufort NAS #1 Engine Transmission Chip Detector illuminated!”
•          I spotted a field to my left front that was a Christmas tree farm.

The entire process from the Master Caution light coming on until the load was on the ground was less than a minute. It was the longest minute of my life. Smitty replied that there was no fire on #1 and he had tried to reset the chip detector from his maintenance panel. (The chip detector will come on from the slightest bit of metal bridging the contacts, the maintenance panel has a reset switch that sends a low voltage charge through the detector and if the metal is a fine metal burr smaller than a human hair it will burn it off and clear the detector.) Even if reset, you still had to land the helicopter, it just gave you a better idea if there was really something bad going on. The detector not resetting was not a good sign.

My co-pilot reached up to take the engine off-line (This is what we always did in training as we never trained for this with an actual load) and I suppose I was a bit sharp with him and I told him to get his hand off that control, "WE NEED THAT!" I pointed to the #1 Engine Gas Temperature gauge and told him to let me know if that went into the red (a normally functioning engine is in the green band, under very heavy load it might go into the yellow. If it went into the red while this was going on, then the transmission case had likely cracked and oil was going into the engine.

I told Smitty: “The hook is hot! You are authorized to release the load if needed.” Letting him know that the power to the cargo hook was on (It is normally in the “SAFE” position during cruise flight) and I told him he was authorized to punch the load if he deemed it was necessary. Punching a load (dropping it from altitude) was an absolute last resort and only done to keep the aircraft from crashing. If that engine or transmission had a catastrophic failure Smitty would have been the first to know. I didn’t want the few seconds it would take for him to tell me to delay any emergence action he needed to take. I knew he wouldn’t punch the load unless there was no way to avoid it, as punching the load caused severe airframe damage and would ground the aircraft for over a month. Smitty replied “Roger, the hook is hot!”

Maybe 20 seconds had elapsed now and I now executed the exact procedure I was taught back at Fort Rucker. I’d started a slow descent and deceleration as soon as I’d spotted the field (We were flying over forest and it was a solid canopy so landing exactly where we were at was out of the question.) Most of the trees in the Christmas Tree farm were a year or two old maybe three feet tall. Slowly and easily, I established our approach angle and had slowed to where I could just feel the shudder of approaching the ETL transition to hover. About 100 ft. from the field and 100 ft. above the ground I started the transition to hover and set the load down with the torque meter never exceeding 82%. As soon as the slings were slack Smitty released the load and it was confirmed by the hook open lights on the Master Caution panel. As we hovered forward I had my co-pilot take the #1 engine off line and shut it down. Then I landed using the #2 engine alone. I radioed to Beaufort Tower that we’d landed safely and gave our coordinates so we could be located.

After we shut down the aircraft, Smitty opened the maintenance platform and pulled the chip detector out of the transmission oil sump. I’d heard stories of chips in engines and transmissions big enough to have serial numbers on them and this in a way validated some of them. All major parts of an aviation transmission are serial numbered so that their source can be tracked. This chip had a complete gear tooth and 3 digits of a serial number on it, so it was fairly conclusive that something bad could have really happened.

Less than an hour later, another aircraft from my unit arrived and we were lucky enough to have a Maintenance Test Pilot flying as the co-pilot on that bird. We discussed the situation and determined that we could swap co-pilots so the LT would now fly with the newly arrived aircraft and that they would take the dozer to its destination, while the Maintenance Test Pilot was now the PIC for “The Lucky Dog” and I was his co-pilot. As a MTP he could fly the helicopter back to Beaufort NAS in Test Flight Status using the #2 engine alone. We made the flight back to Beaufort without incident.

It turned out a week later after the #1 engine transmission had been replaced and flight tested, the N1 control box on the #2 engine failed.  The N1 control box is what allows the pilot to start/stop the engine, and set it for ground idle or flight. We’d just started both engines to fly back to the unit at Fort Stewart and when I took the Engine Control Levers from the ground position to flight, only the #1 engine responded, the #2 stayed in ground. So we aborted the flight and when I went to shut down #1 engine stopped normally, but I had to use the Fire Pull Handle to manually shut off the fuel to the #2 engine to shut it down. So during the emergency landing and the single engine flight back to Beaufort, the engine we were depending on had a failing component and I shudder to think what could have occurred if the #2 engine had failed while we were in flight.

Good thing we were flying in the “Lucky Dog” that day, eh?