GTCP331 PROJECT BY WRITTEN BY E.L. GAMMILL

In the mid 1970's, AiResearch Manufacturing Company of Arizona initiated a study to create an Auxiliary Power Unit (APU) utilizing the basic power section of the production turboprop engine (TPE331). The concept was to direct drive a load compressor and gearbox to provide improved economical capabilities for future commercial aircraft.

Upon receipt of a Request for Proposal form both Boeing and MBB Airbus, Garrett prepared and submitted documents to both companies. The Model GTCP331-250 was proposed to meet the requirements of the Airbus A300/A310 aircraft. Garrett was the successful bidder and was awarded a contract in October, 1978. The Model GTCP331-200 was proposed to meet the requirements of the Boeing 757/767 aircraft. Garrett was the successful bidder and was awarded a contract in January, 1979.

During detail design of the basic APU, specifications for the full authority microprocessor APU Electronic Controller were released to our Tucson facility. Specifications for other parts and units that were to be defined and fabricated by outside sources were also issued I spent much time with Dave Edmonds reviewing, approving and signing detail drawings. Dave’s drafting table was very close to Director of Engineering Frank Roberts office. I had never had much contact with Roberts, just participating in the early morning stand -up reports of the previous days activities. These meetings occurred in Eddie Butler’s Development Assembly Department and always included department heads and some management people.

Since I was in the Air Turbine Motors and Constant Speed Drive Project and Roberts was in Prime Propulsion Project, we only listened to each other’s problems. But I soon learned, that he was a hard man and you had better be prepared when you went to his office. I observed grown men dash from his office with a very worried look and apparent wondering what they would do for an answer to problems. I stored this information, for I knew that my day would arrive!

In 1979 the fabrication of our development units, qualification units and the first flight test

systems for the two customers was initiated, under the supervision of Herb Johnson’s Development Fabrication Department. Herb assigned Bill Stockton and John McKweon to handle this task. Most of everything progressed well except, for a mistake I made in the adaptation of the TPE to our APU needs. I had always insisted on maintaining common parts between units. This became a bad mistake due to Quality Control and disposition of discrepant parts. It soon became evident that APU personnel were not FAA approved to disposition propulsion engine parts, even though the parts were to be utilized by the

APU Project.

This impacted our program when several hundred second stage compressor diffuser vanes from the casting vendor were rejected with minor discrepancies. The TPE Engineer had no requirement for the castings so he reject the lot. Unfortunately, we did not find out about this until it impacted our schedule. I had to quickly create new drawings/part numbers for identical parts! It remains an item that I will never understand, but that’s government work.

Our first design review, with airline and aircraft manufacture representatives in attendance, was held within in this period. After Bob Wells and Skip Stohlgren presented the program status and reviewed future plans, I had the task of presenting all of the features of the GTCP331 APU. The presentation was held in the 301 building second floor conference room. Each participant was provided a table with a complete set of half-size drawing and I utilized full size drawings on a portable bulletin board to present our design concepts. I am sure that the participants appreciated having the drawing to refer to and make notes as the presentation progressed. But it became a serious distraction, for every time I progressed to another drawing there was much shuffling of paper, noise and loss of attention. I gained a valuable lesson and learned the value of a View Graph presentation.

The first units were shipped to Boeing and Airbus in April 1981 as the Qualification test continued. This event rated an article in Engineering News which included this photograph.

June 1981 John Boppart become the Vice President of Engineering and Bob Von Flue replaced him as Director of Engineering. Bob Von Flue and I were friends from our Air Turbine Starter and Air Turbine Motor days.

August 4 the rollout of Boeing 767 was accomplished, many of our people were in attendance and the first flight of the 767 occurred in September 1981. The qualification testing was completed. The reports were issued and approved in October. The GTCP200/250 received FAA Certification December 4, 1981.

The Boeing 757 rollout occurred January 13, 1982 and first flight was in February. MBB A310 first flight occurred in March .

In May, I learned of the ill-treatment of my good friend Perry Sebring. I contacted Bob Orr who was on a one year consulting contract prior to his retirement. Bob knew Perry very well, for they were long time employees, both starting in the Los Angeles AiResearch facilities He was also of the old Garrett school of “employee treatment.” I spent much time in his office on the second floor of the 301 Building talking about the many projects to which Perry had contributed. I expressed my opinion that he was one of our best development engineers and deserved much better treatment. Bob promised to look into the situation, but cautioned me that he no longer had any influence in these matters.

Sometime later, I was called to his office and he told me that there was nothing he could do. To this day I do not know why Perry was treated this way. I entered this information into “things that will influence my retirement” log.

In July, the FAA Certification of the 767 was received, and things became so calm that Bob Wells left the program for a similar position with F109 propulsion engine project. 1982 was a very busy and successful year, in which the GTCP331 APU entered airline service with all three aircraft as a Category Essential APU meaning that the APU was legally qualified to supply electrical or pneumatic power necessary for maintaining safe operation of the aircraft on the ground or in flight. This classification/requirement permitted twin engine aircraft to operate over long oceanic routes. I continued working the GTCP331 Program as Production Engineering gradually assumed responsibility for the program and Skip Stohlgren transferred to the Israeli LAVI (Young Lion) fighter program.

The GTCP331 APU attained several significant advancements for Garrett gas turbine technology, namely:

1. First use at Garrett of a full authority digital electronic engine control. The ECU, manufactured by AiResearch-Torrance, controls all engine functions, provided automatic engine self-protection and contains a broad range of integrated built-in-test.
2. First use at Garrett of powdered metal turbine disk technology. The first stage turbine disk is fabricated from powdered metal Astroloy.
3. The first use in the gas turbine industry of a dual alloy turbine disk. The third stage turbine is fabricated from a powdered metal disk which is diffusion bonded bonded to a cast blade ring.
4. The first at Garrett of extensive internal acoustic treatment, both on the inlet and exhaust  

In September, the Boeing 767 entered airline service. After which I picked up a few additional tasks from Bob Von Flue. One was to join with Bill Shoup and try to secure the Northrup F-20 Secondary Power System. Bill had been working on this activity for some time. I joined in and found that the OEM had once again presented us with a “Blivet” (ten pounds of crap in a five pound bag)! A very limited and odd shaped cavity for the system. A wood and metal mockup was fabricated and furnished for Northrop’s aircraft mockup. The installation was very crowded. It was obvious that it would be a difficult task and the system would have maintenance and life problems.

The Boeing 757 entered airline service in January 1983 and I continued doing odd jobs for Bob von Flue. Some of these tasks were not pleasant because of “the big talkers/little doers” in charge, but I will not go into that. Late in 1983 I joined the LAVI program and that will be the next story.