Chronology of the ATF3

By: John C. Evans

Last Revision December 2, 2009

PRELIMINARY (Living Document)

NOTE: Information in this Chronology was compiled from memory by John C. Evans. The "dates" and some of the "facts" are not totally accurate. If you have information or corrections please contact me at

    To the best of my memory this is a chronology of the ATF3 program. All information prior to my hire-in on December 2, 1968 should be considered hearsay and may be very inaccurate.

    For a description of the original ATF3 engine configuration see link: Aviation Week Article

Around 1966

    The ATF3 engine was designed by Anthony A. Dupont as a college senior engineering project.


    Shortly thereafter, it was sold to Airesearch Manufacturing Company of California and Tony Dupont was hired on as the program manager.


    Six sets of hardware ordered for initial engine development testing.


    The original six development ATF3 engines were not complete engines. They lacked lubrication systems, electrical systems, and surge control systems. These systems were built into the test cell as test equipment. These engines could be best described as design concept and gas path demonstrator rigs. The engines would be identified at SN #1 through SN #6. Only five of these engines, serial number 1 through 5, were ever built and tested.  Engine #6 was used as spare parts to support the other five engines.  Only engines 4 and 5 were built and tested more than once. Numerous design changes were incorporated into these engines over their active years. The 6th set of hardware was used to support the first five development engines.


    Component testing begins at Site A, Torrance California.


    Development engine #1 assembled and sent to test in late 1968.


    Development engine #2 assembled and sent to test in late 1968 & early 1969.


    In late 1968 Site B was completed, and in January 1969 the ATF3 program was moved into its new home.


    Development engine #3 through #5 were assembled and tested in 1969 through 1971, and beyond.


    In 1971 the ATF3 engine was completely redesigned, and was the first design to have a complete lubrication system. The low-pressure compressor had Titanium blades and disks with inner shrouded titanium stators 1 through 4 and a cantilevered 5th stator. The gearbox and oil tank were combined with airframe mounted air-oil coolers.


    These engines were the first fully functional engines and would be designated as engine SN 7 through SN 17.

    Engines SN #19, 20, 29, & 22 were the first four engines assembled in Phoenix Development Assembly by Avery Gauger and Michael McCoy with several Site B employes.  The author was working in the tooling department at Site B at the time and was in phoenix to familiarize the Phoenix staff with tooling and build procedures.  Engine SN 21 was later certified as an ATF3-6A-3C and would be used on the Garrett Falcon Jet F20C Flying Test Bed at the #2 position (right side) as a pusher engine, and for any development flight testing required.


    In 1971 a financial decision was made to de-scale the ATF3 engine program in favor of the TFE731 engine, and half of the ATF3 staff was laid off.


    In 1971 Teledyne-Ryan Aircraft Company was selected for a remote piloted vehicle competition with Boeing-GE. Teledyne-Ryan selected the ATF3 engine rated at 4050 LB FN as their power plant. The Teledyne-Ryan Compass-Cope aircraft was designated YQM-98A. The engines used on this aircraft would be similar to development engine #17 and were designated as XF104-GA100. These engines were considered experimental prototypes and identified with serial numbers P-1, P-2, and P-3. During flight testing this aircraft turned out to be very stealthy. If the U-2 high altitude chase plane lost visual contact he couldn't pick up the aircraft with either radar or IR sensors. ATC would have to fly him out and Radar vector him back at the YQM-98A altitude for a visual reacquisition. During the fly-off the YQM-98A never missed a flight. To this day the YQM-98A still holds altitude and endurance records for 5,000 pound thrust class engines set during the competition. Makes you wonder why Teledyne-Ryan and Airesearch lost the competition doesn't it?


    The engines were returned to Garrett after completion of the competition and destroyed during a Site B cleanup in the early 1990's over the objection of several ATF3 personnel. One of the YQM-98A airframes less engine is currently on display at Pima Air Museum located next to Davis-Monthan Air Base east of Tucson, AZ. The last time I saw it, it was parked next to a SR-71 and D-20 Drone display just west of the Museum entrance.


    In the 1970's Northrop Aircraft Company was selected for a "black program" to develop an aircraft in the 30,000 pound weight class. This program was very secretive with only a hand-full of people ever having any specific knowledge and they weren't talking. I was not one of the privileged few but have obtained some "hearsay knowledge" over the years. Airesearch Manufacturing Company of California was selected to provide ATF3 engines rated at approximately 5000 LB FN as their power plant. Northrop's aircraft program was known as Tacit Blue. I have no knowledge of the aircraft's actual name (if it ever had one). Not naming a product is the best way to maintain security. The engines used on this aircraft were similar to early "Certifiable ATF3 engines (SN 21104 to 21127)". Five of these engines were produced, then their serial numbers were changed and build records "sanitized", and then the engines and records disappeared into a black hole for many years. Occasionally instrumented parts would arrive at night on a red and tan Ford Ranger pickup truck for testing, then disappear the same way. The drivers were dressed in bib overalls, and "didn't know nothing".


    The "black engines" resurfaced in the U.S. Coast Guard inventory in the late 1980's, as SN's P-19101, P-19102, P-19103, P-19104, and P-19105. Garrett was approached by the U.S. Coast Guard to inspect and certify these engines hardware as suitable for spares to support their fleet of HU-25A aircraft. Disassembly and inspection of the engines and review of the engine paperwork indicated 90+% of the parts conformed to current engines operated by the U.S. Coast Guard and were suitable for use only on Military Aircraft. The U.S. Coast Guard was informed that it was financially feasible to convert these engines to ATF3-6-2C/4C for use as spares. I believe three of these engines were converted, SN's P-19103, P-19102, and P-19103, and the remaining two engines disassembled for use by the U.S. Coast Guard as spare modules and parts.


    The ATF3 engine was completely redesigned again in 1975 resulting in the first truly maintainable version of the engine. This engine was designed as a 5050 LB FN engine but exceeded the specification weight which resulted in a negotiated penalty 7.7% cold day thrust increase to 5440 LB FN for certification. The development engines would later be designated at SN 19 through SN 33.


    The ATF3 engine was selected by Dassault Aviation for an upgraded Falcon-20F aircraft. This aircraft would be designated Falcon-20G for the U.S. Coast Guard Guardian application (41 aircraft), and Falcon 20H for the French Navy Gardian (French Spelling) aircraft (5 aircraft) and commercial Falcon-200 aircraft (34 aircraft). The initial flight test aircraft would be a modified Falcon-20F-SN397. At the end of the program this aircraft would be upgraded by AMD (Aviation Marcel Dassault) to the final Falcon-200 aircraft.


    Three initial flight test engines were delivered to AMD for the flight test aircraft, a modified Falcon 20F SN 397. These engines designated SN C-101, C-102, and C-103 were an interim design and would incorporate numerous major improvements prior to certification and production.


    The following Paragraph updated thanks to inputs from USCG CPO (Chief Petty Officer) Chris Wills and ATF3 Program Manager (and retired USCG CPO) Charles “Buddy” Criminale.  CPO Chris Wills was assigned to APO (Aircraft Program Office) Little Rock AR as one of the QA (Quality Assurance Inspectors) on the assembly line for the Coast Guard.  Chris was assigned to this duty for the entire production run of the UACG HU-25 aircraft, and participated in most of the acceptance as well.

    The U.S. Coast Guard Guardian (Falcon 20G) aircraft were manufactured and flight acceptance tested at AMD in Bordeaux France as AMD Falcon Jet Model 20 F’s, the GE CF700 Engines and APU’s removed and the airframe engine pylons replaced with ATF3 compatible pylons.  The aircraft airframes were then disassembled and the airframe parts were loaded aboard a stretched version of a C-130 and delivered to Falcon Jet Aircraft Corporation in Little Rock, Arkansas.  The wings and Empenage were stored at Falcon Jet Little Rock AK and the Fuselage shipped on a flatbed truck to Grumman at LaGuardia for modifications.  Grumman performed five HU-25 specific modifications on the Falcon Jet Airframe,  The modifications included two large rectangular Search windows just aft of the entry door, a drop hatch in the floor just forward of the wing root, a spoiler door for the drop hatch, a drop rail located in the cabin above the drop hatch, and a camera window and door.  Falcon Jet Aircraft were then re-assembled as Falcon Jet (F20G) airframes with HU-25 modifications. Two Garrett ATF3-6-2C engines and a Garrett Auxiliary Power Unit (APU) were installed and the aircraft were completed, flight acceptance tested and prepared for delivery to the United States Coast Guard.  All 41 HU25 aircraft were delivered from Falcon Jet Little Rock AR to the U.S. Coast Guard between February 1982 and May 1984.


    In all five different models of the ATF3 engine were produced for the Military and Commercial markets. One model the XF104-GA-100 was used on the Teledyne-Ryan Compass-Cope YQM98-A aircraft. Two of these engine models with 36 blade fans and Aluminum Accessory Gearboxes were designated ATF3-6-2C and ATF3-6-4C were used on the U.S. Coast Guard Guardian HU25A aircraft. One of these engine models with a 30 blade fan and Aluminum Accessory Gearbox was designated ATF3-6A-3C and was used on the French Navy Gardian (French Spelling) aircraft. The last engine model with a 30 blade fan and Magnesium Accessory Gearbox was designated ATF3-6A-4C and was used on Falcon-200 Corporate Jet aircraft.

May 15, 1981

    The ATF3 engine received FAA Certification under FAR Part 33, Amendment 6. FAA-LAX Engineer William C. Moring signed off the ATF3 engine FAA Type Certificate.

February 1982

    In February 1984 the U.S. Coast Guard received the first of 41 Falcon 20G model, HU25-A aircraft powered by ATF3-6-2C engines. Eventually all U.S. Coast Guard engine would be upgraded to ATF3-6-4C configuration with improved Hot Day performance. These engines would later be upgraded to ATF3-6-4C with higher Hot Day Thrust ratings. This aircraft package contained 105 Certified ATF3 engines SN P-21129 to P-21233. In additional 22 of the Certifiable ATF3-6 engines were returned to Garrett for upgrade to Certified configuration ATF3-6 engines. A total of 127 ATF3-6-2C and ATF3-6-4C engines were delivered to the U.S. Coast Guard, 82 mounted on new HU25 aircraft and 35 spares.

1983 to Present

    In addition to the 41 U.S. Coast Guard HU25-A Guardian aircraft manufactured by AMD, an additional 34 model F20H aircraft for the commercial market designated as Falcon-200's. ATF3-6A-4C engines rated at 5200 LbFn (pounds thrust) cold day and 5050 LbFn hot day (86 Degrees F) powered the Commercial aircraft. The engines were designated SN 20101 to 20168. Garrett maintained a rental bank of up to ten engines to support the commercial fleet, created mostly from the certifiable engines used to ferry the new U.S. Coast Guard aircraft across the Atlantic.


    The French Navy also ordered five Falcon F20H aircraft to be designated French Navy Gardian's. These aircraft were manufactured by AMD at Bordeaux France and finished at Estres France. These aircraft were powered with ATF3-6A-3C engines rated at 5440 LbFn cold day and 5050 LbFn hot day. In all the French Navy ordered 15 engines SN 22101 to 22115, ten on new aircraft and five spares.


    When ATF3 engine production was terminated 227-ATF3 engines were in service, 112 U. S. Coast Guard Guardian ATF3-6-4C engines, 80 Falcon-200 ATF3-6A-4C engines, 15 French Navy Gardian ATF3-6A-3C engines, and 10 Garrett Commercial ATF3-6A-4C rental engines.

    As engine in-service inspection intervals increased it became obvious that the ATF3 engine required increased ITT (Inter Turbine Temperature) margins and improved turbine durability.


    Engine Main-shaft Carbon Face-Seal Cartridge Fix. The #1, #2, #3, and #4 bearings used cartridge type carbon face seals that had a propensity to stick and leak. The floating carbon seal was redesigned to a two piece seal using a Carpenter 42 steel ring, holding a carbon face seal with a narrowed and repositioned sealing surface. The secondary "O" ring seal material was changes to reduce oil-induced swelling and sticking.

    High Pressure Compressor Surge Fix. The high-pressure compressor shroud profile was changed to more closely match the compressor rotor blade profile at high power. A series of holes were also added to the shroud near the rotor blade inlet to match rotor blade inducer (inlet) flow to the blade exit flow throughout the engine operating range. The high-pressure rotor tip clearance was reduced with the addition of the "Huber Bump" to the HP Diffuser. These design changes were created and tested by Engineer John T. Huber at Site B.

    Low Pressure Compressor Surge Fix. The low-pressure compressor was redesigned to improve surge (compressor stall) margin. The fix included 0.020" shorter 2nd stage compressor blades, a 2nd stage blade tip shroud with three stiffening rings, staggered stator anti-rotation lugs, redesigned 5th stage blade tip and shroud angles, and an interrupted 5th stage stator. This fix eliminated 2nd stage compressor blade failures and low-pressure compressor surges. Engineer Mike James was instrumental in the flight test program defining the surge problem as a severe 2nd stage low pressure compressor high altitude blade tip rub that negatively impacted blade tip efficiency.

    #4 and #5 bearing Carbon Seal Fix. The carbon seals were redesigned from a ring type seal to a segmented ring seal, and the metallic cartridge was redesigned to prevent coning of the sealing face. The seal rotor sealing face was coated with Tungsten Carbide for durability.

    #1 Main Bearing Carbon Face Seal Fix. The seal overheated and failing in operation. An oil jet was added to cool the #1 carbon seal rotor resolving the problem.  There is always some seepage from seals, and eliminating this seepage is an on going and never ending process.

    Inlet Guide Vane (IGV) Cable Fix. As certified ATF3 engines had an aft mounted IGV Actuator (on the accessory gearbox) controlling the inlet guide vane positioning in the engine inlet. A "Hard-Linkage" I-Bean type linkage with bell-cranks and bearings attached the Actuator the Vane "Unison-Ring" controlling the vane position. This design was a maintenance nightmare requiring removal on the nacelle tail-cone and lubrication of the bearings every 25 hours of engine operation.  A "Teleforce" cable system had been designed and tested by Engineer John T. Huber at Site B during ATF3 certification appeared to be the solution. John C. Evans was able to introduce the Teleforce cable into the fleet as a Field-Evaluation program, which was immediately embraced by the aircraft Owners-Operators and Maintenance personnel. The cable system extended the IGV inspection interval from a 25-hour lubrication to a 250-hour torque check.

    Electronic Engine Control (EEC) noise reduction fix. The EEC was redesigned to reduce engine inlet noise by more than 30 DbA at idle. The fix repositioned the inlet guide vanes from 40 degrees to 0 degrees below flight idle. The repositioning only occurred on the ground when engine powers below flight idle were selected. Two additional fixes were incorporated. The low-pressure compressor surge fix allowed a change to the inlet guide vane schedule. This change prevented a surge protection schedule from closing the guide vanes at high altitude cruise improving engine high altitude performance and durability. Adding a solenoid to the Generator Control Unit (GCU) circuit improved durability.

    Oil Consumption and Leakage Fix. The ATF3 engines had an oil consumption problem when operating above 24,000 feet. Oil consumption would increase to as much as one quart every 25 hours. The problem was traced to accessory gearbox seals. The Viton shaft lip seals were replaced with Graphite filled Teflon seals and the permanent magnetic generator (PMG) carbon face seal was redesigned virtually eliminating the oil consumption problem.

    "Silver Bullet" Fix. The silver bullet is the traditional method of killing Vampires (in our case low engine overhaul intervals and high maintenance costs). The concept was based on the results of revised fan turbine cooling testing designed and conducted by APE John T. Huber at Site B.  Primary players in the "Silver Bullet" redesign were Engineering Manager A. W. (Fred) Fuller and a recently hired Engineer Kurt Lammon. The primary focus of the silver bullet modifications was to reduce and better control turbine section metal temperatures to extend operating life and reduce repair costs. This was accomplished by revising cooling flows and controlling them with additional metal baffles, revised piston ring seals, and extensive use of ceramics. The design changes also prevented combustion products from entering the engine cooling air passages and contaminating aircraft cabin air. Emphasis was placed on reworking and reusing existing hardware to keep conversion (and engine operating) cost to a minimum. This program was a huge success, reducing turbine metal temperatures by as much as 350 Degrees Fahrenheit and extending fan turbine disk cycle lift threefold.

    4th Turbine "Paired-Seal" Labyrinth Seal Fix.  As designed the ATF3 engine had a 12-inch diameter 4-step knife-seal on the forward side of the 4th turbine disk. This seal had a 0.018-inch radial clearance and was sealing 80-psid air. The seal spacing was only 0.220-inch, which was not adequate for the relative thermal movement of the knife seal to seal land.  A "Paired-Seal" four-knife seal was conceived by John C. Evans. The seal consisted of two pairs of two knives, each pair riding on one of two diameters of the seal-shroud. This change increased seal land width from 0.220-inch to 0.450-inch, doubling the allowable seal axial travel. Seal radial clearance was reduced from 0.018-inch to 0.008-inch reducing loss of turbine cooling air and resulting in 16-Degrees Fahrenheit (10-degree Celsius) increase in engine temperature margin. The "Paired-Seal" fix was incorporated into in-service engines at the same time as the "Silver Bullet" Fix.


Revised 8/18/2008, Revised 7/31/2009, Last revised 12/2/2009