TF34 Engine

The General Electric TF34 axial-flow turbofan engine was originally developed for the US Navy's S-3A Viking surveillance and precision-targeting aircraft. The airplane is powered by two engines installed on pylons mounted under the wing, inboard of the wingfold stations. These TF34-GE-400B high-bypass turbofan engines have a thrust of 9,275 lbf (41.25 kN) thrust each. Two General Electric TF34-GE-100 turbofans of 9065 lbs. thrust each enable the A-10 Thunderbolt close-air support aircraft to operate from short, remote airfields and withstand frequent exposure to ground fire.

The engine delivers the highest thrust-to-weight ratio and the lowest specific fuel consumption of its class. In service, the engine has proven to be highly reliable and maintainable with low operating costs. Hot-section improvements have significantly reduced the unscheduled removal rate and have doubled the engine's on-wing capability to more than 2,000 hours. The first TF34 was shipped in February 1971 and was first delivered on the S3 in January 1974. With more than 11 million fleet hours, the TF34 is projected to remain in service beyond 2028.

The CF34 sparked one of the most important events in commercial aviation: the introduction of the regional jet. The TF34 is the father of the CF34, a commercial version that powers business jets and regional jet airliners. The commercial version of the TF34, the General Electric CF34, powers several types of business jets and regional airliners.Dependability is inherent in the CF34. It is a derivative of GE's rugged, combat-proven TF34 which powers the U.S. Air Force A-10 and U.S. Navy S-3A. The CF34 has evolved from this solid military experience base as a superior commercial engine with excellent performance margin, durability, and a level of reliability that allows today's 50 to 105 passenger regional jets to be flown with utmost confidence throughout the world.

The CF34 family is designed with a particular concern for its effect on the total flying environment inside the cabin and outside. The inherently quiet CF34, helps make travel comfortable and more productive. Low noise also contributes to greater operational flexibility. And the CF34 is not only a quiet engine; it is a "green" engine. The CF34 is well within FAA, U.S. Environmental Protection Agency (EPA) and International Civil Aircraft Organization (ICAO) requirements for smoke and emissions. GE is so committed to the CF34, that it has invested more than $1 billion over the last decade. Today, GE is testing its latest CF34 engine, the CF34-10.

The Base Closure and Realignment Commission's July 1993 recommendations for base closures and realignments included closing three of the Navy' six aviation depots. One of these was the Alameda Naval Aviation Depot, California. Accordingly, the maintenance workloads performed at those facilities were redistributed to remaining depots operated by the Navy and other services. The Alameda depot performed maintenance on the TF34 turbine engine, used by the Navy on the S-3 aircraft and by the Air Force on the A-10 aircraft, and the Navy's version of the T56 turbine engine used on C-130, P-3, and E-2 aircraft. The Alameda workload for the TF34 engines was transferred to the Jacksonville Naval Aviation Depot, Florida, and the T56 engine workload was added to the existing Air Force T56 workload at the San Antonio Air Logistics Center, Texas. The transition of maintenance capability to these facilities began in June 1994 and was completed by May 1996.

The transition of the TF34 and T56 engine workloads from the Alameda Naval Aviation Depot to the Jacksonville Naval Aviation Depot and the San Antonio Air Logistics Center, respectively, took longer than originally anticipated and was not executed in the most efficient manner. During the transfer, significant productivity and quality problems occurred at the gaining depots and the costs associated with establishing production capability were higher than expected. Neither the Air Force nor the Navy could quantify the increased costs to establish maintenance capability or the delays that the problems caused. They did, however, provide examples demonstrating the extent to which the identified problems affected cost and/or the time required to achieve production capability.

Of a total of 27 S-3 and A-10 aircraft units, only 2 units had periods of below mission capable rates for equipment and readiness attributed to "unavailable engines." A total of 12 Navy and 15 Air Force units used the TF34 engine and reported readiness during the 46-month evaluation period. Only 2 of the 12 Navy units examined attributed periods of equipment readiness below mission capable to "unavailable engines." Both of these units reported equipment readiness as mission capable during the transition, but reported readiness levels lower than mission capable after the transition period. Although the lower readiness rates occurred after the transition, a Navy official told us that the engines were unavailable due to the transition. In addition, Navy readiness officials took extraordinary steps to maintain mission capable status. The extraordinary efforts included removing engines from aircraft in depot maintenance to use on aircraft assigned to active or reserve units.

Alameda personnel advised Jacksonville officials that some equipment already in use at Jacksonville would also satisfy repair requirements for the TF34 engines. However, Jacksonville officials discovered that their equipment had to be retooled to meet the new requirements. Jacksonville officials noted that retooling and developing work arounds resulted in higher than anticipated costs and delayed establishment of production capability.

The replacement frequencies (how often a part is replaced during an overhaul process) for TF34 parts were so out of date that they had to be completely revised. When requisitions were made based on the updated frequencies, the supply system was unable to meet the demand. The Air Force required 100-percent certification of all overhaul tasks, both Air Force unique and common, required on the Air Force TF34 engine and engine components at Jacksonville Naval Aviation Depot. According to Jacksonville officials, the certification should have been confined to those tasks unique to the Air Force TF34 engine. Many of the overhaul tasks required on the TF34 were already performed on other engines repaired at Jacksonville. According to Jacksonville officials, the requirement for 100-percent certification was compounded by the lack of Air Force engineering support.

Jacksonville offered skilled personnel at Alameda opportunities to transfer with the TF34 engine workload. However Jacksonville was not able to recruit the full complement of skilled personnel desired. Thirty-two of the 43 Alameda employees offered transfers to Jacksonville to work on the TF34 engines accepted the offer. The shortfall of 11 employees had an impact on establishing production capability, but it was not significant.

As of early 2002 there was an aggressive Time Compliance Technical Order (TCTO) underway to replace the oil pressure transmitter line with a new design that is flexible and requires no clamping. Until this TCTO is complete, the field had inspected all TF34 engines to ensure the oil pressure transmitter lines were clamped properly. While not the primary cause of the 2001 Class A Mishap, a TF34 engine did play a role in the event that promted this TCTO. This TF34-GE-100A engine-related mishap involved an A-10 on a close air support mission. The right engine developed an oil system malfunction during flight and was shut down. The oil system malfunction was attributed to an improperly clamped oil pressure transmitter line that cracked due to contact with the closed engine cowling.

The TCTO is the method used throughout the Air Force to implement aircraft hardware changes. Occasional aircraft modifications are required on an continuing basis over the life of any aircraft. The purpose of these changes varies considerably, including safety-of-flight concerns, increased capability through incorporation of new technology, and improvements designed to make maintenance easier or extend the useful life of the aircraft. As implied in its name, the TCTO sets a timeframe for completion of modifications. The length of the timeframe depends upon such factors as the urgency of the modification, availability of new parts, or the degree of complexity of the modification. Some tasks are so involved that they are best performed at a single location, such as at an Air Logistics Center. Other TCTOs are performed by maintenance personnel at the bases which fly the aircraft.

As formally documented in MSIP ORD (2001), the A-10 has long been recognized as underpowered. As of 2003 General Electric's proposed TF34-GE-100B engine for the A-10 would provide 15 percent more sea-level thrust and about 30 percent more thrust at altitude with improved thrust-specific fuel consumption. Cost for the fleet of about 370 A-10s with flight-testing would come to about $1 billion-the equivalent of 12 F-22s or 33 F-35s.

During FY04, the current Secretary of the Air Force and the Chief of Staff for the Air Force (SECAF/CSAF) requested the USAF address this need. The most effective solution is a kit upgrade to current engine. The upgraded engine must 1) still fit in current nacelle, 2) not require major structural mods, 3) produce sufficient additional thrust to address identified deficiencies, and 4) be funded from within A-10 program in accordance with (IAW) SECAF/CSAF direction. To meet cost and schedule constraints, the A-10 Engine Upgrade must be based on mature technology. The kit approach offers best value, yet meets A-10 and warfighter needs and provides the fastest delivery of the propulsion upgrade at a significantly lower risk. This modification approach saves three to four (3-4) years over development.

In 2005 the United States Air Force (USAF) sought interested sources regarding a requirement for a TF34 propulsion performance upgrade for the A-10 weapon system. The sponsoring activity is Aeronautical Systems Center, Agile Combat Support Wing, Propulsion Squadron, Wright-Patterson Air Force Base, OH. There is a proposed FY06 target year to begin a three (3) year Systems Design and Demonstration (SDD) effort ($160M budget). The modification kit purchases must begin with adequate leadtime to support kit installations by early FY09, which allows synchronization with planned TF34-100A overhaul schedule. Acquisition planning factors include the following assumptions: 1) The acquisition effort begins at Milestone B, 2) 356 A-10s will be modified, 3) in addition, 68 spare engines will be modified. Key A-10 engine upgrade attributes include: air to air refueling at higher altitudes, reduced susceptibility to FOD, maintaining existing TF34 reliability, operating above the threat with a 500 FPM rate of climb on a standard day at 20,000 feet, decreasing fuel flow, and reducing transit time.

In 2006, the A-10 Propulsion Upgrade Program entered the system design and demonstration phase. This program upgrades the A-10's current TF34-100A engines to provide approximately 30% more thrust. This will help overcome some limitations that the A-10 faces when operating from expeditionary airfields at high field elevations and temperatures. It will also improve the A-10 performance at medium altitudes and increase its weapon load, thus improving survivability and more fully leveraging the capabilities of the Precision Engagement modification and ATPs.

As of 2006 the flat-rated TF34-GE-101 doubles the hot day thrust output over current engines, eliminating take-off gross weight limitations that preclude today's A-10 from delivering its most powerful mission punch. Other -101 performance advantages include: A significant reduction in takeoff distances during hot day conditions. Improved high altitude performance. 30% more acceleration capability and a 2X turn rate for improved maneuverability. An approximate 3X time-to-climb improvement at full combat weight. CONUS to European deployment in one-third the time - without tying up tanker assets and valuable manpower. A positive "single engine rate of climb" safety margin at maximum gross takeoff weight.

By leveraging a $400-million GE investment for commercial engine development and a solid production base, the TF34-GE-101 can be procured on an affordable Commercial Off-The-Shelf (COTS) basis. Maintenance costs (including spares, labor and overhaul) are projected to be less than one-fourth the cost of maintaining current engines. Coupled with a lower maximum thrust rating for robust, reliable operation, significant savings can be realized over the remaining life of the A-10 fleet. A true force multiplier, the A-10 with TF34-GE-101 engines can offload the F-16 Block 40/50 aircraft from close-air support missions and free these valuable assets to perform other critical tasks.

Capability Threshold Objective Justification
Operate from high density attitude airfields with militarily significant payloads A 47K lb A/OA-10 (DI of 7.75) operating on a 9000 foot runway at 5,000 feet PA and 35 degrees C can lose an engine at rotation, jettison stores (41.75K lbs remaining, DI of 3.62) and climb with the gear up and failed engine wind milling and maintain a minimum rate of climb of 150 feet per minute (FPM). Same conditions but maintain a minimum climb rate of 500 FPM. Allows safe operations with a militarily significant payload in high DA expeditionary conditions; Enables significantly more worldwide basing options.
A 47 K lb A/OA-10 (DI of 7.75) operating on a 9,000 foot runway at 5,000 feet PA and 35 degrees C must have a critical field length of less than 9,000 feet. Same conditions but have a critical field length of less than 7,500 feet.
Operate from austere expeditionary airfields A 47K lb A/OA-10 (DI of 7.75) operating on a 5,000 foot runway at 2,500 foot PA and 25 degrees C can lose an engine at rotation, jettison stores (41.7 lbs remaining, DI of 3.62) and climb with the gear up and failed engine wind milling and maintain a minimum rate of climb of 150 FPM. Same conditions but maintain a minimum climb rate of 500 FPM. Allows forward basing of "Sandy" role aircraft with CSAR Task Force; Enables rapid response to calls for CAS/CSAR; Minimizes sortie transit times and maximizes employment; Allows more staging options for TST operations; Allows staging closer to the ground forces for emergency/immediate CAS.
A 47K lb A/OA-10 (DI of 7.75) operating on an airfield at a 2,500 foot PA and 25 degrees C must have a critical field length of less than 5,000 feet. Same conditions but have a critical field length of less than 4,500.
Maximize gross weight on take-off (weapons and internal fuel) Operate a 51K lb A/OA-10 (DI of 14.49) on a 9,000 foot runway, sea level, standard day, be able to lose an engine at rotation, jettison stores (41.6K lbs remaining, DI of 3.62( and climb with the gear up and failed engine wind milling and maintain a minimum rate of climb of 150 FPM. Same conditions but operate on a 7,500 foot runway. Leverage PE Mod; Fully capitalize on available hard points in the optimum conditions.

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