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F404 Engine

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Increasing the F404 engine's thrust to 18,000 pounds was necessary to meet Korean and ADF requirements, which required hauling big AIM-7 missiles and an additional 650 gallons of fuel to meet the range/loiter requirements. This was most inexpensively achieved through development of a new Full Authority Digital Engine Control System (FADEC) for the F404. Although this was a linchpin of General Electric's future plans for the engine, as usual, GE insisted that Northrop pay the cost for development of the FADEC and the 18,000-lb-thrust F404. However Northrop would be reimbursed for its investment with only the promise of future royalties on sales of the engine on other aircraft. Remarkably, this royalty arrangement was not formally agreed until after the F-20's cancellation.

Technical Description


  • 18,000 Lb Thrust Class
  • 7.8:1 Thrust To Weight Ratio
  • Stall Free Performance
  • Low Bypass Ratio
  • Smoke Free, Low IR Signature
  • Rapid Throttle Response
  • Idle To Intermediate Rated Power In Less Than 4 Seconds -- No Throttle Restrictions
  • Low Specific Fuel Consumption
  • Utilized Jet A-1, JP-4, JP-5, or JP-8 Type Fuels
  • Pneumatic Cartridge Starter or Optional Jet Fuel Starter
  • Simple Starting Procedures
  • Automatic Restart, and Manual Control Backup Systems
  • Automatic Redundant Ignition
  • Bird Strike Capability of 1.1 Pounds
  • Six Individually Replaceable Modules
  • No Scheduled Overhauls or Time Change Requirements
  • The High Reliability of the F-20A Engine Meant that the Average Engine Would Be in the Shop Only One Time In Two Years of Operation (At 20 Flying Hours per Month)
  • No Engine Trim Required
  • Low Shop Visit Rate: 2.0/1000 Flight Hours
  • Engine Condition Monitoring

Engine line replaceable units (LRUs) were replaceable with the engine installed in the aircraft. Major LRUs were mounted by V band clamps and required no safety wire. Removed engines could be returned to service through simple module replacement by the Intermediate Shop. Modules were then repaired, and only failed components needed to be sent to the depot.

The simplicity of the F-20A engine set a precedent for modern fighter aircraft. Ten compressor stages were used to achieve the pressure ratio in the 26 to 1 class, and there were only two turbine stages. This permitted the use of only three frames and sumps and only five main bearings.

To ensure single engine flight reliability, the F404 GE 100 engine incorporated a highly reliable gear fuel pump and a redundant ignition system. A new gearbox provided additional drive pads for an aircraft hydraulic pump and backup electrical generator, giving the F-20A hydraulic and electrical reliability equivalent to that of a twin engine plane. In addition, the F404 GE 100 engine had a fully redundant control system consisting of independent hydromechanical and electrical backup modes to protect against component or sensor failures.


Organizational level fault isolation procedures benefited from such features as the digital electronic control unit, fault flags, and engine temperature cycle counter. Suspected internal faults could be quickly inspected by borescope while the engine was installed. A parts life tracking system eliminated costly premature replacement of components.


The modular design of the engine permitted intermediate level repair to be accomplished quickly through removal and replacement of any of the six engine modules. Times are shown below, along with crew requirements.

F-20A Engine Change Crew Size Modules Times Requirements

Fan                            2.3 hrs / 3 crew
High pressure compressor      12.6 hrs / 3 crew
Combustor                      6.9 hrs / 2 crew
High pressure turbine          6.0 hrs / 3 crew
Low pressure turbine           3.0 hrs / 2 crew
Afterburner                    1.0 hrs / 3 crew
The F-20A engine could be removed and replaced by a crew of three in less than 2 1/2 hours. Ease of intermediate level engine maintenance ensured quick turnaround and high availability.

Thirteen borescope ports (of which ten were accessible with the engine installed) enhanced conventional monitoring methods. They permitted all major Mowpath components to be visually inspected to detect foreign object damage, structural damage, or hot section distress while the engine was installed.

Borescope inspection capability permitted on condition maintenance and eliminated the time and expense of unnecessary engine removal or the need for component replacement on a fixed time basis.

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© Mark Wade, 1997 - 2006 except where otherwise noted.
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