F-18 IRST Status

Infrared Search and Track (IRST) is one of the hot topics in aviation.  Supporters claim it greatly enhances the stealth of a fighter since it allows search and tracking via passive modes as opposed to active radar use.  It also allows detection of enemy aircraft that are radar stealth’ed and, thus, negates an enemy’s stealth advantage. 

The Navy has an IRST development program underway to equip the F-18E/F Hornet fleet with IRST as an effort to keep the non-stealthy F-18s relevant and combat effective in an age of stealth.

Following is a discussion of the F-18 IRST program as reported in the DOT&E 2016 Annual Report.

The F-18 IRST sensor will be mounted on the nose of a centerline fuel tank under the fuselage of the Hornet.  The current IRST21 unit is being developed by Boeing and Lockheed Martin and is descended from the F-14 IRST.  The Navy plans to procure 170 IRST units.  The current Block I will be fielded as test units and eventually upgraded to the future production Block II. 

Block I was originally scheduled to enter full rate production but the Navy decided to forego production in favor of the Block II version after a program review of the Block I test results.  This suggests that the Block I was deemed insufficiently successful to warrant production and, in typical Navy thinking, the unsuccessful Block I is bypassed in the hope that the non-existent Block II will somehow attain the success that the Block I did not.  There is nothing inherent wrong with this approach as long as we don’t commit to the Block II production before its capabilities are proven.  Too often, the Navy, faced with a failure, opts to incorporate undemonstrated “improvements” that exist only on paper and then immediately commit to production without waiting for demonstrated success.

The key development in the program thus far, Operational Assessment 2 (OA 2), took place in November 2015 when the IRST was tested under realistic combat conditions.  Unfortunately, the results were less than successful.

“The system … could not reliably detect and track targets well enough to support weapons employment in an environment that reflects realistic fighter employment and tactics.”

Immediately subsequent to this assessment, a program review was held.

“Assistant Secretary of the Navy (ASN) for Research, Development, and Acquisition (RDA) held an IRST program review on January 27, 2016, and in a September 8, 2016, Acquisition Decision Memorandum (ADM), ASN (RDA) approved a restructured program that foregoes full-rate production of Block I sensors and proceeds directly to development of the Block II system. The Block I system will not be fielded and IOT&E did not begin in 2016 as planned.

The Navy plans to hold the Block II Preliminary Design Review in May 2017 and begin IOT&E in 2020.”

As discussed, it is clear that the results of the assessment test and subsequent review indicated that the Block I IRST was not successful.  Unfortunately, instead of pausing until development could overcome whatever problems were seen, the Navy has opted to leap into Block II and has already scheduled production.

It is noteworthy that the Hornet-IRST-fuel tank combination has been approved for the full flight envelope as long as the fuel tank is empty.  Some restrictions have been placed on both launch and flight conditions with varying loads of fuel in the tank.

With the tank empty, the IRST becomes, in essence, a giant sensor the size, weight, and drag of a fuel tank!  If the tank can’t be used for fuel or only in partial load conditions, one has to wonder at the wisdom of placing the unit in a centerline fuel tank to begin with as opposed to a wing or nose mounted location.  On the other hand, DOT&E points out that the flight restrictions may not be significant.

“Given the rate at which fuel is consumed from the centerline fuel tank, these restrictions are effective for only a short period at the beginning of the mission profile and should not have an operational impact.”

The under-the-fuselage location also restricts the field of view of the sensor.  Obviously, it can’t see anything above the aircraft.  Thus, it’s only 50% effective to begin with, even if it worked perfectly for the lower field of view.

Reliability is also an issue.

“Demonstrated reliability is below what was expected at this point in the flight test program. As of the time of DOT&E’s OA 2 report, the cumulative Mean Time Between Operational Mission Failure (MTBOMF) was 4.1 hours; the reliability after incorporating known fixes was 19.5 hours. The MTBOMF requirement is 40 hours and the system was expected to have a projected reliability of 38 hours when entering IOT&E.”

DOT&E’s report concludes with this criticism of the Navy and admonishment to learn a lesson.

“Many of the Block I system’s difficulties with detection and tracking seen in OA 1 and OA 2 did not require flight testing to uncover them, but could have been discovered earlier via analysis and modeling and simulation. The Navy expects that the Block II configuration (which includes sensor and aircraft hardware and software), will provide improved capability. This assumption should be tested as early as possible, prior to major decisions …,”

Unfortunately, the Navy seems determined to ignore this lesson, having already scheduled Block II production.

Please don’t read this post as being against fielding an IRST.  ComNavOps believes that a fully functional IRST would be a relatively cheap and highly effective combat aid and is well worth pursuing.  Successful and functional IRST units apparently exist around the world and there is no reason to believe that the Navy and its manufacturing partners cannot produce a functional unit.  However, we need to go about this intelligently.

I would recommend that the Navy reconsider the under-the-fuselage location.  Perhaps there is a good reason why the unit can’t be wing or nose mounted but it would be worth some extraordinary effort to do so.  The actual sensor is small and should be able to be mounted in a more advantageous position.

I also recommend that the Navy stop making production plans for an unproven and, thus far, unsuccessful unit.  By all means, continue development but set production plans aside and remove that artificial deadline from consideration.  Take the time needed to field a fully functioning unit.

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