Written by Nicolette Cormier, PMA265 Program Support

During a January 2002 detachment on board the USS Abraham Lincoln (CVN-72), Strike Fighter Squadron (VFA) 115, the first operational F/A-18E squadron, experienced recurrent external fuel tank transfer problem, which subsequently led to aircraft being diverted to Naval Air Station Lemoore, Calif. Although the technical investigation that followed the squadron's return to home base identified several factors related to the aircraft's external tank transfer issue, a half turn on a tank suspension lug started the ball rolling towards a successful issue resolution.

This simple, but extremely important maintenance practice would ultimately lead the F/A-18 External Tank Tiger Team toward improvement of the tank's loading procedures and discovery of a software anomaly in the aircraft's Signal Data Computer (SDC).

NAVAIR External Tank Tiger Team Lead, Kim Frowein, Fuel Systems Engineer for the F/A-18, explained, "External fuel tanks are vital to this aircraft's mission. The purpose of the tank is to supplement the aircraft's internal fuel. The tanks significantly increase the time the aircraft can stay in the air and the distance it flies. The object, once the aircraft is airborne, is to begin to transfer fuel from the external tanks into the internal tanks as the fuel is consumed from the main tanks. If the aircraft is not capable of transferring the fuel from the external tanks you cannot "trap" aboard the carrier, the only other options are to fly to a land-based airport or jettison the tank or tanks. Jettisoning is a costly measure.

Given the recent frequency of both failure to transfer, and slow to transfer discrepancies, the squadron determined this issue should be addressed prior to the next detachment."

In March, the External Tiger Tank Team, comprised of North Island Fleet (FST) System Team members, Boeing, and NAVAIR Fuel Systems Team engineers, met at NAS Lemoore with VFA-115 maintenance personnel to review the events further, and investigate the root cause of the discrepancy.

Frowein said, "VFA-115 had been tracking the problem and putting together the maintenance data. We had to look at the entire picture because it could have been any number of things that could cause failure to transfer the fuel. That's one of the things that made a resolution difficult. It's hard to solve a problem if you don't have a broken aircraft to troubleshoot."

The squadron's cooperation allowed the team to look at the issue despite the fact that they were doing workups for the next carrier detachment.

Frowein continued, "It wasn't easy to troubleshoot as the squadron had its job to do and we were out there on a 'not to interfere' basis. Fortunately, this turned out to be a good opportunity for us as they were flying quite a few missions using external tanks. We were lucky enough that on the first day one of the aircraft was experiencing some transfer problems."

The team inspected the specific aircraft and fuel tank hardware involved in the events, reviewed technical publication and squadron maintenance procedures for loading and unloading 480 external fuel tanks, and discussed theory of operation of the aircraft fuel systems, which could have contributed to the events. During this time it became obvious that the suspension lug adjustment on the tank didn't correspond with the intent of the tech manual maintenance instructions.

The team soon realized interpretation of the maintenance instructions became subjective when the manual used the term "flush" to describe adjustment of the lugs. A rim around the lug well brought into question what the lug should be flush with.

The tank has two probes that need to be properly engaged with the F/A-18E/F to transfer the fuel. One is a fuel probe; the other is an air probe. Air pressurization is used to get fuel out of the 480-gallon tank. Correct insertion of the probes is essential for fuel transfer.

Frowein said, "Due to the suspension lug not being flush, the air probe was not achieving adequate insertion into the pylon disconnect valve. We were getting either intermittent or no fuel transfer. Once this discovery was made and the maintenance personnel were briefed on the loading procedures, the External Tank Tiger Team completed its mission within three days."

The squadron has reported significantly improved performance of the fuel system during their latest workup detachment aboard the Lincoln. Final closure of this effort is to release and implement the necessary instruction changes in the Integrated Electronic Technical Manual System (IETMS) and related technical publications.

The F/A-18E/F Air Vehicle IPT is now working with Core Avionics IPT to investigate SDC and SDCR software changes to correct the fuel system software anomaly. Greg Drohat, NAVAIR F/A-18E/F Air Vehicle Team Lead, said, "From my perspective, it was a great example of how the fleet, NAVAIR, FST and Boeing can work as a team to bring to bear the resources necessary to solve fleet operational problems and improve the availability of the Super Hornets for the courageous men and women who fly and maintain them in defense of our country."

For more information concerning the U.S. Navy's F/A-18 Program, contact Denise Deon Wilson at 301-481-6263 or visit our web site at http://pma265.navair.navy.mil.

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