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Technician's Bench:
System Fifty Five X

Rodney Sinclair
Tech. Rep.

In the January 2001 issue of the Approach we published an article ex-plaining the differences between the System Fifty Five and Fifty Five X. Since that time,our technical support depart-ment has fielded many questions regarding the differences. This ar-ticle is intended to reiterate some of the differences and to feature new material that may help you in distinguishing between the two systems.

One of the first differences that you will notice about the Fifty Five X is that it displays the software code after the self-test. This is not an error code. The current software version is 4.

The Fifty Five X also has gain enhancement circuitry for tracking GPS in the NAV mode. (Not to be confused with GPSS). To access this feature a ground must be applied to Pin 49 on Pl. This can be done in one of two ways. The first way is by a remote GPS/NAV select switch. Apply a ground from Pin 10 of P1 when GPS is selected. The second way to access this feature is by using the GPS annunciate signal, which is supplied by the Garmin 430/530 (which is a ground when the GPS is selected). By using this signal through a common rectifier diode, the Garmin will automatically switch this feature.

Lift Compensation in turns was also added. Whenever the autopilot detects a change from the turn coordinator, the pitch servo will drive the aircraft up, in proportion to the turn rate, minimizing loss of altitude. Typical loss is about 40-60 feet.

One of the most obvious changes incorporated in the new Fifty Five X is GPSS integrated into the circuitry. This feature is helpful when limited panel space is an issue.

Improved course intercepts in the Fifty Five X allows the autopilot to make large course changes without additional commands to the autopilot.

The heading mode has also received attention, now having two levels of heading gain. When the heading bug is changed to a new heading, the heading gain is briefly reduced for a smooth transition into the turn and to minimize overshooting of the newly selected heading. After reaching the new heading, gain will be increased to reduce minor excursions while tracking the heading selected.

These changes do not indicate the System Fifty Five with external GPSS is any less capable or popular, but how the System Fifty Five X merely represents S-TEC/Meggitt's philosophy and commitment to ongoing product improvement.