The bulletin
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FAA Aircraft Certification Service
SPECIAL AIRWORTHINESS
INFORMATION BULLETIN SUBJ: Navigation: Honeywell Epic and FMZ FMS VGP/VNAV Early Descent Behavior SAIB: NM-08-39 Date: August 5, 2008 This is information only. Recommendations aren’t mandatory.
Introduction
This Special Airworthiness Information Bulletin addresses recent reports of aircraft equipped with Epic Integrated Avionics Flight Management System (FMS) having part numbers EB7031847, EB7033339, EB7036889, EB7034843, or EB7030192, and Honeywell Legacy Flight Management System (FMS) FMZ-2000, part numbers 7018879, 7017300 and 701770, initiating a descent prematurely when coupled to VNAV or VGP. The vertical deviation pointers on the PFD will be incorrect and could lead the aircraft below the intended path.
Background
During an RNAV approach, an operator flying a Honeywell FMS programmed the FMS direct to a waypoint outside the Final Approach Fix (FAF). This resulted in a turn greater than 100 degrees back onto the final approach course, which if continued would turn the aircraft inside the FAF. The flightcrew subsequently turned to a downwind leg being radar vectored to intercept the final course.
With no reprogramming by the flightcrew, the active leg sequenced and made the FAF the "TO" waypoint with the proper inbound course for the procedure. Although the FMS LNAV position and distances were displayed correctly, when coupled to VNAV or VGP, the aircraft initiated the descent prematurely.
Recommendations
Operators of aircraft equipped with the referenced Honeywell FMS’s should provide a means to ensure their flight crews are familiar with the procedures described in the attached Honeywell Technical News Letter D200712000022, dated 04 January 2008.
For Further Information Contact
J. Kirk Baker, Aerospace Engineer, Federal Aviation Administration, Los Angeles Aircraft Certification Office, 3960 Paramount Boulevard, Lakewood, California 90712; phone
(562) 627-5345; fax: (562) 627-5210.
For Related Service Information Contact
Honeywell, 21111 North 19th Avenue, Phoeniz, AZ 85027.