FAA SAIB NM-08-39 - Honeywell Flight Management System (FMS) - Early Descent Behaviour
- Published
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What to do
Operators should ensure that flight crews are trained on the procedures outlined in Honeywell Technical Newsletter D200712000022 dated 04 January 2008. When flying instrument approaches using VNAV or VGP, crews must program the FMS using VECTORS approach transition, ACT VECTORS, or DIRECT-TO INTERCEPT functions to maintain correct vertical navigation. Continuous monitoring of published approach altitudes is advised, and no mandatory compliance deadline is specified.
Summary
FAA SAIB NM-08-39 is a Special Airworthiness Information Bulletin addressing premature descent behavior in certain Honeywell Flight Management Systems (FMS) when coupled to VNAV or VGP. The affected FMS units include Honeywell Epic Integrated Avionics and Legacy FMZ-2000 models installed on various aircraft such as Boeing 727 series, Bombardier CL-600 series, Cessna 650, Dassault Falcon series, Gulfstream G-1159, G-IV, GV, and Hawker Beechcraft HS125 and BAe125 series. The bulletin informs operators about incorrect vertical deviation indications that may lead to early descent below the intended flight path during RNAV approaches.
What changed
This bulletin introduces awareness of a known issue where Honeywell FMS units initiate descent prematurely when coupled to VNAV or VGP during certain approach scenarios. It provides detailed analysis and procedural recommendations to prevent this behavior, including specific programming methods for the FMS to ensure correct vertical navigation functionality. The document does not mandate changes but strongly supports FAA recommendations and Honeywell technical guidance.
Why it matters
This information is critical for aviation professionals to prevent unintended early descents that could compromise flight safety during instrument approaches. Operators and flight crews must understand the FMS behavior to avoid incorrect vertical guidance and ensure compliance with published approach altitudes. Maintenance and training teams need to incorporate these recommendations to maintain safe operation of affected aircraft equipped with Honeywell FMS units.
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