EASA SIB 2024-05: Incorrect Computation of the Hybrid Flight Path Angle by LCR-100 Attitude Heading Reference System

What to do

Type certificate and supplemental type certificate holders should verify if affected LCR-100 AHRS units with mod 28 and/or mod 29 are installed and check if any Lever Arms to Centre of Gravity constants are set to zero in the Installation Data Module. If so, they should develop a design change to upload a minimum lever arm constant of 0.01 m in the x-direction and provide instructions to operators for IDM reprogramming. Results and corrective actions must be reported to the competent authority as per EU regulations. No specific compliance deadline is stated.

Summary

EASA Safety Information Bulletin 2024-05 addresses an incorrect computation of the Hybrid Flight Path Angle by the Northrop Grumman LITEF GmbH LCR-100 Attitude Heading Reference System (AHRS) with specific software part numbers. The issue affects units with modification 28 and/or 29 when zero values are stored for Lever Arms to Centre of Gravity in the Installation Data Module. This bulletin informs type certificate and supplemental type certificate holders about the erroneous data output affecting ARINC Labels 263, 134, and 262.

What changed

EASA SIB 2024-05 identifies a software computation error in the LCR-100 AHRS that causes incorrect Hybrid Flight Path Angle calculations under certain installation data conditions. It clarifies that the Hybrid Flight Path Angle is computed without GNSS augmentation when zero lever arm constants are stored and describes the behavior of ARINC Label 263 under loss of Baro-Inertial Vertical Speed. The bulletin also references previous related information in EASA SIB 2023-09.

Why it matters

This issue can lead to inaccurate flight path angle data being transmitted to aircraft systems relying on the LCR-100 AHRS, potentially affecting navigation and flight control functions. Operators and maintenance organizations need to be aware of the conditions causing erroneous data to ensure proper system performance and safety. Although no unsafe condition requiring an Airworthiness Directive has been identified, awareness and assessment are critical for continued airworthiness compliance.