Attention:
Owners, operators and maintainers of Airbus Canada Limited Partnership (ACLP) aeroplanes model BD‑500‑1A10 and BD‑500‑1A11
| File Classification No.: | Z 5000-35 |
|---|---|
| RDIMS No.: | 21286024 |
| Document No.: | CASA 2026-04 |
| Issue No.: | 01 |
| Effective Date: | 2026-03-16 |
Purpose:
The purpose of this Civil Aviation Safety Alert is to raise awareness of operational effects caused by erroneous height indication from radio altimeters on ACLP model BD-500-1A10 and BD-500-1A11 aeroplanes, and to recommend relevant mitigations to address the issue.
Background:
In-service events have been reported involving unexpected autothrottle (AT) mode changes. These occurrences resulted in AT RETARD mode arming and activation at various phases of flight, thrust mode changes during climb, and erroneous landing gear warning during approach.ACLP’s investigation identified momentary “glitches” in radio altimeter data output as the suspected cause, which can affect AT functionality and the aural warning system.
ACLP issued Flight Operations Transmission (FOT) A220-FOT-22-30-009 and Operations Engineering Bulletin (OEB) 002.01 to raise awareness and provide operational recommendations.
Since then, further investigation has determined that an inadequate thickness of the radio altimeter antenna gel gasket may be a contributing factor to the momentary “glitches” in the radio altimeter data output. The inadequate thickness of the gel gasket may lead to radio altimeter antenna bending, potentially creating internal antenna cracking. As a result, ACLP issued Service Bulletin (SB) BD500-344007 to replace the radio altimeter antenna with a new antenna featuring a modified gasket on applicable aeroplanes.
ACLP continues to assess this issue. Transport Canada (TC) may recommend or mandate additional corrective actions as necessary.
Recommended action:
TC recommends that owners, operators and maintainers of ACLP model BD-500-1A10 and BD-500-1A11 applicable aeroplanes affected by unexpected AT behavior and aural warning system anomalies incorporate the modifications as described in ACLP SB BD500-344007 Issue 001, dated 19 December 2025, or later revisions.
Owners and operators should ensure that all flight crews are aware of and apply the recommended operational procedures provided by ACLP FOT A220-FOT-22-30-009 Revision A and OEB 002.01, both dated 19 April 2023, or later revisions.
Within Canada, in accordance with the reporting requirement of Part V, subpart 21 (521) of the Canadian Aviation Regulations, owners, operators and maintainers should submit a Service Difficulty Report (SDR) to TC for the discovery of each reportable service difficulty. (Please note: if any unexpected AT mode change is experienced, an SDR should be submitted). Outside Canada, report any such occurrence in accordance with local reporting requirements.
Contact office:
For more information concerning this issue, contact a Transport Canada Centre; or contact Hilary Ross, Continuing Airworthiness in Ottawa, by telephone at 1-888-663-3639, or by e-mail at TC.CAWWEBFEEDBACK-retroactionWebMDLN.TC@tc.gc.ca.
Original signed by
Jenny Young
Chief, Continuing Airworthiness
National Aircraft Certification
Erroneous height indication from radio altimeters
(PDF, 243 KB)
The Transport Canada Civil Aviation Safety Alert (CASA) is used to convey important safety information and contains recommended action items. The CASA strives to assist the aviation industry's efforts to provide a service with the highest possible degree of safety. The information contained herein is often critical and must be conveyed to the appropriate office in a timely manner. The CASA may be changed or amended should new information become available.