Safety Valve – Opening During Normal Operation and Ingestion of Insulation Blankets - Civil Aviation Safety Alert (CASA) No. 2023-03


Owners, operators and maintainers of MHI RJ aviation model CRJ 550/700/701/702/705/900 aeroplanes

File Classification No.: Z 5000-35
RDIMS No.: 19342863
Document No.: CASA 2023-03
Issue No.: 01
Effective Date: 2023-08-11


The purpose of this Civil Aviation Safety Alert (CASA) is to emphasize the importance of the proper installation of insulation blankets in the vicinity of the pressurization safety valves and advise operators of an issue with the potential drift of the Safety Valve (SFV) positive pressure mechanism causing the valve to open during normal operation. This CASA provides details of the problems currently experienced and the subsequent actions to correct these issues.


Multiple reports of CABIN ALT caution messages were found to be a result of the inadvertent opening of the SFV due to a drift of the positive pressure mechanism threshold causing the valve to open during normal operation. In some instances, the CABIN ALT warning messages were posted due to the SFV being stuck open caused by insulation blanket ingress into the valve. These events caused increased crew workload.

The investigation of these events found that the SFV part number (P/N) GG698-98005-1, which is an improved version of the GG670-98005-1 SFV, introduced on the CRJ1000, addresses the threshold drift issue. As a result, the Aircraft Illustrated Parts Catalogue (AIPC) has been updated to revise the interchangeability code from 2 to 5 for the GG670-98005-1 SFV and will ensure that the GG670-98005-1 SFV will be replaced by the GG698-98005-1 parts.

In addition, to address the insulation blanket installation, the manufacturer has updated the Aircraft Maintenance Manual (AMM) tasks to emphasize the importance of the proper installation in the vicinity of the SFV.

The AIPC and AMM updates have been published in June 2023.

Recommended action

Care must be exercised when installing and securing the insulation blankets in the vicinity of the SFV. All personnel engaged in this type of installation should be aware of the latest instructions and apply the proper removal and installation procedures and techniques.

MHI RJ CRJ900 Illustrated parts catalog - Safety valve

Figure 1 – IPC View of safety valve installation

Figure 2 – View showing insulation stuck in valve. Note proper installation of insulation is required to prevent this problem.


Contact office:

For more information concerning this issue, contact a Transport Canada Centre; or contact Danilo Verrelli, Continuing Airworthiness in Ottawa, by telephone at 1-888-663-3639 by fax at 613-996-9178 or by e-mail at

Original signed by

Jenny Young
Chief, Continuing Airworthiness
National Aircraft Certification


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.