SAIB NM-05-31

SPECIAL AIRWORTHINESS

INFORMATION BULLETIN

Aircraft Certification Service Washington, DC

U.S. Department of Transportation Federal Aviation Administration

NM-05-31 February 4, 2005 www.faa.gov/certification/aircraft This is information only. Recommendations aren’t mandatory.

Introduction

The Special Airworthiness Information Bulletin (SAIB) advises you, owners and operators of Bombardier model CL-600- 2B19 aircraft, that we have received reports of higher-than-expected levels of dual-channel disconnects of the horizontal stabilizer trim system. This problem posts STAB TRIM and MACH TRIM caution messages on EICAS.

Bombardier is undertaking an engineering investigation to address the root causes of this issue.

Background

Bombardier has issued an All Operator Message (AOM) # 870, (copy attached) to provide advice for aircrew in order to mitigate any handling or control issues which may arise. We anticipate that a further revision to the CL-600-2B19 aircrew publications (FCOM and/or AFM) will follow to formalize some of the advice.

Recommendations

We strongly recommend that you review AOM #870, and familiarize yourselves with the associated abnormal procedures in AFM revision 56.

For Further Information Contact

FAA, Dan Parrillo, NYACO, ANE-172, 1600 Stewart Ave, Suite 410, Westbury, N.Y.

11590; Tel: (516) 228-7305; Fax: (516) 794- 5531; email: daniel.parrillo@faa.gov

AEROSPACE BOMBARDIER Bombardier Inc. 400, Côte-Vertu West Dorval, Québec H4S 1Y9 thd.crj@aero.bom bardier.com TEL 514-855-8500 FAX 514-855-8501 Bombardier CRJ CL-600-2B19 All Operator Message No. 870 ATTN: Director/Manager of: Maintenance Engineering Quality Control Flight Operations DATE: 31 Jan 05 ATA: 2740 MODEL: CL-600-2B19 SUBJECT: Horizontal Stabilizer Trim System - Dual Channel Disconnect Events The following message is sent to all Bombardier CRJ Operators and Bombardier Aerospace Field Service Representatives.

This message contains information requiring attention and/or action. Please ensure timely and appropriate distribution within maintenance and flight operations departments DISCUSSION:

Several CRJ200 operators have reported dual channel disconnects of the horizontal stabilizer trim system resulting in STAB TRIM and MACH TRIM caution messages being posted on EICAS. Bombardier addresses both caution messages in the latest version (REV 56) of the CRJ AFM and FCOM and the associated abnormal procedures should be followed. Bombardier has begun an engineering investigation to address the root cause(s) of this issue.

The following guidance is provided to mitigate handling or control issues that may arise following this type of event. It is anticipated that a revision to the CRJ FCOM and/or AFM will follow to formalize some of the following advice.

In the event of a dual STAB TRIM disconnect event, the following functions will be unavailable:

• STAB TRIM

• MACH TRIM AOM-870 Page 1 of 3

It is possible to inadvertently activate the STAB DISCONNECT switch mounted on the control wheel. Therefore, in accordance with the AFM, an attempt should always be made to re-engage the STAB TRIM and MACH TRIM functions by first depressing the channel 1 and channel 2 engage switches, and then the mach trim engage switch, all located on the STAB/MACH TRIM panel (center pedestal).

Also, preliminary investigation results indicate that following a fault detected on channel 1 of the stabilizer trim system, conditions may prevail that prevent the automatic transfer of function control to channel 2. Following an unsuccessful attempt to re-engage both channels of the stabilizer system, the pilot (or co-pilot) should make an attempt to reengage channel 2 only. If this is successfully completed the STAB TRIM function will be available with a STAB CHI INOP EICAS indication, and an attempt should also be made to re-engage the MACH TRIM function.

It is also possible that the STAB DISCONNECT switch may be stuck in the depressed position, thus preventing the re-engagement of the STAB TRIM and MACH TRIM functions. If this is suspected, the pilot (or copilot) should make an attempt to free the affected switch, by pressing and then releasing it, or by pulling or rocking it.

If the STAB TRIM function cannot be re-engaged, then in the absence of trim capability it will, at some time, be necessary to hand-fly the aircraft, with possibly significant control forces required for the remainder of the flight. The following advice is provided as a guide to manage the aircraft, and to reduce control forces as much as practical.

• If autopilot is engaged:

Leave the autopilot engaged.

Minimize changes to the airspeed and the aircraft configuration. This shall minimize elevator servo motor loads.

The autopilot performs pitch trim monitoring. A pitch mistrim condition may cause the following annunciations to appear:

- "E" in a yellow box on the PFD

- "AP PITCH TRIM", "AP TRIM IS ND" or "AP TRIM IS NU" EICAS caution messages Follow the AFM Abnormal procedures if the above EICAS caution messages appear.

NOTE: Anticipate an out-of-trim condition if the autopilot is disengaged.

AOM-870 Page 2 of 3

Comment:

It is considered that leaving the autopilot engaged is preferable (provided that none of the above EICAS messages are displayed) as disengaging it may require a reduction from normal cruise speeds as per the MACH TRIM abnormal procedure, and this speed change will induce control force requirements, which will have to be borne by the crew for the balance of the flight. Note that the autopilot must be disengaged (refer to AFM) if any of the above EICAS caution messages appear.

• If autopilot is NOT engaged:

Assuming that the loss of the STAB TRIM function occurred while in-trim, changes to airspeed and configuration should be minimized to remain in-trim as long as possible, reducing control force requirements, subject to the restrictions on speed noted in the MACH TRIM caution procedure.

If/when the flaps are extended, the pilot should anticipate a transient pitch effect. Less nose up trim is generally required at the same airspeed with a greater flap angle, therefore, some alleviation in nose-up control forces may be obtained by extending the flaps at a constant speed. If a STAB TRIM message occurs at a flap setting greater than 20 degrees, minimize configuration and speed changes as long as practical to help maintain an "In Trim" condition.

Please direct responses and inquiries to your Bombardier Aerospace Regional Aircraft Field Service Representative or the Technical Help Desk in Montreal at telephone number (514) 855-8500 or facsimile (514) 855-8501 or thd.crj @aero.bombardier.com Tracy Lloyd, Manager and Martin Elliott, Director, In-Service Engineering, Bombardier Aerospace Regional Aircraft.

AOM-870 Page 3 of 3