Bombardier (Canadair) CL-600-2C10 and CL-600-2D24 (CRJ-700/900 Series) - Service Difficulty Alert

AL 2005-03
2 February 2005

Auxiliary Power Unit RE220 (RJ) Failure

Operators have reported incidents of smoke/smell in the cabin causing the lavatory smoke detector alarm to activate shortly after the auxiliary power unit (APU) start-up and/or shutdown. Investigations determined a degraded APU tie-shaft O-ring had allowed oil to migrate down the spline shaft past the tie-shaft threads, mixed with buffer air, and entered the APU inlet during start-up and shutdown only.

Honeywell, the APU manufacturer, has designed a new spline shaft that eliminates the leakage path by preventing oil from contacting the tie-shaft. Bombardier has issued an All Operator Message No. 244, dated 22 July 2004, to inform all CRJ700/900 operators of this problem.

Analysis has determined that the probability of APU tie-shaft O-ring failure is higher for APU's that have accumulated more than 2,600 cumulative operating time. Honeywell has issued Service Bulletin No. RE220-49-7799 to replace the spline shaft, P/N WE897997-3 with P/N WE3822661-1.

This design change will be introduced as follows:

  1. In Production: At APU Serial Number P-288 and subsequent; and
  2. In Service: By the incorporation of Honeywell Service Bulletin RE220-49-7799 or Overhaul Repair Instruction T40925.

Transport Canada recommends operators:

  1. Limit APU pneumatics to on-ground use only, for APUs that have accumulated more than 2,600 cumulative APU hours, and not yet modified as per Honeywell Service Bulletin No.RE220-49-7799, dated 17 June 2004, or Overhaul Repair Instruction T40925 dated 16 April 2004, or later revisions;
    NOTE: During an AFM Emergency or Abnormal situation, the APU can be used as required.
  2. Modify the affected APUs as per Honeywell Service Bulletin No.RE220-49-7799 or Overhaul Repair Instruction T40925 at the next APU shop visit; and
  3. Report any further defects or occurrences via the Service Difficulty Reporting program.

For further information contact a Transport Canada Centre, or call Mr. Luc Deniger, Continuing Airworthiness, Ottawa, telephone 613 952-5385, facsimile 613 996-9178 or e-mail

For Director, National Aircraft Certification

B. Goyaniuk
Chief, Continuing Airworthiness

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