Aviation safety advisory A19W0001-D1-A1

200 Promenade du Portage
Gatineau QC  K1A 1K8

11 June 2019

Letter addressed to:
Director General, Civil Aviation
Transport Canada

The following safety advisory is to bring to your attention a safety issue involving alternating current (AC) connector failures on De Havilland Aircraft of Canada Ltd.^{Footnote 1} (De Havilland) DHC-8-400 series of aircraft.  

On 06 January 2019, a DHC-8-402 aircraft (registration C-FWEP), operated by WestJet Encore, was conducting flight WEN3125 from Edmonton International Airport (CYEG), Alberta, to Kelowna Airport (CYLW), British Columbia. During the climb to cruising altitude after the departure from CYEG, the flight crew observed several caution lights related to various electrical systems and to the failure of both AC generators. The flight crew declared a PAN PAN and executed the appropriate quick reference handbook checklists. After carrying out the checklists, the R TRU, PITOT HEAT 2, ENG ADAPT 2, DE ICE PRESS, and PUSHER SYST FAIL caution lights remained illuminated. The flight crew consulted WestJet Encore's operational and maintenance control centres. Because the aircraft de-icing systems were no longer functional due to the AC system failure, the flight crew decided to divert to Calgary International Airport (CYYC), Alberta, where the aircraft landed without further incident. Data collection for this Class 5 occurrence (A19W0001) is ongoing.

After C-FWEP landed, WestJet Encore maintenance began to inspect the aircraft and found evidence of arcing from a 115 V, 3-phase AC supply feeder in the right-hand wheel well at the AC contactor box connector plug assembly (designator number 2421-P5-2) (Figure 1).

The plug assembly was taken apart during the removal process and shipped to the Transportation Safety Board of Canada (TSB) Engineering Laboratory in Ottawa, Ontario, for analysis. The plug assembly and accompanying wiring were heavily damaged by heat and arcing (Figure 2). The crimp barrels of several pins had completely melted such that the pins’ mating ends were severed from their respective wires. The crimped section of one pin had also melted, and the length of wire extending back to the cable clamp was missing and not recovered.

DHC-8-400 aircraft variable-frequency AC power feeder connectors, installed between the AC contactor box and the flight compartment’s variable-frequency AC circuit breaker panel, have a history of failure due to arcing. In addition to occurring in the AC contactor box in the nacelle, these events have also occurred in the aft wing-root connector (designator number 9811-J711). This is where the No. 1 AC power feed wiring is routed through the left wing to enter the fuselage and then forward to the 115 V variable-frequency AC circuit breaker panel in the flight compartment. TSB Air Transportation Safety Investigation Report A18A0018 featured an arcing and fire event in this area (Figure 3).

In October 2016, following two occurrences involving AC power feeder connectors, Bombardier Inc. issued Service Letter DH8-400-SL-24-016. The service letter advises air operators to carry out inspections to detect play in the pin-locking mechanism and identify conditions that may cause stress in the wires of the AC power feeder connectors in the left and right AC contactor boxes (engine nacelles) and in the left- and right-hand side wing-root connectors. However, the actions published in the service letter have not been made mandatory by an airworthiness directive; it is not known how many air operators have completed the recommended actions specified in the service letter or what conditions have been identified. As a result, the manufacturer may not have the information required to take further action to address this issue.

A search in Transport Canada’s Service Difficulty Reporting System identified 20 occurrences since 2014, in which AC power feeder connectors sustained damage (Appendix A). Thirteen of those events described electrical arcing or heat associated with the connectors, and occurred after the service letter was issued by Bombardier Inc.  Occurrence A19W0001 is the 6th occurrence to have been investigated by the TSB; 4 of those 6 occurrences involved analysis by the TSB Engineering Laboratory. The root cause of these issues have not been determined at this time; nonetheless, it was determined that the connector contacts were rated for a maximum of 46 A, whereas the circuit was protected by a 50 A circuit breaker. Further investigation is required to study the following aspects of the design: installation, quality assurance, circuit breaker protection and wire bundle manufacturing.

As such, Transport Canada may wish to take action to address this safety issue, and work with De Havilland to develop a more robust strategy for inspection and repair/replacement of the AC power feeder connectors in the DHC-8-400 series of aircraft.

The TSB would appreciate being advised of any action that is taken in this regard.

Yours sincerely,

cc:

• De Havilland Aircraft of Canada Ltd.
• Jazz Aviation LP
• WestJet Encore Ltd.
• Porter Airlines Inc.
• Conair Group Inc.
• Hydro-Québec
• World Wide Aircraft Ferrying Ltd.

Appendix A – Previous occurrences found in Transport Canada’s Service Difficulty Reporting System

Background information

Occurrence No.: A19W0001

This Safety Communication No.: A19W0001-D1-A1