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

Re :

Aviation Safety Advisory A19W0001-D1-A1
De Havilland Aircraft of Canada DHC-8-400 – Failure of the alternating current power feeder connectors

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).

Figure 1. DHC-8-400 aircraft maintenance manual, showing location of AC contactor box and connector P5 (Source: Bombardier Inc., with TSB annotations)
Image
DHC-8-400 aircraft maintenance manual, showing location of AC contactor box and connector P5 (Source: Bombardier Inc., with TSB annotations)

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.

Figure 2. View of connector P5, showing burn and heat damage to the wires (Source: WestJet Encore)
Image
View of connector P5, showing burn and heat damage to the wires (Source: WestJet Encore)

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).

Figure 3. Area of heat damage at row 14 of the aircraft in occurrence A18A0018, shown with left cabin wall upholstery removed (arrow indicates electrical connector 9811-J711) (Source: TSB)
Image
Area of heat damage at row 14 of the aircraft in occurrence A18A0018, shown with left cabin wall upholstery removed (arrow indicates electrical connector 9811-J711) (Source: TSB)

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,

Original signed by

Natacha Van Themsche
Director of Investigations — Air
Transportation Safety Board of Canada

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

TSB Occurrence SDR Date Registration Component Connector Operator
A14F0015 20140203016 1/21/2014 5Y-VVY 2531-J711 arcing in connector. MS3450L24-11S Kenya - Blue Bird Aviation
  201508015396 3/17/2015 N412QX Wire shorted to ground between 9811-P718 Pin F and 9811-J611 pin 14 at the wing root.   USA - BCC Equipment Leasing
  20151007007 9/30/2015 GLQC Left hand wing root wire bundle burnt.   Porter Airlines Inc.
  2016010902270 12/18/2015 N423QX Arcing at connector 2421-P5; all pins A through F are damaged; connector replaced. MS3459LS24-10P USA - Horizon Air Industries
A16W0020 20160210004 2/10/2016 GWEP Arcing at connector 2421-P5-1. MS3459LS24-10P WestJet Encore Ltd.
A16C0044 20160509017 5/4/2016 GGCI Left hand AC feeder connector 9811-J711 burnt. Connector 9811-J711 and 9811-P711 located at wing root bulkhead replaced. MS3450L24-11S
MS3459L24-11P 		Jazz Aviation LP
  20160920013 9/18/2016 FENJ 9811-P711 pins D-E-F damaged.
Connector Replace.		 MS3459L24-11P WestJet Encore Ltd.
  20170117017 1/16/2017 GSJZ Wires chafed at wing root to fuselage location.   Jazz Aviation LP
  20170117016 1/16/2017 GSJZ Wing Root connector 9811-J701 and P701 burnt.   Jazz Aviation LP
  20170308014 3/6/2017 GJZH Wiring broken and burnt at clamp location in wing root. The wiring is 3 phase AC which feeds to connector 9811-P712 on rear spar.   Jazz Aviation LP
A17W0040 20170320012 3/17/2017 GGFP Connector 9811-J711 found burnt. MS3450L24-11S Jazz Aviation LP
  20170428001 4/27/2017 GJEN Left hand wing root connector 9811-P701 heat damaged; connector replaced.   WestJet Encore Ltd.
  20180103008 1/3/2018 GGMZ EPCU connector 2431-P12, pin 9, found out of position; pin 9 secured. No. 2 AC generator control unit connector, pin T, shorted to its own shield/ground. The short was traced back between connector 9811-P702 pin V and connector P1, pin 36, located at the wing root clamp.   Jazz Aviation LP
  20180315006 3/12/2018 GLQH The following was found: P746 pin C found loose, P718 pin A found loose, J700 all pins found loose, P712 pins A,B,C,G,H,I found loose, J718 replaced and 9811 J and P found loose.   Porter Airlines Inc.
A18A0018 20180313010 3/12/2018 GLQG Arcing found in connector 9811-J711. Connectors 9811-J711 and 9811-P711 replaced. Maintenance crew aware of Service Letter DH8-400-SL-24-016. MS3450L24-11S
MS3459L24-11P 		Porter Airlines Inc.
  20180316003 3/13/2018 FLQY Connector 9811-J and P reported loose.   Porter Airlines Inc.
  20180719008 7/16/2018 GDEW Heat and arcing damage at the right hand AC contactor box at contactor K7; terminal B2.   WestJet Encore Ltd.
  20181024012 10/21/2018 GLQL Right hand wing root feeder cable terminal mounting stud at position TB 10 found burnt.   Porter Airlines Inc.
A19W0001 20190108007 1/7/2019 FWEP Arcing at connector 2421-P5 pin 2 at right hand AC contactor box. Connector  and AC contactor box replaced. MS3459LS24-10P WestJet Encore Ltd.
  20190318017 3/15/2019 GKUK Arcing connector 2421-P5 Pin D. Connector replaced. MS3459LS24-10P Jazz Aviation LP

Background information

Occurrence No.: A19W0001

This Safety Communication No.: A19W0001-D1-A1