History of Flight
The aircraft, a Boeing 767-300 (registration D-ABUK), was en route from Kangerlussuaq, Greenland to Frankfurt, Germany on a non-revenue commercial air transport flight. During the climb, the flight crew noticed an unusual smell, but it dissipated by the time the aircraft reached cruising altitude, so they continued. Approximately one and a half hours later, the smell reappeared and remained constant. While discussing their options, the first officer observed smoke emanating from around Window 1R (the right windscreen). The crew donned oxygen masks, declared a MAYDAY, and initiated a diversion to Newcastle Airport. After a few minutes, the smoke dissipated, and the aircraft landed without further incident. The flight had four crew and four passengers on board; no injuries were reported.
Aircraft Examination
Troubleshooting by the operator revealed that the right windscreen was damaged, along with its terminal block (J5), terminal lug, and cable loom. The aircraft was subsequently ferried to Frankfurt with the window heat isolated so the damaged components could be replaced. A more detailed examination of the affected parts identified that the terminal lug was not parallel to the terminal block. This misalignment could allow the mounting screw to become loose, creating a high resistance connection with the potential for overheating. No reason for the incorrect alignment was identified. The affected parts were returned to the manufacturer for further examination.
Safety Actions
Following its investigation, the operator took the following safety actions:
- Adopted a double inspection requirement for electrical terminal installation after windscreen replacement.
- Reduced the repeat inspection threshold for windscreen electrical terminals from 500 flight hours to 100 flight hours.
- Introduced an additional engineering condition inspection for all windscreens entering stores.
- Conducted a fleet check to ensure correct installation of windscreen terminal connections.
- Clarified Aircraft Maintenance Manual (AMM) task 56-11-01-404-017 to perform the resistance test of the window heater element before installation to prevent the J5 terminal block connection from being made twice.
- Added advice to AMM task 30-41-00-765-046 to use a torque wrench when connecting wiring to window terminals.
- Evaluated a coordinated replacement of windscreens not using the later design pin and socket connections.