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| Date: | Tuesday 29 November 1994 |
| Time: | c. 17:45 LT |
| Type: |  British Aerospace 4107 Jetstream 41 |
| Owner/operator: | Impulse Airlines |
| Registration: | VH-IMR |
| MSN: | 41038 |
| Year of manufacture: | 1994 |
| Fatalities: | Fatalities: 0 / Occupants: |
| Other fatalities: | 0 |
| Aircraft damage: | None |
| Category: | Serious incident |
| Location: | 80 KM Southwest of Sydney -
 Australia
|
| Phase: | En route |
| Nature: | Passenger - Scheduled |
| Departure airport: | Melbourne-Tullamarine Airport, NSW (MEL/YMML) |
| Newcastle Airport, NSW (NTL/YWLM) | |
| Investigating agency: | BASI |
| Confidence Rating: |  Accident investigation report completed and information captured |
During cruise at FL250 in instrument meteorological conditions with light to moderate icing, the crew reported that the aircraft yawed to the left and the left engine ran down to about 4% torque then recovered in about 2 seconds. About 1 minute later the same problem occurred to the right engine. The pilot requested a descent to FL180 and disconnected the autopilot to hand fly the aircraft. About 30 seconds later both engines almost simultaneously suffered the same problem again. The crew carried out checks for erratic engine behaviour and requested a descent into Sydney for a precautionary landing. The remainder of the flight was uneventful.
Extensive ground checks revealed that neither engine had sustained damage as a result of the event. Flight Data Recorder information indicated that the first event occurred on the left engine when the torque fell to 26.4% with a loss of 1.8% RPM which recovered in about 4 seconds. One minute 24 seconds later the left engine again suffered a torque loss to 18.6% with a loss of 3% RPM recovering in about 3 seconds. About 30 seconds later the right engine suffered a similar event. Torque dropped to 18.7% with an RPM loss of 3.8% recovering in 3 seconds. These events occurred at FL250, and no further events were recorded. Propeller and engine anti-icing were on at the time and continuous ignition was selected.
Information from the Bureau of Meteorology indicated that the aircraft was in light rain at the time and the water droplets were probably supercooled.
Significant Factors:
The following factors were considered relevant to the development of the incident.
1. The aircraft encountered an area of supercooled rain.
2. Both engines have into-wind steps at the inlet cowl to spinner fairing which allowed the formation and probable ingestion of ice.
3. Engine power recovery was effected by the ignition system.
Safety Recommendations:
Recommendation R950102:
The Bureau of Air Safety Investigation recommends that the Civil Aviation Safety Authority amend all Jetstream J 4100 Minimum Equipment Lists to include an audible test of the engine ignitors to ensure correct operation prior to despatch with the auto re-ignition system inoperative.
Accident investigation:
 |
|
Sources:
https://www.atsb.gov.au/sites/default/files/media/4934340/199403561.pdf
https://www.jetphotos.com/photo/8084622 (Photo)
Location
Revision history:
| Date/time | Contributor | Updates |
|---|---|---|
| 13-Oct-2025 02:05 | Justanormalperson | Added |
| 13-Oct-2025 02:07 | Justanormalperson | Updated |
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