Shortly after take-off, in rain and IMC, the master warning lights, right tailpipe hot light on the central warning panel, and the associated aural alarm of the Saab 340 activated. The crew declared a PAN and advised the air traffic controller that they wished to return to the airport.
After completing the appropriate checklist items, the crew shut down the right engine and the captain advised the passengers that the aircraft was returning to Melbourne. The flight attendant then entered the cockpit and advised the flight crew that there appeared to be smoke in the cabin. The captain declared a MAYDAY while the flight attendant returned to the cabin to attempt to identify the source of the smoke. The flight crew put on their oxygen masks. Shortly afterwards, the flight attendant returned to the cockpit and advised that there was no heat in the smoke and it appeared to be mist or water vapor. The flight crew subsequently conducted a normal single-engine landing.
An engineering inspection of the aircraft did not identify any evidence of fire or problems with the heat detector wiring harness. Subsequent testing identified anomolies with one of the heat detectors. The detector was removed, tested, resealed and replaced, and the system functioned normally.
There have been a number of previous incidents of false tailpipe hot warnings involving Australian-registered Saab 340 aircraft, and the aircraft manufacturer has issued a service bulletin that was intended to improve the moisture protection and strength of the heat detection wiring harness. The aircraft had been modified in accordance with the provisions of the service bulletin.
Mist or water vapour emanating from the cabin air conditioning system vents is a relatively common occurrence in Saab 340 aircraft, particularly when the aircraft is operating in conditions of high humidity. The drying function of the environmental control system is not completely effective in these conditions and moisture (in the form of water vapour) may enter the cabin.
|Date:||23 October 2000||Investigation status:||Completed|
|Time:||1923 hours ESuT|
|Location:||5 km SSE Melbourne, Aero.|
|Release date:||04 July 2001|
|Report status:||Final||Occurrence category:||Incident|
|Highest injury level:||None|
|Aircraft manufacturer||S.A.A.B. Aircraft Co|
|Type of operation||Air Transport Low Capacity|
|Damage to aircraft||Nil|
|Departure point||Melbourne, VIC|
|Departure time||1921 ESuT|