Smoke and fumes event involving a Cessna 208, near Horn Island, Queensland, on 18 March 2024

What happened

On 18 March 2024, a Cessna 208 (Caravan) aircraft was being operated with a pilot and one passenger on a service from Horn Island to Murray/Mer Island, Queensland. 

Shortly after take-off, the pilot became aware of very hot air entering the cockpit from beneath the instrument panel. The temperature of the air was such that the pilot chose to return the aircraft to Horn Island, and while doing so, pulled the cabin heat control in an endeavour to diagnose the issue. Shortly after, smoke began entering the cockpit area – described as ‘initially quite thick’, but beginning to clear with only ‘a little bit wafting up’.

After advising Brisbane Centre air traffic control of the decision to return and the flight particulars, the aircraft returned to Horn Island, where the pilot made an uneventful approach and landing. There were no reported injuries or adverse effects to the pilot or passenger.

Engineering inspections

The operator’s engineering inspections of the aircraft while grounded at Horn Island identified an engine bleed air control valve that had stuck and not fully closed, allowing a continuous flow of hot bleed air into the cockpit while the engine was operating. Heating of oil residues within the bleed air diverter box (part of the bleed air management system) created the smoke and fumes reported by the pilot.

Further investigations by engineering staff found that the bleed air control valve as-fitted to the occurrence aircraft was of a poppet-valve type (part number 1H101-3 or -4), whereas other C208 aircraft in the operator’s fleet employed a butterfly-valve type (part number 1422-6 or -7).

The aircraft maintenance documentation noted that the P/N 1H101-3/4 poppet valves were fitted to earlier C208 aircraft with serial numbers less than 20804999, whereas the P/N 1422-6/7 butterfly valves were specified for later aircraft with serial numbers 20805000 and above.

The aircraft operator also noted that the maintenance documentation for the valve removal, installation and servicing was not inclusive of aircraft within their fleet. Advice from the aircraft manufacturer, Textron Aviation, acknowledged the omissions and noted that the instruction scope would be expanded with the next manual revision.

Safety message

Operators and maintainers of Cessna Aircraft Company model 208 and 208B aircraft are advised to ensure the engine bleed air flow control valve/s fitted to their aircraft are inspected and maintained in accordance with the manufacturer’s instructions. In instances where aircraft serial numbers (or number ranges) are not covered by those instructions, operators and maintainers are encouraged to contact the aircraft manufacturer or representative to ascertain the specific maintenance activities that apply to those aircraft.

About this report

Decisions regarding whether to investigate, and the scope of an investigation, are based on many factors, including the level of safety benefit likely to be obtained from an investigation. For this occurrence, no investigation has been conducted and the ATSB did not verify the accuracy of the information. A brief description has been written using information supplied in the notification and any follow-up information to produce a short summary report and allow for greater industry awareness of potential safety issues and possible safety actions.