What happened
On 26 February 2001, a Shorts SD3-60 Variant 100, registration G-BNMW, was prepared for a scheduled passenger service from Glasgow Airport to Islay. Upon arrival at the aircraft, the commander identified significant snow accumulation on the upper surfaces. Following the boarding of 13 passengers, the aircraft underwent de-icing using Type II fluid. During the taxi phase, the crew activated the airframe anti-ice systems and air conditioning bleed valves.
After departing Glasgow at 1024 hrs, the aircraft climbed to approximately 2000 feet when the cabin attendant reported dense, dark grey smoke with a chemical odor filling the rear of the cabin. The commander declared a MAYDAY and requested an immediate return to Glasgow. To mitigate the issue, the first officer switched off both air conditioning valves. During the descent, the crew monitored electrical loads on the anti-ice systems, which remained normal.
The aircraft landed on Runway 05 at 1035 hrs. Following engine shutdown, the crew performed an orderly evacuation via the left rear door. Although the Airport Fire Service used thermal imaging and found no active fire or heat source, they observed large quantities of de-icing fluid dripping from the airframe.
The investigation
An investigation led by the operator's Quality Manager determined that the smoke was caused by the heating of substantial amounts of de-icing fluid within the cabin conditioning pack ducts. It was established that this fluid had entered either the engine intakes or the air conditioning system ducts.
Records indicated that approximately 500 litres of de-icing fluid had been applied to the aircraft, a volume significantly higher than typically required for such operations. The investigation noted that snow deposits had not been brushed off the aircraft prior to the application of the spray, and the operator's existing protocols did not mandate the use of engine intake blanks during the de-icing process.
Findings
- The smoke in the cabin was a result of de-icing fluid entering the air conditioning system and being heated.
- An excessive amount of de-icing fluid, roughly 500 litres, was used during the procedure.
- Snow was not removed from the aircraft surfaces before the de-icing fluid was applied.
- There was no requirement in the operator's procedures to cover engine intakes during de-icing.