On 27 May 2023, a Cessna 650 had just taken off from Aalborg when non-electrical smoke began to enter the flight deck and became so dense that it was impossible to navigate visually. An immediate MAYDAY return was made during which the smoke decreased sufficiently to make an overweight visual landing. It was concluded that failure of one of the air cycle machines had been caused by a contaminated heat exchanger due to maintenance requirements not clearly outlined in the aircraft maintenance programme.

On 12 July 2023, the crew of an Airbus A380-800 in the climb at night after departing from Johannesburg detected an acrid smell in the air circulated in both the flight deck and the passenger cabin. Concern at a possible health issue if the intended long flight was completed prompted the decision to return to Johannesburg. A MAYDAY was declared and the return accomplished without any further worsening of the situation. The cause of the contaminated airflow was later found to be a malfunctioning Air Cycle Machine.

On 9 February 2023, a Boeing 777-200ER was en route near Marseille when the cabin crew observed smoke coming from a rear galley oven, which was spreading into the rear passenger cabin. After an initial use of multiple Halon fire extinguishers, the smoke ceased after about 20 minutes, but the fumes remained. Although this meant no ongoing emergency existed, some cabin crew and passengers experienced breathing difficulties and it was decided to return to Amsterdam. The cabin crew response to the situation was subsequently assessed as contrary to applicable procedures and relevant cabin crew training seemingly inadequate.

On 23 February 2016, a Boeing 737-800 departing New Chitose encountered sudden-onset and unforecast heavy snowfall whilst taxiing out. When the right engine ran down and cabin crew reports of unusual smells in the cabin and flames coming from the right engine were received, it was decided that an emergency evacuation was required. During this evacuation three passengers were injured, one seriously. The engine fire was found to have been in the tailpipe and caused by an oil leak due to engine fan blade and compressor icing which had also led to vapourised engine oil contaminating the air conditioning system.

On 16 March 2020, a PW150A-powered Bombardier DHC8-400 crew declared a PAN and turned back to Port Moresby after abnormal fumes and (much later) some visible ‘smoke’ which had become apparent after takeoff began to intensify causing some passengers breathing difficulties. Once clear of the landing runway, a precautionary rapid disembarkation was completed. The Investigation found that the source of the smoke/fumes was oil leaking from a failed right engine bearing seal. The failure was found to have occurred ahead of the recommended inspection interval for the seal concerned, a risk which engine manufacturer Pratt & Whitney Canada was aware of.