What happened
On January 24, 2018, a Beechcraft C90GTi (registration D-ICMK) was performing a flight from Prague (LKPR) to Coburg, Germany (EDQC) with a pilot and two passengers. During the climb to flight level 160, smoke began emerging from beneath the cockpit floor.
In response to the smoke, the pilot followed emergency procedures, which included turning off the avionics power to isolate potential electrical sources. This action resulted in the loss of SSR transponder information and radio communication with Prague Radar for several minutes. The pilot also executed a turn to return to the departure airport, but did not immediately declare an emergency or set the transponder to code 7700.
After re-establishing contact with air traffic control, the pilot declared an emergency due to the smoke and requested an immediate return to Prague. The aircraft landed on runway 12 at LKPR at 16:26 UTC, where emergency services met the aircraft. All 3 persons on board were evacuated. While no injuries were reported, the aircraft sustained light damage.
The investigation
The ÚZPLN investigation focused on the source of the smoke and the pilot's actions during the emergency. Investigators examined the aircraft's climate control system and the cockpit environment.
Upon inspection, firefighters found no active fire, though smoke was still emanating from the area under the left pilot-side foot controls, and the smell of burnt insulation was present. A subsequent technical inspection by a maintenance engineer identified a failure in the electric motor of the air conditioning blower (EM603-9). The investigation also reviewed the pilot's compliance with the manufacturer's emergency checklists and the effectiveness of the onboard oxygen systems.
Findings
- The primary cause of the incident was a technical failure involving an electrical short circuit in the power supply section of the air conditioning blower motor.
- This short circuit caused the insulation to melt, resulting in intense smoke production within the cabin.
- The pilot followed the manufacturer's emergency procedures correctly regarding the smoke emergency, including the decision to return to the departure airport.
- The pilot failed to promptly report the smoke to ATC or set the transponder to the emergency code 7700, and changed course without prior notification.
- The loss of radar and radio contact was a direct consequence of the pilot's decision to shut down the avionics power to mitigate the electrical risk.
- The passengers utilized oxygen masks, but the open-type masks used for passengers allowed some smoke to enter the breathing area during deep inhalation.