Carbon monoxide poisoning case study

Disclaimer: This case study is based on a real incident.

Simon, a 34-year-old flight instructor, is preparing his Piper PA-28 for a training session at Parafield Airport in Adelaide. Simon is an experienced pilot with more than 3,000 flying hours. Today he is taking a student pilot for their first flight as pilot-in-command.

Jen is a 20-year-old cadet. She has had a passion for aviation since childhood and has proven to be a diligent student in the classroom. She arrives at the airfield bright and early in preparation for the flight.

Simon asks Jen to perform the pre-flight inspection of the aircraft, including reading the latest maintenance release. She conducts them with accuracy, but Simon shadows her to ensure she doesn't miss anything. Jen notes the last maintenance report was signed off a week ago and no deficiencies with the aircraft were recorded.

With checks complete, they both climb into the cabin and set off for the morning.

Early suspicions

Jen taxis the Piper along the apron and confirms the flight path with Parafield tower who gives her take-off clearance. Jen increases the thrust of the aircraft and the engine roars. Within minutes they are up and away – a routine take-off.

It's a crisp July morning. The sun is shining and not a cloud in the sky. The air is clear and smooth – a perfect day for flying. It should only take about 15 minutes to fly to the Western Training Area over St Vincent Gulf, perform a couple of manoeuvres and return to join the circuit before landing.

The Piper reaches the cruising altitude of 2,000 feet when Simon notices the faint smell of exhaust fumes in the cabin. He checks the carbon monoxide detector located near the control panel. The detector changes colour if CO was present, but it has remained its neutral beige. It's a cold morning and they have the cabin heater turned on, so he dismisses the smell as the heater warming up. Besides, as they climb higher, the exhaust smell seems to go away.

After 5 minutes, Simon notices the aircraft banking slightly to the left. He's also starting to feel a slight headache come on. As Simon turns to Jen to ask her to correct the attitude, he notices she is blinking rapidly. Beads of sweat have started to form on her forehead. He checks the CO detector again, but the colour still hasn't changed.

Becoming increasingly suspicious, he reaches inside his flight bag and pulls out his portable electronic CO detector. As soon as he switches it on, a loud alarm immediately blares.

Simon can’t believe it – the cabin air is contaminated with toxic CO gas.

He immediately turns off the heater and opens the fresh air vents. He instructs Jen to turn the aircraft around and head back to the aerodrome. With the high level of CO indicated on the detector, combined with the time they’ve been up in the air, Simon knows there is not much time left until they become incapacitated.

Thankfully, Jen manages to land the aircraft 7 minutes after the detector first alerted them of CO in the cabin. Both pilots exit the aircraft and taken to the local hospital for observation. Doctors diagnosed them with mild CO poisoning.

Maintenance follow up

The next day, after doctors clear both pilots, Simon arranges to meet David, the flight school’s head LAME.

He tells David an electronic CO detector had read elevated levels of the gas were present in the cabin during flight. Yet the flight school-approved fitted colour-metric detector did not.

David opened the engine cowling to inspect the condition and integrity of the engine firewall. From an initial glance, he can’t see anything wrong. However, on closer inspection with a torch and mirror, he notices a small opening in one of the access panels on the engine firewall. The access panel has some missing screws and the seal is missing or deteriorated.

'There's a big part of the problem,' David explains. 'This insecure access panel has allowed engine exhaust gases to seep through the firewall and into the cabin. We now also need to inspect again the entire engine exhaust system to look for leaks. There may be a crack or hole in one of the exhaust manifolds, slip joints or pipes'.

'We need to fix this immediately to ensure the integrity of the engine firewall and prevent further occurrences of CO gases penetrating into the cabin.'

David checks the carbon monoxide detector patch in the aircraft. Although the detector is still within its serviceable date range, he says it is faulty due to heat and sun damage. He tells Simon that pilots often park this aircraft on the apron in direct sunlight for long periods when they are not using it.

The outcome

In response to Simon’s close call, the flight school revised maintenance procedures to include steps to remind engineers to look for cracks or defects in:

  • engine firewalls
  • heating ducts
  • heating control valves
  • exhaust system.

The school fitted all operating aircraft operating with electronic CO detectors. Additionally, the school issued each flight with a handheld CO detector. If one fails, the other will detect any leak.

Simon and Jen were lucky to have been able to land the aircraft safely before the CO affected them too greatly. Not all pilots are as fortunate.

Lesson learnt

Always carry a portable electronic CO detector when you fly and make sure it is turned on. It could save your life one day.

Last updated:
20 Dec 2023
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