I just came across a report of two deaths from carbon monoxide leaking into an aircraft from a defective exhaust system. These type of accidents are not common but do occur from time to time. We need to be constantly reminded of this silent killer and the threat it presents to small aircraft operators, technicians, and repair facilities. This was a tragic loss that did not have to happen.
The accident
The accident occurred during a one hour planned flight to deliver a Piper Lance to a customer. The two men aboard were very experienced pilot flight examiners. The aircraft was observed over-flying the destination airport and continuing flight until it ran a tank dry, lost power and descended in a turn until impact. The heavy wing with fuel will usually drop forcing the uncontrolled aircraft into a spiral descent.
The report stated that the scene was grim but with both bodies intact and no blood anywhere. They were both unconscious at impact. The autopsy found that one man had a 71 percent and the other a 65 percent carbon monoxide blood saturation level. Anything over 50 percent saturation is considered the cause of death. Remember the movie and book by Robin Cook, "Coma"? The fictional story explained clearly what effect carbon monoxide has on the body. These men were probably unconscious within the first 30 minutes of the flight. This accident was totally avoidable.
The cause
Investigators found the heater muff and muffler badly corroded. This allowed exhaust gases to seep into the heater duct. The aircraft was 25 years old and the system was allowing exhaust gases to seep into the cockpit for some time. This can occur even with the heater control valve turned off.
If you have ever experienced a leak in an exhaust heater system, you know it could have been your last. I clearly remember the odor and smell from an exhaust heater as a kid in our family '37 Ford sedan. You pulled a cable and turned on a fan to start the heat flowing. This was very similar to small aircraft heaters. The heater was very efficient. The hot air came through a duct on the lower right hand side of the firewall. You knew right away that exhaust was coming into the heater duct by the odor. I called it the suicide heater. My father disabled this heater for good as soon as the odor was apparent. We all know that CO (carbon monoxide) does not have any odor in its pure form, but when mixed with exhaust gases and oil what you smell is the common exhaust pipe odor. This odor may give you a clue to the danger but it may not be present at all when only small amounts of exhaust gas are admitted to the cockpit. As pilots and mechanics we are all familiar with various odors in the cockpit that we sort of take for granted. It could be our last smell however.
Technicians alert
Technicians should be familiar with the two common combustion heat systems: the exhaust muff type, where both carburetor heat and cabin heat can be supplied and the gas combustion heater common in most piston twins and some singles. Gas combustion heaters are usually regularly pressure checked for combustion gas leaks into the heat system. ADs are usually controlling here.
Both of these sources use the heat from burned fuel and of course, one of the gases produced is CO, a deadly poison when ingested into your body. Your red blood cells absorb CO like a sponge! ("Coma"). The red blood cells have such an affinity for CO that it replaces the oxygen molecules very quickly. You start to feel drowsy and a short time later you are unconscious. It only takes a few minutes to saturate your blood system. Your body is deprived of oxygen and you expire.
There is no doubt in my mind that the technicians or repair facility who performed the last annual inspection on this aircraft and anyone else who recently performed maintenance on this aircraft will be in for a wrongful death lawsuit. The local district attorney may even consider a criminal negligence charge against the responsible party or parties.
Priority items
Heater and associated parts should be considered high priority items for the annual inspection on any equipped aircraft. I fear that not enough attention is paid to this area of the inspection. Exhaust mufflers and other parts should be checked for leaks and removed for any repairs. Special attention should be paid to all carburetor equipped engines with a check on the integrity of the carburetor heat and cabin heat systems. Any checklist used for the annual inspection should clearly show inspection and or repairs to the heater system. Consider a separate inspection sheet for this area by itself to show your emphasis on the importance of this part of the inspection.
Be sure to log any defects in the exhaust system that are not repaired at the time of your inspection. Defects should be clearly pointed out to pilot owners and operators and the danger involved highlighted. Get the customer's acknowledgement of these defects in writing, that is, have them initial your copy of any discrepancies not fixed during the inspection. As I have said many times in the past, this may not prevent a lawsuit when an accident happens but it will make the plaintiff's lawyers think twice about suing you or your company.
Further, I would urge all shops to consider supplying a carbon monoxide detector where none is present in the cabin. A small quality device can be purchased for very little cost that will provide peace of mind to both the pilot and the repair facility.
In addition, you should urge your customers to carry a small portable oxygen system with them in flight. This is of course important in a pressurized aircraft but also handy in the nonpressurized aircraft in case it is necessary for emergency use in the event of an exhaust leak into the cabin or to climb over weather. Some handheld oxygen containers are very light and compact and are reasonably priced for short duration emergency use.
Carbon monoxide
Carbon monoxide poisoning is a serious threat even outside the aviation field. It can affect you within minutes of breathing it and is probably responsible for more deaths than any other single poison. It kills you by replacing the oxygen in your red blood cells and, as stated, your blood absorbs it like a sponge. Most die in fires from the CO before the flames even reach them.
As an example, you might recall the piece I did on the infamous Ricky Nelson DC3 crash in Texas, New Year's Eve 1980. All of the cabin occupants were killed by smoke inhalation before the aircraft made an emergency landing, in an open field. The crew managed to exit via the cockpit windows and drop to the ground. The passengers were already dead in the cabin from inhalation of several poison gases, including CO.
This gas is odorless, tasteless, and colorless and can hurt you slowly in low levels, cause permanent neurological effects in moderate levels, and of course, as in the case cited, kill you in higher levels. We all should be aware of this danger at home, in our cars and anywhere a fossil fuel is being burned for heat. When burned in a heater designed for them, these fuels are usually not harmful. But, if the heating device is defective or not properly ventilated, it can be hazardous. If you have any other examples or comment please forward to [email protected].
Remember, low levels of carbon monoxide that might be leaking into your heating system, whether in the air or in your home, can be confused with other illness symptoms. Nausea, headaches, and light-headedness should be cause for a CO alert, especially if more than one person is showing the symptoms. AMT
