Although there are at least three distinct theories, there can be no solid conclusion as to how or why the pilot lost control of the aircraft. One Internet website makes the statement that the flight crew was overcome by CO2 and lost control of the plane after losing consciousness. While this is a strong possibility, it can not be stated as fact.
The supposition that the flight crew were overcome by CO2, in my opinion, arises from an October 9, 1964 letter from the Civil Aeronautics Board Bureau of Safety to Mr. George Moore, Director of Flight Standards Service for the F.A.A. The letter can be read in its entirety as “Attachment #2” in the Civil Aeronautics Board Aircraft Accident Report.
The letter notifies Mr. Moore of static and inflight tests performed on similar Viscount aircraft fire extinguishing systems for the underfloor cargo compartments; the results of which concluded that there were “certain discrepancies which could seriously affect the safety of the aircraft and passengers”.
Upwards of 15 Pyrene Duo Head Model DCD-10 fire extinguishers (which are located behind the First Officer for portable use)were discharged in to the underfloor compartment using a flexible hose configuration for static tests and a rigid tube for inflight tests. “At least five of the fifteen tests resulted in gas escaping into the cockpit where CO2 concentrations in the atmosphere were measured in maximum values of 12 percent. This leakage occurred at the bayonet floor fitting on the flexible hose installations and at the valve in the bottle discharge head of the extinguishers with the rigid tube installation. In each of these cases very little of the CO2 was discharged into the underfloor compartment.”
The letter mentions a second discrepancy regarding the extinguishers that are discharged electrically in the underfloor cargo area. Several seal diaphragms were improperly installed, off center, on extinguisher discharge heads which tests showed to result in incomplete or improper ruptures. “The Viscount Maintenance Manual contains explicit instructions for ensuring that the seal diaphragm is centered over the discharge valve opening. However, from the number of mispositioned seals noted during tests, it is apparent that the manual instructions are not being followed… the Board believes that the Pyrene fire extinguishing system for the underfloor cargo compartment as installed on Viscount aircraft is not only inadequate for its intended purpose but also poses a danger to the flight crew.”
While the tests and their results should not be discounted, they still do not amount to proof that the flight crew succumbed to CO2. Also, the tests themselves are not an indication that one of the crew manually discharged a fire extinguisher into the cargo bay. Later findings, that the fire took place in the cabin area, would tend to discount the notion that a crew member would have tried to manually discharge the extinguisher into the cargo bay because that, in all likelihood, is not where the fire initially took place.
There was evidence that a CO2 extinguisher had been used by a crew member, but it most likely had been used in the cabin area. The opening of spill valves, the left side cockpit window and emergency exits was, according to the CAB report, probably done in connection with smoke evacuation efforts.“ It was also found that a portable water extinguisher and a flight crew walk-around oxygen bottle had been used. Page 10 of the reports states that the forward cargo compartment CO2 extinguisher had been fired electrically.
The C.A.B report also stated, regarding the discharge of CO2 into the baggage compartment: “Spill valves to “spill” and discharge of CO2 into the baggage compartment are procedural items to combat a cargo compartment fire and were accomplished. It is recognized that accomplishment of these two items is not compatible with the conclusion that an inflight fire did not originate beneath the cabin floor. Any attempted explanation must of necessity be conjecture. However, it is considered likely that as the situation aboard the aircraft became very grave, precise checklist items were supplemented by any action that offered even a remote possibility of being helpful.”
It is important to note that the date that the Civil Aeronautics Board Aircraft Accident Reportwas adopted June 2, 1966. This is almost two years after the C.A.B's Bureau of Safety expressed concerns to the F.A.A Flight Standards Service about the possible risks associated with CO2 entering the cockpit by way of the forward cargo compartment. The risks of CO2 were considered by the Board yet, they were not mentioned in the final conclusion that read, “In examining the final maneuver and crash, it is apparent that the aircraft was not under control of the crew. There are a number of hypotheses that can be advanced to explain this loss of control including: distraction of the pilot; failure of the flight control rods due to fire damage; incapacitation of the pilot by heat and/or smoke, a shift of loading caused by passengers moving to the aft end of the cabin; an overt act by some person aboard the aircraft, or any combination of these.
There is no probative evidence available to the Board on which to base a determination as to the cause of the final maneuver.”
The dangers of CO2 fire extinguishing systems can be found on the Environmental Protection Agency site, in the article:
“The health effects associated with exposure to carbon dioxide are paradoxical. At the minimum design concentration (34 percent) for its use as a total flooding fire suppressant, carbon dioxide is lethal. But because carbon dioxide is a physiologically active gas and is a normal component of blood gases at low concentrations, its effects at lower concentrations (under 4 percent) may be beneficial under certain exposure conditions. ( Appendix B discusses the lethal effects of carbon dioxide at high exposure levels (Part I) and the potentially beneficial effects of carbon dioxide at low exposure concentrations, as well as the use of added carbon dioxide in specialized flooding systems using inert gases (Part II))
At concentrations greater than 17 percent, such as those encountered during carbon dioxide fire suppressant use, loss of controlled and purposeful activity, unconsciousness, convulsions, coma, and death occur within 1 minute of initial inhalation of carbon dioxide.
At exposures between 10 and 15 percent, carbon dioxide has been shown to cause unconsciousness, drowsiness, severe muscle twitching, and dizziness within several minutes. Within a few minutes to an hour after exposure to concentrations between 7 and 10 percent, unconsciousness, dizziness, headache, visual and hearing dysfunction, mental depression, shortness of breath, and sweating have been observed.
Exposures to 4 to 7 percent carbon dioxide can result in headache; hearing and visual disturbances; increased blood pressure; dyspnea, or difficulty breathing; mental depression; and tremors. Part I of Appendix B discusses human health effects of high-concentration exposure to carbon dioxide in greater detail.
In human subjects exposed to low concentrations (less than 4 percent) of carbon dioxide for up to 30 minutes, dilation of cerebral blood vessels, increased pulmonary ventilation, and increased oxygen delivery to the tissues were observed.
These data suggest that carbon dioxide exposure can aid in counteracting effects (i.e., impaired brain function) of exposure to an oxygen-deficient atmosphere. These results were used by the United Kingdom regulatory community to differentiate between inert gas systems for fire suppression that contain carbon dioxide and those that do not (HAG 1995).
During similar low-concentration exposure scenarios in humans, however, other researchers have recorded slight increases in blood pressure, hearing loss, sweating, headache, and dyspnea. Part II of Appendix B discusses these results in greater detail.”
From the very beginning of the investigation into the crash of N7405 until the conclusion of the C.A.B report, the possibility of failure of the flight control rods due to fire has been cited as a possibility for the pilot's loss of control. Initial concerns had to do with a fire in the electrical bay that would have damaged the aluminum alloy flying control push pull rods. According to a British Aircraft Corporation internal memorandum Page 1: “The C.A.B are now of the opinion that the fire probably started in the electrical bay (Fuselage Station 414) below floor at the left side of the aircraft.”
The C.A.B use the following evidence to support their viewpoint, according to the B.A.C memo:
“The assumption is that a crack developed in a high pressure hydraulic pipe, which sprayed hydraulic fluid onto a hot electrical terminal causing a fire which eventually burnt through the aluminum alloy flying push pull rods. The fire also developed from the electrical bay up to the passenger cabin.'
Later on in the document, in preparation for the Public Hearing that was to take place in Knoxville, Tennessee, an anticipated question was raised: “Why were the flying control push pull rods not protected from fire in the cargo and electrics bay, and what would the likely behaviour be of a Viscount if the flying control rods were burnt through?”
At this time it can be said that a copy of the testimony from experts that took place at the Public Hearing January 11-15, 1965, in Knoxville is presently being sought by the author of this website. In my opinion, there can be no doubt that the testimony given played a large part in determining that an inflight fire took place in the cabin area.
To be sure, the tests made on the clothing that belonged to the man who jumped from the aircraft contributed a great deal in changing the minds of those who believed the fire took place in the electrical compartment. (I will devote a whole section to the man who jumped from the plane). However, it is interesting to note the assumption that a leak that sprayed hydraulic fluid onto a hot electrical terminal as being the cause for the fire that damaged the flight control rods was to become something less than what was previously considered.
From Civil Aeronautics Board Aircraft Accident Report Pages 13-14: “As previously stated there was extensive fire damage in the electrical bay. However, this fact alone cannot be considered significant. This area in the Viscount, as in the majority of low configured aircraft, is in close proximity to and between the fuel tanks. Thus, in a breakup, this is a likely area to receive a substantial quantity of spilled fuel and in turn to be heavily damaged by post impact fire. This fire damage pattern has been observed in many accidents where post impact fire occurred. The somewhat conflicting soot and discoloration patterns observed on certain isolated pieces from the electric bay area dictated further considerations with respect to inflight fire. The only likely source of over temperature in this compartment is a gross electrical fault to ground. The emergency procedure executed by the crew does not support a gross electrical system malfunction. An electrical source smoke or fire emergency is combated by turning the emergency power switch on and placing the battery master switch and generators off. Equipment that was operating at impact and DME operation to five miles before impact shows that this particular emergency procedure had not been executed.”
“Historically, under-the-floor fires that have persisted to a catastrophic stage have burned through the relatively light fuselage belly skin, have been observed by witnesses when present, and have left a path of partially burned debris on the ground. This did not happen in this case.”
“Finally, to involve the hydraulic fluid in an electric bay fire would have required two essentially simultaneous failures, fluid leakage and an electrically induced overtemparature or sparking situation for ignition. Physical evidence fails to support either of these occurrences. Although the object of a great amount of investigative effort, the origin of the fuselage fire being in the electrical bay could not be established on the basis of the available evidence.”
It should be noted that a Capital Airlines Vickers Viscount 745D, N7437, crashed and burned near Tri-City Airport, Freeland, Michigan on April 6, 1958. All 44 passengers and 3 crew members were killed.
It was determined in the Civil Aeronautics Board Aircraft Accident Report that “The probable cause of this accident was an undetected accretion of ice on the horizontal stabilizer which, in conjunction with a specific airspeed and aircraft configuration, caused a loss of pitch control.”
Later, on Page 3, the report states, ”…The entire wreckage was confined in an area almost equal to the length and span of the aircraft…Most of the aircraft was consumed by the intense fire which followed ground impact. There was evidence that several minor explosions occurred. These explosions were caused by the ignition of pockets of fuel which were formed after the aircraft struck the ground…The push pull rods, a part of the control system were not intact because portions of these rods, which are made of aluminum, had melted.”
There were no stated reasons in the C.A.B Report, Page 15, as to why “…a shift of loading caused by the passengers moving to the aft end of the cabin…“ is mentioned.
Also, there is no mention as to the discovery of seat belts or seat belt buckles and whether or not any were found fastened or unfastened in the wreckage.
It is my opinion that the Flight crew lost control of the aircraft because of the large amounts of thick smoke and intense heat from the fire.
The moment Flight 823 deviated from the Victor 16 Airway is when I believe the fire started in the passenger cabin.
According to the C.A.B report Page 10, **”All three supercharger spill valves actuators were found with their actuating rods in the “supercharge spill” position. This setting would dump supercharger air overboard rather than using it to pressurize the cabin…The interior locking mechanisms for the No. 4 and No. 9 windows on the left side were in the unlocked position, and the pilot's direct vision (DV) window was found unlocked and partially open.
It should be noted that No. 9 window was located in an area closer to the wreckage, having fallen after the free fall victim had exited the aircraft and before the crash. A British Aircraft Corporation memorandum reports that it was found 1/3 of a mile from the crash site.
Lab results, which will be discussed later, claim that tests on the free fall victims clothing, and burns which he suffered show that the amount of heat inside the aircraft was hotter after he left the aircraft, thus, in my opinion, the Captain lost consciousness and control of the aircraft.
The C.A.B report summary lists another possible scenario as “pilot distraction” being a reason for loss of control. This can be weighed and considered also.
However, it is not hard to imagine that the entirety of the last few minutes prior to the crash had to have been full of distractions.
The lack of radio communications is a great indicator of his being distracted.
Performing such tasks as opening cockpit windows and taking fire extinguishing measures, while having the presence of mind to operate the aircraft, indicates to me that, despite distractions characteristic of what proved to be an impossible situation, he lost consciousness due to heat and smoke.
I'm not certain that exposure to high levels of CO2 would have permitted him to take the measures that he did.