Week 7

Types of Hypoxia

Hypoxic Hypoxia: Results when Oxygen is unable to reach the lungs. When pilots are flying in high altitudes, less Oxygen is available to the lungs due to less atmospheric pressure. When flying in these situations, pilots and crewmembers should be using supplemental Oxygen (above 10,000 ft) to supply sufficient amounts of oxygen to the body at high altitude. If not, Hypoxic Hypoxia can set in a cause several side effects: Cyanosis, Headache, Decreased reaction time, Euphoria, Visual Impairment, Drowsiness, Light headed sensations, Dizziness, numbness and more.

Hypemic Hypoxia: Hypemic translates as “not enough blood”. Hypemic hypoxia results when blood is unable to transport oxygen with the blood cells throughout the body. This type of hypoxia can occur when someone has suffered blood loss such as blood donation. The FAA states that “A pilot who has donated 200cc or more of blood should wait at least 24 hours to fly”.  

Stagnant Hypoxia: Stagnant Hypoxia basically means what it says, the blood is stagnant and cannot flow normally. Stagnant hypoxia can occur when you pull excessive G forces in flight. You may also see stagnant hypoxia in extreme cold temperatures like winter in Alaska. Because its so cold, the blood naturally wants to stay in its core to keep vital organs warm. This prevents blood flow from the extremities and can cause stagnant hypoxia. Good heart health also plays a role in stagnant hypoxia, a heart must be healthy in order to pump healthy sufficient amounts of blood to the rest of the body.

Histotoxic Hypoxia: “Research has shown that drinking one ounce of alcohol can equate to about an additional 2,000 feet of physiological altitude.” When histotoxic hypoxia occurs, the blood is supplying enough oxygen but the tissues in the body are unable to use it due to the impairment effects of alcohol or drugs..

Stages of hypoxia: There are four stages of hypoxia; Indifferent, Compensatory, Disturbance, and Critical. The Indifferent stage is usually the stage where the effected person does not realize that they are becoming hypoxic. The compensatory stage is usually where hypoxia has set in and the pilot claims denial to the effects. Disturbance is where obvious effects of hypoxia show, like numbness and tingling sensations. The Critical stage is where the loss of consciousness has occurred. In this stage, there is basically nothing that can be done to revive the pilot of a flying aircraft as the crew and passengers are usually suffering from the same effects.


Be sure to watch out for yourself and especially the other person you may be flying with if you do fly at high altitudes. Hypoxia can set in quicker than others at lower altitudes as well. Anyone operating an aircraft must begin with examining themselves. Ask yourself whether or not you are fit to complete the task at hand or the flight you will be completing. Take the necessary steps to ensure you are healthy and  know your body so that you can better detect these symptoms in the event you do run into the effects of hypoxia.

Week 6

The FAA issued a new airworthiness directive during March of 2014. This Airworthiness Directive was for Boeing 777 model airplanes for structural cracks near an antenna. This AD will require frequent inspections for cracking and corrosion to the fuselage skin which can cause a rapid decompression or structural failures to the aircraft. Once decompression begins, the aircrafts cabin pressure will begin to equalize with the outside ambient pressure, which at altitudes overs 10,000 can prove to be uneventful for crew and passengers.

14 CFR Part 39
"SUMMARY: We are adopting a new airworthiness directive (AD) for certain The Boeing Company Model 777 airplanes. This AD was prompted by a report of cracking in the fuselage skin underneath the satellite communication (SATCOM) antenna adapter. This AD requires repetitive inspections of the visible fuselage skin and doubler if installed, for cracking, corrosion, and any indication of contact of a certain fastener to a bonding jumper, and repair if necessary. We are issuing this AD to detect and correct cracking and corrosion in the fuselage skin, which could lead to rapid decompression and loss of structural integrity of the airplane."

Department of Transportation Federal Aviation Administration. (2014, March 5). Retrieved September 15, 2014, from http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgad.nsf/0/d91639a24674ca8f86257c920050edf7/$FILE/2014-05-03.pdf

Aloha Airlines flight 243 experienced an explosive decompression at approximately 24,000 feet. The decompression was caused by a large area of the fuselage becoming disconnected with the aircraft due to an exhausted airframe. This aircraft flew in a highly corrosive environment (salt waters) which should have been maintained with proper inspection by the maintenance personnel. Luckily, the pilots were able to initiate and emergency landing and were able to safely land the airplane. Several passengers were inured and some were in critical condition. One flight crew member was ejected out of the aircraft when the explosion happened and was never found.
http://www.ntsb.gov/investigations/summary/aar8903.html
Aircraft Accident Report. (n.d.). Retrieved September 15, 2014.

Corrosion and cracking in the airframe is a serious issue and must be treated with the same respect as any other aircraft maintenance. Failure to due so can result in loss of cabin pressurization whether it be slow or explosive and can cause the crew to become hypoxic and non responsive thus resulting in an aircraft accident like Helios Airways 522.

Week 5

Aircraft have so many systems allow the aircraft to fly properly to its next destination. Of those systems one of the more important for high altitude flight is the pressurization system. Pressurization systems are designed to maintain the proper pressurization needed at high altitudes during flight. Usually the pilot will set the pressurization to the altitude they are taking off from and maintain that during flight and will adjust the pressurization during descent to the destination they will be going to. An aircraft pressurizes its cabin by taking in bleed air from its engines, sends it to compressors, then is cooled, and then is distributed to the cabin. The cabin holds in the air and has a relief valve system in the rear of the aircraft that releases over flow air to maintain regulated pressurization (Cabin Altitude) that is set by the pilots. 

All systems require maintenance. This opens the possibility of maintainer errors that can cause system failure.  As an example, a Boeing 737 experienced a loss of cabin pressurization and immediately initiated a descent and emergency landing to avoid an accident or injury.

"It is estimated that this serious incident would have occurred through the following process: the aircraft encountered turbulence when flying at FL370, quickly reduced the engine power in order to avoid excessive airspeed, and this in turn caused a change of the source of bleed air, which resulted in bleed air with higher temperature flowing into the pre-coolers, but the bleed air was not cooled sufficiently, and the overheat switches activated, closing the bleed valves for both systems and thus preventing the air supply necessary for pressurization of aircraft, ultimately resulting in an abnormal cabin depressurization... It is estimated that contamination deposits on the bleed related valves and other components resulted from incomplete draining of water and detergent which entered these components in large quantities during water washing conducted for engine gas path cleaning." 

(SKYbrary - B735, en-route, SE of Kushimoto Wakayama Japan, 2006 (AW). (n.d.). Retrieved from http://www.skybrary.aero/index.php/B735,_en-route,_SE_of_Kushimoto_Wakayama_Japan,_2006_(AW))

In this scenario, the systems automatically shut themselves down preventing continued pressurization to the cabin. Because the pilots noticed this malfuction early on, they were able to descend and land the air craft to prevent injury to the crew and passengers. In other events like the Helios accident that I previously posted about, where the cabin pressurization system was not functioning because it was set in the manual operation in which the pilots were unaware of, all crew and passengers became hypoxic after running out of oxygen supplied by the oxygen masks.

https://www.youtube.com/watch?v=u63y1vY-dQ0

Provided is a link from the FAA that better explains cabin pressurization.

Here is an example of how the air flows in a cabin pressurization system.

Week 4

I am having a hard time trying to incorporate this weeks chapter with my topic (Aircraft Fire and Hypoxia) so instead, I will be adding more information about hypoxia to this page.

Helios Flight 522
August 14th, 2005
121 Fatalities

This flight was the most devastating accident to ever happen in the aviation history of Greece. Helios Airways was a cheaper airline that was popular among the people of Greece because of the lower airfare.

This accident was determined to have been caused by a loss of pressurization in the aircraft. They determined that after maintenance personnel had performed a pressurization check before the flight. Once completed, they did not turn the pressurization switch back to auto but didn't. Both the Co-Pilot and Pilot did not notice that this switch was in the manual position when they were doing their checks prior to flight. Because of this, The aircraft was never pressurized for flight at the altitude they had flown, which was 32,000 ft. Supplemental oxygen should be used at altitudes above 12,000 ft.

ATC lost contact with the crew within 30 minutes of flight, which was during their climb to 32,000 ft. Crew and passengers were unconscious in the aircraft before impact, they had been flying for about 3 hours before they began to run out of fuel, this flight was scheduled to originally be 1.5 hours. There were no survivors.

Because this crew continued to ascend, the effects of hypoxia worsened. They surely lost consciousness as well as the passengers early on as useful consciousness at 30,000 ft is about 1-2 minutes.

Pilot's Handbook of Aeronautical Knowledge Chapter 15 - American Flyers. (n.d.). Retrieved September 5, 2014.

The effects of hypoxia vary between every pilot and how long they have been at a certain altitude. So to play it safe, you should always follow the FAR.

According to the FAR Part 135 sec 135.89;

"(a) Unpressurized aircraft. Each pilot of an unpressurized aircraft shall use oxygen continuously when flying—
(1) At altitudes above 10,000 feet through 12,000 feet MSL for that part of the flight at those altitudes that is of more than 30 minutes duration; and
(2) Above 12,000 feet MSL. "

Just for clarification..

This blog will be focused on Hypoxia causing aircraft accidents.

Air Detective Tip 13: Paper Trails

Air detective tip 13 talks about paper trails. There are several papers and checklists required in the aircraft before and during flight. An aircraft investigator will collect and examine all documentation from the aircraft after an accident. Weather reports as well as communication and navigation will better help an investigator determine the environment a pilot is in an how they handled their experience or what hindered their flight.

Pilot Hydration

http://www.flyingmag.com/technique/tip-week/pilot-hydration

Here is a nice article to read about staying hydrated in flight. We all know that we usually do not want to drink a lot before a flight because of the lack of facilities to relieve yourself. It is important to prevent dehydration to ensure can complete a safe flight.