Fatal aviation accidents aren't always caused by engine fires and alarms going off in the cockpit. In fact, most deadly accidents are caused by silent threats. Here's what you need to know.

1) Hypoxia

Oxygen deficiency in the blood, body tissues, and cells leads to impairment and total incapacitation if left unchecked. The body's failure to absorb oxygen can be caused by a number of things including (but not limited to): low pressure at high altitudes, alcohol, medications, anemia, G-Forces, shock, etc. It often occurs subtly, and each person reacts differently to hypoxia. So go through altitude chamber training if you can.

It causes dozens of aircraft crashes each and every year. Learn more about hypoxia and why your knowledge of it is so crucial.

2) Pyrolysis - Organophosphates

Pyrolysis can occur from pyrolyzed engine oil or hydraulic fluids. According to medical research, 1 in 10 people are more susceptible than normal. Worse yet, it's symptoms are similar to carbon monoxide, largely undetectable.

Organophosphates are dangerous gases that are associated with engine gases in the aircraft cabin. In 2011, a Lufthansa A380-800 crew experienced one of these occurrences when an engine was washed just before their flight. Upon landing, one cabin crew member tested positive for gas compounds similar to those found in deadly Sarin gas.

3) Bad Attitudes

The FAA's list of hazardous attitudes accurately represents the danger we pose to ourselves in the air. Failing to recognize and change hazardous attitudes can result not only in putting yourself in danger, but your passengers too.

4) Medications

Many medications are banned or restricted by the FAA, for good reason. Not limited to prescriptions, over the counter medications can severely inhibit your mental and physical capacities too, especially during time-sensitive emergency situations.

Additionally, many medications are known to have adverse interactions in the body at altitude, promoting the development of hypoxia symptoms. Always have new medications checked by your local Aviation Medical Examiner before you fly.

5) Complacency

Failing to perform checklists isn't usually thought of as a deadly threat to pilots, but it's one of the worst. Skipping or forgetting procedures before, during, and after a flight makes you less situationally aware, and infinitely more prone to accidents.

6) Icing Conditions

Didn't notice ice building up on your wings? Hopefully it's not to late. Enable deicing and anti-icing equipment right away, or exit icing conditions altogether. Noticing ice buildup can be tough, especially at night. Make sure to check for known icing conditions through weather briefings and pilot reports before you takeoff.

It happens silently. Ice builds up on your aircraft until reaching a critical point where your wings simply won't produce enough lift for flight. Instability, powered descents, and stalls come next. Reacting too late might not get you out of this dangerous situation. Don't forget about Carburetor icing either!

7) Poor Communication

What about communication could be so deadly? There's a number of things that can put you directly at risk if you don't communicate clearly and correctly. Failing to communicate with ATC about emergencies and failing to communicate together with a crew-member are too notable examples.

8) Disorientation

Flying through the clouds is not without risk: between 5-10% of all general aviation accidents result from spatial disorientation, and of those accidents, 90% of them are fatal.

One of the best (and safest) ways to prevent yourself from becoming a victim to one of these illusions is to to grab an instrument instructor on the next cloudy day and go flying. Get an IFR block of airspace and practice some maneuvers in the clouds - climbs, descents, and turns.

9) Fatigue

Whether you're a busy student with lots of ground school work or an airline pilot flying multiple legs per day, fatigue is a threat for aviators. Flying while fatigued is equivalent in many cases to flying under the influence of alcohol.

Fortunately, new FAA regulations are a step in the right direction, giving airline pilots longer rest periods. Sadly, these rules don't apply to every flight department. For instance, many charter and cargo pilots have less stringent rest requirements.

10) Carbon Monoxide

The fumes produced by the combustion your engine can leak into the fresh air supply for the cabin or cockpit, leading to carbon monoxide poisoning. Silent and extremely deadly, carbon monoxide builds up in the blood, causing nausea, weakness, confusion and later total impairment.

Left unaddressed, pilots have frequently lost consciousness during flight from failing to notice symptoms. If a carbon monoxide leak is suspected, follow your checklist or get as much fresh air into the cabin as possible, landing as soon as practical. Read more about how to detect carbon monoxide and what to expect.

11) Time Pressure

It's one of the worst invisible threats. Time pressure kills more pilots yearly than measurable. Get-there-itis, VFR into IMC, or simply failing to calculate performance before flying is a great way to put yourself into life-threatening situations quickly. Relax and take your time. If the weather isn't looking the best, don't go.

It's much better to be on the ground wishing you were in the air, than in the air wishing you were on the ground.

What other silent threats are present in the cockpit? Tell us in the comments below.