Shifting Horizons
As important as visual input is for a pilot, eyes can lie. For example, when flying above a cloud deck, there is a natural tendency to perceive any relatively straight line in the visual field as a horizon—which can lead to very undesirable results in a fast-moving aircraft.

False horizons are everywhere around you in the clouds. Your aircraft’s attitude may seem level, even if you are tilted and in a turn. Mountain ridges might lead you astray as well, and at night the combination of clouds, stars, mountains and lights on the ground can produce impossibly confusing percepts that lead the aircraft away from the safety of true straight and level flight.

Don’t think that you are safe from your own perception, however, just because you are flying above water on a clear day. A fixed horizon can still put you in the drink. Consider what may happen if you approach the beach from over the horizon. You may line up the beach in your sights and then keep it there in anticipation of going “feet dry” (flying from over sea to over land), but if so you will never reach land: the beach is fixed, unlike a true horizon, and the only way to keep it stationary in your sight is to point your aircraft progressively downward.

Choosing a fixed horizon in proximity to wires or cables stretched across a valley is especially problematic. As you approach the fixed horizon (such as where a valley floor and mountain wall meet), you slowly and unnoticeably nose down. As you descend, the approaching wires will appear to rise as if they will pass well above you, whereas in fact they remain well below the aircraft. If you don’t spot the wires until they are very close (because of mountain haze or the fog of war), your natural reaction may be to push the stick forward to dive under the wires. This reaction is what happened to the U.S. Marine pilots of an EA-6B Prowler aircraft on a training mission in 1998 near an active Italian ski resort in the Alps. The aircraft sliced through two wires, which held a cable car holding 20 skiers 370 feet above the ground. None survived.

One might think that objective information from instruments is the logical solution to subjective sensory illusions. The proliferation of instrumentation is part of the problem, however, because of mounting attentional demands on the pilots, which cause cognitive overload during combat and other stressful flight scenarios. This kind of mental distress is an important contributor to spatial D. New avionics are designed with simplicity, not complexity, in mind, and pilots learn how to scan their instruments at just the right times, under conditions of simulated duress. Systematic instrument scanning demands discipline, which may be one of the first casualties of battle, but until we learn better ways to overcome insidious in-flight illusions, it is one of the main techniques that keep pilots and crews safe.

We would like to thank LCDR Brian Swan, USN (Ret.), CDR Tyson Brunstetter, USN, and CDR Fred R. Patterson, USN (Ret.), for their ideas and contributions to this article.

This article was published in print as "The Aviator's Dilemma."

7 Comments

1. 1. jgrosay 04:56 PM 6/4/12

   Yeah!: this is true, I'm aware of an F-86 Sabre pilot that completely convinced the fuel gauge indication of a partly loaded fuel tanks was wrong, and fearing to run out of fuel while still in flight, made an emergency landing in a plowed field just to see the fuel tanks broken and releasing a lot remaining fuel at bellying. It may have burn!

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2. 2. Gousa1 05:53 PM 6/4/12

   I have never read an account of the Italian incident that describes anything but joyriding. He violated air space rules, and then engaged in a coverup. I just started reading this journal and now have questions about the editors.
   
   

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3. 3. mggordon 08:25 PM 6/4/12

   Great article, well explained! I flew in Navy P3's during the Cold War and it was easy to become somewhat disoriented flying *between* cloud layers that seem horizontal but arent always actually horizontal; they form along pressure gradients rather than just altitude.
   
   Not only that, but the relatively slow moving P3 sometimes feels like it is flying *backward* after a great many hours of cruising and not only does one get visual effects, but auditory effects as one's ears try to make sense of the constant droning of engines and avionics. Sometimes I heard classical music; not like a replay in my mind, but I could actually hear it amid the droning of the engines. Knowing it was an illusion did not make it go away.
   
   Then you must drop down to 500 feet above the oft-stormy sea to inspect a ship. You depend almost entirely on radar altimeter and attitude indicator because there is no horizon and you have absolutely no idea whether you are too close to little waves or adequately high above really big waves -- it all looks the same. Then you finally see the ship and realize the waves are REALLY big, twice the distance crest-to-crest as a supertanker is long.

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4. 4. mggordon 08:28 PM 6/4/12

   I should point out that I wasn't the pilot of a P3, nor even strictly speaking crew -- rather, I accompanied P3's from time to time. I did get to sit in the right seat a couple of times and the P3 (Lockheed Orion, beefed up somewhat from the civilian version) was perhaps the best airplane ever made for operating in Alaska.

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5. 5. kienhua68 01:26 PM 6/5/12

   Well this article makes unmanned aircraft all the more
   attractive. Of what use is a control operator that is
   less capable than the machine itself or subject to the
   vagaries of being human.
   Drones are the future. After all it is just a game and
   an example of mans failure to agree sans war.
   Right now America is the best armed second world power,
   where just a few years back we had it all.
   

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6. 6. mggordon 07:14 PM 6/6/12

   kienhua68, I do wish you would make up your mind.
   
   Is it "After all it is just a game" in which case this nation ought not to bother with a military at all, or "America is the best armed second world power,
   where just a few years back we had it all."
   
   What is different? Just a few years back men flew airplanes, not drones.
   
   So you see, you open the door by your own bad logic to more bad logic.
   
   As I think on my own military career, I contemplate whether drones could have done any part of the military mission. The answer is obviously "yes" since drones ARE fulfilling part of the military mission.
   
   But American P3 aircraft performed far more Search and Rescue operations (many) than destroying Russian submarines (zero). So, while one might imagine a drone capable of attacking a submarine, it is not easy to imagine a drone in a meaningful search and rescue operation. But let us consider that drone capable of attacking a submarine. What is the risk that it might be coopted, falling into operational hands of your enemy? There you are with a rogue and armed drone no longer in your control.
   
   The white house still stands because human people onboard a human-piloted jet airliner chose to die in the hinterlands of Pennsylvania rather than allow that aircraft to be used as an agent of destruction.
   
   Furthermore, I have doubts about the viability of drones in electromagnetically unfriendly environments such as was often the case around Iceland during aurora borealis outbreaks.
   
   Back on the search and rescue aspect -- if you were floating on a raft out at sea, would you prefer to see above you a Navy P3 knowing it was crewed by human beings that now know where you are, and are about to toss out survival supplies until a rescue ship arrives, or would you rather see a small Boeing drone buzzing around, knowing that someone in Seattle knows where you are, thank you very much, and might care or might not. He's going home to supper and video games in a hour. No "skin in the game".

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7. 7. northernguy in reply to Gousa1 03:31 PM 6/8/12

   What you say may all be true even if it is based on press reports but the article is talking about something else. The article is describing why the pilot hit the cables even though visibilty was perfect.
   
   Whether he should have been flying in that area or what his motive was for being there is the subject of a different article. The issue is why did he fly into something he could clearly see and could easily have avoided.

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