Within Flight 105
Could the Crew Judge Size and Speed?
Without a known range, the crew could not reliably turn apparent shape and motion into claims about size, altitude or speed.
On this page
- Why open skies defeat depth perception
- How apparent motion becomes misleading
- Which measurements would have resolved the case
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Introduction
One of the most important limitations in the United Airlines Flight 105 sighting was not the honesty of the witnesses but the absence of a known distance to the objects. Captain Emil J. Smith repeatedly stressed that neither he nor his crew could determine the objects’ size, shape or range with confidence. Without those measurements, even experienced pilots could not reliably convert what they saw into estimates of speed, altitude or physical dimensions.[Wikipedia]WikipediaFlight 105 UFO sightingFlight 105 UFO sighting
This matters because many later retellings of the Idaho-linked incident describe large discs travelling at extraordinary speeds. Yet those conclusions depend on assumptions about how far away the objects were. If the range was unknown, then apparent motion across the sky could be interpreted in dramatically different ways. The Flight 105 case therefore illustrates a broader problem in aviation sightings: sincere observation does not automatically produce accurate measurements.
Why Open Skies Defeat Depth Perception
Human depth perception works best when there are reference points. Buildings, mountains, trees and terrain provide visual clues that help observers judge distance. In open sky, especially during twilight, many of those cues disappear. Aviation guidance notes that beyond relatively short distances, pilots rely largely on monocular visual cues rather than the strong stereoscopic depth perception available at close range.[Regulatory Library]regulatorylibrary.caa.co.ukRegulatory LibraryGM1 SPA.NVIS.140 Information and documentationMonocular vision can be accomplished with either eye alone, and is the ty…
Flight 105’s crew were looking ahead into an evening sky while climbing away from Boise. According to contemporary accounts, the objects appeared largely in front of the aircraft rather than against a clear background of terrain. Captain Smith acknowledged that their positions relative to the DC-3 prevented reliable judgments about size or exact shape.[Wikipedia]WikipediaFlight 105 UFO sightingFlight 105 UFO sighting
This created a basic observational problem. Consider three possibilities:
- A small object relatively near the aircraft.
- A medium-sized object at an intermediate distance.
- A very large object far away.
All three can produce nearly identical apparent sizes when viewed from a cockpit. Without independent range information, the eye cannot easily distinguish between them. Aviation research consistently shows that distance estimation becomes less reliable as visibility decreases or visual references are removed.[ResearchGate]researchgate.netAnalysis of Pilot Distance Estimation in Different Lighting…3 Nov 2023 — According to the findings, the accuracy of distan…
For Flight 105, the missing variable was range. Once that value is unknown, every calculation built upon it becomes uncertain.
How Apparent Motion Becomes Misleading
The strongest claims made about UFO sightings often involve speed. Yet speed is impossible to determine directly from appearance alone.
What observers actually see is angular motion: how quickly an object seems to move across their field of view. To convert that into a true speed, they must know how far away the object is.
A simple example shows the problem:
- A nearby object can appear to sweep rapidly across the sky while moving relatively slowly.
- A distant object can seem almost stationary while travelling extremely fast.
- An object travelling roughly parallel to the observer may appear to pace the observer even if the actual speeds are very different.
Flight 105’s crew reported that the objects remained ahead of the aircraft for a substantial period and were never overtaken. Later writers sometimes interpreted this as evidence of exceptional velocity. However, if the objects were much farther away than assumed, their apparent behaviour could look similar without requiring extraordinary speed. Conversely, if they were relatively close, the implied speeds might be very different. Because distance was unknown, neither conclusion can be demonstrated.[Wikipedia]WikipediaFlight 105 UFO sightingFlight 105 UFO sighting
The same uncertainty affects claims that the objects suddenly accelerated away. A change in viewing angle, lighting conditions or relative geometry between the aircraft and an unknown target can create a strong impression of acceleration without supplying enough information to calculate an actual velocity. Aviation safety literature documents numerous situations in which featureless skies and limited visual references distort a pilot’s perception of movement and position.[faa.gov]faa.govSpatial Disorientation: Visual IllusionsStatistics show that between 5 to. 10% of all general aviation accidents can be attributed to…
The Shape Problem Was Really a Distance Problem
Many summaries describe Flight 105 as a classic “flying saucer” report. The original testimony was more cautious.
Smith stated that the objects appeared thin and unusual, but he also emphasised that the crew could not be certain whether they were saucer-shaped, oval or something else entirely. The reason was not indecision. It was geometry.[Wikipedia]WikipediaFlight 105 UFO sightingFlight 105 UFO sighting
When observers do not know the distance to an object, they also struggle to determine:
- Its true dimensions.
- Its exact orientation.
- Whether it is tilted or level.
- Whether visible features are structural details or visual effects.
A distant object viewed nearly edge-on can appear thin. A nearer object seen under different lighting can produce a similar impression. Twilight conditions further complicate interpretation because contrast and surface detail become harder to judge as illumination decreases. Research on aviation vision has repeatedly found that reduced visual cues increase the likelihood of misperceiving both distance and object characteristics.[researchgate.net]researchgate.netAnalysis of Pilot Distance Estimation in Different Lighting…3 Nov 2023 — According to the findings, the accuracy of distan…
This does not mean the crew imagined the objects. It means that visual appearance alone could not reliably reveal what those objects physically were.
Which Measurements Would Have Resolved the Case
The Flight 105 sighting became famous because trained aviation personnel reported it. What it lacked was independent measurement.
Several kinds of information could have greatly strengthened the case:
Radar Tracking
A radar return could have provided range, altitude and relative movement. No such radar data are known to exist for the sighting. Without it, the objects remained visual observations only.
Multiple Observation Points
If observers at a second location had recorded the same objects at the same time, investigators could have used triangulation to estimate distance and altitude. The crew attempted to obtain confirmation from other aviation sources, but no independent observation produced that geometry.[Wikipedia]WikipediaFlight 105 UFO sightingFlight 105 UFO sighting
Precise Angular Measurements
Modern investigations often seek photographs, video, instrument records or carefully documented angular positions against stars or landmarks. None were available in 1947.
Instrument Correlation
Reliable correlations between cockpit instruments, navigation data and the objects’ positions could have narrowed possible explanations. Such evidence was absent.
Because none of these measurements existed, investigators were left with testimony rather than physical data.
What the Distance Problem Means for Flight 105
The Flight 105 crew may well have observed something genuinely unusual. Their account remains noteworthy because multiple trained witnesses described the same event over an extended period. Yet the most cautious part of Captain Smith’s testimony is also the most important: he repeatedly acknowledged that the crew did not know how far away the objects were.[Wikipedia]WikipediaFlight 105 UFO sightingFlight 105 UFO sighting
That single uncertainty cascades through every major claim. Unknown distance means unknown size. Unknown size means uncertain shape. Unknown distance and geometry mean uncertain altitude and speed. As a result, Flight 105 remains a valuable example of the limits of pilot testimony. The witnesses could credibly report what they saw, but the missing range information prevented them from proving what the objects actually were or how they were moving through the sky.
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Endnotes
1.
Source: Wikipedia
Title: Flight 105 UFO sighting
Link:https://en.wikipedia.org/wiki/Flight_105_UFO_sighting
2.
Source: researchgate.net
Link:https://www.researchgate.net/publication/375671690_Analysis_of_Pilot_Distance_Estimation_in_Different_Lighting_and_Visibility_Conditions
Source snippet
Analysis of Pilot Distance Estimation in Different Lighting...3 Nov 2023 — According to the findings, the accuracy of distan...
3.
Source: faa.gov
Link:https://www.faa.gov/pilots/safety/pilotsafetybrochures/media/spatiald_visillus.pdf
Source snippet
Spatial Disorientation: Visual IllusionsStatistics show that between 5 to. 10% of all general aviation accidents can be attributed to...
4.
Source: skybrary.aero
Link:https://skybrary.aero/sites/default/files/bookshelf/177.pdf
Source snippet
Visual Illusions AwarenessVisual illusions take place when conditions modify the pilot's perception of the environment relative t...
5.
Source: Wikipedia
Title: Sensory illusions in aviation
Link:https://en.wikipedia.org/wiki/Sensory_illusions_in_aviation
6.
Source: Wikipedia
Title: 1947 flying disc craze
Link:https://en.wikipedia.org/wiki/1947_flying_disc_craze
7.
Source: researchgate.net
Title: 400689311 Visual Illusions in Aviation Simulating the Black Hole Phenomenon
Link:https://www.researchgate.net/publication/400689311_Visual_Illusions_in_Aviation_Simulating_the_Black_Hole_Phenomenon
8.
Source: regulatorylibrary.caa.co.uk
Link:https://regulatorylibrary.caa.co.uk/965-2012/Content/Document%20Structure/05%20SPA/4%20GM/GM1%20SPA%20NVIS%20140%20Information.htm
Source snippet
Regulatory LibraryGM1 SPA.NVIS.140 Information and documentationMonocular vision can be accomplished with either eye alone, and is the ty...
9.
Source: flightsafety.org
Title: in the dark
Link:https://flightsafety.org/asw-article/in-the-dark/
Source snippet
Flight Safety FoundationIn the Dark20 Jan 2017 — The measurement means that, at a distance of 20 ft/6 m, a person can see what someone wi...
Additional References
10.
Source: indjaerospacemed.com
Title: analysis of problems with distance determination using night vision googles
Link:https://indjaerospacemed.com/analysis-of-problems-with-distance-determination-using-night-vision-googles/
Source snippet
Indian Journal of Aerospace MedicineAnalysis of problems with distance determination using...by VP Baburaj · 2009 · Cited by 3 — This st...
11.
Source: thinkaboutitdocs.com
Link:https://thinkaboutitdocs.com/1947-united-airlines-flight-105-pilots-witness-disc-shaped-objects/
Source snippet
Think About It Docs1947: 105 pilots witness disc-shaped objects4 Jun 2026 — Smith emphasized that they were never certain of sizes and di...
12.
Source: youtube.com
Link:https://www.youtube.com/watch?v=OarL8ymktIE
Source snippet
"Flight 105" UFO Emil Smith Days Before Roswell: The Flight 105 UFO Sighting Curtis Paranormal...
13.
Source: youtube.com
Link:https://www.youtube.com/watch?v=cCxtUqZA2Zw
Source snippet
United Airlines Crew Encounters MYSTERIOUS UFO on July 4th 1947...
14.
Source: facebook.com
Link:https://www.facebook.com/HISTORY/posts/a-pilot-reports-sight-of-a-number-of-flying-discs-near-mount-rainier-historysgre/1536344454725192/
15.
Source: facebook.com
Link:https://www.facebook.com/groups/887033352165681/posts/1006184436917238/
16.
Source: nature.scot
Link:https://www.nature.scot/doc/guidance-aviation-lighting-impact-assessment
17.
Source: danlj.org
Link:https://www.danlj.org/~danlj/Soaring/Clues/SDO.html
18.
Source: scribd.com
Link:https://www.scribd.com/document/397370562/Av-Med-Visual-Illusion-Superstall
19.
Source: quizlet.com
Link:https://quizlet.com/81691267/aeromed-visual-illusions-types-of-vision-and-monocular-cues-flash-cards/