Aviation's Great Oversight: Depicting the Real Approach Path Angle

Aviation’s Great Oversight: Depicting the Real Approach Path Angle

08.08.2026 , David Jacobson , captain-david-jacobson 0

Accurately depicting the final approach path angle in aviation publications is a critical factor in ensuring safe and effective landings. Yet, for well over 100 years, it remains one of aviation’s great and glaring oversights.

The final approach path angle, typically a standard 3-degree glide slope or a steeper custom angle, is not just a technical detail—it is a foundational element that shapes pilot perception, training, and operational safety.

Misrepresentation of this angle, whether through distorted diagrams or unclear labelling, can have far-reaching consequences, from pilot misjudgment to increased runway occupancy and even accidents. Exaggerated or distorted profile illustrations can create dangerous optical illusions, causing pilots to misjudge descent rates, misinterpret visual cues, or lose spatial orientation.

This post explores the vital importance of accurate depiction, the risks of misrepresentation and the best practices that must be followed to uphold safety and clarity in aviation.

The Role of the Final Approach Path Angle

The final approach path angle defines the geometric descent path an aircraft follows during the last phase of landing. For most runways, this is a 3-degree (3º) glideslope, which translates to a very shallow descent—approximately a 1:20 gradient, or 320ft/nm (specifically, 1:19.08). This angle is not arbitrary; it is carefully chosen to balance obstacle clearance, aircraft performance, and passenger comfort. Pilots rely on this angle, as depicted in approach charts and training materials and, conventionally, to assist in judging their descent rate, flare timing, and touchdown point.

Despite its shallow appearance in profile – ‘though not when viewed from the cockpit – the 3º path flown by an airplane at a groundspeed of 150kts/28km/hr translates to a rate of descent of approximately 800ft/min. This is very close to the maximum rate of descent of 1000 ft/min, on approach below 1000ft HAT (Height above Threshold), specified by aircraft manufacturers and the major carriers, so it is easily apparent why 3º is generally accepted as the standard approach path angle.

Dangers of Distorted Depictions

1. Spatial Misperception

When profile illustrations exaggerate the vertical dimension, a standard 3-degree path can appear much steeper—sometimes resembling a 25-35 degree slope. This visual distortion tricks the human eye, leading pilots to believe they are approaching at a much steeper angle than reality. The result is a tendency to ‘duck under‘ the glide path, descending below the intended path during the transition to visual landing. Such misperceptions are especially dangerous at night or in poor visibility, where external visual cues are limited.

2. Training Deficiencies

The problem is not limited to operational charts. For decades, classroom materials and textbooks have perpetuated this error, presenting approach profiles with exaggerated angles. Student pilots, trained on these distorted diagrams, develop flawed mental models of what a proper approach looks like, from the very beginning.

This can lead to poor flare technique, misjudged touchdown points, and a misunderstanding of the relationship between vertical and longitudinal errors. For example, a 1-foot error in estimating flare height on a true 3-degree path results in a nearly 20-foot longitudinal error along the runway—a 2000% amplification. Such mathematical realities are obscured when the angle is misrepresented. Let’s say that again:

For a standard 3º approach path, any error of flare height judgement is compounded approximately twenty times, longitudinally, along the runway.

3. Operational Consequences

Misjudging the approach path can have operational impacts beyond the individual landing. Conservative flare heights, often derived from flawed diagrams or radio altitude sampling in auto-land systems, can cause aircraft to land short or long. This affects runway occupancy, as pilots may miss taxiway turn-offs, leading to longer runway use and potential delays for other aircraft. The collective touchdown footprint for a given aircraft type becomes unnecessarily large, reducing airport efficiency and increasing risk.

The Importance of True Geometric Scaling

To prevent these issues, aviation publications must adhere to true geometric scaling in their profile views. This means:

1. Never stretching vertical dimensions

The profile should accurately reflect the shallow nature of the approach, making it clear that a 3-degree slope is far from a cliffside drop.

2. Explicitly labelling numeric values

The exact Vertical Descent Angle (VDA) or Glidepath Angle (GPA) should be clearly marked next to the profile, eliminating the need for pilots to estimate visually. And why not acknowledge that the runway centreline markings are not randomly positioned but, in fact, form an effective calibrated ‘ruler‘.

3. Illustrating Threshold Crossing Height (TCH)

Clearly illustrate and distinguish where the geometric main-wheel path and the pilot’s eye path each cross the threshold and intersect the runway, to prevent short or long landings.

4. Correlation with Visual and Electronic Aids

Accurate depiction is not just about the diagram—it must be tied directly to the physical aids pilots use. The charted angle should match the setup of Precision Approach Path Indicator (PAPI) and Visual Approach Slope Indicator (VASI) systems.

This ensures that the visual cues on the runway correspond to the information in the publication, reinforcing correct approach technique. Additionally, publications must clarify that a centred electronic glide slope or VDA guarantees the correct path, regardless of how external factors—such as a dark or unusually wide/narrow runway—might skew visual perception.

However, it must be understood that PAPI and VASIS systems at airports, world-wide, are set up for the largest airplane type that regularly operates into a given runway and, below 300ft HAT. Their use is secondary to the correct visual aim point for a given airplane type. The installations, then, are something of a compromise for all other aircraft:

The pilot of anything smaller than the benchmark airplane either has to fly the PAPI/VASIS (or ILS) and land long; or, at some vague point on the approach, discontinue using the electronic aids and pitch down, briefly, to re-aim at the correct visual aim point for that aircraft. This can de-stabilise the approach badly, if left too late in the approach.

To be frank: the Departments of ILS/PAPI/VASIS don’t seem to talk to the Department of White Paint! Those large pairs of white painted fixed-distance runway markings are certainly vital in assisting with roll stability during the flare; Yet, back around 1993 at a formal meeting in their office, I had first-hand experience of government agency aviation engineers simply not understanding that their lovingly-applied ‘artwork’ had another vital role: They are also accurate visual aim points for a wide range of aircraft types.

Their question was: “Is that what they’re there for??” Words failed me!!

Avoiding Common Misconceptions

Several misconceptions can arise from poor depiction:

1. The “Steepness” Illusion

Exaggerated graphics make normal approaches seem dangerously steep, prompting low ‘duck-under’ manoeuvres during the transition from instrument approach to visual landing.

2. Instrument vs. Visual Disconnect

Pilots may distrust their instruments if the visual scene does not match their expectations, leading to unsafe deviations. Clarify that a centred electronic glide slope or VDA guarantees the path, regardless of how a dark or unusually wide/narrow runway skews visual perspective.

3. Constant Descent vs. Step-Down

Modern Continuous Descent Final Approach (CDFA) techniques rely on a steady, energy-efficient descent. Publications must differentiate these from outdated “dive-and-drive” methods, reinforcing the importance of maintaining the correct and STABLE path angle throughout the approach to reinforce study energy management.

Best Practices for Aviation Publications

To ensure safety and clarity, aviation publications should:

1. Use true aspect ratios in all profile diagrams

Avoid vertical exaggeration; show the actual 3º shallow angle; don’t depict as a cliffside drop.

2. Label all approach angles and threshold crossing heights explicitly

Provide clear, unambiguous numeric values.

Clearly illustrate and distinguish where the geometric main-wheel path and the pilot’s eye path each cross the threshold and intersect the runway to prevent short or long landings.

3. Correlate diagrams with physical and electronic aids

Ensure that PAPI, VASI, and electronic glide slopes match the depicted path, where possible, (bearing in mind the comment above).

4. Educate pilots on the significance of small errors

Highlight how minor vertical misjudgments can lead to large longitudinal errors.

5. Update training materials to reflect accurate geometry

Replace outdated, exaggerated diagrams with true-to-scale representations.

And then, since 1987, there is the Jacobson Flare:

I made the point earlier that, for a standard 3º approach path, any error of flare height judgement is compounded approximately twenty times longitudinally along the runway.

However, in marked contrast, any longitudinal inaccuracy when applying the flare fix concept – the essential keynote of the Jacobson Flare approach and landing technique – will reflect a greatly diminished error of only one twentieth of that figure, vertically. Such inaccuracies could be caused by seat height variations, a disturbance in pitch attitude close to the flare point, or due to likely errors in estimating distance along a grass, gravel or snow-covered airstrip which, of course, have no white paint calibrations. The longitudinal flare fix concept is therefore extremely tolerant of error, unlike the concept of using an estimate of vertical flare height to cue the flare commencement point.

The twenty-times expanded scale along the runway centreline (when compared with a vertical flare height), together with the longitudinal visual flare fix, provides a model framework that is both visible and precise. This provides unparalleled accuracy and consistency for all pilots, at any level of experience. The longitudinal cue to flare is 400 times more accurate than the vertical one, based on an ‘educated guess’ of vertical main wheel height above the runway.

Conclusion

The accurate depiction of the final approach path angle is not a mere technicality—it is a vital safety measure that underpins effective pilot training, operational efficiency, and the prevention of accidents. By adhering to true geometric scaling, explicit labelling, and direct correlation with visual and electronic aids, aviation publications can eliminate dangerous misconceptions and support pilots in executing safe, precise landings. The aviation community must remain vigilant against the perpetuation of distorted diagrams and ensure that every chart, manual, and training resource reflects the reality of the approach path. Only through such diligence can we maintain the highest standards of safety and professionalism in aviation.

Wishing you many safe landings

Captain David M Jacobson FRAeS MAP

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Aviation’s Great Oversight: Depicting the Real Approach Path Angle